Morphotropic Phase Transition Research Articles

Phase structure of the ceramic samples of the BiScO3–PbTiO3–PbMg⅓Nb⅔O3 system near the morphotropic phase boundary studied by the Rietveld method

Abstract An X-ray diffraction study of ceramic samples of the BiScO3–PbTiO3–PbMg⅓Nb⅔O3 system with compositions close to the morphotropic phase boundary was carried out at room temperature. The existence of wide areas of solid solutions has been established. The symmetry of the PbTiO3-based solid solutions is tetragonal (space group P4mm). The symmetry of the PbMg⅓Nb⅔O3-based solid solutions is cubic (space group Pm3‾m). Near the BiScO3 side, the solid solutions are rhombohedral (space group R3m). During the morphotropic phase transition from the cubic solid solutions to the tetragonal ones, additional phases appear. If a tetragonal phase prevails ((1 − 2x)BiScO3–xPbTiO3–xPbMg⅓Nb⅔O3 x = 0.46; (1 − 2x)BiScO3–1.1xPbTiO3–0.9xPbMg⅓Nb⅔O3 x = 0.45 and 0.42), a satisfactory model is a model with a minority cubic phase (space group Pm3‾m). If a cubic phase prevails ((1 − 2x)BiScO3–1.1xPbTiO3–0.9xPbMg⅓Nb⅔O3 x = 0.39 and 0.36; (1 − 2x)BiScO3–0.8xPbTiO3–1.2xPbMg⅓Nb⅔O3 x = 0.4), a model with a minority monoclinic phase (space group Cm) or with two minority phases: tetragonal (space group P4mm) and monoclinic (space group Cm) is satisfactory.

Phase formation and structure in the solid solutions of the (1 – <i>х</i>)BiFeO<sub>3</sub>–<i>x</i>/2PbFe<sub>1/2</sub>NB<sub>1/2</sub>O<sub>3</sub>–<i>x</i>/2PbFe<sub>2/3</sub>W<sub>1/3</sub>O<sub>3</sub> system

The solid solutions of the (1 – х)BiFeO3–x/2PbFe1/2Nb1/2O3–x/2PbFe2/3W1/3O3 system in the concentration range 0.05 ≤ х ≤ 0.50 were produced by solid state method and sintering using conventional ceramic technology. In the range 0.25 x 0.35, a morphotropic phase transition from the rhombohedral phase to the cubic phase was found. The difference in symmetry when “scaling” the material is shown. The influence of PbFe1/2Nb1/2O3 and PbFe2/3W1/3O3 on the grain structure formation was established.

Morphotropic Phase Boundary Enhanced Photocatalysis in Sm Doped BiFeO3.

This paper presents the results of the synthesis of samarium-doped bismuth ferrite (BFO) nanoparticles by the solution combustion method. The dependence of BFO properties on the amount of the samarium (Sm) in the composition was studied. The synthesized nanocomposites were characterized by scanning electron microscopy SEM), X-ray diffractometry (XRD), Raman, Electron Diffuse Reflectance Spectroscopy (EDRS) and Electron Magnetic Resonance (EMR). The photocatalytic (PC) measurements showed the absence of a strict correlation between the PC activity and the crystallite size and band gap. An increase in the PC activity of BFO samples with 10 and 15% doping was observed and it was concluded that in controlling the PC properties in doped BFO, the processes of interfacial polarization at the boundaries of the morphotropic phase transition are of decisive importance. It was supposed that the internal electric field formed at these boundaries contributes to the efficient separation of photogenerated charge carriers.

Thickness‐Driven Morphotropic Phase Transition in Metastable Ferroelectric CaTiO3 Films

AbstractThe intimate coexistence of multiple phases in ferroelectrics has been shown to result in exotic electromechanical properties, such as giant piezoelectricity. Here, via a thickness‐driven phase transition, the phase coexistence and enhanced piezoelectricity in a few tens of nanometers thick, Pb‐free CaTiO3 films are demonstrated. Due to the competition between interfacial and bulk energies, as film thickness increases, epitaxial CaTiO3 films exhibit a ferroelectric‐to‐paraelectric phase transition that is concomitant with the rhombohedral‐to‐orthorhombic structural transition. This so‐called thickness‐driven morphotropic phase transition (MPT) in nanoscale CaTiO3 films stems from the metastable nature of ferroelectricity. The resulting morphotropic phase boundary at the atomic scale in nanoscale CaTiO3 films is visualized. It is also shown that this thickness‐driven MPT can lead to reasonably good piezoelectricity at the nanoscale. This study highlights the rich phase evolution of complex ferroelectrics as a novel platform to control the functionality of nanoscale electromechanical devices.

Influence of the Degree of Phase Transition Diffuseness on the Depolarization Temperature in Relaxors of Different Types

The relationship between the temperatures of depolarization (Td) and morphotropic phase transition (TF-R) in crystalline relaxor solid solutions of various types, such as PbMg1/3Nb2/3O3-29PbTiO3 (PMN-29PT), PbZn1/3Nb2/3O3-9PbTiO3 (PZN-9PT) and NaBi1/2Ti1/2O3-xBaTiO3 (x=5,7.5%) (NBT-xBT) has been studied. For this purpose, dielectric measurements of polarized samples were carried out, and the process of induction of the ferroelectric phase in an electric field applied below the TF-R temperature was also studied. It was found that the structure of the low-temperature phases in these compounds is different, which leads to significant differences not only in the induction of the ferroelectric phase, but also to different relative positions of the temperatures Td and TF-R. In PMN-29PT, the formation of ferroelectric phases is preceded by some delay time, which is one of the hallmarks of a non-ergodic glassy phase, and in this case the temperatures Td and TF-R coincide. In PZN-9PT and NBT-5BT, the ferroelectric phase is induced immediately after the field is applied without a delay time, which indicates that below the TF-R temperature, the non-ergodic glassy phase does not appear, and the temperatures Td and TF-R do not coincide in them. The results obtained are discussed from the point of view of different degrees of diffuseness of the phase transition and different sizes of the polar regions. It is suggested that the coincidence of temperatures Td and TF-R is a consequence of the non-ergodic glassy phase and the small sizes of the polar regions. Keywords: relaxors, phase transitions, degree of smearing, depolarization temperature.

Влияние степени размытия фазового перехода на температуру деполяризации в релаксорах разного типа

The relationship between the temperatures of depolarization (Td) and morphotropic phase transition (TF-R) in crystalline relaxor solid solutions of various types, such as PbMg1/3Nb2/3O3-29PbTiO3 (PMN-29PT), PbZn1/3Nb2/3O3-9PbTiO3 (PZN- 9PT) and NaBi1/2Ti1/2O3-xBaTiO3 (x=5.7.5%) (NBT-xBT) has been studied. For this purpose, dielectric measurements of polarized samples were carried out, and the process of induction of the ferroelectric phase in an electric field applied below the TF-R temperature was also studied. It was found that the structure of the low-temperature phases in these compounds is different, which leads to significant differences not only in the induction of the ferroelectric phase, but also to different relative positions of the temperatures Td and TF-R. In PMN-29PT, the formation of ferroelectric phases is preceded by some delay time, which is one of the hallmarks of a non-ergodic glassy phase, and in this case the temperatures Td and TF-R coincide. In PZN-9PT and NBT-5BT, the ferroelectric phase is induced immediately after the field is applied without a delay time, which indicates that below the TF-R temperature, the non-ergodic glassy phase does not appear, and the temperatures Td and TF-R do not coincide in them. The results obtained are discussed from the point of view of different degrees of diffuseness of the phase transition and different sizes of the polar regions. It is suggested that the coincidence of temperatures Td and TF-R is a consequence of the non-ergodic glassy phase and the small sizes of the polar regions.

Peculiarities of the induced phase transition in single-crystal solid solutions Na-=SUB=-1/2-=/SUB=-Bi-=SUB=-1/2-=/SUB=-TiO-=SUB=-3-=/SUB=--5 %BaTiO-=SUB=-3-=/SUB=-

The dielectric and optical properties, as well as the time dependences of the permittivity in an electric field applied along the [001] direction, are studied in Na1/2Bi1/2TiO3-5 %BaTiO3 single crystals lying near the morphotropic phase boundary. It is shown that, even in the absence of an electric field, dielectric and optical hysteresis associated with the coexistence of tetragonal and rhombohedral phases is observed in a wide temperature range, and the relative volume fractions of the two phases largely depend on temperature. It was found that at temperatures below the temperature of the morphotropic phase transition, the induction of the ferroelectric phase occurs without a delay time, which distinguishes the samples under study from PbMg1/3Nb2/3O3-xPbTiO3 solid solutions. The results obtained are explained by different sizes of polar nanoregions in the low-temperature phase. Keywords: ferroelectricity, relaxors, induced phase transition.

Induced phase transition in monocrystalline solids solutions PbMg-=SUB=-1/3-=/SUB=-Nb-=SUB=-2/3-=/SUB=-O-=SUB=-3-=/SUB=--29PbTiO-=SUB=-3-=/SUB=- and PbZn-=SUB=-1/3-=/SUB=-Nb-=SUB=-2/3-=/SUB=-O-=SUB=-3-=/SUB=--9PbTiO-=SUB=-3-=/SUB=-: similarity and difference

The kinetics of the induced phase transition in single-crystal relaxor solid solutions PbMg1/3Nb2/3O3-29PbTiO3 and PbZn1/3Nb2/3O3-9PbTiO3 is studied when an electric field is applied along the [001] direction. At temperatures below the temperature of the morphotropic phase transition, the changes in the dielectric constant and optical transmission in electric fields are studied. It is shown that the decrease in optical transmission with time is associated only with a change in the sizes of nanoregions during the phase transition. It was found that the induced phase transition proceeds differently in these crystals. In PMN-29PT crystals, the formation of ferroelectric phases and the rapid establishment of macroscopic polarization are preceded by a certain delay time, while in PZN-9PT crystals, the ferroelectric phase is induced immediately after the application of the field without a delay time. The results obtained are explained by the different structures of the low-temperature phases in these compounds. Keywords: ferroelectricity, relaxors, induced phase transition.

Phase equilibria of the GeTe−Bi2Te3 quasi-binary system in the range 0–50 mol% Bi2Te3

ABSTRACT The GeTe-GeBi2Te4 part of the GeTe-Bi2Te3 quasi-binary system was re-examined in the 700-1000 K temperature interval by using PXRD, DTA, and SEM techniques, and the corresponding fragment of the phase diagram was constructed. The existence of 4 ternary compounds is confirmed in the system. Ge2Bi2Te5 (863 K) and GeBi2Te4 (854 K) compounds formed by peritectic reactions, while Ge3Bi2Te6 and Ge4Bi2Te7 decompose by solid-phase reactions. The system is also characterized by the formation of large areas of solid solutions based on both modifications of GeTe. Besides, rhombohedral→cubic morphotropic phase transition occurs between 9 and 10 mol% Bi2Te3 compositions. The homogeneity field of the cubic phase does not exceed 2-3 mol% at 700 K and layered phases are formed as the concentration of Bi2Te3 increases. Crystallographic parameters of ternary compounds, as well as solid solutions, were determined by the Rietveld method. A comparative analysis of obtained results with literature data is performed.

Composition Dependent Electrical Properties of (Ba1−xCaxZr0.1Ti0.9)O3 Ceramics, Near Morphotropic Phase Boundary (0.140 ≤ x ≤ 0.160)

In this work, pellet samples of (Ba1−xCaxZr0.1Ti0.9)O3, (0.140 ≤ x ≤ 0.160) were prepared using solid-state reaction route with double sintering. The dielectric and structural properties of the prepared samples were measured, from room temperature to 250 °C, at different frequencies, in the range 10–1000 KHz. A peak shifting anomaly in the X-ray diffraction peaks patterns, an anomalous change in the slope of c/a vs x plot, and the observed minimum values of dielectric constant, loss and conductivity of the prepared compositions show a strong compositional dependent dielectric and structural properties, indicating a morphotropic phase transition type behavior, at the composition with x = 0.150.

Индуцированный фазовый переход в монокристаллических твердых растворах PbMg-=SUB=-1/3-=/SUB=-Nb-=SUB=-2/3-=/SUB=-O-=SUB=-3-=/SUB=--29PbTiO-=SUB=-3-=/SUB=- и PbZn-=SUB=-1/3-=/SUB=-Nb-=SUB=-2/3-=/SUB=-O-=SUB=-3-=/SUB=--9PbTiO-=SUB=-3-=/SUB=-: сходство и различие

The kinetics of the induced phase transition in single-crystal relaxor solid solutions PbMg1 / 3Nb2 / 3O3-29PbTiO3 and PbZn1 / 3Nb2 / 3O3-9PbTiO3 is studied when an electric field is applied along the [001] direction. At temperatures below the temperature of the morphotropic phase transition, the changes in the dielectric constant and optical transmission in electric fields are studied. It is shown that the decrease in optical transmission with time is associated only with a change in the sizes of nanoregions during the phase transition. It was found that the induced phase transition proceeds differently in these crystals. In PMN-29PT crystals, the formation of ferroelectric phases and the rapid establishment of macroscopic polarization are preceded by a certain delay time, while in PZN-9PT crystals, the ferroelectric phase is induced immediately after the application of the field without a delay time. The results obtained are explained by the different structures of the low-temperature phases in these compounds. Key words: ferroelectricity, relaxors, induced phase transition.

Enhancing the dielectric, electrocaloric and energy storage properties of lead-free Ba0.85Ca0.15Zr0.1Ti0.9O3 ceramics prepared via sol-gel process

The Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT) ceramics were successfully prepared by the sol-gel process and sintered at 1420 °C. The effect of sintering times (2, 4 and 6 h) on structural, microstructural, electric properties, energy storage, and electrocaloric effect was systematically examined. X-ray diffraction (XRD) results show that all the samples crystallize in the pure perovskite structure. The morphotropic phase transition from the tetragonal to the orthorhombic phase (T-O) was identified and confirmed by Rietveld refinement. The BCZT ceramic sintered at 1420 °C for 4 h possesses a good relative density of 98% and exhibits optimal properties with a high dielectric permittivity (εr,max) ~16310, a large electrocaloric effect coefficient (ξ) ~ 0.244Kmm/kV and a high energy storage efficiency of 63.65%.

Melting of spatially modulated phases at domain wall/surface junctions in antiferrodistortive multiferroics

The interplay between the surface and domain wall phenomena in multiferroic LaxBi1-xFeO3 in the vicinity of morphotropic phase transition is explored on the atomic level. Scanning Transmission Electron Microscopy (STEM) has enabled mapping of atomic structures of the material with picometer-level precision, providing direct insight into the spatial distribution of the order parameters in this material and their behavior at surfaces and interfaces. Here, we use the thermodynamic Landau-Ginzburg-Devonshire (LGD) approach to explain the emergence of spatially modulated phases (SMP) in La0.22Bi0.78FeO3 films, and establish that the change of polarization gradient coefficients caused by La-doping is the primary driving mechanisms. The suppression, or "melting", of the SMP in the vicinity of the domain wall surface junction is observed experimentally and simulated in the framework of LGD theory. The melting originated from the system tendency to minimize electrostatic energy caused by long-range stray electric fields outside the film and related depolarization effects inside it. The observed behavior provides insight to the origin of surface and interface behaviors in multiferroics.

Emergent Antipolar Phase in BiFeO3-La0.7Sr0.3MnO3 Superlattice.

Ferroelectric-paraelectric superlattices show emerging new states, such as polar vortices, through the interplay and different energy scales of various thermodynamic constraints. By introducing magnetic coupling at BiFeO3-La0.7Sr0.3MnO3 interfaces epitaxially grown on SrTiO3 substrate, we find, for the first time in thin films, a sub-nanometer thick lamella-like BiFeO3. The emergent phase is characterized by an arrangement of a two unit cell thick lamella-like structure featuring antiparallel polarization, resulting an antiferroelectric-like structure typically associated with a morphotropic phase transition. The antipolar phase is embedded within a nominal R3c structure and is independent of the BiFeO3 thickness (4-30 unit cells). Moreover, the superlattice structure with the morphotropic phase demonstrates azimuth-independent second harmonic generation responses, indicating a change of overall symmetry mediated by a delicate spatial distribution of the emergent phase. This work enriches the understanding of a metastable state manipulated by thermodynamic constraints by lattice strain and magnetic coupling.

Magnetostrictive Anomalies of Rare Earth Laves Phases with Morphotropic Phase Transition

In the recent years, a number of pseudo-binary RT2 Laves phases with morphotropic phase transitions, i.e., systems of compounds having a morphotropic phase boundary in the phase diagram, have attracted special attention in the process of searching for compounds with high or, on the contrary, almost zero magnetostriction values. In this work, we study the magnetic and magnetostrictive properties of multicomponent systems based on compounds Tb0.2Dy0.8 – xGdxCo2 and Tb0.2Dy0.8 – xGdxCo1.9Al0.1, in which a morphotropic phase transition is observed when dysprosium is replaced by gadolinium. A relationship between the temperature behavior, the sign and magnitude of magnetostrictive deformations, and the type of cubic lattice distortion of the studied Laves phases is revealed. In the region of magnetic phase transitions, the magnetocaloric effect is investigated.

Piezoelectric properties of Na1−xKxNbO3, near x = 0.500 morphotropic phase region

Sodium-potassium niobate (Na1-xKxNbO3) ceramic pellets were prepared, near equimolar Na- K composition, by solid state reaction method with double sintering. Remnant polarization, coercive field, polarization current and converse piezoelectric coefficient (d*33) of the prepared samples were measured. The observed properties exhibit strong composition dependence- a morphotropic phase transition type behavior, showing extremal piezoelectric properties for potential lead free transducer applications, at the composition with x = 0.500.

The Behavior of 33PbYb1/2Nb1/2O3–22PbZrO3–45PbTiO3 Ceramic Solid Solutions in an Electric Field

The temperature dependences of dielectric properties and the time-dependent dielectric permittivity are investigated for 33PbYb1/2Nb1/2O3–22PbZrO3–45PbTiO3 ceramics in electric fields with 0 < E < 8 kV/cm. Our data show that a small fraction of pseudocubic relaxor phase is present along with rhombohedral and tetragonal phases in the phase that exists in this material below the morphotropic transition temperature. In contrast to other relaxors, the dielectric permittivity of the phase existing below the morphotropic phase transition temperature does not vary with time in an applied electric field. The causes of such behavior are discussed.

Магнитострикционные аномалии редкоземельных фаз Лавеса c морфотропным фазовым переходом

Оver recent years in the process of searching for compounds with high or almost zero magnetostriction values, a number of pseudo-binary Laves RT2 phases with morphotropic phase transitions are attracted particular attention. That is, systems of compounds with a morphotropic phase boundary in the phase diagram. In this paper, the magnetic and magnetostrictive properties of multicomponent systems of compounds Tb0.2Dy0.8-хGdxCo2 and Tb0.2Dy0.8-хGdxCo1.9Al0.1 in which a morphotropic phase transition is observed when replacing dysprosium with gadolinium have been studied. A relationship between the temperature behavior, the sign and magnitude of magnetostrictive deformations, and the type of distortion of the cubic lattice of the studied Laves phases is revealed. In the region of magnetic phase transitions, the magnetocaloric effect was investigated.

Поведение керамических твердых растворов 33PbYb-=SUB=-1/2-=/SUB=-Nb-=SUB=-1/2-=/SUB=-O-=SUB=-3-=/SUB=--22PbZrO-=SUB=-3-=/SUB=--45PbTiO-=SUB=-3-=/SUB=- в электрическом поле

The temperature dependences of the dielectric parameters were studied, as well as the changes in the dielectric constant with time in ceramic 33PbYb1 / 2Nb1 / 2O3-22PbZrO3-45 PbTiO3 samples in electric fields (0 &lt;E &lt;8 kV / cm). It is shown that in the phase existing below the temperature of the morphotropic phase transition, in addition to the rhombohedral and tetragonal phases, a small fraction of the relaxor pseudocubic phase is present. It was found that, unlike other relaxors, the dielectric constant practically does not change with time when an electric field is applied in the phase below the temperature of the morphotropic phase transition. Possible reasons for this behavior are discussed.

Evolution of Oxygen–Ion and Proton Conductivity in Ca-Doped Ln2Zr2O7 (Ln = Sm, Gd), Located Near Pyrochlore–Fluorite Phase Boundary

Sm2−xCaxZr2O7−x/2 (x = 0, 0.05, 0.1) and Gd2−xCaxZr2O7−x/2 (x = 0.05, 0.1) mixed oxides in a pyrochlore–fluorite morphotropic phase region were prepared via the mechanical activation of oxide mixtures, followed by annealing at 1600 °C. The structure of the solid solutions was studied by X-ray diffraction and refined by the Rietveld method, water content was determined by thermogravimetry (TG), their bulk and grain-boundary conductivity was determined by impedance spectroscopy in dry and wet air (100–900 °C), and their total conductivity was measured as a function of oxygen partial pressure in the temperature range: 700–950 °C. The Sm2−xCaxZr2O7−x/2 (x = 0.05, 0.1) pyrochlore solid solutions, lying near the morphotropic phase boundary, have proton conductivity contribution both in the grain bulk and on grain boundaries below 600 °C, and pure oxygen–ion conductivity above 700 °C. The 500 °C proton conductivity contribution of Sm2−xCaxZr2O7−x/2 (x = 0.05, 0.1) is ~ 1 × 10−4 S/cm. The fluorite-like Gd2−xCaxZr2O7−x/2 (x = 0.1) solid solution has oxygen-ion bulk conductivity in entire temperature range studied, whereas proton transport contributes to its grain-boundary conductivity below 700 °C. As a result, of the morphotropic phase transition from pyrochlore Sm2−xCaxZr2O7−x/2 (x = 0.05, 0.1) to fluorite-like Gd2−xCaxZr2O7−x/2 (x = 0.05, 0.1), the bulk proton conductivity disappears and oxygen-ion conductivity decreases. The loss of bulk proton conductivity of Gd2−xCaxZr2O7−x/2 (x = 0.05, 0.1) can be associated with the fluorite structure formation. It is important to note that the degree of Ca substitution in such solid solutions (Ln2−xCax)Zr2O7−δ (Ln = Sm, Gd) is low, x < 0.1. In both series, grain-boundary conductivity usually exceeds bulk conductivity. The high grain-boundary proton conductivity of Ln2−xCaxZr2O7−x/2 (Ln = Sm, Gd; x = 0.1) is attributable to the formation of an intergranular CaZrO3-based cubic perovskite phase doped with Sm or Gd in Zr sublattice.