Temperature-driven Phase Transition Research Articles

Interacting Floquet topological magnons in laser-irradiated Heisenberg honeycomb ferromagnets

Upon irradiation with high-frequency circularly polarized light, the Heisenberg spin system on a honeycomb lattice develops a next-nearest neighbor Dzyaloshinskii-Moriya interaction (DMI) term, transforming it into a magnonic Floquet topological insulator with intriguing physical properties. In this context, we investigate the many-body interaction effects of Floquet magnons in a laser-irradiated Heisenberg honeycomb ferromagnet featuring DMI under circularly polarized off-resonant light illumination. Our analysis employs the magnon Floquet-Bloch theory and Green's function method. We demonstrate that quantum ferromagnet systems driven periodically by lasers exhibit temperature-driven topological phase transitions due to Floquet magnon-magnon interactions, transitions that are absent when such interactions are neglected. Furthermore, we observe that the critical temperature necessary for reversing the sign of the topological phase gradually increases with elevated light intensity. This study introduces a novel approach to constructing Floquet topological phases in periodically driven quantum magnet systems.

Pressure-induced temperature-driven phase transition and compressibility studies on nanocrystalline and bulk -U3O8 at extreme conditions of pressure and temperature

The study investigates the structural transition pathways of U3O8 under varying temperature and pressure conditions, focusing on both bulk and nanocrystalline forms. The bulk U3O8 is known to undergo reversible phase transitions to a hexagonal structure at temperatures above 150°C and irreversible transitions to a fluorite structure under pressure at ambient temperature. High-pressure XRD experiments reveal a significant decrease in transition pressure for the hexagonal to fluorite phase transition in bulk U3O8, with the HT-hex phase exhibiting a bulk modulus of 155 ± 21 GPa at 450°C. In 82 nm nanocrystalline U3O8, the transition from orthorhombic to hexagonal phase is reversible up to 1.0 GPa and 500°C but becomes irreversible above 1.7 GPa. The bulk modulus of the hexagonal phase of nanocrystalline U3O8 is estimated to be 168±12 GPa and 146±16 GPa at 400°C and 500°C, respectively. The findings highlight the complexity of structural transformations in U3O8 and their dependence on temperature and pressure, offering insights valuable for materials science and nuclear reactor engineering.

Symmetry Breaking and Ascending in the Magnetic Kagome Metal FeGe

Spontaneous symmetry breaking—the phenomenon in which an infinitesimal perturbation can cause the system to break the underlying symmetry—is a cornerstone concept in the understanding of interacting solid-state systems. In a typical series of temperature-driven phase transitions, higher-temperature phases are more symmetric due to the stabilizing effect of entropy that becomes dominant as the temperature is increased. However, the opposite is rare but possible when there are multiple degrees of freedom in the system. Here, we present such an example of a symmetry-ascending phenomenon upon cooling in a magnetic kagome metal FeGe by utilizing neutron Larmor diffraction and Raman spectroscopy. FeGe has a kagome lattice structure with simple A-type antiferromagnetic order below Néel temperature TN≈400 K and a charge density wave (CDW) transition at TCDW≈110 K, followed by a spin-canting transition at around 60 K. In the paramagnetic state at 460 K, we confirm that the crystal structure is indeed a hexagonal kagome lattice. On cooling to around TN, the crystal structure changes from hexagonal to monoclinic with in-plane lattice distortions on the order of 10−4 and the associated splitting of the double-degenerate phonon mode of the pristine kagome lattice. Upon further cooling to TCDW, the kagome lattice shows a small negative thermal expansion, and the crystal structure gradually becomes more symmetric upon further cooling. A tendency of increasing the crystalline symmetry upon cooling is unusual; it originates from an extremely weak structural instability that coexists and competes with the CDW and magnetic orders. These observations are against the expectations for a simple model with a single order parameter and hence can only be explained by a Landau free energy expansion that takes into account multiple lattice, charge, and spin degrees of freedom. Thus, the determination of the crystalline lattice symmetry as well as the unusual spin-lattice coupling is a first step towards understanding the rich electronic and magnetic properties of the system, and it sheds new light on intertwined orders where the lattice degree of freedom is no longer dominant. Published by the American Physical Society 2024

Gravity- and temperature-driven phase transitions in a model for collapsed axionic condensates

Gravity- and temperature-driven phase transitions in a model for collapsed axionic condensates

First-principles investigation of the structure and thermodynamic properties of titanium hydrides

The formation of titanium hydrides is closely related to the hydrogen embrittlement in titanium and its alloy. In this work, a comprehensive study on the stable and metastable structures of TiHx (x=0.5, 1, 1.5 and 2) has been performed by means of first-principles calculations in combination with the evolutionary algorithm. The structural features, dynamical stability and elastic properties of these searched titanium hydrides have been systematically investigated. The influence of temperature on the structure stability and phase transition of the Ti2H, TiH, Ti2H3 and TiH2 phases is considered using the quasi-harmonic approximation theory. Our calculations predict that Ti2H, Ti2H3 and TiH2 undergo temperature-driven phase transitions. The reason that the theoretical calculation overestimates the critical temperature of the tetragonal to cubic phase transition in TiH2 within the quasi-harmonic approximations approach is also explored and discussed. The thermodynamic stability of these TiHx (x=0.5, 1, 1.5 and 2) structures is further analyzed over the temperature range of 0–1100 K. TiH2 is the only stable structure in the Ti–H system and Ti2H, TiH, and Ti2H3 are thermodynamically metastable within 900 K.

Chemical composition-induced evolution of the structure, domain and electrical properties of Sm-doped (1 - x)Pb(Ni1/3Nb2/3)O3-xPbTiO3.

As the two typical basic binary solid solutions of the relaxor-PbTiO3 family, Pb(Mg1/3Nb2/3)O3-PbTiO3 (PMN-PT) has been widely investigated, whereas Pb(Ni1/3Nb2/3)O3-PbTiO3 (PNN-PT) has not. Here, 1.5 mol% Sm-doped (1 - x)Pb(Ni1/3Nb2/3)O3-xPbTiO3, (1 - x)PNN-xPT:0.015Sm with x = 0.33-0.39, ceramics have been prepared and the chemical composition-induced evolution of crystal structure, domain, and electrical properties investigated systematically. With increasing PT content, evolution of the rhombohedral-tetragonal structure was observed. A rhombohedral-tetragonal morphotropic phase boundary occurred around x = 0.36-0.37, which showed a peak piezoelectric property with piezoelectric constant d33 = 531 pC N-1 and planar electromechanical coupling factor kp = 0.37 at room temperature. At the same time, the x = 0.36 composition showed improved ferroelectric behavior with remanent polarization Pr = 13.4 μC cm-2 and coercive field Ec = 3.2 kV cm-1. Interestingly, different from its PMN-PT counterpart, there is no temperature-driven phase transition between room temperature and the Curie temperature for (1 - x)PNN-xPT:0.015Sm. These parameters indicated that the PNN-PT system is worthy of more attention and is a promising platform for further development of high-performance piezo/ferroelectric materials.

The wondrous world of ABX3 molecular perovskites.

The substitution of atoms with molecular building blocks to form hybrid organic-inorganic networks has been an important research theme for several decades. ABX3 molecular perovskites (MolPs) are a subclass of hybrid networks, adopting the perovskite structure with cationic and anionic molecules on the A-site and X-site. MolPs such as ((CH3)2NH2)Zn(HCOO)3 or ((n-C3H7)4N)Mn(C2N3)3 show a range of fascinating structure-chemical properties, including temperature-driven phase transitions that include a change of polarity as interesting for ferroelectrics, pressure-driven order-disorder phase transitions as interesting for barocaloric solid-state refrigeration, and most recently, melting-behaviour before decomposition with subsequent glass formation after cooling. In this feature article, we take a more personal perspective, overviewing the field's current state and outlining future directions. We start by comparing the MolPs' structural chemistry with their inorganic parents, a comparison that helps us identify opportunities for material design. After discussing the MolPs' potential as barocalorics, ferroelectrics, and in the area of glasses, we outline some challenges that lie ahead. Beyond their relevance as a hybrid analogue of inorganic perovskites, we find that MolPs' chemical parameter space provides exciting opportunities for systematically developing design guidelines for functional materials.

Facile microplastic recovery in soil using temperature-driven phase transition of saturated fat: Optimization and evaluation

Extracting microplastics (MPs) from soil matrices is challenging due to their heterogeneous distribution and the lack of standardized recovery techniques. Addressing this, we introduce a cost-effective and eco-friendly method utilizing the temperature-driven phase transitions of saturated fats for efficient and accurate MP separation. Among the evaluated saturated fats - butter, lard, and coconut oil - coconut oil demonstrated a 100% recovery of five MP types (LDPE, PP, PS, PET, and PTFE) from soil across three consecutive cycles, owing to its solidification characteristics. The process was further examined by exploring the effects of agitation force and soil texture (sea sand and agricultural soil), where agitation force impacted efficiency, while soil texture remained insignificant. The technique utilizing coconut oil demonstrated high matrix retaining efficiencies for both soil matrices, signifying its ability to separate MPs without soil contamination. To ensure MPs' integrity, isopropanol was used for solidified coconut oil removal, which did not alter the MPs' pristine state, as validated by microscopy, FTIR spectroscopy, and Py-GC/MS. In comparison to prior methods, our approach significantly reduces both operating costs and environmental impact. Overall, our study paves the way for a sustainable and affordable solution to MP contamination in soils.

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.

True First-Order Surface Phase Transition without Nanoscale Phase Separation.

Nanoscale phase separation is common in many materials ranging from correlated electron systems to semiconductor surfaces undergoing phase transitions. On solid surfaces, nanoscale phase separations are known to occur over an extended temperature range during temperature-driven first-order surface phase transitions, precluding the true first-order transitions in thermodynamics. Here, we report the case of a surface phase transition very close to a true first-order transition. An array of indium wires on Si(111) undergoes a first-order charge-density-wave (CDW) transition with surprisingly little or no phase separation when prepared free of indium adatom impurities. The lack of phase separation was attributed to the small difference in strain with the substrate between the two competing normal and CDW phases. Indium adatom impurities cause phase separation and blur the transition, making it gradual and incomplete. These experimental observations provide insight into the surface phase transition at the nanoscale level.

Modular development of deep potential for complex solid solutions

The multicomponent oxide solid solution is a versatile platform to tune the delicate balance between competing spin, charge, orbital, and lattice degrees of freedom for materials design and discovery. The development of compositionally complex oxides with superior functional properties has been largely empirical and serendipitous, in part due to the exceedingly complex chemistry and structure of solid solutions that span a range of length scales. The usage of classical molecular dynamics (MD), a powerful statistical method, in computer-aided materials design has not yet reached the same level of sophistication as that in computer-aided drug design because of the limited availability and accuracy of classical force fields for solids. Here, we introduce the strategy of ``modular development of deep potential'' (ModDP) that enables a systematic development and improvement of deep-neural-network-based model potential, termed as deep potential, for complex solid solutions with minimum human intervention. The converged training database associated with an end-member material is treated as an independent module and is reused to train the deep potential of solid solutions via a concurrent learning procedure. We apply ModDP to obtain classical force fields of two technologically important solid solutions, ${\mathrm{Pb}}_{x}{\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{TiO}}_{3}$ and ${\mathrm{Hf}}_{x}{\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$. For both materials' systems, a single model potential is capable of predicting various properties of solid solutions including temperature-driven and composition-driven phase transitions over a wide range of compositions. In particular, the deep potential of ${\mathrm{Pb}}_{x}{\mathrm{Sr}}_{1\ensuremath{-}x}{\mathrm{TiO}}_{3}$ reproduces a few known topological textures such as polar vortex lattice and electric dipole waves in ${\mathrm{PbTiO}}_{3}/{\mathrm{SrTiO}}_{3}$ superlattices, paving the way for MD investigations on the dynamics of topological structures in response to external stimuli. MD simulations of ${\mathrm{Hf}}_{x}{\mathrm{Zr}}_{1\ensuremath{-}x}{\mathrm{O}}_{2}$ reveal a substantial impact of composition variation on both the phase transition temperature and the nature of the high-temperature nonpolar phase.

Polymorphism in LiDy(WO4)2: Phase tunable synthesis, neutron diffraction, and symmetry-driven upconversion red emission

Tunable polymorphic structures to achieve novel properties are of great concern for energy-related applications. Herein, we demonstrate temperature-driven irreversible structural phase transition in LiDy(WO4)2 (β-LiDyW and α-LiDyW). A facile sol-gel method has been employed to achieve phase pure crystalline polymorphs at relatively lower temperatures and time. LiDy(WO4)2 crystallizes in a monoclinic wolframite-type structure (space group, P21/n, No = 14) at ambient temperature and a Scheelite-like tetragonal structure (space group, I41/a, No = 88) upon heating at high temperature. Crystal structure analysis shows that Li+ and Dy3+ occupy the distinct site, and W forms a distorted WO6 octahedron in the β-LiDyW phase. In contrast, Li+ and Dy3+ are statistically distributed on a dodecahedral S4 site sharing a similar crystallographic lattice site, and W forms a WO4 tetrahedron in the α-LiDyW phase. The Wolframite to Scheelite (β → α) transformation is due to the increase in the crystal symmetry on the heating function where distorted WO6 transformed to free WO4 going from β → α phase and coordination of W+6 is lowered. Density functional theory calculations at 0 K revealed that the β-LiDyW is energetically more favorable than α-LiDyW by 337.3 meV per formula unit. The co-substitution of the Yb3+−Er3+ pair in LiDy(WO4)2 lattice displays a concentration-dependent upconversion red emission when excited with 980 nm. The monoclinic phase of LiDy0.7Yb0.2Er0.1(WO4)2 shows an intense red emission at 656 nm due to inherent lower crystal symmetry. Distorted WO6 and chemically induced lattice distortions in β-LiDy0.7Yb0.2Er0.1(WO4)2 would have strongly influenced the coordination environment of the Er3+ to achieve red emission. This study presents the structural relationship among the tunable crystallographic phases of LiDy(WO4)2 with the observed red emission induced by Yb3+−Er3 upon 980 nm irradiation.

Gate and Temperature Driven Phase Transitions in Few-Layer MoTe2

MoTe2 has a stable hexagonal semiconducting phase (2H) as well as two semimetallic phases with monoclinic (1T') and orthorhombic (Td) structures. A structural change can thus be accompanied by a significant change in electronic transport properties. The two semimetallic phases are connected by a temperature driven transition and could exhibit topological properties. Here we make extensive Raman measurements as a function of layer thickness, temperature, and electrostatic doping on few layer 2H-MoTe2 and also on 1T'-MoTe2 and Td-WTe2. Recent work in MoTe2 has raised the possibility of a 2H-1T' transition through technology compatible pathways. It has been claimed that such a transition, of promise for device applications, is activated by electrostatic gating. We investigate this claim and find that few-layer tellurides are characterized by high mobility of Te ions, even in ambient conditions and especially through the variation of external parameters like electric field or temperature. These can generate Te clusters, vacancies at crystalline sites, and facilitate structural transitions. We however find that the purported 2H-1T' transition in MoTe2 cannot be obtained by a pure electrostatic field.

The Highly Accurate Interatomic Potential of CsPbBr3 Perovskite with Temperature Dependence on the Structure and Thermal Properties

CsPbBr3 perovskite has excellent optoelectronic properties and many important application prospects in solar cells, photodetectors, high-energy radiation detectors and other fields. For this kind of perovskite structure, to theoretically predict its macroscopic properties through molecular dynamic (MD) simulations, a highly accurate interatomic potential is first necessary. In this article, a new classical interatomic potential for CsPbBr3 was developed within the framework of the bond-valence (BV) theory. The optimized parameters of the BV model were calculated through first-principle and intelligent optimization algorithms. Calculated lattice parameters and elastic constants for the isobaric-isothermal ensemble (NPT) by our model are in accordance with the experimental data within a reasonable error and have a higher accuracy than the traditional Born-Mayer (BM) model. In our potential model, the temperature dependence of CsPbBr3 structural properties, such as radial distribution functions and interatomic bond lengths, was calculated. Moreover, the temperature-driven phase transition was found, and the phase transition temperature was close to the experimental value. The thermal conductivities of different crystal phases were further calculated, which agreed with the experimental data. All these comparative studies proved that the proposed atomic bond potential is highly accurate, and thus, by using this interatomic potential, the structural stability and mechanical and thermal properties of pure inorganic halide and mixed halide perovskites can be effectively predicted.

Nanothermometer with Temperature Induced Reversible Emission for Evaluation of Intracellular Thermal Dynamics.

Temperature dynamics reflect the physiological state of cells, and accurate measurement of intracellular temperature helps to understand the biological processes. Herein, we report a novel nanothermometer by conjugating a fluorescent probe 3-ethyl-2-[4-(1,2,2-triphenylvinyl)styryl]benzothiazol-3-ium iodide (TPEBT) with a thermoresponsive polymer poly(N-isopropylacrylamide-co-tetrabutylphosphonium styrenesulfonate) [P(NIPAM-co-TPSS)]. The derived nanoprobe TPEBT-P(NIPAM-co-TPSS) self-assembles into micelles with TPEBT as hydrophobic core and PNIPAM as hydrophilic shell. It exhibits aggregation-induced emission (AIE) at λex/λem = 420/640 nm in aqueous medium with a quantum yield of ΦF 11.9%. The rise in temperature transforms PNIPAM chains from linear to compact spheres to serve as the core of micelles, and meanwhile converts TPEBT from the state of aggregation to dispersion and redistributes in the micellar shell. Temperature-driven phase transition of P(NIPAM-co-TPSS) mediates the reversible aggregation and disaggregation of TPEBT and endows the nanothermometer with temperature-dependent AIE features and favorable sensitivity for temperature sensing in 32-40 °C. TPEBT-P(NIPAM-co-TPSS) is taken up by HeLa cells to distribute mainly in lysosomes. It enables quantitative visualization of in situ thermal dynamics in response to stimuli from carbonyl cyanide 4-(trifluoromethoxy)phenylhydrazone, oligomycin, genipin, and lipopolysaccharide. The real-time monitoring of photothermal-induced intracellular temperature variation is further conducted.

Temperature-Driven Transformation of the Crystal and Magnetic Structures of BiFe0.7Mn0.3O3 Ceramics.

The compound BiFe0.7Mn0.3O3 consisting at room temperature of coexistent anti-polar orthorhombic and polar rhombohedral phases has a metastable structural state, which has been studied by laboratory X-ray, synchrotron and neutron diffraction, magnetometry, differential thermal analysis, and differential scanning calorimetry. Thermal annealing of the sample at temperatures above the temperature-driven phase transition into the single phase rhombohedral structure (~700 K) causes an increase of the volume fraction of the rhombohedral phase at room temperature from ~10% up to ~30%, which is accompanied by the modification of the magnetic state, leading to strengthening of a ferromagnetic component. A strong external magnetic field (~5 T) applied to the sample notably changes its magnetic properties, as well as provides a reinforcement of the ferromagnetic component, thus leading to an interaction between two magnetic subsystems formed by the antiferromagnetic matrix with non-collinear alignment of magnetic moments and the nanoscale ferromagnetic clusters coexisting within it. The modification of the structural state and magnetic properties of the compounds and a correlation between different structural and magnetic phases are discussed focusing on the effect of thermal annealing and the impact of an external magnetic field.

Exploring the effects of temperature-driven phase transition on supercapacitive performance of cobalt diselenide

Recently, doping-induced phase transition of cobalt diselenide have been explored extensively for applications in the electrocatalysis, lithium-ion batteries, and sodium-ion batteries, however, there are very few works on understanding of the relationship between phase transition and supercapacitor performance up to now. Herein, we report a temperature-driven phase transformation strategy to synthesize metastable orthorhombic o-CoSe2 and stable c-CoSe2 by the thermal induced in-situ reaction of cobalt precursor and selenium powder. The o-CoSe2 shows a higher specific capacity (244.2 mAh g−1 at 1.0 A g−1), while c-CoSe2 shows a better cycling stability (103.0% capacity retention after 2000 cycles at 10.0 A g−1). Combing density functional theory (DFT) calculations and experimental results, we explain the unique effects of phase structure on supercapacitive performance. Furthermore, a hybrid supercapacitor of o-CoSe2//AC delivers a high energy density of 79.1 Wh kg−1 at a power density of 850.0 W kg−1, which suggests the prospects of practical application as energy storage device. Our work provides useful guidance for the design of cobalt diselenide based materials for supercapacitors.

Electric-field-driven resistive transition in multiferroic SrCo2Fe16O27/Sr3Co2Fe24O41 composite

We report on the observation of electric-field-driven resistive transition [abrupt rise in resistivity (ρ)] at a characteristic threshold field Eth(T) in an off-stoichiometric composite of W- and Z-type hexaferrite (∼80%)SrCo2Fe16O27/(∼20%)Sr3Co2Fe24O41. The dielectric constant ε and the relaxation time constant τ also exhibit anomalous jump at Eth(T). The Eth(T), the extent of jump in resistivity (Δρ), and the hysteresis associated with the jump [ΔEth(T)] are found to decrease systematically with the increase in temperature (T) across a range of 10–200 K. They also depend on the extent of nonstoichiometry. In addition, several temperature-driven phase transitions have been noticed both in the low and high resistive states. The entire set of observations has been discussed within the framework of structural evolution of the point defect (cation vacancies or oxygen excess) network and its influence on electronic conduction. The magnetocapacitive effect, measured under ∼20 kOe field, turns out to be substantial (∼4%–12%) and exhibits clear anomaly at Eth. This comprehensive map of esoteric ρ−E−T and ε−E−T patterns provides insights on defect-driven effects in a multiferroic composite. These effects could be useful for tuning both the resistive transition and the multiferroicity.

A micromechanical model for phase-change composites

Phase-change composites have a wide range of tunable mechanical properties caused by temperature-driven phase transition, and have been widely applied in many cutting-edge fields like soft robotics. Previous studies on the effective mechanical properties of phase-change composites mostly use experimental methods, and there have been few theoretical approaches. In this work, we develop a micromechanical framework capable of tracking the effective mechanical properties of phase-change composites throughout the entire phase transition. The phase-change materials embedded in the composites are modelled as inclusions, and the non-phase-change materials are modelled as the matrix. This allows us to determine the effective mechanical properties of phase-change composites via the energy equivalency approach. Moreover, since the new phase will be generated inside the phase-change inclusions in the form of sub-inclusions during the phase transition, the inclusions are modelled as two-phase composites, and their effective mechanical properties are then determined using the Mori–Tanaka method. Finally, by comparing theoretical predictions with experimental data, the accuracy and reliability of the present model are verified. We believe that the proposed model can serve as a powerful tool for evaluating the effective mechanical properties of phase-change composites and provide theoretical guidelines for the design of advanced devices with tunable mechanical performance.

Temperature-driven order-disorder structural transition in the oxygen sub-lattice and the complex superstructure of the high-temperature polymorph of CaSrZn2Ga2O7.

Structural order-disorder plays a decisive role in the physical properties of materials, such as magnetism, second-order harmonic generation, and ionic conductivity, and it is thus widely utilized to manipulate the crystal structure and understand structure-property correlations. Herein, we report the structural polymorphism, complex crystal structure and temperature-driven irreversible order-disorder phase transition of the polar oxides (Sr1-xCax)SrZn2Ga2O7. The low-temperature (LT) structure crystallizes in Pna21 with partial Zn/Ga ordering. Upon heating, (Sr1-xCax)SrZn2Ga2O7 undergoes an irreversible phase transition from orthorhombic Pna21 to hexagonal P63. Interestingly, the high-temperature (HT) P63 structure possesses an unexpected 3/2-fold superstructure rather than a substructure of the low-temperature (LT) Pna21 structure, which is a rare structural phenomenon in solid-state chemistry. This new HT superstructure is the most complex one in this series of oxides with 21 crystallographically independent sites determined accurately by a combination of the maximum entropy method and Rietveld refinement against high-resolution neutron powder diffraction data. In terms of the mechanism, this is a temperature-driven order-to-disorder transition in the oxygen sublattice. A careful structural analysis revealed that the oxygen disordering mainly occurs in the [SrO3] layers of the HT structure and it can be understood as respective clockwise and anticlockwise rotations of distinct GaO4-tetrahedra along the c-axis. Alternating current electrochemical impedance spectroscopic analysis revealed that the oxygen disordering in the HT structure is incapable of giving rise to oxide ionic conductivity but does lead to increased electronic conduction compared to the LT structure. The optical properties of the CaSrZn2Ga2O7 and Sr2Zn2Ga2O7 representatives are also investigated in-depth via diffuse reflectance spectroscopy and theoretic calculations.