General conclusions [609952]

235
General conclusions

The objectives of this thesis were to study the structure, microstructure, ferroelectric, dielectric
and piezoelectric properties , phase transitions of Pb1-xLax(Zr 0.9Ti0.1)1-x/4O3 (PLZT x/90/10 ) system
with compositions across the ferroelectric/antiferroelectric (FE/AFE ) boundary. The thesis is
mainly focused to study the AFE -to-FE switching . The experimental results have reve aled new
findings which are important in understanding of the field-induced AFE -to-FE transition . The
main results are summarized below:

 The influence of the La addition on the micro structure of PLZT x/90/10 ceramics

 Increasing the amount of La3+ from 2 at.% to 4 at.% result in a slight decrease of ceramic
grain size from 5 μm to 1 μm , for the same calcination and sintering parameters (calcination
at 850C for 4h and sintering at 1250  C for 2h ).

 The influence of the La addition on crystalline structure of PLZT x/90/10 ceramics

 Dense PLZT ceramics with pure perovskite phase have been produced by co nventional
solid state reaction.
 The complex structural analysis (XRD, HRXRD, TEM, Raman) have revealed that
increasing La content from 0 to 4% in the PZT 90/10 system produces a crossover from
FE long -range order toward s AFE state : the comp ositions with x≤0.025 have a
macroscopic rhombohedral R3c symmetry and develop locally AFE clusters with lower
symmetry FE phase; the range of compositions 0.025≤x≤0.035 show a phase coexistence
region with the rhombohedral R3c and orthorhombic Pbam struct ure; at higher values of
x≥0.035 the orthorhombic Pbam structure to PbZrO 3 was stabilized .
 In addition, Raman spectroscopy indicates that this compositions may develop locally other
low symmetry phases at room temperature

 The influence of the La addition on dielectric and piezoelectric properties of PLZT
x/90/10 ceramics

236
 Dielectric and piezoelectric studies confirm ed the results of the structural analysis showing a
large compositional rang e with AFE –FE phase coexistence across the FE/AFE border .
 The room temperature permittivity has a maximum for x = 0.03, while the piezoelectric
constants show anomalies in the range of compositions x = (0.03, 0.035). These anomalies
were interpreted as being related to the phase superposition or to the development of a
morphotropic phase boundary.

 Study of the AFE -to-FE field induced transition in PLZT x/90/10 system

 Polarisation vs. electric field dependence confirm s the structural calculations according to
which these compositions trans form from FE to AFE states , with a stabili zation of the AFE
phase at higher La3+ content.
 The AFE PLZT x/90/10 ceramics shows the ability to switch between an antipolar AFE and a
polar FE state under high electric field, similar ly with PbZrO 3-based ceramics.
 The study of P(E) loops indicated that La3+ chemical m odifier helps to stabili ze the AFE phase
and hence to manipulate the AFE-to-FE phase transition in PLZT x/90/10 based ceramics : the
composition with x≤3.1 show s macroscopic FE behavior; the compositions with x=3.2 and
x=3.3 show an irreversible AFE -to-FE transition ; the ceramics with La3+ content, x≥3.5,
present a field induced AFE -to-FE reversible phase transition. The AFE -to-FE switching field
increases as the amount of AFE phase increases in PLZT x/90/10 compositions .
 In situ X-ray diffraction study indicate s that PLZT 4/90/10 and PLZT 3/90/10 compositions ,
in addition to the AFE -FE phase switching , exhibit irreversible preferred orientation after
experiencing the field -induced AFE -to-FE phase switching. An electric field -induced structure
develops in both compositions , which has a reversible character during the field decreas e in
PLZT 4/90/10 and an irreversible character in PLZT 3/90/10.
 Structural analysis of pre -poled PLZT 3/90/10 ceramics show s that it is possible to induce
successive FE-to-AFE and AFE -to-FE transitions when fields with reversed polarity are
applied in sequence. The field range required to induce the AFE phase is broad, and the phase
transition is kinetically slow. This kind of transition s has been rarely reported before.
 A remarkable result of this study is that the PLZT 3/90/10, PLZT 3.2/90/10 and PLZT 4/90/10
compositions show very high remnant p olarization Pr~58 µC/cm2 during the application of
electric field E≥E AF of very low frequency f~1/300 Hz . These results are confirmed by Rietveld
study of ex situ HXRD data obtained for powders from poled PLZT 3/90/10 composition ,
which stated that the system is monoclinic.

237
 A study regarding the composition and electric field -dependent energy storage properties in
PLZT ceramics across the FE-AFE boundary has been performed . A recoverable energy
density of 1.8 J cm−3 and a high efficiency (η~60) have been achieved on 3.5% of La
modification , which suggests that these AFE compositions are interesting for potential
applications for energy storage.

 Study of the influence of the La addition on phase transitions sequence in PLZT x/90/10
ceramics

 The substitution with La3+ of Zr/Ti ions in the B -site perovskite position s leads to the decrease
of stability of the FE phase and decrease of the critical temperature for the FE/AFE -PE phase
transition. Th is transition for compositions with x≥3 is highly diffuse. The diffusene ss of the
phase transition increases considerably when the composition of the solid solution moves
toward the compositions corresponding to the pure AFE phase.
 It was proposed a new phase diagram of the PLZT x/90/10 system where new temperature
phase bound aries are proposed : a border between monoclinic and low temperature FE or high
temperature FE phases; a boundary between low temperature FE phase and AFE
commensurate ; in a limited temperature range there is a transition between AFE commensurate
and AFE incommensurate state, a high temperature FE phase was found between AFE
incommensurate and PE phase. Therefore , the knowledge concerning the phase transition
sequence was completed for PLZT x/90/10 ceramics.

238

List of Figures

Fig. 1. 1 An ideal cubic ABO 3 perovskite unit cell ………………………….. ………………………….. ……..
Fig. 1. 2 Network of corner -linked octahedral where the A sites (yellow ball) is inside an
octahedral cage of Oxygens ………………………….. …………………… Error! Bookmark not defined.
Fig. 1. 3 Schematic illust rations of the polarization switching: (A -C) the initial poling, (C -E) the
electrical reversal, and (F -A) the electrical cycling. Under the application of an electric field, the
B cations displacement is shifted along the electric field direction, giving r ise to the lattice
distortion. (The rectangles with blue arrows represent schematically the repartition of the two
polarization states in the material ( e.g. in the cermic grains) at different fields. Error! Bookmark
not defined.
Fig. 1. 4 Current vs. field during domain switching in FEs (“current hysteresis”) ………….. Error!
Bookmark not defined.
Fig. 1. 5 Schematic diagram of the evolution of AFE -FE phase switching during application and
releasing of adequate electric field. Figure adapted from [ 59] ….. Erro r! Bookmark not defined.
Fig. 1. 6 Representative electric -field-induced polarization hysteresis loop of AFE materials.
………………………….. ………………………….. ………………………….. … Error! Bookmark not defined.
Fig. 1. 7 Current -field dependence of AFEs ………………………….. Error! Bookmark not defined.
Fig. 1. 8 Typical field dependence of the dielectric permittivity of a tunable ferroelectric ceramic
………………………….. ………………………….. ………………………….. … Error! Bookmark not defined.
Fig. 1. 9 DC field dependence of pemittivity in AFEs with reverssibile AFE to FE field induced
transition [3] ………………………….. ………………………….. ………….. Error! Bookmark not defined.
Fig. 1. 10 a) DC field dependence of permittivity and b) its corresponding P(E) loop in AFEs
with irreversible AFE to FE field induced transition [71] ……….. Error! Bookmark not defined.
Fig. 1. 11 P(E) hysteresis loop and energy storage characteristics for a) FE and b) AFE ceramics
………………………….. ………………………….. ………………………….. … Error! Bookmark not defined.
Fig. 1. 12 Second order phase transition. (a) Free energy (F) as a function of the polarization (P)
at T > T 0, T = T 0, and T < T 0; (b) Spontaneous polarization P 0 (T) as a function of temperature
(c) The susceptibility χ and its inverse, at the equilibrium condition P0(T) Error! Bookmark not
defined.
Fig. 1. 13 First order phase transition. a) Free energy as a function of the polarization ……. Error!
Bookmark not defined.

239
Fig. 1. 14 Schematic hysteresis in an idealized ferroelectric …….. Error! B ookmark not defined.
Fig. 1. 15 Theoretical temperature –electric field (T –E) phase diagram associated with the free –
energy given by Eq. (1.6.2) for 𝛽 > 0 and 𝛼 >0. Hatched and hatched -dotted curves represent,
respectively, second -order transition and limit of stability curves. The thermodynamic paths for
T > T C, TC > T > T 0 and T < T 0 are described in the text. ………… Error! Bookmark not defined.
Fig. 1. 16. Temperature dependence of the dielectric susceptibility as given by Eq. (1.6.10)
across a second -order (a) and first -order (b) transition ……………. Error! Bookmark not defined.
Fig. 1. 17 Typical electric field dependence P(E) of the polarization of an AFE material together
with the energy diagrams explaining the double hysteresis lo ops Error! Bookmark not defined.
Fig. 2. 1 Phase diagram of PZT according to Jaffe et al. [1, 33] with the newly discovered
monoclinic phase according to Noheda et al. [34-38]. P C means the paraelectric cubic phase, F T
the FE tetragonal phase, F R the FE rhombohedral phase, F M the monoclinic phase, A T the AFE
tetragonal phase, and A O an orthorh ombic AFE phase ……………. Error! Bookmark not defined.
Fig. 2. 2 Phase diagram of PLZT system after Haertling et al. [24] ……….. Error! Bookmark not
defined.
Fig. 2. 3 PLZT phase diagram, after Haertling and Land a) across entire compositon Zr/Ti ratio.[3]
Points indicate the compositions fabricated, PLZT 100x/90/10 (100x 0, 2, 4, and 10). AFE
antiferroelectric, FERh ferroelectric rhombohedral, FETet ferroelectric tetragonal, SFE slim –
loop ferroelectric, and PECubic paraelectric cubic and b) detail of the AFE/FE phase boundary
………………………….. ………………………….. ………………………….. … Error! Bookmark not defined.
Fig. 2. 4 Phase diagram of PLZT constructed from the data reported by A. Pelaiz –Barranco et
al. [71, 72] and Knudsen et al. [57] ………………………….. ………… Error! Bookmark not defined.
Fig. 2. 5 Phase diagram of 2/95/5 and 4/5/95 as function of temperature and field [55] …… Error!
Bookmark not defined.
Fig. 3. 1 Flow diagram of the experimental procedure of the PLZT powder synthesis …….. Error!
Bookm ark not defined.
Fig. 3. 2 Crucibles setup for sintering dense PLZT ceramics ……. Error! Bookmark not defined.
Fig. 3. 3 Flow diagram of the PLZT samples preparation from powder calcined at 800°C for 4h
………………………….. ………………………….. ………………………….. … Error! Bookmark not defined.
Fig. 3. 4 Illustration of the X -Ray Diffraction setup showing the symmetry of the experiment as
well as the Braggs law ………………………….. ………………………….. Error! Bookmark not defined.
Fig. 3. 5 Sawyer -Tower circuit used for polarization measurement ……….. Error! Bookmark not
defined.
Fig. 3. 6 Poling sample holder ………………………….. ……………….. Error! Bookmark not defined.

240
Fig. 4. 1 Goldsmith tolerance factor t for all PLZT x/90/10 investigated composition …….. Error!
Bookmark not defined.
Fig. 4. 2. Comparison of XRD patterns of PLZT calcined powders for four La concentrations
(2.0, 2.5, 3.0, 4.0 at % ) calcined at a) 800C and b) 850 C for 4 h ………… Error! Bookmark not
defined.
Fig. 4. 3 Comparison of XRD patterns of PLZT sintered ceramics obtained from powders
calcined at 800 C with La content of 2.0, 2.5, 3.0, 4.0 at % sintered at: a) 1200C and b) 1250 C.
………………………….. ………………………….. ………………………….. … Error! Bookmark not defined.
Fig. 4. 4 Comparison of XRD patterns of PLZT sintered ceramics obtained from powder
calcined at 850 C with four La concentrations (2.0, 2.5, 3.0, 4.0 at %) si ntered at: a) 1200 C and
b) 1250C for 2 h ………………………….. ………………………….. …….. Error! Bookmark not defined.
Fig. 4. 5 Lanthanum concentration dependences of the experimental (Archimede’s) absolute and
relative densities of the PLZT ceramics: a) variation of PLZT density at various sintering
temperatures for four representative compositions and b) the evolution of PLZT density for all
the investigated compositions (calcination at 850oC, sint ering at 1250 C). Error! Bookmark not
defined.
Fig. 4. 6 SEM micrographs of the fractured surfaces of PLZT 100x/90/10 compositions: (a)
x=0.0 at. %, (b) x=2.0 at. %, (c) x=2.5 at. % and (d) x=3.0 at. %. Error! Bookmark not defined.
Fig. 4. 7 SEM micrographs of the fractured surfaces of PLZT 100x/90/10 compo sitions: (a)
x=3.1 at. %, (b) x=3.2 at. %, (c) x=3.3 at. % and (d) x=3.5 at. %, ………… Error! Bookmark not
defined.
Fig. 4. 8 SEM micrographs of the fractured surfaces of PLZT x/90/10 compositions: (a) x=3.8 at.
% and (b) x=4.0 at. %. ………………………….. ………………………….. Error! Bookmark not defined.
Fig. 4. 9 X-ray diffraction patterns (a) and detai ls b) at room temperature for all the investigated
PLZT x/90/10 compositions. ………………………….. ………………….. Error! Bookmark not defined.
Fig. 4. 10 Lorenzian fit peaks and peaks deconvolutions for PLZT composition 3/90/10 … Error!
Bookmark not defined.
Fig. 4. 11 The evolution with x of the (111)/(11 -1)R intensities ratio and of the (001)/(100) O
intensities ratio ………………………….. ………………………….. ……….. Error! Bookmark not defined.
Fig. 4. 12 Powder HXRD of PLZT x/90/10 ceramics with compositions x=0.00, 0.020, 0.025,
0.030, 0.031, 0.032, 0.033, 0.035, 0.038, 0.040 ……………………… Error! Bookmark not defined.
Fig. 4. 13 Evolution of the HXRD profiles of pseudocubic (111), (200), and (211) reflections
with compositions (x) for PLZT x/90/10 ………………………….. ….. Error! Bookmark not defined.

241
Fig. 4. 14 Observed (dots), calculated (continuous line), and difference (bottom line) profiles of
PLZT (a) 0/90/10, (b) PLZT2/90/10, (c) PLZT 2.5/90/10 and (d) PLZT 3/90/10 obtained after
Rietveld refinement using R3c and Pbam structural models. Vertical ticks b elow the peaks
mark the position of the Bragg reflections. ………………………….. .. Error! Bookmark not defined.
Fig. 4. 15 Observed (dots), calculated (continuous line), and diff erence (bottom line) profiles of
(a) PLZT 3.1/90/10, (b) PLZT3.2/90/10, (c) PLZT 3.3/90/10 and (d) PLZT 3.5/90/10 obtained
after Rietveld refinement using R3c and Pbam structural models. Vertical ticks below the peaks
mark the position of the Bragg reflect ions. ………………………….. .. Error! Bookmark not defined.
Fig. 4. 16 Observed (dots), calculated (continuous line), and difference (bottom line) profiles of
(a) PLZT 3.8/90/10 and (b) PLZT 4/90/10 obtained after Riet veld refinement using Pbam
structural model. Vertical ticks below the peaks mark the position of the Bragg reflections .
………………………….. ………………………….. ………………………….. … Error! Bookmark not defined.
Fig. 4. 17 Variation of ferroelectric phase volume ( R3c) and antiferroelectric phase volume
(Pbam ) with La content for PLZT x/90/10 compositions (the unit size of the volume is A˚3 )
………………………….. ………………………….. ………………………….. … Error! Bookmark not defined.
Fig. 4. 18 Variation of rhombohedral R3c and orthorhombic Pbam phase fraction with increasing
La amount for PLZT x/90/10. ………………………….. ………………… Error! Bookmark not defined.
Fig. 4. 19 Schematic illustration of the rotation (left) and in phase tilting (right) effect of TiO 6
octhaedra where Pb/La ions are in the center of octahedra. ……… Error! Bookmark not defined.
Fig. 4. 20 Schematic illustration of the antiphase tilting (right) effect TiO 6 octhaedra obtained
from the antiferroelectric Pbam phase for the composition PLZT 4/90/10 Pb/La Ions are in the
center between octahedra while Zr/Ti are inside of octhaedra. …. Error! Bookmark not defined.
Fig. 4. 21 (a) Bright Field TEM image of PLZT 3.2/90/10 specimen showing a multi -domain
grain with alternating AFE/FE configuration. Domains 1, 3, 5 present both the incommensurate
spots 1/n(a*+b*) with n=8-9 in the <001> pc ZA and ½(ooo) superlattice reflections in the
<011> pc while for domains 2, 4 both features are missing. (b) Bright Field and (c) Dark Field
TEM images showing the nanostructure streaking inside the AFE domains perpendic ular to the
direction of the satellite spots. ………………………….. ………………… Error! Bookmark not defined.
Fig. 4. 22. Diffraction patterns obtained from PLZT x/90/10 samples indexed with zone axes
˂011˃ P which evidenced the superstructure reflections arising from antiphase tilting of R3c
structure for PLZT composition a) 2.5/90/10, b) 3/90/10, c) 3.2 90/10, d) 3.3/90/10, e) 3.5/90/10
and f) 4/90/10. ………………………….. ………………………….. ………… Error! Bookmark not defi ned.
Fig. 4. 23 Diffraction patterns obtained from PLZT x/90/10 samples indexed with zone axes
˂010˃ P which evidenced the superstructure reflections arising from antiphase tilting of Pbam

242
structure for PLZT composition a) 2.5/90/10, b) 3/90/10, c) 3.2 90/10, d) 3.3/90/10, e) 3.5/90/10
and f) 4/90/10 ………………………….. ………………………….. …………. Error! Bookmark not defined.
Fig. 4. 24. Selected area diffraction patterns obtained from PLZT x/90/10 samples indexed with
zone axes ˂001˃ which evidenced the1/4(110) superattice reflec tions arising from AFE
incommensurate phase for PLZT composition a) 2.5/90/10, b) 3/90/10, c) 3.2 90/10, d)
3.3/90/10, e) 3.5/90/10 and f) 4/90/10 ………………………….. ……… Error! Bookmark not defined.
Fig. 4. 25 Selected -area electron diffraction obtained from composition PLZT 3.5/90/10 .. Error!
Bookmark not defined.
Fig. 4. 26 . Compositional dependence of the Raman spectra of PZT ceramics at 4 K, 75 K, 100
K and 300 K, respectively corrected from the Bose -Einstein factor. The proposed labels of the
vibrational modes are in agreement with ones of the PbTiO 3. Raman features are numbered
consecutively from 1 to 17, starting from low wavenumbers (see text). ….. Error! Bookmark not
defined.
Fig. 4. 27. Compositional dependence of the Raman spectra in the low frequency band of PZT
ceramics at 4 K, 75 K, 100 K and 300 K corrected from the Bose -Einstein factor. The proposed
labels of these modes was realised according to ones reported for PbTiO 3 [67] Error! Bookmark
not defined.
Fig. 4. 28. The evolution of the frequency for the characteristic Raman modes as a Function of
La content in PLZT x/90/10 (100K). ………………………….. ……….. Error! Bookmark not defined.
Fig. 4 . 29. Position (characteristic frequency) and integrated intensity (amplitude), of the ~60
cm-1 peak of the Raman spectrum of the PLZT x/90/10 compositions as a function of La
addition. ………………………….. ………………………….. ………………… Error! Bookmark not defined.
Fig. 5. 1 Room temperature dielectric properties: a) composition – dependence of permittivity at
a few selected frequencies and b) composition – dependence of dielectric losses at a few selected
frequencies for PLZT x/90/10 ceramics Error! Bookmark not defined.
Fig. 5. 2 Dependence of the room temperature pie zoelectric coefficients upon the La
concentration for PLZT x/90/10 ceramics. ………………………….. .. Error! Bookmark not defined.
Fig. 6. 1 Room temperature P(E) hysteresis and I(E) loops of La3+ modified PZT x/ 90/10 during
first and second loading (frequency of 1 Hz) from virgin sample at room temperatures. The
hysteresis loops and current curves from (a) and (b) were obtained for the composition PLZT
3/90/10, (c) and (d) for P LZT 3.2/90/10 and (e) and (f) for PLZT 4/90/10, respectively. Here, the
EAF-virgin and EAF represents the forward switching fields required to induce AFE -to-FE phase
transition, the EFA is the threshold field for the recovery of the AFE phase and the Ec represents
the coercive field of FE phase ………………………….. ………………… Error! Bookmark not defined.

243
Fig. 6. 2 Room temperature dynamic P(E) hysteresis loops of La3+-modified PZT x/ 90/10
ceramics at different magnitudes of the applied field at frequency of 1 Hz. (a), (b), (c), (d), (e),
(f), (g), (h) and (i) represent 2.0 %, 2.5%, 3.0 %, 3.1 %, 3.2 %, 3.3 %, 3.5 %, 3.8 % and 4.0 %
La3+ compositions, respectively. The shaded area repr esents the highest recoverable energy
density for each composition, Wre=PrPmaxEmaxdP . (Oy axis is in µC/cm2 and Ox axis is in
kV/cm). The P(E) hysteresis loops were obtained on samples already exposed to electric field
E≥E AF ………………………….. ………………………….. ……………………. Error! Bookmark not defined.
Fig. 6. 3 The dependences of the forward switching field E AF necessary to induce the AFE -to-FE
phase transition as a function of La3+ composition in PLZT x/90/10 ceramics. . Error! Bookmark
not defined.
Fig. 6. 4 The dependences of P s, Pr, Ps-Pr as a function of the La3+ composition in PLZT x/90/10
ceramics. ………………………….. ………………………….. ……………….. Error! Bookmark not defined.
Fig. 6. 5 a) Field -dependent polarization P(E) loops with the virgin loop obtained for frequency
of 1 Hz and , b) Field -dependent hysteresis loops with the vi rgin loop obtained for frequency of
1/300s Hz and c) current curves obtained in the same condition as a) for PLZT 3/90/10 bulk
ceramic. ………………………….. ………………………….. …………………. Error! Bookmark not defined.
Fig. 6. 6 a) Field -dependent hysteresis P(E) loops and b) current curves I(E) at various frequency
and fixed amplitude of electric field 60 kV/cm for PLZT 3.2/90/10 bulk ceramic. The data were
acquired starting from 1 to 3, r espectively. ………………………….. . Error! Bookmark not defined.
Fig. 6. 7 a) Field -dependent hysteresis loops and b) current curves at various representative
frequencies and at fixed field amplitude for PZT PLZT 4//90/10 bulk ceramic. The data were
acquired in a continuos sequence, starting from high to low frequencies. .. Error! Bookmark not
defined.
Fig. 6. 8 Contour plots of diffraction intensities for a) and b) 002 pc/200 pc, and c) 111 pc reflections
for the PLZT 4/90/10 composition during a complete triangular field cycle with amplitude ±74
kV/cm and frequency 0.8 mHz d uring a) and c) first and b) second electrical cycle. The
diffraction profiles from d) show the (002) pc/(200) pc reflections before application of electric
field (black), at the coercive field of -74 kV/cm (red) and after application of electric field
(gree n). The subscript pc indicates reflections indexed with the pseudocubic primitive cell. A
schematic drawing to describe the experimental sequence of applied electric field is included in
the left hand side of the figure. E AFE -FE and E FE-AFE represent the forward switching field for
inducing the AFE -to-FE transition and the backward switching field of the FE -to-AFE recovery,
respectively. ………………………….. ………………………….. …………… Error! Bookmark not defined.

244
Fig. 6. 9 Contour plots of diffraction intensities for a) and b) 111 pc/-111 pc, c) and d) 200 pc/002 pc
reflections for the PLZT 3/90/10 composition as a function of triangular bipolar electric field of
±45 kV/cm amplitude and frequency of 0.8 mHz during a) and c) first, and b) and d) second
electrical cycle. The subscript pc indicates reflections indexed w ith the pseudocubic primitive
cell. A schematic diagram to describe the experimental sequence of applied electric field is
included on the left side of the figure. E AFE -FE and E FE-AFE represent the forward switching field
for inducing the AFE -to-FE transit ion and the reverse switching field of the FE -to-AFE
recovery, respectively. ………………………….. ………………………….. Error! Bookmark not defined.
Fig. 6. 10 Electric field dependence of FWHM of the (111) diffraction peak during FE -to-AFE
and AFE -to-FE induced transitions for the composition PLZT 3/90/10. …. Erro r! Bookmark not
defined.
Fig. 6. 11 Selected pseudocubic Bragg profile of electrically poled and of virgin PLZT 3/90/10
powders ………………………….. ………………………….. …………………. Error! Bookmark not defined.
Fig. 6. 12 The observed (dots), calculated (continuous line) and difference (bottom) HXRD
profiles after Rietveld refinement of the structure of poled PLZT 3/90/10 powder using Cm and
Pbam space groups. The Bragg positions are shown in the bottom inset by vertical lines: the top
one corresponds to Cm and the bottom one corresponds to Pbam structure. ….. Error! Bookmark
not defined.
Fig. 6. 13 The observed (dots), calculated (continuous line) and difference (bottom) HXRD
profiles of the enlarged views for the 110 pc, 111 pc, 200 pc, 211 pc, 220 pc and 222 pc peaks obtained
after Rietveld refinement of the structure of poled PLZT 3/90/10 powder using Cm and Pbam
space groups ………………………….. ………………………….. …………… Error! Bookmark not defined.
Fig. 6. 14 a) Energy storage density Wre and b) efficiency η at room temperature for PLZT 90/10
samples with various amounts of La3+ under different applied electric field Emax. ………….. Error!
Bookmark not defined.
Fig. 6. 15 Electric field -dependence of the recoverable energy storage density Wre (a) and of the
lost energy Wloss (b) of the La3+ modified PZT 90/10 ceramics with La3+ at. % content varying
from 2 to 4 ………………………….. ………………………….. ……………… Error! Bookmark not defined.
Fig. 7.1 a) Real part of permittivity ( ε’), b) imaginary part of permittivity ( ε”), c) detail from a)
and d) dielectric losses ( tan δ ) of PLZT x/90/10 compositions measured during heating at a fixed
frequency of 100 kHz. ………………………….. ………………………….. Error! Bookmark not defined.
Fig. 7. 2 Maximum permittivity εm and its corresponding temperature Tm as a function of La
composition obtained at 100 kHz. ………………………….. …………… Error! Bookmark not defined.

245
Fig. 7.3 Temperature dependence of real part of dielectric permittivity and dielectric losses at
various frequencies for PZT 90/10 and PLZT 2/90/10 ceramics. . Error! Bookmark not defined.
Fig. 7.4 Temperature dependence of real part of dielectric permittivity and dielectric losses at
various frequencies for PLZT 2.5/90/10 and PLZT 3/90/10 ceramics. ……. Error! B ookmark not
defined.
Fig. 7. 5 Temperature dependence of real part of dielectric permittivity and dielectric losses at
various frequencies for PLZT 3.1/90/10 and PLZT 3.2/90/10 ceramics. …. Error! Bookmark not
defined.
Fig. 7. 6 Temperature dependence of the real par t of dielectric permittivity and dielectric losses
at various frequencies for PLZT 3.3/90/10 and PLZT 3.5/90/10 ceramics. Error! Bookmark not
defined.
Fig. 7. 7 Temperature dependence of real part of dielectric permittivity and dielectric losses at
various frequencies for PLZT 3.8/90/10 and PLZT 4/90/10 ceramics. ……. Error! Bookmark not
defined.
Fig. 7.8 (a) Reciprocal dielectric constant 1/’ as a function of temperature at 100 kHz for PLZT
x/90/10 compositions (the dashed lines are fittings with the Curie -Weiss law); (b) Tm and TCW vs.
La addition; (c) Frequency dependence of Curie Weiss temperatures …….. Error! Bookmark not
defined.
Fig. 7. 9 Log(1/ε -1/εm) vs. Log(T−T m) for two representative PLZT compositions …………. Error!
Bookmark not defined.
Fig. 7. 10 Diffuseness exponent λ and modified Curie Weiss constant C’ vs. La content for PLZT
x/90/10ceramics ………………………….. ………………………….. ……… Error! Bookmark not defined.
Fig. 7. 11 Variation with temperature of the real part of dielectric permittivity ε’, loss tangent tan
δ, of poled ceramics withy compositions: a) PLZT 3/90/10 sample, b) PLZT 3.1/90/10 and c)
PLZT 4/90/10 measured during heating in the temperature range of 25 –300°C at the frequency
of 10 kHz. ………………………….. ………………………….. ………………. Error! Bookmark not defined.
Fig. 7.12 A contour plot of diffraction intensities as a function of temperature obtained from
{001}pc for PLZT x/90/10 ceramics ………………………….. ……….. Error! Bookmark not defined.
Fig. 7.13 . A contour plot of diffraction intensities as a function of temperature obtained for
{200}pc of PLZT x/90/10 ceramics ………………………….. ………… Error! Bookm ark not defined.
Fig. 7.14 The evolution of lattice parameters (a, b, c) and of the unit cell volume with
temperature for a) PLZT 3.5/90/10 and b) PLZT 4/90/10 ceramics ……….. Error! Bookmark not
defined.

246
Fig. 7. 15 a) Variation with temperature of the real part of dielectric permittivity ε’, loss tangent
tan δ , and reciprocal permittivity ( 1/ε’) of the virgin PLZT 3/90/10 sample, measured during the
heating in the temperature range of 25 –300°C at the frequency of 10 kHz. The pink line
represents the fit with the Curie -Weiss relation in the high temperature range. The AFE/FE -PE
transition temperature Tm, and Curie -Weiss temperature TCW are marked by arrows. b) Contour
plots of {111} pc and c) {200} pc regions of diffraction patterns for PLZT 3/90/10. Data from a)
were obtained during heating of virgin PLZT 3/90/10 ceramic while the selected areas of X -ray
patterns of b) {111} pc and c) {200} pc were obtained during cooling of poled PLZT 3/90/10
ceramic. ………………………….. ………………………….. …………………. Error! Bookmark not defined.
Fig. 7.16 a) Variation with temperature of the real part of dielectric permittivity ε’, loss tangent
tan δ , and reciprocal permittivity ( 1/ε’) of the PLZT 3/90/10 sample after applying a field of
30kV/cm field at frequency of 10 kHz, measured during the he ating in the temperature range of
25–300°C. The red line is the fitting with the Curie -Weiss relation from high temperature
dielectric data. The AFE/FE -PE transition temperature Tm, depolarization temperature Td and
Curie -Weiss temperature TCW are marked b y arrows. A contour plot of diffraction intensities as a
function of temperature obtained from b) {111} pc and c) {200} pc. Data from a), b) and c) were
obtained during heating of poled PLZT 3/90/10 ceramic …………. Error! Bookmark not defined.
Fig. 7. 17 Raman spectra at different temperatures of PLZT a) 2/90/10, b) 2.5/90/10, c) 3/90/10
and d) PLZT 3.1/90/10 ceramics ………………………….. …………….. Error! Bookmark not defined.
Fig. 7. 18 Raman spectra at different temperatures of PLZT x/90/10 ceramics . Error! Bookmark
not defined.
Fig. 7.19 Raman spectra at different temperatures of PLZT x/90/10 ceramics .. Error! Bookmark
not defined.
Fig. 7. 20 Phase diagram of PLZT x/90/10, based on structural results, dielectric and anelastic
data as published in Ref. [19] ………………………….. …………………. Error! Bookmark not defined.

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List of abbreviations
FE – ferroelectric
AFE – antiferroelectric
PE – paraelectric
MPB – morphotropic phase boundary
PZT – PbZr xTi1-xO3
PLZT – La-substituted PZT
PLZTx/10/90 – Pb1-xLax(Zr 0.9Ti0.1)1-x/4O3

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List of original publications

1. I.V. Ciuchi , F. Craciun, L. Mitoseriu, C. Galassi, Preparation and properties of La doped
PZT 90/10 ceramics across the ferroelectric -antiferroelectric phase boundary , J. Alloys
Compd. 646 (2015) 16-22. (I.F.=3.014 , A.I=0.558)
Cited by 2 publications :
[1] X. Wang, T. Yang, J. Shen, Y. Dong, Y. Liu, Phase transition and dielectric properties of
(Pb,La)(Zr,Sn,Ti)O 3 ceramics at morphotropic phase boundary, J. Alloys & Compd. 673 (2016)
67-72.

2. F. Craciun, F. Cordero, I.V. Ciuchi , L. Mitoseriu, C. Galassi, Refining the phase diagram
of Pb 1-xLax(Zr 0.9Ti0.1)1-x/4O3 ceramics by structural, dielectric, and anelastic spectroscopy
investigations , J. Appl. Phys. 117(18) (2015) 184103 (1 -8). (I.F. =2.101 , A.I=0.68)
Cited by 1:
[1] A. Peláiz -Barranco, Y. González -Abreu, Y. Gagou, P. Saint -Grégoire, J.D.S. Guerra, Raman
spectroscopy investigation on (Pb 1−xLax)(Zr 0.90Ti0.10)1−x/4O3 ceramic system, Vib. Spectrosc. 86
(2016) 124 –127.

3. I.V. Ciuchi , L. Mitoseriu , C. Galassi, Antiferroelectric to Ferroelectric Crossover and
Energy Storage Properties of (Pb 1-xLax)(Zr 0.90Ti0.10)1-x/4O3 (0.02 ≤x ≤0.04) Ceramics , J.
Am. Ceram. Soc. 99(7) (2016) 2382 -2387. (I.F.=2.841 , A.I=0.70)

Cited by 8:
[1] R. Xu, Q. Zhu, J. Tian , Y. Feng, Z. Xu, Effect of Ba -dopant on dielectric and energy storage
properties of PLZST antiferroelectric ceramics, Ceram. Int. 43(2) (2017) 2481 -2485.
[2] D. Zheng, R. Zuo, Enhanced energy storage properties in La(Mg 1/2Ti1/2)O3-modified BiFeO 3-
BaTiO 3 lead-free relaxor ferroelectric ceramics within a wide temperature range, J. Eur. Ceram.
Soc. 37(1) (2017) 413 -418.
[3] B. Luo, X. Wang, E. Tian, H. Song, H. Wang, L. Li, Enhanced Energy -Storage Density and
High Efficiency of Lead -Free CaTiO 3–BiScO 3 Linea r Dielectric Ceramics, ACS Appl. Mater.
Interfaces. 9(23) (2017) 19963 -19972.

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[4] R. Xu, J.T. , Q. Zhu, T. Zhao, Y. Feng, X. Wei, Z. Xu, Effects of phase transition on discharge
properties of PLZST antiferroelectric ceramics, J Am. Ceram. Soc. 100(8) (2017 ) 3618 -3625.
[5] B. Li, Q. Liu, X. Tang, T. Zhang, Y. Jiang, W. Li, J. Luo, High Energy Storage Density and
Impedance Response of PLZT2/95/5 Antiferroelectric Ceramics, Materials 10(2) (2017) 143.
[6] B. Li, Q. -X. Liu, X. -G. Tang, T. -F. Zhang, Y. -P. Jiang, W.-H. Li, J. Luo, High temperature
dielectric anomaly and impedance analysis of (Pb 1−3x/2Lax)(Zr 0.95Ti0.05)O3 ceramics, J. Mater. Sci.:
Mater. El. (2017) 1 -10.
[7] F. Li, J. Zhai, B. Shen, X. Liu, K. Yang, Y. Zhang, P. Li, B. Liu, H. Zeng, Influence of s tructural
evolution on energy storage properties in Bi 0.5Na0.5TiO 3-SrTiO 3-NaNbO 3 lead-free ferroelectric
ceramics, J. Appl. Phys. 121(5) (2017) 054103.
[8] R. Xu, J. Tian, Q. Zhu, T. Zhao, Y. Feng, X. Wei, Z. Xu, Effects of phase transition on discharge
properties of PLZST antiferroelectric ceramics, J Am. Ceram. Soc. 100(8) (2017) 3618 -3625.

4. M. Cernea, P. Galizia, I. V. Ciuchi , G. Aldica, V. Mihalache, L. Diamandescu, C. Galassi,
CoFe 2O4 magnetic ceramic derived from gel and sintered by spark plasma sintering, J.
Alloys Compd , (2016), volum, numar (I.F. = 3.133 , A.I=0.551)

Cited by 6 :
[1] P. Galizia, C. Baldisserri, C. Capiani, C. Galassi, Multiple parallel twinning overgrowth in
nanostructured dense cobalt ferrite, Mater. Des. 109 (2016) 19 -26.
[2] J. Jin, X. Sun, M. Wang, Z.L. Ding, Y.Q. Ma, The magnetization reversal in CoFe 2O4/CoFe 2
granular systems, J. Nanopart. Res. 18 (2016) 383.
[3] R. Zhang, L. Sun, Z. Wang, W. Hao, E. Cao , Y. Zhang, Dielectric and magnetic properties of
CoFe 2O4 prepared by sol -gel auto -combustion method, Mater. Res. Bull. (2017).
[4] P. Galizia, M. Cernea, V. Mihalache, L. Diamandescu, G. Maizza, C. Galassi, Easy batch -scale
production of cobalt ferrite n anopowders by two -step milling: Structural and magnetic
characterization, Mater. Des. 130 (2017) 327 -335.
[5] P. Galizia, C.E. Ciomaga, L. Mitoseriu, C. Galassi, PZT -cobalt ferrite particulate composites:
Densification and lead loss controlled by quite -fast sintering, J. Eur. Ceram. Soc. 37(1) (2017)
161-168.
[6] P. Galizia, Production and morphological and microstructural characterization of bulk
composites or thick films for the study of multiphysics interactions, PhD Thesis, Politecnico di
Torino, Port o Institutional Repository, (2017 ).

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5. A. Neagu, I.V. Ciuchi , L. Mitoseriu, C. Galassi, C. -W. Tai, Study of ferroelectric –
antiferroelectric phase coexistence in La -doped PZT ceramics, European Microscopy
Congress 2016: Proceedings, Wiley -VCH Verlag GmbH & Co. KGaA (2016) ( http://emc –
proceedings.com/abstract/study -of-ferroelectric -antiferroelectric -phase -coexistence -in-
la-doped -pzt-ceramics/ )

6. I. V. Ciuchi , C. C. Chung, C. M. Fancher, J. Guerrier, J. S. Forrester, J. L. Jones, L.
Mitoseriu and C. Galassi , “Field -induced antiferroelectric to ferroelectric transition in
(Pb 1–xLax)(Zr 0.90Ti 0.10)1–x/4O3 investigated by in situ X -ray diffraction”, J. Eur. Ceram.
Soc. , 2017, volum, numar daca au aparut sau doi (In Press) (I.F.=3.411 , A.I=0.697)

7. I.V. Ciuchi , C. M. Fancher, C. Capiani, J.L. Jones, L. Mitoseriu, C. Galassi, Field induced
metastable ferroelectric phase in PLZT 3/90/10 ceramics, J. Eur. Ceram. Soc. (2017),
(Review to be submitted) (I.F.=3.411 , A.I=0.697)

251

List of participations to i nternational conferences

1. I. V. Ciuchi , C. Capiani, L. Mitoseriu and C. Galassi, Composition -dependen t dielectric and
energy -storage properties of Pb 1-xLax(Zr 0.9Ti0.1)1-x/4O3 ceramics , Ceramics for Energy, June
2017 , Faenza, Italy, (Oral)
2. I. V. Ciuchi , L. Mitoseriu, and C. Galassi, PLZT x/90/10 ceramics for energy storage , Piezo
2017 -Electroceramics for End Users IX, Madrid (Spain), February 2017, (Oral)
3. A. Neagu, I. V. Ciuchi , L. Mitoseriu, C. Galassi, C. -W. Tai, Study of ferroelectric –
antiferroelectric phase coexistence in La -doped PZT ceramics, The 16th European Microscopy
Congress, Lyon, France , 2016 (Poster) (http://emc -proceedings.com/abstract/study -of-
ferroelectric -antiferroelectric -phase -coexistence -in-la-doped -pzt-ceramics/)
4. I. V. Ciuchi , J.E. Guerrier, C. Chung, L. Mitoseriu, J.L. Jones and C.Galassi, Diffuse Phase
transitions and Curie Weiss behavior of of Pb 1-xLax(Zr 0.9Ti0.1)1-x/4O3 (0.02 ≤ x ≤ 0.04) ceramics ,
1st Research Triangle Nanotechnology Network Research Symposium, Raleigh, US, 2016
(Oral)
5. I.V. Ciuchi , F. Craciun, M. Deluca, L. Mitoseriu and C. Galassi , Phase transitions and Curie
Weiss behaviour in La3+ doped PZT 90/10 ceramics with compositions across the
antiferroelectric/ferroelectric phase boundary, 13th European Meeting on Ferroelectricity,
Porto, Portugal, July 2015 ( Oral )
6. R. Pul lar, I. V. Ciuchi , P. Galizia and C. Galassi , Novel TiO 2-doped semiconducting hexagonal
ferrites, 13th European Meeting on Ferroelectricity, Porto, Portugal, July 2015 ( Poster )
7. I.V. Ciuchi , F. Craciun, L. Mitoseriu, C. Galassi, Temperature dependence of dielectric,
piezoelectric and elastic properties of La -doped PZT 90/10 across ferroelectric –
antiferroelectric boundary , International Confere4nce European Ceramic Society, Toledo,
Spain, June 2015 (poster)
8. I. V. Ciuchi , L. Mitoseriu, C. Galassi, PLZT Based Antiferroelectric Plate Capacitors with
High Energy Storage Density , Ceramics For Energy, Faenza, Italy, May 2015 (poster)
9. I.V. Ciuchi , P. Galizia, L. Mitoseriu, C. Galassi, Magnetic and dielectric properties of cobalt
ferrite/titania composites, Magnet, Bologna, Italy, Febbruary 2015 (poster)

252
10. I.V. Ciuchi , F. Craciun, L. Mitoseriu, C. Galassi, Dielectric Properties of La3+ doped PZT
Ceramics across the antiferroelectric/ferroelectric phase boundary, PIEZO -Electroceramics
for End -Users VIII conference, Maribor, Slovenia, January 2015 (oral)
11. P. Galizia, C. Baldisserri, I. V., Ciuchi , C. Galassi, Investigation of new magneto -dielectric
titania -cobalt ferrite composites, E-MRS Fall Meeting, Warsaw, September 2014 (Oral)
12. I. V. Ciuchi , F. Craciun, C. Galassi, L. Mitoseriu , Piezoelectric Properties of La3+ doped PZT
Ceramics across the antiferroelectric/ ferroelectric phase boundary , European Conference on
Application of Polar Dielectrics , July, Vilnius 2014 (Poster)
13. I. V. Ciuchi , M. Cernea , B. S. Vasile, R . Trusca, C . Galassi , Synthesis and dielectric properties
of one -dimensional BNT -BTCe@SiO 2 core-shell heterostructures, Electroceramics XIV
Conference, June 2014, Bucharest (Oral)
14. I.V. Ciuchi , F. Craciun, C. Galassi, L. Mitoseriu , Lanthanum Dependence of Piezoelectric
Properties of PLZT Ceramics with Zr/Ti Ratio of 90/10, Electroceramics XIV Conference, June
2014, Bucharest (Poster)
15. R. Stanculescu, I. V. Ciuchi , I. Turcan, P. Galizia, C. Capiani, C. Galassi and L. Mitoseriu,
Prepara tion and dielectric investigations of Ba 0.60Sr0.40TiO 3 ferroelectric ceramics with
different degree of porosity, Electroceramics XIV Conference, June 2014, Bucharest (Oral)
16. I. V. Ciuchi , M. Cernea, C . Galassi, Piezoelectric and Dielectric Characterization of BNT 0.92
BT0.08 (5 mol% Ce doped), Coated with SiO 2, COST Action MP0904 -Closing Conference,
Genoa, January, 2014, (Poster)
17. R. Stanculescu, I. V. Ciuchi , I. Turcan, P. Galizia, C. Capiani, C. Galassi and L. Mitoseriu ,
Microstructural and dielectric investigations of Ba 0.60Sr0.40TiO 3 ferroelectric ceramics with
different degree of porosity, COST Action MP0904 -Closing Conference, Genoa, 2014,
(Poster)
18. L. Stoleriu, L. Curecheriu, I. V. Ciuchi , C. Galassi, L. Mitoseriu , FORC Investigation of
Ferroelectric -Antiferroelectric Crossover in PLZT (x/90/10) Ceramics , COST MP0904
Single – and multiphase ferroics and multiferroics with restricted geometries, (SIMUFER),
January 2014 (Poster, Presenting Author)
19. R. E. Stanc ulescu, I. Turcan, I. V. Ciuchi , Investigation of the role of porosity on the functional
properties of Ba 1-XSr xTiO 3 ceramics produced by using graphite forming agent ,, “The Tenth
Students’ Meeting”, SM-2013 Processing and applications of ceramics , The Third Early Stage
Researchers Workshop” COST MP0904 – SIMUFER, Novi Sad, Serbia, November, 2013
(oral)

253
20. I. V. Ciuchi, C. Galassi, L. Mitoseriu, Temperature dependence of the main piezoelectric
paramaters in very soft, soft and hard piezoelectric ceramic discs, “The Tenth Students’
Meeting”, SM -2013 Processing and applications of ceramics , The Third Early Stage
Researchers Workshop” COST MP0904 – SIMUFER, Novi Sad, Serbia, November, 2013
(oral)

254

Research stages and participations to training schools during the PhD activity

1. JECS TRUST Research Stage (15 February -15 May 2016) performed in collaboration with
Prof. J. Jones Research Group, Department of Materials Science, in North Carolina State
University, Raleigh, North Carolina, USA
The main activity was:
▪ Investigation of the structure and phase transitions of PLZT (according to the formula
Pb1-xLax(Zr0.9Ti0.1)1 –
has been c arry on by using in situ XRD field measurements and in situ temperature XRD
measurements
▪ Rietveld Refinement on high resolution Synchrotron XRD data and on traditional XRD

2. Research Stage (26 May -31 May 2014) performed in Department of Radiophysics, Vilnius
University, 3 Universiteto St, LT -01513 Vilnius, Lithuania
The main activity was:
▪ Magnetic permeability measurement of magneto -dielectric ceramic composites
▪ Learning about measuring magnetic permeability and dielectric permittivity with EIA
Bullet

3. “One day satellite workshop -Inelastic scattering in ferroic materials” (28 th June 2015)
The main thematic wastheoretical and practical demo courses regarding RAMAN spe ctroscopy
in ceramic composites. The stage was performed at University of Porto, Portugal
4. International FIB -SEM/AFM (JECS Trust) school ( 29 September -03 October 2014)
performed at Sabanci University Campus, Istanbul, Turkey
The main thematic was:
 Theore tical courses and practical deomos concering SEM, FIB and AFM

255
 Basics and special application of this techniques on powder, bulk solid ceramic materials
and ceramic based nanocomposite systems