Isostructural Phase Research Articles

High-temperature photoluminescence OF CsPbBr3 perovskite nanocrystals in the fluorophosphate glasses

For the first time the temperature dependence of the photoluminescence of the semiconductor CsPbBr3 perovskite nanocrystals with sizes of 6.0–9.0 nm in fluorophosphate glass were investigated in the temperature range from 300 K to 423 K. It was shown that temperature dependence of the photoluminescence intensity and the band gap shift coefficient change at 350 K corresponding to the isostructural phase transition. The photoluminescence intensity decreased radically above this temperature. The temperature energy gap coefficients of the CsPbBr3 nanocrystals depending on the size and temperature range were found.

Effect of isostructural phase transition on cycling stability of ZrCo-based alloys for hydrogen isotopes storage

ZrCo alloy as a promising candidate for hydrogen isotopes storage and delivery in the international thermonuclear experimental reactor (ITER) has attracted considerable attention. However, its capacity retention after 50 cycles is 22.4%, resulting from the disproportionation reaction during repeated phase transitions between cubic ZrCo phase and orthorhombic ZrCoH3 phase. Herein, a single isostructural phase transition with high thermal stability and structural stability in ZrCo-H system is achieved by multicomponent substitution for the first time. Considering the computational screening results, cost and gravimetric hydrogen capacity, a series of Zr0.8Nb0.2Co0.6Cu0.4−xNix (x = 0.2–0.3) alloys are designed and synthesized. The compositional dependence of phase component is further discussed in detail. Specifically, Zr0.8Nb0.2Co0.6Cu0.15Ni0.25 alloy with single orthorhombic phase exhibits high thermal stability (up to 550 °C) and maintains the orthorhombic structure during the de-/hydrogenation process at 380 °C. Thermodynamic destabilization of hydride (ΔH = 71.95 kJ·mol−1 H2) and nearly no de-/hydrogenation hysteresis contribute to a significantly low desorption temperature of 283 °C at 100 kPa. Thanks to superior thermal stability and structural stability, no attenuation of hydrogen storage performances including thermodynamics and kinetics can be observed during 200 de-/hydrogenation cycles, and the supereminent cycling stability of 100% and cyclic hydrogen capacity of 1.65 wt% are achieved. Combined with first-principles calculations, the improved cycling stability of Zr0.8Nb0.2Co0.6Cu0.15Ni0.25 alloy can be ascribed to the reduced lattice expansion and atomic motion during the orthorhombic isostructural phase transition.

Dielectric Relaxation and Dielectric Switching Behaviors in (N,N-Diisopropylethylamine) Tetrachloroantimonate(III).

Dielectric switches have drawn renewed attention to the study of their many potential applications with the adjustable switch temperatures (Ts ). Herein, a novel antimony-based halide semiconductor, (N,N-diisopropylethylamine) tetrachloroantimonate ((DIPEA)SbCl4 , DIPEA+ =N,N-diisopropylethylamine), with dielectric relaxation behavior and dielectric switches has been successfully synthesized. This compound, consisting of coordinated anion chains and isolated DIPEA+ cations, undergoes an isostructural order-disorder phase transition and shows a step-like dielectric anomaly, which can function as a frequency-tuned dielectric switch with highly adjustable switch temperature (Ts ). Variable-temperature single-crystal structure analyses and first-principles molecular dynamics simulations give information about the general mechanisms of molecular dynamics. This work enriches the dielectric switch family and proves that hybrid metal halides are promising candidates for switchable physical or chemical properties.

Phase Transitions and Physical Properties of the Mixed Valence Iron Phosphate Fe3(PO3OH)4(H2O)4.

Iron phosphate materials have attracted a lot of attention due to their potential as cathode materials for lithium-ion rechargeable batteries. It has been shown that lithium insertion or extraction depends on the Fe mixed valence and reduction or oxidation of the Fe ions' valences. In this paper, we report a new synthesis method for the Fe3(PO3OH)4(H2O)4 mixed valence iron phosphate. In addition, we perform temperature-dependent measurements of structural and physical properties in order to obtain an understanding of electronic-structural interplay in this compound. Scanning electron microscope images show needle-like single crystals of 50 μm to 200 μm length which are stable up to approximately 200 °C, as revealed by thermogravimetric analysis. The crystal structure of Fe3(PO3OH)4(H2O)4 single crystals has been determined in the temperature range of 90 K to 470 K. A monoclinic isostructural phase transition was found at ~213 K, with unit cell volume doubling in the low temperature phase. While the local environment of the Fe2+ ions does not change significantly across the structural phase transition, small antiphase rotations occur for the Fe3+ octahedra, implying some kind of electronic order. These results are corroborated by first principle calculations within density functional theory, which also point to ordering of the electronic degrees of freedom across the transition. The structural phase transition is confirmed by specific heat measurements. Moreover, hints of 3D antiferromagnetic ordering appear below ~11 K in the magnetic susceptibility measurements. Room temperature visible light absorption is consistent with the Fe2+/Fe3+ mixed valence.

Pressure-induced structural phase transitions of zirconium: an ab initio study based on statistical ensemble theory

Recently, we put forward a direct integral approach to solve the partition function with ultrahigh efficiency and precision, which enables the rigorous ensemble theory to investigate phase behaviors of realistic condensed matters and has been successfully applied to the phase transition of vanadium metal (Ning et al 2022 J. Phys.: Condens. Matter 34 425404). In this work, the approach is applied to the structural phase transitions of zirconium metal under compressions up to 160 GPa and ultrahigh calculation precision is achieved. For the obtained equation of state with pressure over 40 GPa, the deviations from latest experiments are within and the computed transition pressure of is 6.93 GPa, which is about five times larger than previous theoretical predictions and in excellent agreement with the measured range of 5–15 GPa. Our results support the argument that there is no existence of the isostructural phase transition of Zr metal that was asserted by recent experimental observations.

Zinc additions in calcium phosphate system. Phase behavior, microstructural and mechanical compatibility during sequential heat treatments

The study investigates the structural and mechanical stability of the calcium phosphate - ZnO composites during sequential heat treatments. The composites were synthesized through a solution based co-precipitation technique by varying the precursor concentrations. The characterization results infer the Zn2+ insertion in calcium phosphate and moreover the isostructural phase of β-Ca3(PO4)2 → Ca19Zn2(PO4)14 is preserved until 1300 ℃. The upsurge in Zn2+ concentration ensure the presence of apatite trace at 1300 ℃. Zn2+ inclusion tends to the alter the calcium phosphate structure, mainly by delaying the allotropic β → α-Ca3(PO4)2 conversion until 1300 ℃. Zn2+ prefers to accommodate at Ca2+(4), and Ca2+(5) sites of Ca19Zn2(PO4)14 lattice, while the Zn2+ ions exceeding the saturation limit crystallize as ZnO. The structural distortion of PO4 bands due to the inclusion of Zn2+ concentration is verified from FTIR and Raman results. Zn2+ play a crucial role in the microstructural features and density of the resultant calcium phosphate system thus displaying the constant distribution of grains and resilient solidity in the system. Low ZnO content tends to boost the Youngs modulus and hardness while an inverse trend is noticed in case of high ZnO content.

Role of exact exchange in the structural and electronic properties of the α and γ phases of cerium: a density functional theory study

Modeling the α–γ isostructural phase transition of cerium (Ce) within the framework of density functional theory is challenging because the 4f electron in Ce is difficult to characterize. The use of a fraction of exact exchange in the hybrid functional (2012 Phys. Rev. Lett. 109 146402) predicts the existence of the α and γ phases but their relative energy is inconsistent with the experiments. In fact, the role of exact exchange in affecting properties of the α and γ phases has not been well investigated. In this regard, we choose a variable amount of exact exchange (0.05–0.4) and systematically explore the properties of the α and γ phases of Ce including cohesive energies, lattice constants, bulk moduli, magnetic moments, and 4f electron numbers. Notably, a small portion of exact exchange close to 0.1 yields an accurate description of these properties, in particular the predicted relative energy between the α and γ phases agrees with the experiment. We further analyze the density of states, partial density of states, band structures and electron densities of the two phases. We observe that the exact exchange substantially affects the γ phase by localizing the 4f electrons, while it tends to delocalize the electrons in the α phase. Our work provides deep insights into the structural and electronic properties of the α and γ phases of Ce by elucidating the role of exact exchange in hybrid functional calculations.

Pressure-Induced Structural Phase Transition, Anomalous Insulator-to-Metal Transition, and n-p Conduction-Type Switching in Defective, NiAs-Type Cr1-δTe.

Cr1-δTe, as a unique series of defective compounds with a NiAs-type structure and periodic metal vacancies, has attracted intensive research interest because of its diversity in structure and property dependent on the tunable stoichiometric ratio. Another feature of these compounds is their ability to switch between NiAs- and MnP-type structures, in which there often exist composition-, temperature-, or pressure-induced phase transitions accompanied by intriguing physical property switching. Herein, we report the syntheses of a series of Cr1-δTe compounds with similar compositions but distinct crystal structures, their phase transitions, anomalous transport, and photoelectric conduction behaviors under high pressure (HP). For the three Cr1-δTe compounds with δ = 0, 0.25, 0.375, CrTe undergoes pressure-induced NiAs-to-MnP phase transition at around 15 GPa, while Cr3Te4 and Cr5Te8 undergo isostructural phase transitions at around 12 and 11 GPa, respectively. Electrical transport measurements indicate anomalous conduction behaviors: CrTe undergoes a semiconductor-to-metal transition at around 24 GPa, while Cr3Te4 and Cr5Te8 show unexpected metal-semiconductor-metal transitions sequentially upon compression. Besides, CrTe and Cr5Te8 exhibit pressure-induced n-p conduction-type switching at around 9 and 3 GPa, respectively, while Cr3Te4 shows p-type conductivity in the full pressure range. Local structure analyses based on in situ HP Raman spectra are performed to understand the structure and property evolutions of Cr1-δTe under HP. Defective transition-metal chalcogenides with pressure-induced NiAs-to-MnP phase transition and conduction-type conversion provide a potential platform for the rational design of photoelectric conversion devices.

Short range spin-spin correlation, spin-phonon coupling and isostructural phase transition in hetero-tri-spin 3d-5d-4f double perovskite Sm2CoIrO6

The low temperature vibrational properties of Ir-based double perovskite Sm2CoIrO6 (SMCO) has been investigated by Raman scattering to gain an insight into the mechanism of the isostructural phase transition present at ​∼ ​104 ​K under ambient atmospheric pressure. The temperature dependent Raman study also reveals the development of short range magnetic correlation above the long range magnetic ordering. From the comprehensive temperature dependent study, it is found that the system before entering the state of long range ferrimagnetic ordering, undergoes from a state of conventional paramagantism to a state of correlated paramagnetism. The interaction of the phonons with the underlying magnetic degrees of freedom has been studied for the most prominent mode in terms of Fano asymmetric parameter. The strong spin-phonon coupling below the global ordering temperature results in a significant softening of the phonon modes involving stretching and/or vibration of the (Co/Ir)O6 octahedra.

Ternary antimonide NaCd4Sb3: hydride synthesis, crystal structure and transport properties

AbstractA new compound NaCd4Sb3 (R m, a=4.7013(1) Å, c=35.325(1), Å, Z=3, T=100 K) featuring the RbCd4As3 structure type has been discovered in the Na−Cd−Sb system, in addition to the previously reported NaCdSb phase. NaCd4Sb3 and NaCdSb were herein synthesized using sodium hydride as the source of sodium. The hydride method allows for targeted sample composition, improved precursor mixing, and an overall quicker synthesis time when compared to traditional methods using Na metal as a precursor. The NaCd4Sb3 structure was determined from single‐crystal X‐ray diffraction and contained the splitting of a Cd site not seen in previous isostructural phases. NaCd4Sb3 decomposes into NaCdSb plus melt at 766 K, as determined via in‐situ high‐temperature PXRD. The electronic structure calculations predict the NaCd4Sb3 phase to be semi‐metallic, which compliments the measured thermoelectric property data, indicative of a p‐type semi‐metallic material. The crystal structure, elemental analysis, thermal properties, and electronic structure are herein discussed in further detail.

Buffering Octahedra in Mo4Zr9P: Intergrowth as a Solution to the Frustrated Packing of Tricapped Trigonal Prisms and Icosahedra.

Atomic packings based on icosahedra and tricapped trigonal prisms are prone to frustration─indeed, these polyhedra represent common configurations in metallic glasses. In this Article, we illustrate how these packing issues can serve as a driving force for the formation of modular intermetallic structures. Using Density Functional Theory-Chemical Pressure (DFT-CP) analysis, we relate the Hf9Mo4B-type structure of Mo4Zr9P to interatomic pressures experienced by the atoms in two parent structures: Zr3P, whose structure is built from tricapped trigonal prisms, and ZrMo2, a Laves phase containing icosahedra. CP analysis of Zr3P reveals that it has particularly frustrated packing because of the entangling of its tricapped trigonal prisms. In the ternary phase, the frustration is significantly relieved as the units become isolated from each other. Further analysis points to the stabilizing effect of a face-sharing network of octahedra in Mo4Zr9P that largely separates the structure into Zr-Mo and Zr-P domains and serves as a buffering region for the relaxation of interatomic distances. These conclusions are generalized to the broader members of this structure type with the examination of the CP schemes for the isostructural Mo4Zr9B, Al5Co2, and Mg5Pd2 phases. Finally, we screen the structural literature using the ToposPro software to identify three additional structure types that have similar intergrowth patterns: the Dy4CoCd, La23Ni7Mg4, and Gd14Co3In3 types. An analysis of the interatomic distances within the octahedral networks of these structures suggests that these networks commonly facilitate the reconciliation of packing incompatibilities in intermetallic chemistry.

Pressure‐Induced Isostructural Phase Transition in Biskyrmion Host Hexagonal MnNiGa

Magnetic skyrmions are vortex‐like spin textures, which can be manipulated by external stress or pressure via magnetoelastic effects. Herein, the observation of isostructural phase transition in a biskyrmion host hexagonal MnNiGa at pressureP ≈4 GPa using pressure‐dependent synchrotron X‐Ray powder diffraction (XRD) data analysis is presented. The XRD data reveals anisotropic compression behavior with pressure with different compression rates of thea‐axis in the basal plane and thec‐axis in the prismatic plane. However, the hexagonal symmetry remains unchanged for pressure up to 14 GPa. Fitting of unit cell volume with pressure using a second‐order Birch–Murnaghan equation of state reveals that the data fall into two distinct curves for those above and below 4 GPa. Herein, the understanding of crystal structure with the application of hydrostatic pressure in the biskyrmion host MnNiGa is contributed to, wherein the skyrmion textures can be manipulated by pressure due to their magnetoelastic character.

Interplay between External High Pressure and Intrinsic Jahn–Teller Effect in the Compression Behavior of Clinoatacamite

Clinoatacamite (γ-Cu2(OH)3Cl) possesses a geometrically frustrated kagome lattice for the S = 1/2 antiferromagnetic spin system. Thus, it is deemed as the mother compound of many promising quantum spin liquid materials. Here, we synthesized clinoatacamite consisting of homogeneous octahedron-like particles with an average size of 1-2 μm via a hydrothermal strategy. Clinoatacamite crystallizes in a monoclinic lattice composed of Jahn-Teller distorted Cu(OH)6 and Cu(OH)4Cl2 octahedrons. The bonding nature of clinoatacamite is characterized using Raman scattering and FTIR absorption spectroscopies, which reveal the existence of trimeric hydrogen bonds. The magnetic measurements indicate that at temperatures below about 6 K, the magnetic response of the prepared samples is dominated by weak ferromagnetic contributions. The compression behavior is investigated by in situ high-pressure synchrotron radiation X-ray diffraction and Raman scattering spectroscopy. An isostructural phase transition is observed at about 8.4 GPa, which is evidenced by the anomalies in the variation curves of the lattice parameters and Raman scattering frequencies with pressure. The occurrence of the isostructural phase transition is attributed to the competition and cooperation of the external pressure and intrinsic Jahn-Teller effect, together with the interplay of intrastructural hydrogen bonding.

A novel 1-D square-pyramidal coordinated palladium (II) hybrid compounds [C9H16N2]PdX4 (X=Cl, Br) showing broadband emission, electrical properties and narrow optical band gap

Hybrid halide perovskite-like semiconductors are attractive materials for various optoelectronic applications, from photovoltaics to smart devices. Here, two new one-dimensional palladium halides, [C9H16N2]PdCl4 (1) and [C9H16N2]PdBr4 (2) showing electrical and optical properties were prepared by reaction of 2,4,6-trimethyl-m-phenyl-enediamine with PdX2 (X ​= ​Cl, Br) in the corresponding concentrated halogen acids HX.Single-crystal X-ray diffraction analysis reveals that compounds [C9H16N2]PdX4(X ​= ​Cl,Br) belong to isostructural phases and crystallize in the orthorhombic system with non-centrosymmetric space group Pmc21. The basic unit of the crystal structure in each compound is composed of an independent [PdX4]2- anion charge balanced by a [C9H16N2]2+ cation. Remarkably, the central Pd(II) atom is coordinated by five halogen atoms PdX5 forming a distorted square-pyramidal coordination geometry. These hybrid compounds present good thermal stability up to 500 ​K. The DSC and electric measurements show that no phase transition occurs in the compounds over the temperature range 300–400 ​K. Optical absorption measurements suggest that the two hybrids Pd(II)-based metal halides have a narrow optical band gap (Eg) of ∼3.26 ​eV (X ​= ​Cl) and ∼2.98 ​eV (X ​= ​Br) which makes them promising materials in optoelectronic devices. Besides, compounds exhibit broadband green emission excited by UV light at room temperature. The electrical study shows the contribution of the grain and grain boundary in the conduction of these materials and confirms the optical result where the conductivity of the compound (1) is higher than the compound (2). The variation of the conductivity of grain confirms the activation energies calculated for the two regions.

Thermal Properties and Ionic Conductivity of Tetra-n-Butylammonium Perchlorate

The thermal parameters of the phase transitions and transport properties of tetra-n-butylammonium (TBA) perchlorate (n-C4H9)4NClO4 (TBAClO4) were investigated. TBAClO4 has a polymorphous transition at 330 K and melts at 487 K. The structure of the high-temperature (HT) phase belongs to cubic symmetry and is similar to the HT phases of TBABF4 and TBAI salts. The conductivity parameters of the low-temperature and HT phases of TBAClO4 were determined from the Arrhenius plots. The thermodynamic parameters and transport properties of TBAClO4 were compared with those of other TBA salts having isostructural HT phases. The polymorphous phase transition entropy was found to correlate with the conductivity of HT phases of TBA salts; TBAClO4 has the lowest conductivity compared to TBABF4 and TBAI salts.

Reversible Pressure-Dependent Mechanochromism of Dion-Jacobson and Ruddlesden-Popper Layered Hybrid Perovskites.

Layered Dion-Jacobson (DJ) and Ruddlesden-Popper (RP) hybrid perovskites are promising materials for optoelectronic applications due to their modular structure. To fully exploit their functionality, mechanical stimuli can be used to control their properties without changing the composition. However, the responsiveness of these systems to pressure compatible with practical applications (<1GPa) remains unexploited. Hydrostatic pressure is used to investigate the structure-property relationships in representative iodide and bromide DJ and RP 2D perovskites based on 1,4-phenylenedimethylammonium (PDMA) and benzylammonium (BzA) spacers in the 0-0.35GPa pressure range. Pressure-dependent X-ray scattering measurements reveal that lattices of these compositions monotonically shrink and density functional theory calculations provide insights into the structural changes within the organic spacer layer. These structural changes affect the optical properties; the most significant shift in the optical absorption is observed in (BzA)2 PbBr4 under 0.35GPa pressure, which is attributed to an isostructural phase transition. Surprisingly, the RP and DJ perovskites behave similarly under pressure, despite the different binding modes of the spacer molecules. This study provides important insights into how the manipulation of the crystal structure affects the optoelectronic properties of such materials, whereas the reversibility of their response expands the perspectives for future applications.

Pressure-Induced Structural Phase Transition and Metallization of CrCl3 under Different Hydrostatic Environments up to 50.0 GPa.

High-pressure structural, vibrational, and electrical transport properties of CrCl3 were investigated by means of Raman spectroscopy, electrical conductivity, and high-resolution transmission electron microscopy under different hydrostatic environments using the diamond anvil cell in conjunction with the first-principles theoretical calculations up to 50.0 GPa. The isostructural phase transition of CrCl3 occurred at 9.9 GPa under nonhydrostatic conditions. As pressure was increased up to 29.8 GPa, CrCl3 underwent an electronic topological transition accompanied by a metallization transformation due to the discontinuities in the Raman scattering and electrical conductivity, which is possibly belonging to a typical first-order metallization phase transition as deduced from first-principles theoretical calculations. As for the hydrostatic condition, a ∼2.0 GPa pressure delay in the occurrence of two corresponding transformations of CrCl3 was observed owing to the different deviatoric stress. Upon decompression, we found that the phase transformation from the metal to semiconductor in CrCl3 is of good reversibility, and the obvious pressure hysteresis effect is observed under different hydrostatic environments. All of the obtained results on the structural, vibrational, and electrical transport characterizations of CrCl3 under high pressure can provide a new insight into the high-pressure behaviors of representative chromium trihalides CrX3 (X = Br and I) under different hydrostatic environments.

Calculation Of Gruneisen Parameter, Compressibility, And Bulk Modulus as Functions Of Pressure In (C6H5CH2NH3)2 PBI4

Hybrid organic-inorganic perovskites (HOIPs) exhibit multiple structural phase transitions, which result in enhanced mechanical and electronic properties of these perovskites. Order-disorder of organic components was thought to be the main factor to cause these phase transitions up to the last decade; however, recent research about HOIPs have shown that the structural phase transition also occurs with the induced pressure or temperature. The research studies related to the pressure have attracted a great deal of scholarly interest due to its contribution to the func-tionality of HOIPs in many current applications. Two-dimensional halide perovskites having been synthesized in the last few years have been increasingly studied thanks to its superior hysteresis in flexibility and mechanical properties under pressure. It is important to understand and model theoretically how induced pressure affects mechanical and electronic properties of (PMA)2PbI4 in order to develop new potential applications in optoelectronics. In this study, the isothermal mode-Grüneisen parameter, the isothermal compressibility, and the bulk modulus were calculated as functions of pressure at ambient temperature by using the calculated Raman frequencies and observed volume data for the selected IR modes in (PMA)2PbI4. These calculated parameters were compared with the observed measurements reported for the Pbca, Pccn and Pccn (isostructural) phases in the studied perovskites. The results obtained in the present study, which were highly compatible with the experimental measurements, showed that (PMA)2PbI4 is usable in optoelectronic applications.

Comment on "Mechanisms for Pressure-Induced Isostructural Phase Transitions in EuO".

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Manifestations of Spinodal Decomposition into Dilute Pd1-xFex “Phases” in Iron-Implanted Palladium Films: FMR Study

Palladium-iron alloys produced by high-dose implantation of iron ions into epitaxial palladium films were investigated with the ferromagnetic resonance (FMR) and vibrating sample magnetometry (VSM) techniques. The samples reveal distinct multiple FMR responses depending on the dose of iron ion implantation. The post-implantation annealing at 770 K does not bring the implanted films to a homogeneous solid solution state, as might be expected from the Pd-Fe phase diagram. On the contrary, the system approaches a stable state composed of several magnetic phases. FMR spectra exhibit an angular behavior specific for a stack of interacting magnetic layers. This observation, correlated with the magnetometry data, indicates that the palladium-iron binary alloy has a previously unknown tendency towards spinodal decomposition into isostructural phases with well-defined iron concentrations and, accordingly, with different temperatures of ferromagnetic ordering and saturation magnetizations.