Intermediate Metastable Phase Research Articles

Nonclassical Nucleation—Role of Metastable Intermediate Phase in Crystal Nucleation: An Editorial Prefix

Classical nucleation theory (CNT), which was established about 90 years ago, represents the most commonly used theory in describing nucleation processes. For a fluid-to-solid phase transition, CNT states that the solutes in a supersaturated solution reversibly form small clusters. Once a cluster reaches its critical size, it becomes thermodynamically stable and is favored for further growth. One of the most important assumptions of CNT is that the nucleation process is described by one reaction coordinate and all order parameters proceed simultaneously. Recent studies in experiments, computer simulations, and theory have revealed nonclassical features in the early stage of nucleation. In particular, the decoupling of order parameters involved during a fluid-to-solid transition leads to the so-called two-step nucleation mechanism, in which a metastable intermediate phase (MIP) exists in parallel to the initial supersaturated solution and the final crystals. These MIPs can be high-density liquid phases, mesoscopic clusters, or preordered states. In this Special Issue, we focus on the role of the various MIPs in the early stage of crystal nucleation of organic materials, metals and alloys, aqueous solutions, minerals, colloids, and proteins, and thus on various scenarios of nonclassical pathways of crystallization.

Critical nuclei at hetero-phase interfaces

Two-step nucleation, in which a metastable intermediate phase acts as a precursor for nucleating a thermodynamically stable phase, has been widely observed in many materials systems and solid-state reactions. Among the advantages of two-step nucleation is that the stable phase may nucleate heterogeneously at the hetero-phase interface between the original and the precursory phases. Although heterogeneous nucleation (HN) theories for homo-phase grain boundaries and inert surfaces are well established, our understanding of HN at reactive hetero-phase interfaces remains incomplete. This deficiency stems from the discontinuity of the chemical potential driving force across the hetero-phase interface, which profoundly affects the fundamental properties of the nucleus in a way that is not properly accounted for in existing models. Herein, we incorporate these effects to extend the classical nucleation theory to HN at hetero-phase interfaces. Our extended model demonstrates that the nucleus shape along the minimum energy path is strongly size-dependent, and this additional degree of freedom can result in the reduction of the critical nucleus volume and associated activation energy barrier by orders of magnitude relative to conventional predictions. The simulation results are used to construct a sensitivity map in the parameter space of interfacial energy and bulk driving force ratios, which quantifies the difference in nucleation barriers predicted by different models.

High Yield Synthesis of Violet Phosphorus Crystals

Violet phosphorus is the most stable phosphorus allotrope with a layered structure. The corresponding violet phosphorene, a more stable two-dimensional semiconducting structure than black phosphorene, is a promising two-dimensional material for electronic and optoelectronic devices. The synthesis of violet phosphorus is the key factor to its experimental research. However, no clear evidence has been reported for the synthesis of violet phosphorus since its first proposal in 1865. The violet phosphorus was even debated to be a metastable intermediate phase. Until recently, the violet phosphorus crystals have just been successfully produced and exfoliated to give violet phosphorene. High yield synthesis of highly crystalline and pure violet phosphorus is crucial for the further exploration of violet phosphorus and phosphorene. In this work, highly crystalline and pure violet phosphorus crystals have been produced with a yield as high as 80%. The vapor transport, nucleation, crystal growth conditions, and synthesis mechanism have been studied to obtain violet phosphorus instead of black phosphorus. The mixture of transport agents and amorphous red phosphorus was heated to 600 °C to form P–Sn–I vapor and transported to the cooler zone (580 °C). The phosphorus was separated out from the P–Sn–I composites after cooling down to 530 °C to form violet phosphorus nuclei. The nucleation time and further cooling time correspond to the amount and crystallinity of violet phosphorus crystals. The precipitation has been demonstrated to be SnI2 crystals with a space group of C2/m (12) after the growth of violet phosphorus crystals. The synthesis of highly crystalline and pure violet phosphorus with high yield provides the application possibility of violet phosphorus and phosphorene in mechanic, electronic, optoelectronic, catalysts, and medical fields.

Mechanisms for texture in BaTiO3 thin films from aqueous chemical solution deposition

The prototype piezoelectric material BaTiO3 is widely used in e.g., capacitators. Chemical solution deposition (CSD) of BaTiO3 films is a simple and environmentally friendly processing route, but insight in the crystallization process is crucial to tailor the film properties. In this work, the influence of the annealing conditions on the crystallization behavior of BaTiO3 thin films from aqueous chemical solution deposition is presented. In situ synchrotron X-ray diffraction was used to reveal the phase evolution, crystallization of the films, and to study how the degree of crystallographic texture in the polycrystalline films evolved. Our results revealed that the formation of an intermediate metastable oxycarbonate phase is critical for the formation of BaTiO3 thin films prepared by aqueous CSD. The pyrolysis products present in the film before crystallization determine the degree of preferential orientation and by tuning the heating program, especially the heating rate through nucleation (<0.2 °C/s), control of the microstructure and degree of preferential orientation in the films was demonstrated.In situ X-ray diffraction patterns of a BaTiO3 film, prepared by spin coating of an aqueous chemical solution, as a function of time and temperature, showing the phase evolution and crystallization of BaTiO3.

A Review of H2, CH4, and Hydrocarbon Formation in Experimental Serpentinization Using Network Analysis

The origin of methane and light hydrocarbons (HC) in natural fluids from serpentinization has commonly been attributed to the abiotic reduction of oxidized carbon by H2 through Fischer-Tropsch Type (FTT) reactions. Multiple experimental serpentinization studies attempted to identify the parameters that control the abiotic production of H2, CH4, and light HC. H2 is systematically and significantly formed in experiments, indicating that its production during serpentinization is well established. However, the large variance in concentration (eight orders of magnitude) is difficult to address because of the large number of parameters that vary from one experiment to another. CH4 and light HC production is much lower and also highly variable, leading to a vivid debate on potential role of metal catalysts and organic contamination. We have built a dataset that includes experimental setups, conditions, reactants, and products from 30 peer-reviewed articles reporting on experimental serpentinization and performed dimensionality reduction and network analysis to achieve an unbiased reading of the literature and fuel the debate. Our analysis distinguishes four experimental communities that highlights usual experimental protocols and the conditions tested so far. As expected, H2 production is mainly controlled by T and P though a strong variability remains within a given P-T range. Accessory metal-bearing phases seem to favor H2 production, while their role as catalyst or reactant is hampered by the lack of mineralogical characterization. CH4 and light HC concentrations are highly variable, uncorrelated to each other, and much lower than concentrations of potential reactants (H2, initial carbon). Accessory phases proposed as FTT catalysts do not enhance CH4 production, confirming the inefficiency of this reaction. CH4 only displays a positive correlation with temperature suggesting a kinetic/thermal control on its forming reaction. The carbon budget of some experiments indicates contamination in agreement with available labeled 13C studies. Salts in initial solutions are possible sources of organic contaminants. Natural systems certainly exploit longer reaction time or other reactional paths to form the observed CH4 and HC. The reducing potential of serpentinization can also produce intermediate metastable carbon phases in liquid or solid as observed in natural samples that should be targeted in future experiments.

Mechanism for structure conversion of FeSi under pressures

The atomistic mechanism for the structure conversion of FeSi from B20 to B2 phase at high pressures is a long-standing problem in Fe-Si system. Here we explore the atomistic mechanism about this intriguing structure conversion by first-principle calculations. We find the structure conversion from B20 to B2 is inhibited by the high kinetic barriers and the weak driving forces from low relative enthalpy under pressures. We also identify an orthorhombic structure with Pbcm symmetry as an intermediate meta-stable phase along the minimum energy path, which is possibly the precursory state of the B2 phase. These results can help to explain experimental findings and explore the kinetic origin of this intriguing structure conversion of FeSi at high pressure and temperature.

The transformation of diamond to graphite: Experiments reveal the presence of an intermediate linear carbon phase

Natural diamonds that have been partially replaced by graphite have been observed to occur in natural rocks. While the graphite-to-diamond phase transition has been extensively studied the opposite of this (diamond to graphite) remains poorly understood. We performed high-pressure and temperature hydrous and anhydrous experiments up to 1.0 GPa and 1300 °C using Amplex premium virgin synthetic diamonds (20–40 μm size) as the starting material mixed with Mg(OH)2 as a source of H2O for the hydrous experiments. The experiments revealed that the diamond-to-graphite transformation at P = 1.0 GPa and T = 1300 °C was triggered by the presence of H2O and was accomplished through a three-stage process. Stage 1: diamond reacts with a supercritical H2O producing an intermediate 200–500 nm size “globular carbon” phase. This phase is a linear carbon chain; i.e. a polyyne or carbyne. Stage 2: the linear carbon chains are unstable and highly reactive, and they decompose by zigzagging and cross-linking to form sp2-hybridized structures. Stage 3: normal, disordered, and onion-like graphite is produced by the decomposition of the sp-hybridized carbon chains which are re-organized into sp2 bonds. Our experiments show that there is no direct transformation from sp3 C-bonds into sp2 C-bonds. Our hydrous high-pressure and high-temperature experiments show that the diamond-to-graphite transformation requires an intermediate metastable phase of a linear hydrocarbon. This process also provides a simple mechanism for the substitution of other elements into the graphite structure (e.g. H, S, O).

Aspects of lithium tri- and tetraborate synthesis in the subsolidus region

The present work is focused at studying the transformation patterns for the crystalline structure of phases formed during the synthesis of polycrystalline lithium tri- and tetraborate. In the field of lithium triborate (LiB 3 O 5 ) and tetraborate (Li 2 B 4 O 7 ) of the Li 2 O – B 2 O 3 system, LiB 3 O 5 and Li 2 B 4 O 7 polycrystalline powders were synthesised. In terms of precursors, lithium carbonate (Li 2 CO 3 ) and boric acid (H 3 BO 3 ) were selected. Two synthesis methods were tested including precipitation from solution and solid-phase synthesis. As a result, the direct sintering of a mechanically-grinded stoichiometric precursor mixture is shown to be the optimal method for crystallising LiB 3 O 5 and Li 2 B 4 O 7 . The crystallisation patterns of lithium borates were studied in a temperature range of 500-850 °C with sampling carried out every 50 °C. Individual phase portraits were established presenting a set of process character-istics depending on the level of substance particle organisation and subsolidus crystallisation from the initial reagent mixture of lithium tri- and tetraborate at the phase, local and structural levels. In a lithium triborate stoichiometric mixture, the maximum conversion of crystalline phases is observed in the region of 500–600 °C, while, for lithium tetraborate, the temperature maximum is in the range of 600–700 °C. The sequence of phase transformations re-mains almost unchanged and occurs according to the following scheme: starting reagents > intermediate metastable phases > final borates. The local level of phase portraits characterises the interaction of coordination polyhedra forming the crystal lattice of the studied phases. Solid-phase synthesis of crystalline LiB 3 O 5 from the Li 2 CO 3 and H 3 BO 3 takes place as a result of (BO 3 ) 3- → (B 3 O 7 ) 5- transition with the (BO 3 ) 3- → (B 4 O 9 ) 6- scheme realised in obtaining Li 2 B 4 O 7 . At the crystal structure level, such transitions correspond to transformations of the monoclinic lattice of the Li 2 CO 3 and H 3 BO 3 primary phases into the LiB 3 O 5 and Li 2 B 4 O 7 rhombic and tetragonal structure, respectively. In this case, an intermediate step of this transformation consists in formation of the LiBO 2 trigonal chain metaborate and metastable Li 2 B 8 O 13 .

Growth modes of quasicrystals involving intermediate phases and a multistep behavior studied by phase field crystal model

Understanding the microscopic kinetics of quasicrystal formation via nucleation and growth is crucial. Here, we report unusual pathways to nucleation and growth of dodecagonal quasicrystals via a phase field crystal model incorporating a two-length-scale potential. Under certain thermodynamic parameters, both quasicrystal growths via heterogeneous and homogeneous nucleation may be associated with a multistep behavior and the transient appearance of triangular and intermediate phases, different from classical nucleation pathways. The metastable intermediate phase spontaneously occurs to bridge the triangular phase and quasicrystal nuclei of different orientations to reduce the total free energy of the system. Decomposition of an undercooled fluid phase into quasicrystal phase shows a multistep pathway wherein the triangular phase and the intermediate phase may occur faster than the quasicrystal phase, when the growth rate of one length-scale ordering is significantly different from the other and the subsequent competing and coupling of both length scales are involved. The calculated structure factor, radial distribution function, and the aperiodic tiling structure of the intermediate phase explain why it appears during the quasicrystal formation.

Continuous/reversible phase transition behaviors and their effect on the hysteresis energy loss of the anodes in Na-ion batteries

Alloying anode materials undergo a continuous and reversible phase transition during battery cycles, and the energy consumed during this process determines the energy efficiency of the anode. In this study, using the combined technique of voltammetric experiments and first-principles calculations, comparative studies are performed on P and Sb anodes to identify their phase transition behaviors, associated with the charge–discharge processes of Na-ion batteries (NIBs). To quantitatively establish the phase transition vs energy efficiency relationship of the anode materials of NIBs, we developed a thermodynamic model that replicates the polarization curves observed in voltammetric measurements. We obtained theoretical polarization curves by analyzing the phase transformation sequence and corresponding changes in the resistivity values of intermediate phases of the Na–P and Na–Sb systems under various applied potentials. The formation of various intermediate metastable phases and their high electrical resistivity are identified to be responsible for the increased loss in energy at the anodes. While filling the knowledge gaps on the reasons as to why the Na–P and Na–Sb systems exhibit different hysteresis losses, the outcomes of this study provide a crude yet basic guideline for the appropriate choice of potential anode materials with superior energy efficiencies suitable for NIBs.

High-Resolution Electron Microscopy and Kinetic Studies of Precipitation Hardening Reactions in Cast Al-5.8Zn-2.2Mg-2.5Cu

Precipitation age hardening (T6) response of Al-5.8Zn-2.2Mg-2.5Cu alloy in near-net-shaped cast condition was investigated. Cast samples were manufactured using the controlled diffusion solidification (CDS) technology combined with a metallic mold tilt pour gravity casting process. This study was conducted using (1) non-isothermal aging during differential scanning calorimetry (DSC) experiments and (2) isothermal aging during which transient bulk and micro-hardness measurements taken at four aging temperatures of 343, 393, 433 and 473 K. A detailed microstructural investigation combined with a quantitative image analysis was carried out on both DSC and hardness specimens using high-resolution electron microscopy (HREM) and energy-dispersive spectroscopy (EDS) elemental mappings. Hardness measurements were analyzed using a kinetic modeling approach (single state variable combined with a kinetic equation that is valid for the Al-Zn-Mg-Cu alloys). The results confirm the formation of hardening phases of GP zone, intermediate hardening metastable phase η′ and equilibrium phase η. The results of calorimetric measurements, electron microscopy and selected area diffraction patterns are in good agreement and confirm transient precipitation/dissolution sequences. A mean value of activation energy $$Q_{\text{A}}$$ of 75 kJ/mol was evaluated for combined bulk diffusion rate of alloying elements during precipitation of strengthening phases within Al matrix.

Improved phase-change properties of Sn–Zn–Sb alloys with a two-step crystallization process for multi-level data storage applications

Abstract We investigated Te-free ZnSb films for the potential applications in multi-level data storage. It was found that, the films could exhibit three phases during crystallization process, e.g., high amorphous phase, intermediate metastable ZnSb phase, and low stable ZnSb phase. However, the formation of the voids in the metastable ZnSb phase, high crystallization temperature and large amorphous resistance have an influence on the structure stability and SET power consumption during the repeated switching process. Interestingly, doping of Sn with a concentration of 11.1 at% into ZnSb can prevent the growth of metastable ZnSb grains, and different crystals like SnSb and ZnSnSb2 can be precipitated out during heat treatment, but the two-step crystallization process is kept unchanged. Moreover, the chemical environment of Sn in Zn–Sb studied by X-ray photoelectron spectroscopy indicates the formation of the large number of Sn–Sb and Sn–Zn bonds, which in turn reduces the crystallization temperature, lowers crystallization activation energy as well as decreases the amorphous resistance. The in situ transmission electron microscopy measurements on the optimized (ZnSb)88.9Sn11.1 composition confirms a two-step phase transition process from amorphous to rhombohedral SnSb crystals first, and then to the stable tetragonal ZnSb2Sn crystals. These excellent properties make Zn–Sb–Sn materials useful as a phase-change layer in low-power and high-density memory.

Structure-induced metastable phase transformation in Cu6Sn5 intermetallics

The retarded η → η′ phase transformation in Cu6Sn5 has become a potential risk to the service reliability of micro-solder joints. In this paper, both Cu6Sn5 crystal and powder samples were fabricated to explore the phase transformation behaviour of Cu6Sn5. Because of the difference in stress accumulation, η′ ↔ ηc ↔ η and η′ ↔ η phase transformations occurred in the Cu6Sn5 core layers and surface layers, respectively. Moreover, formation of the metastable intermediate ηc phase was confirmed to be both stress induced and structure dependent. In addition, by decreasing the crystal size or using a proper isothermal treatment, formation of the metastable phase in Cu6Sn5 can be significantly reduced. Our study can provide an understanding of the phase transformation behaviour of Cu6Sn5 and may provide visual data for solving the risk of retarded Cu6Sn5 phase transformation.

High Rate Performance of Dual-Substituted LiFePO4 Based on Controlling Metastable Intermediate Phase

High rate capability is one of the most important properties in Li-ion batteries for electric vehicle and/or energy grid use. Herein, a high-power electrode material consisting of dual-substituted LiFePO4 by zirconium and silicon, Li(Fe0.95Zr0.05)(P0.9Si0.1)O4, was developed as it exhibits small lattice volume change between Li-rich and Li-poor phases. The dual-substituted cathode exhibited 1.1–4.4 times larger charge/discharge capacities for upper 10 C rates than that of the undoped material. Time-resolved XRD measurements at the high rate of 10 C revealed the formation of a metastable intermediate phase during the Li intercalation/deintercalation processes which triggers the continuous phase transition in Li(Fe0.95Zr0.05)(P0.9Si0.1)O4 with moderation of the lattice mismatch. Controlling the lattice volume change between the initial and end phase of the intercalation materials is key to achieving high rate capabilities.

Formation of a Graphene-Like SiN Layer on the Surface Si(111)

00-The kinetics of the formation and thermal decomposition of a two-dimensional SiN-(8 x 8) nitride layer on a Si(111) surface is studied. The SiN-(8 x 8) structure is a metastable intermediate phase formed during the nitridation of silicon before the formation of a stable amorphous Si3N4 phase. Studying the SiN-(8 x 8) structure by scanning tunneling microscopy shows its complex structure: it consists of an adsorption (8/3 x 8/3) phase, with the lateral period 10.2 angstrom, and a honeycomb structure with a 6 angstrom side of a hexagon that is turned 30 degrees with respect the adsorption phase. The band gap of the SiN-(8 x 8) phase is measured and found to be 2.8 eV, which is smaller compared to the band gap of the -Si3N4 crystal phase 5.3 eV. The interplanar spacings in the (AlN3)/(SiN)(2) structure on the Si(111) surface are measured. The spacings are 3.3 and 2.86 angstrom in SiN and AlN, respectively. Such interplanar spacings are indicative of weak van der Waals interaction between the layers. A model of the SiN-(8 x 8) structure as a flat graphene-like layer is suggested. The model is consistent with the diffraction and microscopy data.

DSC analysis of phase transformations during precipitation hardening in Al–Zn–Mg alloy (7020)

The hardening of the Al–Zn–Mg alloys during ageing process is based on very complex phase transformations. In order to contribute to the comprehension of these phenomena, we proceed to study the phase transformations of 7020 alloy using differential scanning calorimetry and X-ray diffraction analysis. The results confirm the formation of hardening phase GP zones, intermediate hardening metastable phase η′ and the equilibrium phase η. The calorimetric and X-ray diffraction results are in good agreement and confirm the successive precipitation/dissolution sequence. The dissolution of the precipitates is accompanied by the increase in the crystallographic lattice parameter due to the increase in solid solution concentration and by the softening of the material. On the contrary, the precipitation produces a lower concentration of the Zn/Mg solutes in the Al matrix, which generates a decrease in the lattice parameter value. These precipitates produce the hardening of the alloy. The sequence of phase formation and dissolution explains the evolution of the 7020 hardness as a function of the ageing temperature.

Common mechanism for controlling polymorph selection during crystallization in supercooled metallic liquids

Despite the fundamental and technological importance, the physical scenario of polymorph selections during crystallization in metals remains poorly understood. Here, through the extensive molecular dynamics simulation, we study the crystallization pathway of face-centered cubic (fcc) metals aluminum and copper. We reveal two different crystallization pathways at ambient pressure: involving the metastable body-centered cubic (bcc) polymorph (Cu) or not involving the bcc polymorph (Al). Interestingly, by varying pressure on Al, we successfully control polymorph selection and observe crystallites containing the metastable bcc polymorph. These findings are in line with the phonon dispersion analyses, which indicate that the bcc structure of Cu at ambient pressure and of Al at high pressure remain stable whereas that of Al at low pressure is thermally unstable. More importantly, we demonstrate that it is the profile of the free energy surface related to the phase stability, rather than the strong cohesive interactions of metals, encodes the crystallization pathway in metals. Our findings not only shed important light on a common thermodynamic mechanism of polymorph selections, but also pave a new way for better controlling the crystallization pathway in industrial and metallurgical applications by regulating the stability of the intermediate metastable phases.

An in situ study of the phase transitions among CaCO3 high-pressure polymorphs

AbstractThe phase transitions involving calcite (CaCO3-I), CaCO3-II, CaCO3-III and CaCO3-IIIb were investigated using a diamond anvil cell and micro-Raman spectroscopy. Based on the results obtained from in situ observations and Raman measurements made with six natural calcite crystals, the phase transition from calcite to CaCO3-II took place between 1.56 and 1.67 GPa under ambient temperature. Under a precise pressure of 1.97 ± 0.03 GPa, three CaCO3 samples were observed to transform from CaCO3-II directly to CaCO3-III, while in the other three samples both CaCO3-III and CaCO3-IIIb crystal structures were detected. Transformation from CaCO3-IIIb to CaCO3-III was completed in a short period in one sample, whereas in the other two samples coexistence of CaCO3-III and CaCO3-IIIb was observed over a wide pressure range from 1.97 to 3.38 GPa, with sluggish transformation from CaCO3-IIIb to CaCO3-III being observed after the samples were preserved under 3.38 GPa for 72 h. Hence, it can be concluded that CaCO3-IIIb is a metastable intermediate phase occurring during the reconstructive transformation from CaCO3-II to CaCO3-III. Splitting of the C–O in-plane bending (ν4) and symmetric stretching (ν1) vibrations and appearance of new lattice vibrations in the Raman spectra of CaCO3-III and CaCO3-IIIb suggest a lowering in crystal symmetry during the transformation from CaCO3-II through CaCO3-IIIb to CaCO3-III, which is in good agreement with the observed sequence of phase symmetries.

Формирование графеноподобного слоя SiN на поверхности (111)Si

Abstract00-The kinetics of the formation and thermal decomposition of a two-dimensional SiN-(8 × 8) nitride layer on a Si(111) surface is studied. The SiN-(8 × 8) structure is a metastable intermediate phase formed during the nitridation of silicon before the formation of a stable amorphous Si_3N_4 phase. Studying the SiN-(8 × 8) structure by scanning tunneling microscopy shows its complex structure: it consists of an adsorption (8/3 × 8/3) phase, with the lateral period 10.2 Å, and a honeycomb structure with a ~6 Å side of a hexagon that is turned 30° with respect the adsorption phase. The band gap of the SiN-(8 × 8) phase is measured and found to be ~2.8 eV, which is smaller compared to the band gap of the β-Si_3N_4 crystal phase 5.3 eV. The interplanar spacings in the (AlN_3)/(SiN)_2 structure on the Si(111) surface are measured. The spacings are 3.3 and 2.86 Å in SiN and AlN, respectively. Such interplanar spacings are indicative of weak van der Waals interaction between the layers. A model of the SiN-(8 × 8) structure as a flat graphene-like layer is suggested. The model is consistent with the diffraction and microscopy data.

Nanoscale LuFeO3: shape dependent ortho/hexa-phase constitution and nanogenerator application.

In multiferroic LuFeO3 the hexagonal (-h) phase is an intermediate metastable phase encountered during the amorphous to orthorhombic (-o) transformation and is ferroelectric in nature. Thus far it has only been stabilized in a substrate-supported few layered ultrathin film form. Herein we show that the surface-induced strain field intrinsically present in nano-systems can self-stabilize this phase and the hexagonal to orthorhombic phase constitution ratio depends on the shape of the nanomaterial. Thus, nanoparticles (nanofibres) strain-stabilize the o : h ratio of about 75 : 25 (23 : 77). The inclusion of nano-LuFeO3 into PDMS renders impressive nanogenerator performance, consistent with the ferroelectric phase content.