Structural Phase Transition Temperature Research Articles

Active learning-based automated construction of Hamiltonian for structural phase transitions: a case study on BaTiO3

The effective Hamiltonians have been widely applied to simulate the phase transitions in polarizable materials, with coefficients obtained by fitting to accurate first-principles calculations. However, it is tedious to generate distorted structures with symmetry constraints, in particular when high-ordered terms are considered. In this work, we implement and apply a Bayesian optimization-based approach to sample potential energy surfaces, automating the effective Hamiltonian construction by selecting distorted structures via active learning. Taking BaTiO3(BTO) as an example, we demonstrate that the effective Hamiltonian can be obtained using fewer than 30 distorted structures. Follow-up Monte Carlo simulations can reproduce the structural phase transition temperatures of BTO, comparable to experimental values with an error<10%. Our approach can be straightforwardly applied on other polarizable materials and paves the way for quantitative atomistic modelling of diffusionless phase transitions.

Lattice Softening and Band Convergence in GeTe-Based Alloys for High Thermoelectric Performance.

GeTe-based alloys have been studied as promising TE materials in the midtemperature range as a lead-free alternate to PbTe due to their nontoxicity. Our previous study on GeTe1-xIx revealed that I-doping increases lattice anharmonicity and decreases the structural phase transition temperature, consequently enhancing the thermoelectric performance. Our current work elucidates the synergistic interplay between band convergence and lattice softening, resulting in an enhanced thermoelectric performance for Ge1-ySbyTe0.9I0.1 (y = 0.10, 0.12, 0.14, and 0.16). Sb doping in GeTe0.9I0.1 serves a double role: first, it leads to lattice softening, thereby reducing lattice thermal conductivity; second, it promotes a band convergence, thus a higher valley degeneracy. The presence of lattice softening is corroborated by an increase in the internal strain ratio observed in X-ray diffraction patterns. Doping also introduces phonon scattering centers, further diminishing lattice thermal conductivity. Additionally, variations in the electronic band structure are indicated by an increase in density of state effective mass and a decrease in carrier mobility with Sb concentration. Besides, Sb doping optimizes the carrier concentration efficiently. Through a two-band modeling and electronic band structure calculations, the valence band convergence due to Sb doping can be confirmed. Specifically, the energy difference between valence bands progressively narrows upon Sb doping in Ge1-ySbyTe0.9I0.1 (y = 0, 0.02, 0.05, 0.10, 0.12, 0.14, and 0.16). As a culmination of these effects, we have achieved a significant enhancement in zT for Ge1-ySbyTe0.9I0.1 (y = 0.10, 0.12, 0.14, and 0.16) across the entire range of measured temperatures. Notably, the sample with y = 0.12 exhibits the highest zT value of 1.70 at 723 K.

Exploring the Possibility of Thermally Assisted Creation and Annihilation of Anti‐Frenkel Defects in a Multiferroic Oxide for Tuning Interfacial Ferroelectricity

AbstractLattice defects such as oxygen vacancies, interstitials, and their complexes are present in crystalline oxide materials. In particular, anti‐Frenkel defects, which refer to charge‐neutral anion vacancy‐interstitial pairs, are strongly coupled with ferroelectric and dielectric properties as electric dipoles. However, in order to observe their macroscopic manifestation, delicate defect controls are required to the extent that electronic and ionic charges are almost completely suppressed. Here, the thermal cycle dependence of dielectric and piezoelectric properties is scrutinized in the strain‐driven morphotropic phase boundaries of multiferroic La‐substituted BiFeO3 thin films. Electrochemical impedance spectroscopy provides the Warburg feature that is considered evidence of the ionic origin. The observations are discussed based on anti‐Frenkel defects that are created or annihilated reversibly by thermal cycles through high‐temperature structural phase transition temperature or magnetic Néel temperature. The defect dipoles are spontaneously aligned by the flexoelectric effect in the phase boundaries inducing a metastable interfacial ferroelectric phase. The findings offer useful insight into defect dipoles.

Structural phase transitions in multicomponent La0.2Nd0.2Sm0.2Gd0.2RE50.2NbO4 (RE5 = Ho, Y, Tb, Eu, Pr) oxides

AbstractIn this work, the influence of compositional complexity on the structural and thermal properties of multicomponent rare‐earth ortho‐niobates from the La0.2Nd0.2Sm0.2Gd0.2RE50.2NbO4 (RE5 = Ho, Y, Tb, Eu, Pr) series was investigated. Based on X‐ray powder diffraction studies using synchrotron radiation, it was found that all tested materials were pure single‐phase compositions and showed stability in the monoclinic I2/c crystal structure at room temperature. High‐temperature X‐ray powder diffraction studies and dilatometry studies confirmed the presence of a structural phase transition between low‐temperature (I2/c) and high‐temperature (I41/a) polymorphs. The structural phase transition temperatures are between 676°C and 701°C. Interestingly, despite their compositional complexity, the structural phase transition temperature behaves similarly to conventional ortho‐niobates, that is, it depends on the radius of the A‐cation; that is, as the ionic radius increases, the phase transition temperature decreases. The transition has been categorized as a second‐order phase transition based on the observed relationship between the Landau order parameter and spontaneous strain. The coexistence of the tetragonal and monoclinic phases has been seen in all compositions around the temperature of the structural phase transition. The presence of two orientation states in the monoclinic structure leads to the so‐called spontaneous strain, which consists of longitudinal (u) and shear (v) strain components. The values of these strains at 300°C range between 2.42 and 2.58 × 10−2 for longitudinal, 2.98 and 3.04 × 10−2 for shear, and 5.46 and 5.57 × 10−2 for scalar spontaneous strain. It was found that the spontaneous strain in each of the materials under test was very little impacted by the variation in the complexity of the A sublattice's composition. In addition, thermal expansion coefficients of both polymorphs were determined, which range from 12.7 × 10−6 K−1 to 13.2 × 10−6 K−1 for the monoclinic structure and 9.7 × 10−6 K−1 to 9.9 × 10−6 K−1 for the tetragonal one.

The varying nature of the martensitic phase transition and associated entropy changes in a Co and Cr doped pseudo-ternary Heusler alloy system

We have investigated the magnetostructural phase transitions and the associated entropy changes in a system of three Heusler alloys, namely: Ni2Mn0.55Cr0.45Ga, Ni2Mn0.55Co0.10Cr0.35Ga, and Ni2.15Mn0.75Cr0.1Ga. All three alloys exhibited first-order martensitic phase transition. An inter-martensitic phase transition raised the magnetic and structural phase transition temperatures, and partially decoupled the said transitions. Furthermore, field magnetization measurements demonstrated that a significant reduction in magnetic hysteresis is achieved in the Ni2Mn0.55Co0.10Cr0.35Ga compound, resulting in improved effective refrigerant capacity values. The largest magnetic entropy change of −23.5 J/kg K and refrigeration capacity of 97.7 J/kg were observed in Ni2.15Mn0.75Cr0.1Ga. This observation of mitigated deficiencies in materials experiencing a first-order phase transition is relevant towards their application in magnetic refrigeration.

Multi-Stimuli-Responsive photoluminescence of cesium manganese bromide by temperature and solvent-induced structural phase transitions

Metal halide perovskites showing responses to external stimuli have emerged as a new class of stimulus-responsive smart materials. Specifically, their photoluminescence (PL) intensity, color and lifetime can change with different external stimuli. However, most of the existing metal halide perovskites only show PL response to a single stimulus. For encryption security applications, it is desired to have selective PL response to multiple stimuli. Herein, we developed a new type of cesium (Cs) manganese (Mn) bromide (Br) perovskite (Cs2MnBr4(H2O)2) single crystal with PL response to temperature, humidity and solvent by taking advantage of its structural phase transition, which causes its PL intensity (from non-luminescent to near unity luminescence) and color change (from green to red). Stimuli-responsive PL can be achieved by engineering the phase structure of Cs-Mn-Br perovskites from Cs2MnBr4(H2O)2 to Cs2MnBr4, Cs3MnBr5, CsMnBr3(H2O)2 and CsMnBr3 via temperature and different solvents. Such multiple stimuli responsive material is promising for multidimensional information encryption.

Structure of Bi2Rh3Se2 above and below charge density wave transition determined by Bi Lα and Lγ X-ray fluorescence holography.

The local structure of a two-dimensional layered material, Bi2Rh3Se2, in which superconducting (SC) and charge-density wave (CDW) states coexist, was investigated using Bi Lα and Lγ X-ray fluorescence holography (XFH). The crystal of Bi2Rh3Se2 adopts a monoclinic lattice with a space group of C2/m (No. 12) at room temperature; however, the structure below the CDW transition (∼240 K) is still unclear because of the difficulty in analyzing single-crystal X-ray diffraction. Therefore, information on the crystal structure below 240 K is significant to fully investigate the relationship between the SC and CDW states. Precisely, the value of β has not been definitely determined, i.e., β ∼ 90° or ∼134° is still unclear. Therefore, the crystal structure above 240 K is still under discussion. In this study, we attempted to determine the crystal structure at 300 and 200 K by comparing the atomic images reconstructed from Bi Lγ holograms with images simulated based on crystal structure models. A Bi Lα hologram was also exploited to determine suitable atomic locations by comparison with the simulated ones. The atomic image simulated with the crystal structure of Bi2Rh3S2 below the structural phase transition temperature reproduced well the experimental atomic image at 200 K. Specifically, the line profiles of the reconstructed images at 300 and 200 K, which exactly reflect the intensity of the atomic spots, clearly indicate the structural variation above and below the CDW transition temperature, i.e., the supercell structure is suggested as the atomic location for Bi2Rh3Se2 below the CDW transition temperature.

Study of Elastic and Structural Properties of BaFe2As2 Ultrathin Film Using Picosecond Ultrasonics.

We obtain the through-thickness elastic stiffness coefficient (C33) in nominal 9 nm and 60 nm BaFe2As2 (Ba-122) thin films by using picosecond ultrasonics. Particularly, we reveal the increase in elastic stiffness as film thickness decreases from bulk value down to 9 nm, which we attribute to the increase in intrinsic strain near the film-substrate interface. Our density functional theory (DFT) calculations reproduce the observed acoustic oscillation frequencies well. In addition, temperature dependence of longitudinal acoustic (LA) phonon mode frequency for 9 nm Ba-122 thin film is reported. The frequency change is attributed to the change in Ba-122 orthorhombicity (a-b)/(a+b). This conclusion can be corroborated by our previous ultrafast ellipticity measurements in 9 nm Ba-122 thin film, which exhibit strong temperature dependence and indicate the structural phase transition temperature Ts.

Entropy change reversibility in MnNi1−x Co x Ge0.97Al0.03 near the triple point

The nature of the phase transition has been studied in MnNi1−x Co x Ge0.97Al0.03 (x= 0.20–0.50) through magnetization, differential scanning calorimetry and x-ray diffraction measurements; and the associated reversibility in the magnetocaloric effect has been examined. A small amount of Al substitution for Ge can lower the structural phase transition temperature, resulting in a coupled first-order magnetostructural transition (MST) from a ferromagnetic orthorhombic to a paramagnetic hexagonal phase in MnNi1−x Co x Ge0.97Al0.03. Interestingly, a composition-dependent triple point (TP) has been detected in the studied system, where the first-order MST is split into an additional phase boundary at higher temperature with a second-order transition character. The critical-field-value of the field-induced MST decreases with increasing Co concentration and disappears at the TP (x= 0.37) resembling most field-sensitive MST among the studied compositions. An increase of the hexagonal lattice parameter a hex near the TP indicates a lattice softening associated with an enhancement of the vibrational amplitude in the Ni/Co site. The lattice softening leads to a larger field-induced structural entropy change (structural entropy change≫ magnetic entropy change, for this class of materials) with the application of a lower field, which results in a larger reversibility of the low-field entropy change (|ΔS rev| = 6.9 J kg−1 K for Δμ 0 H = 2 T) at the TP.

Enhanced spall strength of single crystal aluminum by temperature rise mitigation and structural phase transition under shock pulse

Investigating the spalling behavior is beneficial for the microscale modeling of impact failure. However, the correlation between pulse shape and spallation remains elusive due to limited experimental methods. Here, we simulate the shock deformation and spalling behavior of [100] single-crystal aluminum by Molecular Dynamics under equivalent ramp waves, square waves, and decaying shock waves. The synergistic effects of structural transition and thermodynamic path from the pulse shape affect the systems' fracture. Despite the intersecting influences of spall mechanisms like defects dominating heterogeneous void nucleation, pulse shape primarily affects the spall strength by influencing the compression temperature rise. Higher spall strength σsp and milder injuries in a wide range are achieved by the ramp wave loading pattern through gradual compression with subtle temperature softening. Additionally, pulse shape regulates the evolution of damage through wave propagation and applied tensile strain rates, in which a ramp wave causes rapid and a decaying shock wave delays the coalescence of voids. This study provides new insight for predicting the dynamic failure of metal materials.

Ultrasonic investigation of the elastic properties of the approximant GdCd6

We have investigated complementarily the magneto-elastic coupling in the approximant GdCd6 by measuring the temperature and magnetic field dependence of the longitudinal elastic constant C11. A pronounced elastic softening toward the phase transition temperature Ts= 156 K was observed in the temperature dependence of the C11, suggesting the presence of a structural phase transition. Furthermore, anomalous elastic behavior was observed in the temperature dependence of the C11 below 20 K, closely related to the already known consecutive magnetic phase transitions. The H–T magnetic phase diagram deduced from elastic anomalies appearing at the different phase transitions are consistent with our previous data of the other independent elastic constants CE= (C11−C12)/2 and C44 for a cubic crystal. We argue the origin of the structural phase transition and low temperature elastic property including a possible origin of such a rich variety of magnetic phases.

Evaluation of Hybrid Perovskite Prototypes After 10‐Month Space Flight on the International Space Station (Adv. Energy Mater. 19/2023)

Aerospace In article number 2203920, Lyndsey McMillon-Brown, Sayanatani Ghosh, and co-workers report on the first long duration space flight of a metal halide perovskite photoactive layer on the International Space Station. Post-flight analysis reveals that samples exhibit superior photo-stability, no irreversible radiation damage, and a suppressed structural phase transition temperature, broadening the photovoltaic operational range. These results confirm that perovskite photovoltaics can be designed to endure the space environment.

Atomic structure evolution and linear regression fitting models for pre-breakdown electric field strength of FCC, BCC and HCP metal nano-emitters under high electric field from PIC-ED–MD simulations

Multi-scale and multi-physics simulations are carried out for nano-emitters consisting of FCC (Al, Cu and Au), BCC (V, Mo and W) and HCP (Ti, Zn and Zr) metals, using hybrid electrodynamics coupled with molecular dynamics-particle in cell simulations (PIC-ED–MD). We show that the tilting of the nano-emitter at low temperature and small electric field (E-field) is mainly caused either by the movement of partial dislocations at the apex of the nanotip or by the elastic local distortions of atomic registries away from their ideal lattice sites (FCC/BCC/HCP). At high E-field, the intense resistive heating due to the strong electron emission leads to the direct melting of the apex of nano-emitters. For nano-emitters consisting of low melting point metals such as Al, Zn and Au, the thermal runaway is driven by the elongation, thinning and necking of the molten region. Meanwhile, the elongation, thinning and sharpening produce the nano-protrusion at the apex of metal nano-emitters, and the detachment of atoms or atomic clusters from the nano-protrusion mainly contributes to the thermal runaway event for refractor metals such as Ti, Zr, Mo and W. The critical E-field strength of metal nano-emitters is found to be strongly correlated with structural parameters (atomic coordination number of liquid and equilibrium lattice constant), thermodynamic quantities (cohesive energy and enthalpy of evaporation) and phase transition temperatures (melting point and boiling point). These correlations enable us to establish either single-variable linear fitting models or multi-variable linear regression models to predict the critical E-field value for metal nano-emitters with good credibility.

Nanostructured Ruddlesden–Popper-Layered Lead Bromide Perovskites with Stable and Selected Wavelength for Photodetection Applications

Success in photovoltaic power generation has raised a huge possibility in metal halide perovskites to exhibit excellent photodetection performance with the same physics of photocarrier generation, and their collection at terminal electrodes is employable with less defect-assisted carrier recombination loss. To test this, nanostructured Ruddlesden–Popper (RP)-layered perovskite series were synthesized based on a cyclic organic moiety and Br– halide, resulting in (CH)2(MA)n−1PbnBr3n+1 [where CH─2-(1-cyclohexenyl) ethylamine, MA─methylammonium, Br─bromine, and n = 1–4], to explore how best its mono-to-few layer (n) 2D and quasi 2D-structures can offer photodetection performance with maximum absorbance in the unexplored blue-to-green band gap RP perovskites with maximum stability. Thermogravimetric analysis revealed that the very stable nature of these RP perovskites is accompanied by a linear rise in the structural phase transition temperatures, which range from 270 °C (CH)2PbBr4 (n = 1) to 304 °C (CH)2(MA)3Pb4Br13. The RP perovskites (CH)2(MA)n−1PbnBr3n+1 (n = 1–4) demonstrated sharp exciton emission peaks from blue (∼408 nm) to green (∼528 nm). The X-ray diffraction results confirmed the highly crystalline nature of quasi-2D perovskite thin films. Layer-dependent photoluminescence studies exhibit strong room-temperature exciton photoluminescence and high carrier lifetime. The transient photocurrent measurements for (CH)2(MA)3Pb4Br13 (n = 4) RP perovskite thin films show nearly six times the bias voltage changed from 1 to 5 V at 405 nm laser light excitation. In addition, with respect to performance, the (CH)2(MA)3Pb4Br13 photodetector has shown the highest responsivity (67.2 mA/W), ultrafast transient photocurrent response (122 nA), and high EQE (20.6%) as compared to (CH)2(MA)2Pb3Br10 (n = 3) and (CH)2(MA)Pb2Br7 (n = 2) in ambient temperature.

Persistent modification of magnetotransport properties in LaAlO3/SrTiO3 by gate-induced modification of structural domains

We investigate the influence of large electric fields on the transport properties of nanostructures patterned into the electron gas at the interface between ${\mathrm{LaAlO}}_{3}$ and ${\mathrm{SrTiO}}_{3}$ (100). In these nanostructures, the transport is largely dominated by domain walls between structural domains in the ${\mathrm{SrTiO}}_{3}$ appearing below a structural phase transition temperature. We find that both positive and negative gate voltages applied in a side-gate configuration can induce persistent changes in the sample that are only reversed by warming through the phase transition. These changes include a resistance increase and a change in magnetoresistance in magnitude and sign. Furthermore, a resistance anomaly during warm-up that has been observed in the past can be further increased by briefly applying a side-gate voltage. These effects are typically observed in nanostructures below a certain size limit. The electric fields also increase this size limit from a few-hundred nm to more than 1 $\ensuremath{\mu}\mathrm{m}$. All these observations can be consistently explained by a field-induced removal of specific domain-wall types accompanied by an increasing domain size and a reduced number of domain walls in the structures. The results not only show that under certain conditions domain walls can dominate the transport properties even of micron-sized structures, but they also provide an additional tuning knob to induce nonvolatile changes in the transport properties of ${\mathrm{LaAlO}}_{3}\text{/}{\mathrm{SrTiO}}_{3}$ interfaces at low temperatures.

Evaluation of Hybrid Perovskite Prototypes After 10‐Month Space Flight on the International Space Station

AbstractMetal halide perovskites (MHPs) have emerged as a prominent new photovoltaic material combining a very competitive power conversion efficiency that rivals crystalline silicon with the added benefits of tunable properties for multijunction devices fabricated from solution which can yield high specific power. Perovskites have also demonstrated some of the lowest temperature coefficients and highest defect tolerance, which make them excellent candidates for aerospace applications. However, MHPs must demonstrate durability in space which presents different challenges than terrestrial operating environments. To decisively test the viability of perovskites being used in space, a perovskite thin film is positioned in low earth orbit for 10 months on the International Space Station, which was the first long‐duration study of an MHP in space. Postflight high‐resolution ultrafast spectroscopic characterization and comparison with control samples reveal that the flight sample exhibits superior photo‐stability, no irreversible radiation damage, and a suppressed structural phase transition temperature by nearly 65 K, broadening the photovoltaic operational range. Further, significant photo‐annealing of surface defects is shown following prolonged light‐soaking postflight. These results emphasize that methylammonium lead iodide can be packaged adequately for space missions, affirming that space stressors can be managed as theorized.

Phase Transition and Optical Properties of VO2 and Al: ZnO/VO2 Thin Films

Thermochromic Vanadium dioxide (VO2) has strong potential for smart window applications but its commercial scale usage is limited due to low visible light transmission. To address this issue, aluminum doped zinc oxide (AZO) anti-reflecting layer is integrated with VO2 layer in the present work. VO2 single layer and AZO/VO2 bilayer thin film samples were deposited by sputtering technique on quartz substrate. The single-phase growth of VO2 and AZO in single layer and bilayer thin film samples is confirmed by X-ray diffraction measurements. Monoclinic M1 phase of VO2 is detected in VO2 and AZO/VO2 thin film samples at room temperature. Monoclinic to rutile structural phase transition (SPT) in these samples is studied by performing temperature-dependent X-ray diffraction measurements. SPT in VO2 thin film samples is close to 68 °C and SPT temperature appears slightly lower in AZO/VO2 sample as compared to VO2 sample. Spectral transmittance measurement at room temperature showed significant improvement in the visible transmittance of AZO bilayer film than that of single layer VO2 thin film. These results demonstrate the possibility of integration of anti-reflecting layers such as AZO with VO2 layer for better visible transmittances suitable for large-scale smart window applications.

Study on magnetic properties and magnetocaloric effect of DyVO4

We prepared DyVO4 polycrystal by solid-state reaction. We tested the magnetization of the samples under field cooling and zero field cooling conditions, and analyzed the magnetic phase transition. It was found that Dy3+ had a paramagnetism to antiferromagnetism phase transition near 3.9 K. The isothermal magnetization curve of the sample was drawn under 0–5 T magnetic field, and the maximum magnetic entropy change (−Smmax) under 5 T magnetic field was calculated to be 25.5 J/kg. Interestingly, we found that with the increase of magnetic field, the maximum magnetic entropy change tends to move towards high temperature, which also leads to the relative refrigeration efficiency (RCP) as high as 522 J/kg. We think this may be related to the structural phase transition in the material, which is confirmed by two abnormal peaks on the heat capacity curve. The anomaly near 3 K comes from the antiferromagnetic phase transition of Dy3+, while the anomaly near 13 K comes from the structural phase transition from tetragonal phase to orthorhombic phase. With the increase of the magnetic field, the −ΔSm near the structural phase transition is larger. We calculated the adiabatic temperature change (ΔTad) of the sample by the heat capacity, and showed two peaks near the magnetic phase transition temperature and the structural phase transition temperature, with ΔTadmax of 9.9 K. We use heat capacity curve, Arrott plot and phenomenological universal curve to judge the order of phase transition. Finally, we think that the two phase transitions of the sample are all first order, but the hysteresis loop results show that the hysteresis is very small, which makes DyVO4 have a potential application prospect in magnetic refrigeration materials.

Talnakhite: A potential n-type thermoelectric sulphide with low thermal conductivity

The mineral talnakhite, Cu18Fe16S32, is an n-type semiconductor with low thermal conductivity (average value of 1.5 ​W ​m−1 ​K−1), making it an attractive candidate for thermoelectric applications. The effect of partial cation substitutions and of deviations from the ideal Cu:Fe ratio on the thermoelectric properties of this material, has been investigated through synthesis of Cu17.58M0.02Fe17.6S32 (M ​= ​Ag, In, Zn) and Cu17.6+xFe17.6-xS32 (−0.03 ≤ x ​≤ ​0.03) by high-temperature methods. The results demonstrate that talnakhite exhibits a narrow range of compositional stability for substitution at the cation sites. X-ray photoelectron spectroscopy (XPS) measurements indicate that all compositions contain Fe3+ and Fe2+ cations, together with Cu+. The electrical and thermal transport properties show two anomalies, at approximately 460 and 510 ​K, which can be related to structural phase transitions. The maximum value of the thermoelectric figure of merit occurs at the temperature of the first structural phase transition, making talnakhite a potential n-type candidate for near room-temperature thermoelectric applications. While substitution with silver, zinc or indium does not lead to any significant improvement in thermoelectric performance, changes in the Cu:Fe ratio result in significant reductions in the total thermal conductivity. This is likely to be associated with increased point defect scattering due to the presence of additional vacancies at the cation sites over which iron and copper are partially ordered. For copper-poor phases, the combination of a slightly improved power factor with a reduced thermal conductivity results in an increase in the figure-of-merit by approximately 20% when compared to the stoichiometric phase.

Photoelectric properties of KNN ceramics

In this work. we studied the photocurrent behavior in (1-x)(K0.5Na0.5) (Nb0.93Sb0.07)O3–xBaTiO3+0.5 mol.%MnO2, (KNNS7–xBT) ceramics illuminated by light in the optical range of 0.15 mW/cm2. We detected a decrease in values of both maximum current and steady-state current in the area of structural phase transition temperature. The influence of long-term sample (aging) exposure on the behavior of maximum current (I max) and steady-state current (I st) values was revealed. After a certain period of time, the I max values remained constant for the entire time interval, in contrast to the I st values, which always decreased over time.