Investigating of Structural, Morphology, Optical, Transport and Magnetic properties of [602584]

Indian Journal of Physics
Investigating of Structural, Morphology, Optical, Transport and Magnetic properties of
Mg1-xCuxO
–Manuscript Draft–

Manuscript Number: INJP-D-18-00278R1
Full Title: Investigating of Structural, Morphology, Optical, Transport and Magnetic properties of
Mg1-xCuxO
Article Type: Original Scientific Research
Keywords: Crystal structure; Optical properties; Dielectrical properties; Magnetic
properties
61.50.−f , 78.20.−e ,77.22.−d ,75.50.Pp
Corresponding Author: samia Ahmed gad, Ph.D.
National Research center,Dokki,Giza,Egypt
cairo, giza EGYPT
Corresponding Author Secondary
Information:
Corresponding Author's Institution: National Research center,Dokki,Giza,Egypt
Corresponding Author's Secondary
Institution:
First Author: samia Ahmed gad, Ph.D.
First Author Secondary Information:
Order of Authors: samia Ahmed gad, Ph.D.
G. M. El Komy, phd
A. M. Moustafa, phd
A. A. Ward, phd
Order of Authors Secondary Information:
Funding Information:
Abstract: Effect of Cu2+ content on different properties is investigated. Mg1-xCuxO (0.05≤ x ≤
0.2) powder was prepared via solid state reaction. Samples were examined by X-ray
diffraction (XRD) and the results were analyzed by using Full Prof program by
employing Rietveld refinement technique. The results showed that samples with Cu
content up to x 0.15 had a single phase of MgO rock salt structure type and for x 0.2
two phases were detected; namely, MgO rock salt structure and Cu2O cuprite cubic
phase. Also, it was found that, a small increase in the lattice constants with increasing
the Cu content. Moreover, the crystallite size was found to decrease with increasing
the Cu concentration. The transmission electron microscopy (TEM) studies have been
performed for studying their morphology. The optical energy gap had been calculated
and was found that there are two energy gaps. The energy gaps decreased with
increasing the Cu content. The dielectric constant ′, the loss factor tan and conductivity
increased with increasing Cu concentration. This increase can be directly related to the
increase in the concentration of charge carriers and interfacial polarization effects. The
saturation magnetization and the retentivity were found to decrease with the increase
in Cu concentrations but the coercivity increased with increasing Cu content.
Response to Reviewers: Dear Editor and Reviewers:
For Reviewer #1:
The paragraph concerning the morphological study dealing with divalent Cu. The
author must rewrite the text with monovalent copper.
The valency of Copper at CuO oxide is divalent because of one copper atom with
valence 2+ combine with one oxygen atom -2, while the valency of Copper at Cu2O
Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation

oxide is monovalent because of two copper atoms combine with one oxygen atom.
For reviewer 2 :
Comment 1: According to literature, atomic radius of Cu+2 is smaller than that of
Mg+2. But with the higher Cu content in the doped systems, the lattice parameters are
gradually increasing. This point must be elucidated in the revised manuscript.
According to literature, atomic radius of Cu+2 is smaller than that of Mg+2. But with the
higher Cu content in the doped systems, the lattice parameters are gradually
increasing. This point must be elucidated in the revised manuscript.
Page 5 paragraph 2 line
According to literature, atomic radius of Cu+2 is smaller than that of Mg+2. But with the
higher Cu content in the doped systems, the lattice parameters are gradually
increasing. This point must be elucidated in the revised manuscript.
The Crystal ionic radius for MgO is 0.86 Å at six coordination, while for Cu2+ is 0.87 Å
at the same coordination, while the effective ionic radius of MgO is 0.72 Å and for CuO
is 0.73 Å [1,2]. So either of the crystal ionic radius or the effective ionic radius of Cu2+
are larger than that for MgO2+. So a little bet increase in the unit cell dimension, was
observed due to the substitution of Mg2+ by Cu2+
[1]“Effective Ionic Radii in Oxides and Fluorides” , R.D. SHANNON and C.T.
PREWITT, ActaCryst., B25, 925 (1969).
[2] “Revised Effective Ionic Radii and Systematic Studies of Interatomie Distances in
Halides and Chaleogenides” , R. D. SHANNON, ActaCryst., A32, 751 (1976).
Comment 2: The authors claim that both the dielectric constant and electrical
conductivity of the samples increase with increasing Cu doping because of free
charge. But usually the presence of free charge contributes to electrical conductivity,
whereas the effect is detrimental to dielectric constant. Contradiction of this general
notion is not clear in the present manuscript.
The explaining of these comments are shown in the manuscript (the change is
indicated by the red color) ( page 7 paragraph 1 line 59, and page 8 paragraph 1) .
Comment 3: With the increasing Cu content, the nature of the magnetic hysteresis
gradually transforms from ferromagnetic to super-paramagnetic nature. Will the authors
explain this in the revised manuscript?
The obtained hysteresis at room temperature supports the fact that the magnetic
behavior is weakly ferromagnetic and not superparamagnetic. To verify this, we must
plot M /Ms (Ms = saturation magnetization) versus H/ T for the M-H data at different
temperatures and all the curves remain distinct. So, we need measure the
magnetization with temperature, we can make this studying after that. For
superparamagnetic systems, as is well-known, the curves merge into a single one. [1-
B. Martinez, F. Sandiumenge, Ll. Balcells, J. Arbiol, F. Sibieude and C. Monty,
Phys. Rev. B 72, 165202 (2003). 2- R. H. Kodama and A. E. Berkowitz, Phys. Rev.
B 59
, 6321 (1999). ]
Comment 4: The authors should include Cole-Cole plot to explain the nature of
electrical conductivity.
The authors see that there is no need for including Cole-Cole plot to explain the nature
of electrical conductivity as they have already explained the nature of conduction on
the basis of the widely used universal power law.
Comment 5: It is mentioned that "the values of the saturation magnetization and the
retentivity found to decrease with the increase in Cu concentration", however, there is
no qualitative explanation in the manuscript.
I have modified this part in the manuscript (page 8 last paragraph lines 26- 32)
Previously in TM doped oxide systems, it has been reported that as the concentration
of magnetic impurities is increased in the host oxide matrix, the saturation magnetic
moment decreases which is attributed to the antiferromagnetic (AFM) interaction
between the dopants (Singhala et al., 2008). Therefore, we feel that in the presently
Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation

studied samples, as Cu concentration is increased the possibility of enhanced AFM
interaction between neighbouring Cu-Cu ions would decrease, leading to the observed
behaviour at high magnetic field values. Consequently, ferromagnetic interaction
strengthens as the Cu concentration increases. As the average crystallite size
increases, the values of saturation magnetization increase.
[Singhala, A., Acharya, S.N., Tyagia, A.K., Mannab, P.K. and Yusuf, S.M. (2008) ‘
Colloidal Fe-doped ZnO nanocrystals: facile low temperature synthesis,
characterization and properties’
Materials Science and Engineering B, Vol. 153, Nos. 1–3, pp.47–52.].
For reviewer 3: Moreover, the authors should be more careful regarding the term
'nano'. They are claiming MgO nanoparticles however the XRD of the materials show
bulk nature.
The calculated values of the crystallite size after doing the instrumental correction and
Rietveld refinement was 121nm, 60nm, 63nm and 49 nm with increasing the doping
level. Usually the term nanomaterials applied for all values of crystallite size less than
100 nm. In addition, the scale of the X-ray diffractograms were in arbitrary units.
The doped XRD diffractorgrams show peaks of CuO also. This is not doping but
blending.
The doped XRD diffractomgram for Mg1-xCuxO, x= 0.05, 0.1, 0.15 consists of one
phase related to the MgO and the Copper oxide formed solid solution with MgO. While
for x=0.2 consists of two phases, one of them related to MgO and the other one is
Cu2O as shown in Figure (1) indicated by the arrow.
The introduction and the discussion of electrical are modified as shown in the
manuscript.
For reviewer 4:
I have made some changes over the manuscript and I have added some explanation
for the discussion of the results as shown in the manuscript. I have changed the
abstract as you suggested (page 1 lines 28 ,30)
Also, the references [ Preparation of nanocrystalline NiO-MgO solid solution powders
as catalyst for methane reforming with carbon dioxide: Effect of preparation conditions
Advanced Powder Technology
Volume 25, Issue 3, May 2014, Pages 1111-1117
2.NiO-MgO Solid Solution Prepared by Sol-Gel Method as Precursor for Ni/MgO
Methane Dry Reforming Catalyst: Effect of Calcination Temperature on
Catalytic Performance
Mohammad JafarbeglooAliakbar Tarlani A. Wahid MesbahJacques MuzartSaeed
Sahebdelfar
Catalysis Letters,January 2016, Volume 146, Issue 1, pp 238-248] are added and have
the numbers 25 and 26 in references of the manuscript (pages 10 and 11 ) .
For reviewer 5:
I have modified the introduction, the reasons of decreasing the optical energy gap with
Cu content are shown in the manuscript (page 6 last paragraph lines 40-44) .
I have placed TEM images with the same scale for the samples (as shown in Figs.)
We have already included updated references and added another two references
(pages 10,11)
Manuscript Classifications: 4: Condensed matter and materials physics; 8: Optics and spectroscopy
Powered by Editorial Manager® and ProduXion Manager® from Aries Systems Corporation

1
Investigating of Structural, Morphology, Optical, Transport and Magnetic
properties of Mg 1-xCuxO
S. A. Gad*, G. M. El Komy1, A. M. Moustafa2, A. A. Ward3

*,2 Solid State Physics Department, Physics Division , National Research Centre, 33 El Bohouth
St. (former El
Tahrir St.), Dokki, P.O. Box 12622, Giza, Egypt

1 Electron Microscope and Thin films Dept., Physics Division National Research Centre, 33 El
Bohouth St.
(former El Tahrir St.), Dokki, P.O. Box 12622, Giza, Egypt

3 Microwave Physics and Dielectrics Department, Physics Division, National Research
Centre, 33 El Bohouth St.(former El Tahrir St.), Dokki, P.O. Box 12622, Giza, Egypt

Abstract
Effect of Cu2+ content on different properties is investigated. Mg 1-xCuxO (0.05≤ x ≤ 0.2)
powder was prepared via solid state reaction. Samples were examined by X-ray diffraction
(XRD) and the results were analyzed by using Full Prof program by employing Rietveld
refinement technique . The results showed that samples with Cu content up to x  0.15 had a
single phase of MgO rock salt structure type and for x 0.2 two phases were detected; namely,
MgO rock salt structure and Cu2O cuprite cubic phase. Also , it was found that, a small increase
in the lattice constants with increasing the Cu con tent. Moreover, the crystallite size was found to
decrease with increasing the Cu concentration. The transmission electron microscopy (TEM)
studies have been performed for studying their morphology . The optical energy gap had been
calculated and was found that there are two energy gaps. The energy gaps decreased with
increasing the Cu content. The dielectric constant ′, the loss factor tan  and conductivity
increased with increasing Cu concentration. This increase can be directly related to the increase
in the concentration of charge carriers and interfacial polarization effects . The saturation
magnetization and the retentivity were found to decrease with the increase in Cu concentratio ns
but the coercivity increased with increasing Cu content.
Key Words : Crystal structure; Optical properties; Dielectrical properties; Magnetic
properties
PACS Nos .: 61.50.−f , 78.20.−e ,77.22.−d ,75.50.Pp Manuscript
Click here to download Manuscript manusc..docx
Click here to view linked References
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

2
Corresponding author: S.A.Gad E -mail: samiagad2000@yahoo.com
1. Introduction

Magnesium oxide ( MgO ) is one of many advanced engineering materials that have been
investigated intensively in recent years because of their potentials for many applications in b ulk,
powder, and thin film forms. Magnesium oxide is a semiconductor/ insulator which crystallize in
rock salt/sodium chloride ( NaCl ) type cubic structure. It is a nonmagnetic insulator with a band
gap of 7.809 eV [ 1]. Many binary oxides, such as, CaO, SrO, BaO, NiO, and CoO , like MgO
crystallize in rock salt structure [1]. MgO is an attractive material which has many applications
[2–15], such as water purification, optoelectronics, microelectronics, and additive in heavy fuel
oil, paint, gas separation, bactericides, and insulator in industrial cables, crucibles, and refractory
materials superconductor physics, fire-retardant, UV – protection, dental cement . Moreover, it
has been used as an oxide barrier in spin tunneling devices as well as substrate i n super
conducting and ferroelectric film s. Also, MgO is used in medical and pharmaceutical products
[16-18] and toxic waste remediation [19, 20]. On the other hand, recent attention has been
focused [21, 22] on the transparency behavior of bulk polycrystalline MgO for infrared
electromagnetic waves, the mat erial that can be a potential substitute for sapphire IR – windows
and protectors for sensor devices.
MgO nano powders are very interesting because of its applications in many industrials areas,
such as a candidate material for translucent ceramics [23] , catalyst, catalyst carriers and
absorbent for many pollutants [24]. On the other hand , Ni/MgO catalysts are prepared by
impregnation, precipitation and mechanical mixing methods [25, 26 ]. Also, MgO nanoparticles
have high catalytic activity due to the presence of active sites or oxygen vacancies on surfaces
and edges which have the potentiality of charge transfer between substrate and adsorbate [27,
28]. Moreover, Nano -MgO materials are found to catalyze efficiently in variety of organic
reactions due to its high specific area [2 9, 30]. The applications of MgO can be outspread by
adjusting the lattice constant, physical and chemical properties by doping other elements such as
Zn, Ni, and Cu. MgO doped with Cu nano powders were prepared by different methods such as
chemical co -precipitation and the effect of Cu on the morphology and structure was studied [ 31].
MgO was portending to display magnetic properties, offering possibility applications of Cu
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

3
doped MgO as diluted magnetic semiconduct ors [3 2]. Thus the new properties are expected in
the MgO doped with other elements. The aim of this work is to study the effect of Cu on the
structure, optical, magnetic and dielectric properties of MgO .

2. Sample Preparation
Polycrystalline Mg 1-xCux O (where x = 0.05, 0.1, 0. 15 and 0. 2) samples were prepared using
solid reaction technique , using high purity (99 .99%) MgO and CuO obtained from Sigma –
Aldrich. Stoichiometric amounts of the starting materials were mixed followed by grinding , to
get a homogenous mixture. The mixed samples were then compressed under a pressure of
3ton.cm-2 in rectangular form. The pressed samples were sintered at 900 °C in air for 23 h. Then
the samples are sintered at 1050 °C for 23h . Finally, the temperature of the furnace was gradually
cooled to room temperature.
3. Experimental details

The X -ray powder diffraction data of the constituent phases were collected on Emprean
Panalytical X -ray diffractometer equipped with Cuk  radiation (1.5406 Å) using a step scanning
mode, in the angular range 30 to 100 2 was carried out in the step size 0.02° of 2 and step time
20 sec/step. Diffuse reflection measurements were done in the wavelength range from 200 nm to
2500 nm using Jasco (V-570) spectrophotometer. A vibrating sample magnetometer model 9600 –
1-VSM was used for the magnetic properties measurements. In the present study, dielectric and
conductivity measurements were carried out by means of high -resolution broad band impedanc e
analyzer (Schlumberger Solartron 1260). The frequency range of the applied ac electric field was
between 0. 1 Hz and 1 MHz. Electromagnetic shielding was implemented to the whole sample
holder in order to diminish noise problems that are common especiall y at low frequencies. The
measurements were automated by interfacing the impedance analyzer with a personal computer
through a GPIB cable IEE488. A commercial interfacing and automation software Lab VIEW
was used for acquisition of data. The error in ' & ε″ amounts to 1% and 3%, respectively.

4. Results and Discussion
4.1 Structure

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

4
111 200
220
311 222
400 MgO
Cu2O The X -ray diffraction patterns for the series Mg 1-xCuxO, 0.05≤x≤0.2 are depicted in Fig. 1.
Applying the search -match program, X'Pert High Score Plus, for phase analysis, it was found
that samples with Cu content up to x  0.15 resemble a single phase solid solution of MgO rock
salt structure type ICDD card no. 98 -006-0497,of space group Fm -3m. While for x 0.2 two
phases were detected; namely, MgO rock salt structure ICDD card no. 98 -006-0497and Cu2O
cuprite cubic phase card no. 98 -017-3982 related to Pn -3m space group. This indicated that the
limited miscibility of Cu2+ ions in the MgO lattice to be around 15%. The phase percentage of
the Mg 1-xCuxO rock salt structure from quantitative phase analysis was 82.8% at the doping level
x0.2. Moreover, as the Cu substitution c ontent increasing, there was a continuous shift in 2θ
towards a low angle side, indicating corresponding increase in lattice parameters. Figure 2 shows
the shifting of (200) peaks and this is true with the other peaks as well .
In order to extract the structural details from powder diffraction data, all the X -ray
diffraction (XRD) patterns were analyzed with the help of Full Prof program by employing
Rietveld refinement technique. The method employs a least -squares procedure to compare Bragg
intensi ties and those calculated from a possible structural model. For the samples with doping
concentration from 0.05 -0.15 a single phase model was used in the refinement where, the space
group was Fm -3m in which the oxygen anions occupy the Wyckoff position 4b, with
coordinates 1/2; 1/2; 1/2, while the Mg and Cu cations occupy the A -site at Wyckoff position 4a,
with coordinates 0; 0; 0.While for the sample with doping level 0.2 a two phase model was used
one of them was MgO model as before and the other one was for Cu2O model in which the Cu
atom occupies the 4b Wyckoff position 4b, with coordinates 0; 0; 0, and oxygen atom occupies
2a position, with the coordinates 0.25;0.25;0.25. A parameterized modified Thompson –Cox–
Hasting pseudo -Voigt function [ 33] was used to fit the peak shape. All the atomic positions we re
considered as fixed parameters while other parameters such as lattice constants, isothermal
parameters, scale factors and shape parameters were considered as free parameters. The
agreement between the observed and the calculated diffraction profiles of the sample with x =
0.05 and 0.20 as representative example s of the investigated compounds are shown in Fig ures.
(3&4).The quality of the agreement between observed and calculate d profiles is estimated by
profile factor (Rp), weighted profile factor (Rwp). The small weighted profile Rp and Rwp
illustrate that the proposed model can be reasonable. Table 1 depicts the lattice parameter (a), the
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

5
unit cell volume the crystallite size (D), and the XRD density (dx), all obtained from Rietveld
refinement. The goodness of fit indices is given in Table (1). Their values signify that the fitting
qualities are good enough for all experimental patterns.

From the lattice parameter values tab ulated in table one, it is clearly indicated that there is
a small increase in their values from x 0.05 up to x  0.15 this may be due to the difference in the
ionic radius between MgO  0.86 Å and CuO 0.87 Å as it compared with the lattice parameters
of pure MgO and the lattice parameters becomes nearly constant from x 0.15 up to x 0.2 and
this may be due to the effect of the second phase. The crystallite size was found to decrease from
121 nm to 49 nm with corresponding increase in Cu content from x=0 .0 5 to x=0.2, which means
that the Cu acts as the grain growth inhibitor. Also we can deduce that, the reduction in particle
size associated with lattice expansion, the same behavior was obtained for CeO 2 nanocrystals
containing dopants larger than Ce4+, such as Nd3+ [34].

The MgO crystal structure can be described as cubic close packed structure of oxygen
atoms and Mg atoms occupying octahedral sites i.e each Mg cations surrounded by 6 Oxygen
anions as shown in Fig. 5. In which the interatomic distances are: Mg–O ranges from 2.1065 to
2.1092 Å, while the O –O ranges from 2.9790 to 2.9829 Å as the copper doping increases and
this may be due to the difference in the ionic radius between Mg2+ and Cu2+.

4.2 Morphologic al study ( TEM)

Fig. 6a-d shows the HR -TEM images of Mg 1-xCuxO. All images indicate aggregates of
uniform shapes of nanoparticles for all samples doped with different Cu concentrations . The
described aggregates composed of sets of welded uniform sphere like particles (see inset figures
(a and b) . The particles in the aggregates having diameters in the range from 80 – 5nm as the Cu
content increases from x=0.05 to 0.2.as clearly observed from Fig. 6a -d. Furthermore, more
welded and clear boundaries of nan oparticles can be observed with increasing Cu content in
MgO . The average particle size detected from the HR -TEM micrographs is smaller than that
obtained from XRD measurement due to the difference in the resolution of both analyses. The
corresponding sele cted area electron diffraction (SAED) of all samples shows highly oriented
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

6
poly crystalline structure with very fine particles in the aggregates. The orientation increases
with increasing the Cu content. The information obtained from the electron microscop y
investigations are in line with those obtained from the XRD analysis .

4.3 Optical Properties
The diffuse reflectance spectrum of semiconducting powder is analogous to their transition
spectrum. A study of the tail of the absorption curve of semiconductor shows that it has an
exponential drop [ 35]. The onset of this drop has been taken and suggested as more universal
method of deducing the positio n of the absorption edge [ 36]. So Fosch [ 36] has taken the onset
of the linear increase in diffuse reflectance R, i.e. the linear decrease in the absorption spectrum
as a measure of the forbidden gap.
The diffuse reflectance spectra of Mg 1-xCuxO (x = 0.05, 0.1, 0.15, 0.2) were measured in
the spectral range 200 –2000 nm. To calculate the optical band -gap energy ( Eg), the fundamental
absorption of light, which corresponds to an electronic excitation from the valance band to the
conduction band, can be applied. Fig.7 shows the reflectance spectra of pure MgO and Cu doped
samples with different concentration of Cu. Further, the optical band gap is evaluated using K –M
function as follows [ 37]:
K/S = (1 -R)2 / 2R (1)

Where R is the absolute reflectance of the sample, K is the molar absorption coefficient and S
is the scattering coefficient. It is shown that from figure 7, there are two optical energy gaps.
Moreover, CuO has two optical energy band gaps as reported in another reference [3 8]. A
decrease in the energy band gap may be due to the combination of higher band gap material
MgO with smaller band gap material CuO and may be due to the increase of the lattice constants
[39, 40]. Fig. 8 shows the relation between energy gaps and the Cu content. The values of the
energy gaps are tabulated in table 2.

4.4 Dielectric properties
Plots of the dielectric constant ( ′) and loss factor ( tan) versus frequency for the series Mg 1-
xCuxO, 0.05≤ x≤ 0.2 are illustrated in Figs. 9 and 10 respectively. Obviously, the permittivity
(ε′) decreases with increasing frequency till reaching a constant value at higher frequencies. The
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

7
highest values of permittivity at low frequencies are due to interfacial polarization effects
associated with an inhomogeneous dielectric medium holding layers of materials with different
permittivity and conductivity . Moreover , an increase in ′ by increasing Cu doping can be seen in
Fig. 9. This increase can be directly related to the increase in the concentration of (Cu2+ ions)
dissolved in MgO lattice . Moreover , it can be explained on the basis of the defect change
according to Warren et al [41]. Accordingly, the presence defect dipoles such as cations of Cu2+
formed by Cu doping assist to increase the total polarizability of the medium , which in turn gives
rise to the dielectric constant of Cu – doped Mg. Moreover, the presence of Cu2+ in MgO lattice
may result in more localization of charge carriers in conju nction with mobile ions causing higher
ionic conductivity this can be another reason for strong low frequency dispersion of dielectric
constant . However, this result is in a good agreement with the results of XRD measurements
which revealed that the Cu ion substitutes for the Mg ion in the MgO lattice.

On the other hand, Fig. 10 for tan  shows a broad relaxation process in the low frequency
region for all the investigated samples within the frequency range (0.1 Hz -1 MHz). This
relaxation process is attributed to Maxwell –Wanger or interfacial polarization, arising from
building -up of charges on boundaries and interfaces between materials with different electrical
properties [ 42, 43].

However, it is slightly shifted towards higher frequency ran ge with increasing the Cu doping
due to the increase of the conductivity of the samples. Ionic conductance probably results from
mobile protons arising from Cu2+ ions dissolved in MgO lattice which is reflected by both of an
increase of free charge mobility and the shift of the peak towards the higher frequency side with
a synchronized increase of its magnitude. The overall result is an enhancement of conductivity
on addition of Cu.

4.4.1 Electrical conductivity

The variation of ac electrical conductivity versus the frequency is depicted in Fig. 11. From
this figure, it is obvious that the electrical conductivity σ increases as the frequency increases in
accordance to universal power law 𝜎(𝜔)=𝜎𝑑𝑐+𝐴𝜔𝑠 [44, 45].

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

8
Where A is dependent on temperature, 𝜎𝑑𝑐 is the dc conductivity (frequency independent
plateau in the low frequency region) , the factor s was calculated from the slope of the
logarithmic plot between σ and the angular frequency where 0< s<1. In general, for ionic
conductors, the values of exponent s lies between 0.5 and 1 demonstrating ideal long -range drift
and limited hopping diffusion (tortuous pathway) [46]. Stand on the obtained results; s is slightly
decreasing by Cu doping (0.845< s <0.955). These values of exponent – s clarify that the long –
range pathway of ions could be one of the sources of the ion conduction. However The right -side
image in Fig.1 1 shows also that dc conductivity (σ dc ) increases with increasing Cu doping
fraction . In particular the trend of the total conductivity σ is generally related to the charge
transport behavior of charge carriers. This trend has been widely noticed in conducting glasses
[47] conducting polymers and doped crystalline solids [ 48].

4.5 Magnetic Properties

The magnetic properties of MgO doped Cu has been studied by VSM measurements and
performed at room temperature. . The relation between the magnetization and the applied
magnetic field is shown in figure 12a-d . It is clearly from th is figure , ferromagnetic behavior
for all samples of Mg 1-xCuxO (x= 0.05, 0.1, 0.15 and 0.2). This type of magnetic behavior may be
explained on the basis of bound magnetic polarons (BMP) model suggest ed by Coey et al. [49].
Oxygen vacancies can induce a ferromagnetic coupling with Cu2+ ions through an indirect
exchange . Similar results have been reported with Mn, Co and Ni-doped ZnO [50- 52] and boost
the results of increase in the defects states with Cu2+ doping which leads to enhance magnetic
properties of Mg 1-xCuxO. Moreover, several reports have tried to explain the origin of
ferromagnetism in MgO . It is believed that the ferromagnetic behavior is related to Mg vacancies
and/or oxygen vacancies and lattice distortion in the MgO structure [ 53, 54, 55-58, 59-66].

Table 3 shows the values of saturation magnetization, coercivity and the retentiv ity. It is clear
that, the values of the saturation magnetization and the retentivity found to decrease with the
increase in Cu concentration s. Previously in TM doped oxide systems, it has been reported that
as the concentration of magnetic impurities is increased in the host oxide matrix, the saturation
magnetic moment decreases which is attributed to the antiferromagnetic (AFM) interaction
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

9
between the dopants (Singhala et al., 2008) [6 7]. Moreover, it is found that improving in
coercivity with Cu concent ration i.e. increasing in coercivity with increasing Cu concentrations.

5. Conclusion
Mg 1-xCuxO samples were successfully prepared by solid state reaction. XRD results
demonstrated that samples with Cu content up to x  0.15 like a single phase solid solution of
MgO rock salt structure type while for x 0.2 two phases were detected; namely, MgO rock salt
structure and Cu2O cuprite cubic phase. The lattice constants increase with increasing the Cu
content indicating that the Cu ion substitutes for the Mg ion in the MgO lattice. The crystallite
size decrease s with increasing the Cu concentration. The optical energy band gap calculated from
the optical properties indicated that, it decreases with increasing the Cu content. The dielectric
constant, the loss factor and the electrical conductivity increased with the doping concentration .
The Mg 1-xCuxO samples showed ferromagnetic behavior . The saturation magnetization and the
retentivity decrease with the increase in Cu concentrations. The coercivity increases with
increasing Cu concentrations .

References :
[1] G Spoto, E N Gribov, G Ricchiardi et al., Progress in Surface Science , 3(76) 71 (2004 ).
[2] K Kaviyarasu and P A Devarajan Der Pharma Chemica 5(3) 248 (2011 ).
[3] S Suresh and D Arivuoli Digest Journal of Nanomaterials and Biostructures 4(6)
1597 (2011 ).
[4] F Gu, S F Wang, M K L¨u et al., Journal of Crystal Growth 3 (260) 507(2004 ).
[5] B Nagappa and G T Chandrappa Microporous and Mesoporous Materials 1(106)
212( 2007 ).
[6] S M Maliyekkal, K R Antony, and T Pradeep Science of the Total Environment 10(408)
2273 (2010 ).
[7] K V Rao and C S Sunandana Journal of Materials Science 1(43) 146 (2008 ).
[8] V R Orante -Barrn, L C Oliveira, J B Kelly et al., Journal of Luminescence 5(131) 1058
(2011 ).
[9] I E Agranovski, A Y Ilyushechkin, I S Altman, T E Bostrom and M Choi Physica C
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

10
1(434) 115 (2006 ).
[10] T Mathews, R Subasri, and O M Sreedharan Solid State Ionics 1(148) 135(2002 ).
[11] N C S Selvam, R T Kumar, L J Kennedy, and J J Vijaya Journal of Alloys and
Compounds 41(509) 9809 (2011 ).
[12] L C Oliveira, E D Milliken, and E G Yukihara Journal of Luminescence 133 211(2013 ).
[13] K D Bhatte,D N Sawant, K M Deshmukh, and B M Bhanage Particuology 3(10) 384
(2012 ).
[14] R Kumar, A Subramania, N T K Sundaram,GV Kumar, and I Baskaran Journal of
Membrane Science 1(300) 104 (2007 ).
[15] F Granados -Correa, J Bonifacio -Mart´ınez, V H Lara, P Bosch and S Bulbulian
Applied Surface Science 15(254) 4688 (2008 ).
[16] J M Hanlon, L Bravo Diaz, G Balducci, B A Stobbs, M Bielewski et al., Cryst. Eng.
Comm . 17 5672 (2015).

[17] M R Bindhu, M Umadevi, M Kavin Micheal, M VArasu, N Abdullah Al -Dhabi
Mater. Lett . 166 19 (2016).

[18] K Krishnamoorthy, G Manivannan, S J Kim, K Jeyasubramanian, M Premanathan

J. Nanopart. Res . 14 (2012).

[19] R Darvishi Cheshmeh Soltani, M Safari, M Mashayekhi Ultrason . 30 123 (2016).

[20] N Salehifar, Z Zarghami, M Ramezani Mater. Lett . 167 226 (2016).

[21] Patent: Jr E Carnall, S E Hatch, Magnesium oxide infrared transmitting optical elements,
US 3236595 A (1966 ).
[22] D C Harris, Infrared Phys. Techn 39 185 (1998).

[23] T Misawa, Y Moriyoshi, Y Yajima, S Takenouchi, T Ikegami ceramic. J. Ceram. Soc.
Jpn. 107 343 (1999).

[24] L M Chen, X M Sun, Y N Liu, Y D Li Apply. Catal. A.: Gen . 265 123 (2004).

[25] Mohammad Jafarbegloo, Aliakbar Tarlani, A Wahid Mesbah , Jacques Muzart , Saeed
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

11
Sahebdelfar Catalysis Letters 146 238 (2016).

[26] Rasoul Zanganeh, Mehran Rezaei, Akbar Zamaniyan Advanced Powder Technology 25(3)
1111 (2014).

[27] E Florez, P Fuentealba, F Mondrago´n, surface Catal. Today 133 216 (2008).

[28] Y X Li, K J Klabunde Langmuir 7 1388 (1991).

[29] V ˇStengl, S Bakardjieva, M Maˇr´ıkov´a, P Bezdiˇcka, and J ˇSubrt Materials Letters
24(57) 3998 (2003).
[30] M B Gawande, P S Branco, K Parghi et al., Catalysis Science & Technology 9(1) 1653
(2011 ).
[31] H Cui, X Wu, Y Chen, J Zhang, R I Boughton Mater. Res. Bull . 61 511 (2015).

[32] FG Kuang, XY Kuang, SY Kang, ZH Wang,AJ Mao Chem.Phys. Lett 621 52 (2 015).

[33] P Thomson, D E Cox, J M Hasting J. Appl. Cryst . 20 79 (1987).

[34] L Li, X Lin, G Li, and H Inomata, J. Mater. Res . 16 3207 (2001).

[35] F Urbach, Phys. Rev . 92 1324 (1953).

[36] P D Fochs, The measurement of the energy gap of semiconductors from their
diffuse reflection spectra. Proc. Phys. Soc. B 69 70 (1956).
[37] J Liu , Y Lu, , X Yang,.; X Yu J. Alloys Compd . 496 261 (2010).

[38] A Asha Radhakrishnan, B Baskaran Beena Indian Journal of Advances in Chemical
Science 2(2) 158 (2014) .

[39] R Dalven, Empirical relation between energy gap and lattice constant in cubic
semiconductors. Phys. Rev. B 8 6033 (1973).

[40] W L Waren, G E Pike, K Vanheusden , D Domos and B A Tuttle J. Appl.. Physics 79
9250 (1996).
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

12
[41] Mohammad L Hassan , Shaimaa M Fadel, Azza A Ward, Charles M. Moorefield, George
R Newkome Polym . Comps . 37 2734 (2016) .

[42] S A Gad, A M Moustafa, A A Ward , J. Inorg. Organomet Polym . 25 1077 (2015) .

[43] H P De Oliveira, MV B dos Santos, CG dos Santos, and C P de Melo, Mater. Charact .,
50 223 (2003).

[44] Ashraf F Ali, Mohammad L Hassan, Azza A Ward, Emad M El -Giar,. Polym .
Compos . 38 893 (2017).

[45] K A Mauritz, Macromolecules 22 4483 (1989).

[46] D K Pradhan, R N P Choudhary, B K Samantaray Int. J. Electochem. Sci . 3 597 (2008).

[47] B Deb, S Bhattacharya, A Gosh Europhysics Letters 96(3) 37005 (2011) .
[48] A M Khalil, Mohammad L Hassan, A A Ward Carbohydrate Polymers 157 503 (2017).
[49] J M D Coey, M Venkatesan and C B Fitzgerald, Nat. Mater . 4 173 (2005) .
[50] Y M Sun, Ph.D. thesis, University of Science and Technology of China (2000) .
[51] U Koch, A Fojtik, H Henglein, Chem. Phys. Lett . 122 507 (1985) .
[52] L Spanhel, M A Anderson J. Am. Chem. Soc. 113 2826 (1991) .
[53] J G Zhu, C Park , Mater. Today 9 36 (2006).
[54] L Guodong, J Shulin, Y Liangliang, F Guangtao, Y Changhui J. Phys .: Condens.
Matter. 22 046002 (2010).

[55] C Martínez -Boubeta, J I Beltrán, L Balcells, Z Konstantinovi ć, S Valencia, D
Schmitz et al., Phys. Rev. B. 82 024405 (2010).

[56] C M Araujo, M Kapilashrami, X Jun, O D Jayakumar, S Nagar et al., Appl. Phys.
Lett. 96 232505 (2010).

[57] J Li, Y Jiang, Y Li, D Yang, Y Xu, M Yan Appl. Phys. Lett. 102 072406 (2013).
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

13

[58] F Wang, Z Pang, L Lin, S Fang, Y Dai, S Han Physical Review B 80 (2009).

[59] T Uchino, T Yoko, Physical Review B 85 012407 (2012).

[60] A Droghetti, C D Pemmaraju, S Sanvito Phys. Rev. B . 81 (2010).

[61] N. Kumar, D Sanyal, A Sundaresan Chem. Phys. Lett . 477 360 (2009).

[62] S Xie, X. Han, Q Kuang, Y Zhao, Z. Xie, L Zheng, J. Mater. Chem. 21 7263 (2011).

[63] L Balcells, J I Beltrán, C Martínez -Boubeta, Z Konstantinovi ć, J Arbiol, B
Martínez Appl. Phys. Lett . 97 252503 (2010).

[64] G Feng, S Van Dijken, J F Feng, J M D Coey, T Leo, D J Smith J. Appl. Phys .
105 033916 (2009).

[65] K Mizunuma, M Yamanouchi, H Sato, S Ikeda, S Kanai et al., Appl. Phys. Express 6
063002 (2013).

[66] K Tamanoi, M Sato, M Oogane, Y Ando, T Tanaka et al., J. Magn Magn Mater. 320
2959 (2008).

[67] A Singhala, S N Acharya, A K Tyagia, P K Mannab, and S M Yusuf Materials Science and
Engineering B 153(1-3) 47 (2008) .

Figure Captions:

Fig.(1): X-ray powder diffraction pattern for the samples Mg 1-xCuxO, 0.05 x≤0.2.
Fig. 2: Zoom on (200) reflection in MgO.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

14
Fig. 3: Final Rietveld refinement for Mg 0.95Cu0.05O sample as representative one. The observed
(closed circles) and calculated (solid line) X -ray diffraction profiles and the difference between
them (on the bottom). Vertical bars refer to calculated Bragg peak positions .

Fig. 4: Final Rietveld refinement for Mg 0.8Cu0.2O sample as representative one. The observed
(closed circles) and calculated (solid line) X -ray diffraction profiles and the difference between
them (on the bottom). Vertical bars refer to calculated Bragg peak positions.

Fig.5: MgO crystal structure, the Mg cation surrounded by 6 Oxygen anions forming octahedra.

Fig.6a -d : HRTEM images of Mg 1-xCuxO, where , 0.05≤ x ≤0.2 (a) x= 0.05, (b) x= 0. 1,(c) x=
0.15 and (d) x= 0.2

Fig.7: k/s versus the wavelength λ for Mg 1-x CuxO.

Fig.8: The optical energy band gap as a function of Cu content.

Fig 9. Dependence of the dielectric constant ε ′ on frequency for Mg 1-xCuxO, 0.05≤ x ≤ 0.2 at
room temperature (30oC). The right -side image shows the data of dielectric constant ε′ at
fixed frequencies of 10 Hz and 10 kHz respectively.

Fig 10. Dependence of the loss factor tan on frequency for Mg 1-xCuxO, 0.05≤ x ≤0.2 at room
temperature (30oC). The right -side image show the data of tan  at fixed frequencies
of 10 Hz and 10 kHz respectively.

Fig 11. Dependence of the electrical conductivity σ on frequency for Mg 1-xCuxO, 0.05≤x≤0.2
at room temperature (30oC). The right -side image show the data of dc conductivity for
Mg 1-xCuxO, 0.05≤ x≤ 0.2 at room temperature (30oC).

Fig.12a-d : The magnetic hysteresis of Mg 1-xCuxO samples at room temperature.

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

15

1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65

Dear Editor and Reviewers:
For Reviewer #1 :

The paragraph concerning the morphological study dealing with divalent Cu. The author must
rewrite the text with monovalent copper.

 The valency of Copper at CuO oxide is divalent because of one copper atom with valence 2+
combine with one oxygen atom -2, while the valency of Copper at Cu 2O oxide is monovalent
because of two copper atoms combine with one oxygen atom.
For reviewer 2 :
Comment 1: According to literature, atomic radius of Cu+2 is smaller than that of Mg+2. But
with the higher Cu content in the doped systems, the lattice parameters are gradually increasing.
This point must be elucidated in the revised manuscript.

 According to liter ature, atomic radius of Cu+2 is smaller than that of Mg+2. But with the
higher Cu content in the doped systems, the lattice parameters are gradually increasing. This
point must be elucidated in the revised manuscript.

Page 5 paragraph 2 line
According t o literature, atomic radius of Cu+2 is smaller than that of Mg+2. But with the higher
Cu content in the doped systems, the lattice parameters are gradually increasing. This point must
be elucidated in the revised manuscript .
The Crystal ionic radius for MgO is 0.86 Å at six coordination, while for Cu2+ is 0.87 Å at the
same coordination, while the effective ionic radius of MgO is 0.72 Å and for CuO is 0.73 Å
[1,2]. So either of the crystal ionic radius or the effective ionic radius of Cu2+ are larger than that
for MgO2+. So a little bet increase in the unit cell dimension, was observed due to the
substitution of Mg2+ by Cu2+
[1]“Effective Ionic Radii in Oxides and Fluorides” , R.D. SHANNON and C.T. PREWITT,
ActaCryst., B25, 925 (1969).
[2] “Revised Effec tive Ionic Radii and Systematic Studies of Interatomie Distances in Halides
and Chaleogenides” , R. D. SHANNON, ActaCryst., A32, 751 (1976).

Comment 2: The authors claim that both the dielectric constant and electrical conductivity of the
samples increa se with increasing Cu doping because of free charge. But usually the presence of
free charge contributes to electrical conductivity, whereas the effect is detrimental to dielectric
constant. Contradiction of this general notion is not clear in the present manuscript. Authors' Response to Reviewers' Comments
Click here to download Authors' Response to Reviewers'
Comments Dear Editor and Reviewers.docx

 The explaining of th ese comment s are shown in the manuscript (the change is indicated by
the red color) ( page 7 paragraph 1 line 59 , and page 8 paragraph 1) .
Comment 3: With the increasing Cu content, the nature of the magnetic hysteresis gradually
transforms from ferromagnetic to super -paramagnetic nature. Will the authors explain this in the
revised manuscript?
 The obtained hysteresis at room temperature supports the fact that the magnetic behavior is
weakly ferromagnetic and not superparamagnetic. To verify this, we must plot M /Ms (Ms =
saturation magnetization) versus H/ T for the M -H data at different temperatures and all the
curves remain distinct . So, we need measure the magnetization with tem perature, we can
make this studying after that . For superparamagnetic systems, as is well -known, the curves
merge into a single one. [1- B. Martinez, F. Sandiumenge, Ll. Balcells, J. Arbiol, F. Sibieude
and C. Monty,
Phys. Rev. B 72, 165202 (2003). 2 – R. H. Kodama and A. E. Berkowitz, Phys. Rev. B 59
, 6321 (1999). ]

Comment 4: The authors should include Cole -Cole plot to explain the nature of electrical
conductivity.

 The authors see that there is no need for including Cole -Cole plot to explain the nature of
electrical conductivity as they have already explained the nature of conduction on the basis of
the widely used universal power law.

Comment 5: It is mentioned that "the values of the saturation magnetization and the retentivity
found to decrease with the increase in Cu concentration", however, there is no qualitative
explanation in the manuscript.

 I have modified this part in the manuscript (page 8 last paragraph lines 26 – 32)

Previously in TM doped oxide systems, it has been reported that as the concentration of
magnetic impurities is increased in the host oxide matrix, the saturation magnetic moment
decreases which is attributed to the antiferromagnetic (AFM) interaction between the dopants
(Singhala et al., 20 08). Therefore, we feel that in the presently studied samples, as Cu
concentration is increased the possibility of enhanced AFM interaction between neighbouring
Cu-Cu ions would decrease, leading to the observed behaviour at high magnetic field values.

Consequently, ferromagnetic interaction strengthens as the Cu concentration increases. As the
average crystallite size increases, the values of saturation magnetization increase .
[Singhala, A., Acharya, S.N., Tyagia, A.K., Mannab , P.K. and Yusuf, S.M. (2008) ‘ Colloidal
Fe-doped ZnO nanocrystals: facile low temperature synthesis, characterization and properties’
Materials Science and Engineering B, Vol. 153, Nos. 1 –3, pp.47 –52.].

For reviewer 3: Moreover, the authors should be more careful regarding the term 'nano'. They
are claiming MgO nanoparticles however the XRD of the materials show bulk nature.
 The calculated values of the crystallite size after doing the instrumental correction and
Rietveld refinement was 121nm, 60nm, 6 3nm and 49 nm with increasing the doping level.
Usually the term nanomaterials applied for all values of crystallite size less than 100 nm. In
addition, the scale of the X -ray diffractograms were in arbitrary units.
The doped XRD diffractorgrams show peak s of CuO also. This is not doping but blending.
 The doped XRD diffractomgram for Mg 1-xCuxO, x= 0.05, 0.1, 0.15 consists of one phase
related to the MgO and the Copper oxide formed solid solution with MgO. While for x=0.2
consists of two phase s, one of them related to MgO and the other one is Cu 2O as shown in
Figure (1) indicated by the arrow.

 The introduction and the discussion of electrical are modified as shown in the
manuscript.

For reviewer 4:
 I have made some changes over the manus cript and I have added some explanation for the
discussion of the results as shown in the manuscript. I have changed the abstract as you
suggested (page 1 lines 28 ,30)
 Also, the references [ Preparation of nanocrystalline NiO -MgO solid solution powders as
catalyst for methane reforming with carbon dioxide: Effect of preparation conditions
Advanced Powder Technology
Volume 25, Issue 3, May 2014, Pages 1111 -1117

2.NiO -MgO Solid Solution Prepared by Sol -Gel Method as Precursor for Ni/MgO Methane Dry
Reforming Catalyst: Effect of Calcination Temperature on
Catalytic Performance
Mohammad JafarbeglooAliakbar Tarlani A. Wahid MesbahJacques MuzartSaeed Sahebdelfar
Catalysis Letters,January 2016, Volume 146, Issue 1, pp 238 -248] are added and have the
numbers 25 and 26 in references of the manuscript (pages 10 and 11 ) .

For reviewer 5 :
 I have modified the introduction, the reasons of decreasing the optical energy gap with Cu
content are shown in the manuscript (page 6 last paragraph lines 40 -44) .
 I have placed TEM images with the same scale for the samples (as shown in Figs.)
 We have already included updated references and added another two references (pages
10,11)

111 200
220
311 222
400 MgO
Cu2O

Fig.1

Fig.2

Figure

Fig.3

Fig.4

Fig.5

Fig.6a-d

500 1000 1500 20000102030405060
S1(Mg0.95Cu0.05O)
S2(Mg0.9Cu0.1O)
S3(Mg0.85Cu0.15O)
S4 (Mg0.8Cu0.2O) F(R) =K/S
Wavelength(nm)S1
S2
S3
S4
Fig.7
0.00 0.05 0.10 0.15 0.202.02.53.03.54.0Eg(eV)
Composition (x)Eg1Eg2

Fig.8

Fig.9

Fig.10

Fig.11

-20000 0 20000-0.50.00.5Magnetization(emu/g)
Magnetic field(G) Mg0.95Cu0.05O
a

-20000 0 20000-0.50.00.5 Mg0.9Cu0.1OMagnetization(emu/g)
Magnetic field(G)b

-20000 0 20000-0.30.00.3Magnetization(emu/g)
Magnetic field(G) Mg0.85Cu0.15O
C
-20000 0 20000-0.20.00.20.4Magnetization(emu/g)
Magnetic field(G) Mg0.8Cu0.2O
d

Fig12a -d

Table 1 : The refined unit cell parameters and agreement factors of Mg 1-xCuxO with
indicated x.

Criteria of fit and
structure parameters x0.05 x0.10 x0.15 x0.2
Atomic positions for Mg1 -xCuxO Mg
Cu
O 0,0,0 0,0,0 0,0,0 0,0,0
0,0,0 0,0,0 0,0,0 0,0,0
0.5,0.5,0.5 0.5,0.5,0.5 0.5,0.5,0.5 0.5,0.5,0.5
Atomic positions for CuO Cu
O –– –– –– 0,0,0
–– –– –– 0.25,0.25,0.25
Isotropic Thermal displacement parameter –– –– ––
O 0.18(4) 1.15(8) 0.11(4) 1.7(2)
Mg 0.19(5) 0.72(5) 0.25(3) 0.81(5)
Cu 0.19(5) 0.72(5) 0.25(3) 0.81(5)

Rp 26.6 31.5 57.0 41.2
Rwp 22.0 23.2 32.3 26.5
Rexp 22.47 24.27 30.88 27.68

a (Å) 4.21297(1) 4.21530(1) 4.21835(2) 4.21844(2)
Cell volume(Å3) 74.776(2) 74.901(1) 75.063(1) 75.068(1)
Crystallite Size nm 121 60 63 49
Density (gm/Cm3) 3.892 3.922 4.393 4.234
Mg-O 2.1065 2.1076 2.1092 2.1092
O-O 2.9790 2.9807 2.9828 2.9829 Table

Table 2: The calculated values of the optical energy gaps of Mg 1-xCuxO.

Composition (x) Optical energy gaps
(Eg 1) ( E g2)
0.05 2.41 3.68
0.1 2.3 3.6
0.15 2.12 3.46
0.2 1.994 3.24

Table 3: The values of Magnetization M s, Coercivity H c and Retentivity M r of
Mg 1-xCuxO
Composition Ms(emu/g) HC(G) Mr(memu/g)
0.05 0.61329 98.032 57.946
0.1 0.51263 118.02 35.393
0.15 0.31891 133.2 28.828
0.2 0.25662 154.54 25.125