Rhombohedral Ferroelectric Phase Research Articles

Significantly enhanced energy-storage properties in NaNbO3-based relaxor ferroelectric ceramics via introducing a wide band-gap linear dielectric

The achievement of simultaneous high energy-storage density and efficiency is a long-standing challenge for dielectric ceramics. Herein, a wide band-gap lead-free ceramic of NaNbO3–BaZrO3 featuring polar nanoregions with a rhombohedral local symmetry, as evidenced by piezoresponse force microscopy and transmission electron microscopy, were reported to exhibit a giant energy-storage density of ∼5.0 J/cm3 and a high efficiency of ∼85 % as well as excellent charge-discharge properties simultaneously. Enhanced breakdown strength from a synergistic effect of wider band gap and decreased grain size provides a prerequisite for improving energy-storage performance. Meanwhile, the substitution of linear dielectric BaZrO3 can not only adjust the low-temperature ferroelectric rhombohedral phase of NaNbO3 into near room temperature, but also significantly reduce the FE domain size owing to the increased local random fields. Therefore, suppressed polarization hysteresis and delayed polarization saturation can be observed with increasing BaZrO3 content, leading to the significantly enhanced overall energy-storage properties.

Thermal conductivity of lead zirconate titanate PbZr1−x Ti x O3

We present the thermal conductivity (κ) of perovskite PbZr1−x Ti x O3 (PZT) for 0 ≤ x ≤ 1 and 300 K ≤ T ≤ 873 K, the composition and temperature ranges covering the classic phase diagram of this important piezoelectric system. The glasslike dκ/dT > 0 behavior is observed for the ferroelectric rhombohedral phases and much of the paraelectric cubic phase, implying the presence of strong phonon damping in these regions of PZT. For all the temperatures studied in this work, the κ becomes lowest at x = 0.5.

Temperature-driven structural phase transitions in 0.05(Na0.50Bi0.50)TiO3-0.95NaNbO3 solid solution via amplitude mode analysis

Structural phase transitions in the ABO3-type lead-free eco-friendly piezoelectric (05NBT) have been studied as a function of temperature using dielectric and X-ray diffraction techniques. Below 300 K, we observed dispersion in dielectric permittivity with the frequency, which confirmed relaxor behaviour in 05NBT. Using detailed analysis of temperature-dependent powder X-ray diffraction data of 05NBT, four phase transitions were identified across 600 K, 773 K, 823 K and 923 K. We found that on doping 5% NBT in pure sodium niobate, the low-temperature rhombohedral ferroelectric (N) phase and the high-temperature (S) phase of the sodium niobate get suppressed. To get a better insight about the temperature-driven structural phase transitions, various antiferrodistortive and additional distortive mode as well as the mode amplitude relative to high-symmetry cubic phase were computed and results are discussed.

Thermodynamic prediction of ferroelectric mechanical to electrical energy harvesting capabilities utilizing phase dependent electromechanical coupling factors

Prediction of the mechanical to electrical energy harvesting capabilities in [011]C cut PIN-PMN-PT is presented as a function of thermodynamic analysis of hysteresis in the stress induced ferroelectric phase transformation, and phase dependency of the electromechanical coupling factors. Energy conversion rates vary from 0.528 for low transformation hysteresis to 0.432 for high transformation hysteresis. While these predicted values are lower than the experimentally determined value from literature (“approximately 60%”), differences are explained through limitations of the mechanical loading mechanism. This brings the predicted values into agreement with literature. Ferroelectric rhombohedral phase behavior is found to dominate energy harvesting capabilities.

B-site ion driven morphotropic phase transformation in NN-BT-ABO3 lead-free ceramics through chemical pressure

Forming morphotropic phase boundary (MPB) is crucial to improve the piezoelectric properties of lead-free NaNbO3-BaTiO3-xABO3 (NN-BT-xABO3) ceramics. In this work, four NN-BT-xABO3 systems (ABO3 = K0.5Bi0.5TiO3 (KBT), Bi0.5Na0.5TiO3 (BNT), K0.5Bi0.5ZrO3 (KBZ), and Bi0.5Na0.5ZrO3 (BNZ)) were constructed to analyze the relationship between ABO3 characteristic and phase transformation behavior. The results showed that the NN-BT-xKBT/xBNT systems underwent ferroelectric tetragonal (T)-relaxor ferroelectric T phase transformation with d33 ∼ 150 pC/N and kp ∼ 0.2 in NN-BT-0.11KBT and NN-BT-0.09BNT compositions, while the NN-BT-xKBZ/xBNZ systems underwent ferroelectric T- ferroelectric rhombohedral (R) morphotropic phase transformation with improved d33 ∼ 256 pC/N and kp ∼ 0.31 in NN-BT-0.04BNZ composition. The B-site ion radius was found to be a key factor in inducing phase transformation. The incorporation of small Ti4+ ions tends to break the long ordering of ferroelectrics, inducing the normal-relaxor ferroelectric phase transformation, however, the appearance of the R phase in NN-BT-xAZrO3 compositions was attributed to the chemical pressure caused by buckled Zr-O-Zr bonds as larger Zr4+ ions enter the NN-BT matrix lattices. This study will deepen the understanding of the ferroelectric phase transformation mechanism in the lead-free NaNbO3 material system and provide a guidance for designing morphotropic NN-based lead-free piezoelectric ceramics.

Improved piezoelectric properties through manganese-doping in phase coexistence region in lead strontium zirconate titanate (PSZT) thin films

In the quaternary system PbTiO3-PbZrO3-SrTiO3-SrZrO3, compositions that lie close to the antiferroelectric tetragonal and ferroelectric rhombohedral (AFET-FER) phase boundary have potential applications in micro-actuators. However, in thin films, this phase boundary is reported to shift significantly to the zirconium-rich region. Hence, it is necessary to seek alternative approaches to stabilize the tetragonal AFE phase in such compositions. Therefore, this study explores the effect of B-site Mn3+-doping on their structure. Dielectric, ferroelectric, and piezoelectric characteristics of such thin films have been compared with those with increasing Zr/Ti ratios to understand the efficacy of this approach. Transverse piezoelectric coefficient, e31,f, and bipolar strain are found to be higher in Mn3+-doped thin films. Furthermore, large strains and e31,f in thin films have been correlated with structural modifications revealed by systematic Raman spectroscopic investigations.

A combined powder x-ray and neutron diffraction studies on (1-x) NaNbO3-x Na0.50Bi0.50TiO3 solid solution

Solid solution of sodium niobate and sodium bismuth titanate [(1-x)NaNbO3-x(Na0.5Bi0.5)TiO3: xNBT)] is an important lead-free eco-friendly piezo-ceramic material. In the present work, we report an investigation of the phase stabilities of this solid solution using powder x-ray and neutron diffraction techniques for the entire range of composition. We observed the disappearance of certain peaks and changes in the main perovskite peaks in the powder diffraction data suggesting structural phase transitions with composition. Rietveld analysis of combined x-ray and neutron powder diffraction data is performed to obtain single correct structural model wherever possible. Detailed analyses of powder diffraction data for composition range 0.0 ≤ x ​< ​0.15 revealed the coexistence of orthorhombic (Pbma) and (Pmc21) phases and an orthorhombic phase with space group Pbnm and cell dimensions √2ap ​× ​√2 bp ​× ​6 cp gets stabilized for 0.15 ≤ x ​< ​0.20. On further increasing NBT content in NaNbO3 matrix (0.20 ≤ x ​< ​0.60), a mixed orthorhombic (Pbnm) phase and tetragonal (P4bm) phase is confirmed by Rietveld refinement. Further, in the composition range 0.60 ≤ x ​≤ ​0.80, the tetragonal (P4bm) phase coexists with the ferroelectric rhombohedral (R3c) phase and finally for composition x ​> ​0.80, it completely transforms to rhombohedral (R3c) phase. The presence of phase coexistence in various composition ranges indicates the first order nature of these phase transitions. A detailed structural phase diagram of the system is presented at ambient conditions.

Excellent piezoelectric performance of BiFeO3–BaTiO3– La(Mg2/3Nb1/3)O3 lead-free ceramics via relaxation regulation near the morphotropic phase boundary

Although BiFeO3–BaTiO3-based lead-free ceramics have attracted much attention in recent years as a high temperature piezoelectrics, their d33 value is still difficult to exceed 200 pC/N through conventional methods. In this work, a novel (0.7-x)BiFeO3-0.3BaTiO3-xLa(Mg2/3Nb1/3)O3 (x = 0–0.005) ternary system was reported to own excellent room-temperature piezoelectric constant (d33) ∼216 pC/N and high Curie temperature (480 °C) at x = 0.003 simultaneously. It reveals that the compositions undergo an obvious phase transition from ferroelectric (FE) rhombohedral (R) phase to relaxor pseudo-cubic (PC) phase via an R–PC morphotropic phase boundary (MPB). More importantly, piezoelectric nonlinear Rayleigh analysis and S-E/P-E curves suggest that the significantly enhanced domain dynamics due to the coexistence of macrodomain and nanodomain can be observed in the x = 0.003 sample. The synergy of these two effects induce the improved d33 value observed in the x = 0.003 sample. In addition, the compositions exhibit the inhibition of defect dipoles and the improvement of the high temperature resistivity, leading to the excellent thermal stability with sensitivity coefficients ƞ less than ± 5% in the annealing temperature range of 25–400 °C. The present work provides a guideline for the subsequent design of high-temperature lead-free ceramics.

Temperature‐stable Na0.5Bi0.5TiO3‐based ceramics with favorable low‐temperature dielectric and energy storage property

AbstractIn this work, (1 − x)(0.94Na0.5Bi0.5TiO3–0.06BaTiO3)–xKTaO3 (x = 0–0.30) ceramics are developed for dielectric capacitor applications. The introduction of KTaO3 from x = 0 to 0.30 increases the tolerance factor t from 0.984 to 1.005 and causes the decrease of ferroelectric rhombohedral phase in the ceramics. Besides, a gradual structural change toward a higher symmetry can be detected, accompanied by the obvious domain refinement. In the aspect of electrical property, the strengthened dielectric relaxation leads to the greatly enhanced thermal stability of dielectric response. The decline in Ts from 98 to −96°C causes a significant widening of the low‐temperature region with temperature‐stable dielectric constant εr and low dielectric loss tan δ. The x = 0.30 ceramic shows a high εr (25°C) of 1094 with the temperature coefficient of capacitance ≤±15% over −70 to 200°C, which exceeds the X9R standard. Meanwhile, tan δ is less than 0.02 in a wide temperature range of −35 to 300°C. In addition, the ultrafine grain size of 290 nm, large bandgap of 3.22 eV, and high resistance of the x = 0.30 ceramic contribute to its electrical breakdown strength. A linear‐like P–E loop with the large discharged energy density WD ∼ 3.50 J/cm3 and high energy efficiency η ∼ 90.1% is obtained under 28 kV/mm at room temperature. The thermal stability of the energy storage performance is also satisfactory with the variation of WD less than 15% over −40 to 200°C, and the η is higher than 85%.

Anisotropic Strain‐Mediated Symmetry Engineering and Enhancement of Ferroelectricity in Hf0.5Zr0.5O2/La0.67Sr0.33MnO3 Heterostructures

AbstractHafnium‐based binary oxides have attracted considerable attention due to their robust ferroelectricity at the nanoscale and compatibility with silicon‐based electronic technologies. To further promote the potential of Hafnium oxides for practical device applications, it is essential to effectively harness the interplay between structural symmetry, domain configuration, and ferroelectricity. Here, using Hf0.5Zr0.5O2/La0.67Sr0.33MnO3 (HZO/LSMO) heterostructures as a model system, the anisotropic strain‐mediated symmetry engineering and ferroelectricity enhancement are systematically investigated. By growing the heterostructures on (110)‐oriented perovskite substrates, considerable anisotropic strain is imposed on the LSMO bottom electrodes. Such an anisotropically‐strained LSMO layer acts as a structural template and effectively tune the structural symmetry, polar/non‐polar phase ratio, and ferroelectricity of the HZO top layer. Specifically, the anisotropic tensile strain stabilizes the ferroelectric rhombohedral and orthorhombic phases, thus enhancing the remnant polarization (Pr) up to 22 µC cm−2. In contrast, the anisotropic compressive strain facilitates the formation of non‐ferroelectric tetragonal phases, leading to a suppressed Pr down to 8 µC cm−2. These findings provide a guideline for understanding and modulating the intrinsic structure‐ferroelectricity relationship of HZO through anisotropic strain‐mediated symmetry engineering, which may shed light on the development of hafnium‐oxide‐based electronic devices.

Synaptic behaviour in ferroelectric epitaxial rhombohedral Hf0.5Zr0.5O2 thin films

The discovery of ferroelectricity in HfO2-based thin films brings tremendous opportunities for emerging ferroelectric memories as well as for synaptic devices. The origin of ferroelectricity in this material is widely attributed to the presence of a polar orthorhombic phase. However, a new ferroelectric rhombohedral phase displaying large polarization with no need of pre-cycling, has more recently been reported in epitaxial Hf0.5Zr0.5O2 (HZO). In this work, the switching mechanism of the rhombohedral phase of HZO films is characterized by a two-stage process. In addition, the synaptic behaviour of this phase is presented, comparing it with previous reports on orthorhombic or non-epitaxial films. Unexpected similarities have been found between these structurally distinct systems. Even though the epitaxial films present a larger coercive field, the ration between the activation field for intrinsic polarization switching and the coercive field (F a/E c) has been found to be close to 2, in agreement with that reported for other hafnia samples. This is about 5 times smaller than in most other ferroelectrics, confirming this characteristic as a unique feature of hafnia-based ferroelectrics.

Annealing-Dependent Morphotropic Phase Boundary in the BiMg0.5Ti0.5O3-BiZn0.5Ti0.5O3 Perovskite System.

The annealing behavior of (1-x)BiMg0.5Ti0.5O3–xBiZn0.5Ti0.5O3 [(1-x)BMT–xBZT] perovskite solid solutions synthesized under high pressure was studied in situ via X-ray diffraction and piezoresponse force microscopy. The as prepared ceramics show a morphotropic phase boundary (MPB) between the non-polar orthorhombic and ferroelectric tetragonal states at 75 mol. % BZT. It is shown that annealing above 573 K results in irreversible changes in the phase diagram. Namely, for compositions with 0.2 < x < 0.6, the initial orthorhombic phase transforms into a ferroelectric rhombohedral phase. The new MPB between the rhombohedral and tetragonal phases lies at a lower BZT content of 60 mol. %. The phase diagram of the BMT–BZT annealed ceramics is formally analogous to that of the commercial piezoelectric material lead zirconate titanate. This makes the BMT–BZT system promising for the development of environmentally friendly piezoelectric ceramics.

Stabilization of the epitaxial rhombohedral ferroelectric phase in ZrO2 by surface energy

Doped ${\mathrm{HfO}}_{2}$ and ${\mathrm{HfO}}_{2}\text{\ensuremath{-}}{\mathrm{ZrO}}_{2}$ compounds are gaining significant interest thanks to their ferroelectric properties in ultrathin films. Here, we show that ${\mathrm{ZrO}}_{2}$ could be a playground for doping and strain engineering to increase the thickness in epitaxial thin films. Based on surface-energy considerations supported by ab initio calculations, we find that pure ${\mathrm{ZrO}}_{2}$ exhibits a ferroelectric rhombohedral phase ($r$ phase, with $R3m$ space group) more stable than for the HZO and pure ${\mathrm{HfO}}_{2}$ cases. In particular, for a thickness up to 37 nm we experimentally evidence a single (111)-oriented $r$ phase in ${\mathrm{ZrO}}_{2}$ films deposited on ${\mathrm{La}}_{2/3}{\mathrm{Sr}}_{1/3}{\mathrm{MnO}}_{3}$-buffered ${\mathrm{DyScO}}_{3}(110)$ substrate. The formation of this $r$ phase is discussed and compared between ${\mathrm{HfO}}_{2}$, ${\mathrm{ZrO}}_{2}$ and HZO, highlighting the role of surface energy.

Effect of sintering temperature on phase formation and dielectric property of modified PLZT ceramics with addition of BT and PZN

ABSTRACT The modified-lead lanthanum zirconate titanate (PLZT) ceramics with the addition of barium titanate (BT) and lead zinc niobate (PZN) were prepared. PLZT 9/65/35–BT ceramics changed from ferroelectric rhombohedral phase to paraelectric cubic phase as the content of BT was increased. The optimized dielectric constant at room temperature and frequency of 1 kHz could be obtained when 5 mol% BT was added and the ceramic was sintered at 1275 °C (ϵr = 10463, tanδ = 0.0125). PLZT 8/40/60–PZN ceramics had a perovskite structure with a decrease of unit cell volume as the content of PZN was increased. The optimized dielectric constant at room temperature and frequency of 1 kHz could be obtained when 20 mol% PZN was added and the ceramic was sintered at 1250 °C (ϵr = 14290, tanδ = 0.0081).

Формирование фазовых состояний PbFe-=SUB=-0.5-=/SUB=-Nb-=SUB=-0.5-=/SUB=-O-=SUB=-3-=/SUB=-: описание на основе многоминимумных моделей

Two ferroelectric phase transitions are observed in the PbFe0.5Nb0.5O3 crystal. The first is between the cubic and tetragonal phase, the second is between the tetragonal and monoclinic phases. To describe phase transitions and emerging phases, a statistical model is proposed, based on the composition of two multi-minimum models - a six-minima model for the Pb cation and an eight-minima model for the Nb cation. Adjusting the model parameters, makes it possible to reproduce all the characteristic features of the thermodynamic behavior of the crystal. The most interesting is the formation of a ferroelectric, complexly ordered monoclinic phase with Cm symmetry. It is shown that the mentioned monoclinic phase arises due to the fact that the first-order phase transition to the rhombohedral ferroelectric phase occurs in the presence of an "external field" of tetragonal symmetry. The contribution of the subsystems of Pb and Nb cations to the features of the dielectric and structural properties of the crystal is estimated.

Formation of phase states in PbFe-=SUB=-0.5-=/SUB=-Nb-=SUB=-0.5-=/SUB=-O-=SUB=-3-=/SUB=-: Description based on multiminima models

Two ferroelectric phase transitions are observed in the PbFe0.5Nb0.5O3 crystal. The first is between the cubic and tetragonal phase, the second is between the tetragonal and monoclinic phases. To describe phase transitions and emerging phases, a statistical model is proposed, based on the composition of two multi-minimum models --- a six-minima model for the Pb cation and an eight-minima model for the Nb cation. Adjusting the model parameters, makes it possible to reproduce all the characteristic features of the thermodynamic behavior of the crystal. The most interesting is the formation of a ferroelectric, complexly ordered monoclinic phase with Cm symmetry. It is shown that the mentioned monoclinic phase arises due to the fact that the first-order phase transition to the rhombohedral ferroelectric phase occurs in the presence of an &amp;quot;external field&amp;quot; of tetragonal symmetry. The contribution of the subsystems of Pb and Nb cations to the features of the dielectric and structural properties of the crystal is estimated. Keywords: ferroelectric relaxors, phase transitions, multiminima models, ferroelectric monoclinic phase.

Wake-up Free Ferroelectric Rhombohedral Phase in Epitaxially Strained ZrO2 Thin Films.

Zirconia- and hafnia-based thin films have attracted tremendous attention in the past decade because of their unexpected ferroelectric behavior at the nanoscale, which enables the downscaling of ferroelectric devices. The present work reports an unprecedented ferroelectric rhombohedral phase of ZrO2 that can be achieved in thin films grown directly on (111)-Nb:SrTiO3 substrates by ion-beam sputtering. Structural and ferroelectric characterizations reveal (111)-oriented ZrO2 films under epitaxial compressive strain exhibiting switchable ferroelectric polarization of about 20.2 μC/cm2 with a coercive field of 1.5 MV/cm. Moreover, the time-dependent polarization reversal characteristics of Nb:SrTiO3/ZrO2/Au film capacitors exhibit typical bell-shaped curve features associated with the ferroelectric domain reversal and agree well with the nucleation limited switching (NLS) model. The polarization-electric field hysteresis loops point to an activation field comparable to the coercive field. Interestingly, the studied films show ferroelectric behavior per se, without the need to apply the wake-up cycle found in the orthorhombic phase of ZrO2. Overall, the rhombohedral ferroelectric ZrO2 films present technological advantages over the previously studied zirconia- and hafnia-based thin films and may be attractive for nanoscale ferroelectric devices.

Physics-based optimization of Landau parameters for ferroelectrics: application to BZT–50BCT

In analogy to thermochemical parameter optimization in the CALculation of PHAse Diagrams (CALPHAD) approach that relies on a wide variety of experimental measurements, a thermodynamic parameter optimization strategy to describe the polarization response with single-crystal Landau coefficients is documented herein to bridge the gap between CALPHAD, Landau theory and the generality of phase field theory. As an example, anisotropic Landau coefficients are obtained by starting from experimental parameters for Pb-free 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–50BCT). Thermodynamic parameters are optimized separately for the rhombohedral (R) and tetragonal (T) ferroelectric phases using a combination of single-crystal and polycrystalline polarization and permittivity data. Parameters are validated against dielectric permittivity as a function of temperature from single-crystal and polycrystalline samples. The optimized parameters correctly predict the sequence of phase transitions as a function of temperature and the paraelectric–ferroelectric transition at 355.5 K is within the experimentally reported range. An upper thermodynamic limit is predicted for R + T metastable coexistence at 302.3 K in agreement with the experimentally measured transition to a stable single T phase for this chemistry at 302 K. The detailed parameter optimization procedure enables the identification of single-crystal tensor properties from experimental measurements for a wide variety of chemistries.

Role of A and B site doping on antiferrodistortive phase transition in sodium bismuth titanate

We report the results of temperature-dependent powder X-ray diffraction studies on lead-free piezoelectric sodium bismuth titanate (NBT) modified by partially substituting Ba at the A site or Nb at the B site. We observed the disappearance of certain reflections and a change in the main perovskite peaks of the rhombohedral phase suggesting a structural phase transition. Detailed Rietveld refinements revealed that both the ferroelectric and the antiferrodistortive phase transitions occur together at high temperature leading to a change in crystal structure from the low-temperature ferroelectric rhombohedral phase (space group: R3c) to the high-temperature paraelectric cubic phase (space group:Pm3¯m). This suggests the suppression of the intermediate tetragonal phase of pure NBT. We found that substituting Ba onto the A site enhances the lattice strain and lowers the antiferrodistortive phase transition temperature.

Design morphotropic phase boundary composition in the Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTio3 system and its performance

ABSTRACT Using composition designing, Pb(In1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 (PIN-PMN-PT) ceramics with compositions around the morphotropic phase boundary (MPB) were prepared by the solid-state reaction method via the columbite and wolframite precursor techniques. X-ray diffraction (XRD) measurement and XRD peaks fitting combined with electrical performance characterization confirm the occurrence of composition-induced ferroelectric phase change, and the sintered PIN-PMN-PT ceramics present the coexistence of rhombohedral and tetragonal ferroelectric phases. Composition exerts great influence on the relative density of the sintered ceramics, and the 0.28Pb(In1/2Nb1/2)O3-0.40Pb(Mg1/3Nb2/3)O3-0.32PbTiO3 (0.28PIN-0.40PMN-0.32PT) ceramics exhibit rather uniform microstructural morphology with high relative density of 94.4%. Dielectric, ferroelectric, and piezoelectric performance characterization also confirm the existence of the MPB effects, where the composition having performance maximum presents slight difference, proving that MPB has the composition region. Dielectric response behavior fitting and Raman spectroscopy measurement confirm the PIN-PMN-PT ceramics approach normal ferroelectrics with apparent diffusive transition characteristic and the occurrence of composition-induced ferroelectric phase change.