Pressure-induced Phase Transition Research Articles

Significant strength enhancement of high-entropy alloy via phase engineering and lattice distortion

The extraordinary mechanical properties of high-entropy alloys (HEAs) hold great promise for their applications under extreme conditions (high pressure, high temperature, etc.). However, investigations on the mechanical properties of HEAs under extreme conditions (especially at high pressures) are extremely scarce, preventing their future applications. In this study, significant strength enhancement of Cantor (CoCrFeMnNi) HEA is achieved via phase engineering by using high-pressure techniques. The pressure-induced fcc-hcp phase transition of Cantor HEA leads to a strength increase of 65 % across the phase transition. Consequently, the hcp-Cantor HEA behaves as strongly as typical superhard ceramic B4C and surpasses corundum at moderate pressures. Moreover, the hcp-Cantor HEA quenched to ambient pressure is 47 % harder than the pristine fcc phase. In addition, by substituting the Mn atom with the Pd atom to introduce a severe lattice distortion in Cantor HEA, the CoCrFePdNi HEA turns out to be almost twice harder than Cantor HEAs at ambient pressure. The excellent mechanical properties of HEAs promise their potential applications at high pressures. These results also demonstrate that phase engineering and the introduction of severe lattice distortion represent two promising methods of developing high-strength HEAs in the future.

Spectroscopic pressure investigation of a novel high energy system

AbstractThis work combines a novel multimodal spectroscopic technique, O‐PTIR and Raman spectroscopy, which allows for the simultaneous collection of infrared and Raman spectra, with traditional diamond anvil cell techniques to explore pressure induced phase transitions in a high energy material. Two phase transitions are revealed, with the first transition emerging below 0.23 GPa, to a higher order phase, followed by a broad transition to a lower order phase. Aside from the pressure studies, hyperspectral imaging was performed, confirming the homogeneous nature of the system.

Pressure-induced superconductivity and phase transitions in Bi2S3 under non-hydrostatic conditions

Despite extensive and systematic studies on pressure-induced phase transitions and superconductivity in sesqui-chalcogenide A2B3 (A=Sb, Bi; BS, Se, and Te) compounds, the detailed transporting properties of Bi2S3 have rarely been reported. Here, we discovered an unambiguous correlation between superconductivity and phase transitions in Bi2S3 under non-hydrostatic conditions. The rapid decrease in resistance below 10 GPa and the occurrence of superconductivity at approximately 25.5 GPa should be caused by the two unusual pressure-induced isostructural transitions. Subsequently, the superconducting transition temperature (TC) increased to around 7.3 K, which was accompanied by the amorphization of Bi2S3 above 43 GPa. Furthermore, divergence between the theoretical calculations and experimental measurements showed that the above phase transitions and pressure-induced charge transfer had a critical effect on the electronic properties of this compound. The results of this study indicated that high pressure could help to improve thermoelectric properties.

Unraveling the effect of pressure on structural phase transition, electronic, and optical properties of Hf1-xSixO2 (x = 0, 0.03, 0.06, 0.09): A first-principles investigation

The non-centrosymmetric phase of HfO2 with excellent Si compatibility has great importance in integrated photonic circuits, non-volatile memory, and ferroelectric field effect transistors. We report a theoretical study of pressure-induced phase transition from a centrosymmetric m-HfO2 to non-centrosymmetric o-HfO2 with Si doping. The reported phase transition pressures, i.e. 15, 14, 8, and 8 GPa for x = 0, 0.03, 0.06, and 0.09, respectively, for Hf1-xSixO2 are in excellent agreement with available experimental results. With increasing Si concentrations, the transition pressures reduce significantly, which is explained in terms of bond length and charge transfer. The thermal stability of the obtained o-HfO2 phase is examined via ab-initio molecular dynamics up to its synthesis temperature. The negative formation energy also confirms its thermodynamical stability. Density of states indicates the noticeable appearance of Si states in the lower conduction band and an increase in the extent of hybridization between Hf-5d, O-2p, and Si-2p atomic states. The doping changes the nature of band gap from indirect to direct, concurrently reducing the magnitude. The o-HfO2 shows a low value of static dielectric constant, which results in a smaller refractive index (1.82) and lower reflectivity in the infrared and visible regions.

Pressure-induced phase transition and electronic properties of CdPX3 (X = S and Se) by first-principles calculation

Pressure-induced phase transition and electronic properties of CdPX3 (X = S and Se) by first-principles calculation

Anomalous Loading Rate Dependence of the Mechanical Properties of Metal-Organic Framework Crystals: Latent Heat Effects of the Pressure-Induced Local Phase Transition.

The loading rate dependence of the mechanical properties of metal-organic framework (MOF) crystals is key in determining their performance in many engineering applications, which, however, remains almost unexplored. Here, in situ nanoindentation experiments were conducted to investigate the impact of loading rate on mechanical properties of HKUST-1, a classic MOF. The Young's modulus and hardness of crystalline HKUST-1 are found to stay stable or decline with decreasing loading rate by creeping when the loading rate is below a particular speed, but they significantly decrease as the loading rate grows when it has higher magnitudes. Our molecular dynamics simulations indicate that the anomalous loading rate dependence of mechanical properties is attributed to the competition between the release and transfer of latent heat from the pressure-induced amorphous HKUST-1 because the increase in local temperature at large loading rates could induce the softening of HKUST-1 and the increase in the volume of transformed materials.

Pressure-induced phase transition, its mechanism and compressibility studies on nanocrystalline and bulk U3O8

High Pressure X-Ray Diffraction (HPXRD) studies were conducted on powder samples of U3O8 with crystallite sizes of 54 nm, 82 nm, as well as bulk U3O8. The investigation revealed that U3O8 undergoes a phase transition to a fluorite phase through an intermediate tetragonal structure, with the (200) plane of the orthorhombic structure playing a pivotal role. This transition occurs through the movement of uranium atoms while maintaining the overall integrity of the lattice. The phase transition is sluggish, and an extensive coexistence regime of the ambient and High-Pressure (HP) fluorite phase is observed in nano form as compared to bulk- U3O8. Moreover, the ambient phase of nano- U3O8 exhibits an elevated bulk modulus of 92 GPa, in contrast to the bulk sample's modulus of 78 GPa. Similarly, for the high-pressure phase, the bulk modulus is 419 GPa for nano- U3O8 and 367 GPa for bulk- U3O8. These findings provide valuable insights into the phase behavior and compressibility of U3O8, thereby carrying potential implications for nuclear technologists.

When Quantum Fluctuations Meet Structural Instabilities: The Isotope- and Pressure-Induced Phase Transition in the Quantum Paraelectric NaOH.

Anhydrous sodium hydroxide, a common and structurally simple compound, shows spectacular isotope effects: NaOD undergoes a first-order transition, which is absent in NaOH. By combining abinitio electronic structure calculations with Feynman path integrals, we show that NaOH is an unusual example of a quantum paraelectric: zero-point quantum fluctuations stretch the weak hydrogen bonds (HBs) into a region where they are unstable and break. By strengthening the HBs via isotope substitution or applied pressure, the system can be driven to a broken-symmetry antiferroelectric phase. In passing, we provide a simple quantitative criterion for HB breaking in layered crystals and show that nuclear quantum effects are crucial in paraelectric to ferroelectric transitions in hydrogen-bonded hydroxides.

Pressure-Induced Phase Diagram and Electronic Structure Evolves during the Insulator-Metal Transition of Bulk BiFeO3.

BiFeO3 is the most widely known multiferroic at room temperature, possessing both ferroelectricity and antiferromagnetism. It has high Curie temperature and Néel temperature, i.e., 1103 and 643 K, respectively. Despite these unique properties, the pressure-induced phase diagram of bulk BiFeO3 has remained controversial. Based on the ab initio evolutionary algorithm, we systematically searched for the potential stable structures of bulk BiFeO3 at 0-50 GPa. It is identified that there are five pressure-induced phase transition sequences R3c-G-AFM →(5GPa) C2/m-G-AFM →(15GPa) Pnma-G-AFM →(24GPa) Pnma-FM →(35GPa) Imma-FM →(45GPa) Cmcm-FM, which provided a comprehensive pressure-induced phase diagram. As the pressure increases, we discovered an interesting phenomenon: a pressure-induced magnetic sequence transition, i.e., BiFeO3 transitions from an antiferromagnetic to a ferromagnetic sequence. Concurrently, the electronic structure evolves during the insulator-metal transition, influenced not only by the pressure but also by the phase transition. Our research has elucidated the long-standing question of the phase transition sequence of the BiFeO3 system under pressure and provided theoretical support for the insulator-metal transition.

Coupled magnetic and structural transition in topological antiferromagnet EuAgAs under high pressure

Recently, EuAgAs and its derivatives have emerged as a promising platform for studying the interplay of transports, magnetism and topology. Herein, we report construction of a temperature-pressure phase diagram for antiferromagnetic Dirac semimetal EuAgAs, through electrical transport, synchrotron x-ray diffraction and Raman spectroscopy measurements in diamond anvil cells at high pressures up to 48.6 GPa. At Pc1∼3–5 GPa, we found a pressure-induced magnetic phase transition with accompanying a structural P63/mmc→Pnma transition. In the pristine antiferromagnetic phase, negative colossal magnetoresistance is observed mainly below the Néel temperature TN along with a field-induced metamagnetic transition; in the emergent magnetic phase, however, it is evident both above and below the magnetic critical temperature TC yet with no field-induced metamagnetic transition. These distinct features lead us to argue a ferromagnetic-like state for EuAgAs above Pc1, which is further supported by observation of a T5/3 temperature dependence of low-temperature resistance, a characteristic of marginal Fermi-liquid state expected to exist close to a ferromagnetic instability by spin fluctuations in metallic ferromagnets. At Pc2∼20 GPa, a possible phase transition of electronic origin may take place, which is revealed jointly by change of a T5/3→T5/2 temperature dependence of low-temperature resistance and change in slope of linear-in-T resistance at high temperatures.

Pressure-induced phase transition in cubic Yb2O3 and phase transition enthalpies

The high pressure structural evolution of cubic Yb2O3 has been studied using in situ synchrotron angle dispersive x-ray diffraction in combination with diamond anvil cell techniques up to 44.1 GPa. The XRD measurements revealed an irreversible reconstructive phase transition from cubic to monoclinic Yb2O3 at 11.2 GPa and extending up to 28.1 GPa with ∼8.1% volume collapse and a subsequent reversible displacive transition from monoclinic to hexagonal phase starting at 22.7 GPa. The monoclinic phase coexists with the hexagonal phase up to 44.1 GPa. After pressure releases, the hexagonal Yb2O3 reverts to the monoclinic structure. The second-order Birch–Murnaghan equation of state fit to the pressure–volume data yields a bulk modulus of 201 (4), 187 (6), and 200 (4) GPa for the cubic, monoclinic, and hexagonal phases, respectively. Furthermore, the effects of the hydrostatic pressure state on the diffraction patterns, bulk modulus, and onset transition pressure of Yb2O3 under high pressure have been discussed. It is concluded that the bulk modulus of the cubic Ln2O3 phase increases with decreasing cation radius due to lanthanide contraction. Another important work in this study is the determination of the enthalpies of the cubic to monoclinic and monoclinic to hexagonal phase transitions of Yb2O3 of 37.0 and 17.4 kJ/mol, respectively, based on the basic thermodynamic equations and using the onset transition pressures and corresponding volume changes obtained from high pressure XRD experiments.

GPa level pressure-induced phase transitions and enhanced corrosion resistance of AlCrMoSiTi high-entropy alloys

This study aims to comprehensively determine the influence of high pressure on the microstructure and corrosion properties of a designed high-entropy alloy (Al3Cr2Mo2SiTi2). By characterizing the microstructure and morphology of the alloy, we have confirmed that the intermetallic compound volume fraction decreases and the peritectic reaction occurs during the solidification process of the alloy under 4 GPa. Moreover, the intermetallic compound phase A1 changes from (Ti, Mo)5Si3 (K1 phase) at ambient pressure to (Ti, Mo) Si2 at 4 GPa, and the volume fraction of the Cr-rich (C1 phase) phase increases from 20% to 64%. This special transformation, induced by high pressure, significantly optimizes the corrosion resistance of the alloy.

Pressure-induced phase transitions and metallization in layered SnSe

The group IV–VI monochalcogenides have attracted widespread attention because of their diverse physical properties and promising applications in electronics and optoelectronics. As a typical IV–VI semiconductor, SnSe displays ultra-low thermal conductivity and excellent thermoelectric properties, which deeply depends on its layered structure. The layered crystal structure and associated physical properties are sensitive to external pressure. Here, we have systematically investigated the structural behaviors and optical and electrical properties of layered SnSe under high pressure. The SnSe transforms from Pnma phase to Cmcm phase above 10 GPa, and a CsCl-type structure with a space group of Pm3¯m emerges around 30 GPa and coexists with Cmcm phase up to 42.5 GPa. The optical bandgap of SnSe shows gradual narrowing with increasing pressure, indicating gradual metallization of SnSe under compression. The pressure-induced metallization of SnSe is verified by electric transport experiments. The initial semiconducting SnSe transforms to a metallic state with increasing pressure up to 9.8 GPa. Both phase transitions and optical and electrical properties of SnSe at high pressure are reversible after releasing pressure. Our study provides a modulation strategy of crystal structures and physical properties for the group IV–VI monochalcogenides to broaden their applications in thermoelectric and optoelectronic fields.

Observation of a Pressure Effect on an Al-substituted λ-Ti3O5 Heat-storage Material

Abstract We report a pressure effect on a heat-storage material, Al-substituted lambda-trititanium-pentoxide (λ-AlxTi3−xO5, 0 < x ≤ 0.29), showing a phase transition to β-AlxTi3−xO5 by pressure application. The transition pressure is 23 MPa and 43 MPa for x = 0.01 and 0.04, respectively, which are available pressures for practical applications. First-principles electronic structure calculations of λ-Al0.25Ti2.75O5 were conducted to investigate the substitution site selectivity of the Al3+ ion and the substitution effect on the pressure-induced phase transition.

First-principles Study of the Structural Properties of RbSnI2Br Perovskites Under Pressure

As a member of lead-free perovskite, tetragonal phase perovskite RbSnI2Br has a long-term development prospect. Due to the effect of structural changes on physical properties, we have explored the pressure-induced phase transition of RbSnI2Br perovskite. For this project, the structural properties of the tetragonal phase perovskite RbSnI2Br are studied by using the Perdew-Burke-Ernzerhof (PBE) functional for the generalized gradient approximation (GGA) under pressure conditions of 0 GPa–1 GPa. The calculation results of structural factors were in excellent agreement with those obtained from previous studies at the ground state, which ensures the accuracy of the study. The results show phase transitions occur with increasing pressure. The structural space group of β-RbSnI2Br changes from P4/MMM (tetragonal system) to P1 (triclinic system) under pressure in the range of 0 GPa–1 GPa. All these provide a relative theoretical basis for our further understanding of α-RbSnI2Br perovskite.

Pressure-driven structural transition in CoNi-based multi-principal element alloys

Pressure-driven phase transition in metals has been a hot topic because it is an effective means to induce fresh phase, benefit of tuning the properties of materials. Herein, CoNiFe, CoNiCr, and CoNiV multi-principal element alloys (MPEAs) were investigated by an in situ high-pressure x-ray diffraction technique. It is found that the pressure-induced phase transition from face-centered cubic to hexagonal close-packed phase occurs at 15.60, 13.84, and 8.20 GPa, respectively. The atomic size misfit of CoNiFe, CoNiCr, and CoNiV MPEAs is estimated to be 0.653%, 2.077%, and 3.013%, respectively, illustrating that the lattice distortion degree is increasing. The increase in lattice distortion can decrease the initial phase-transition-pressure because lattice distortion could reduce the strain to nucleate Shockley partial dislocation, which promotes the formation of a stacking fault (SF) stack of three atomic layers with hcp stacking. However, the quantitative calculation of stacking fault probability α as a function of pressure demonstrates that the probability of SF formation gradually increases in order of CoNiFe, CoNiCr, and CoNiV, which is in line with the critical pressure of phase transition decreasing orderly. Furthermore, the first peak in the pair distribution function curve after entirely decompression not fully reverts to its initial state, proving the densification of MPEAs under pressure. These findings provide an innovative light for understanding pressure-induced phase transitions in MPEAs.

High-pressure polymorphism in amoxicillin

This work is devoted to the pressure-induced structural transformations of amoxicillin by Raman and infrared spectroscopy at pressures up to 10 GPa. The Raman and infrared results indicate that amoxicillin underwent two phase transitions upon compression, specifically phase α → β and β → γ phase transitions at 2.71 GPa and 7.45 GPa. The significant changes of hydrogen bonding are indicated by the softened Raman modes, suggesting that the α → β phase transition may be a molecular layering reorganization process. The retrieved Raman and FT-IR spectra demonstrate that pressure-induced phase transitions are reversible upon decompression from 10 GPa to ambient pressure.

Pressure-induced reversible structural phase transitions and metallization in GeTe under hydrostatic and non-hydrostatic environments up to 22.9 GPa

The pressure-dependent vibrational and electrical transport properties of GeTe have been investigated in a diamond anvil cell through in-situ Raman spectroscopy and electrical conductivity measurements under hydrostatic and non-hydrostatic environments up to 22.9 GPa. Upon compression, two structural transformations from rhombohedral to cubic NaCl-type to orthorhombic GeTe occurred at 3.2 GPa and 12.3 GPa under non-hydrostatic condition. Similarly, two corresponding phase transitions were detected at much higher pressures of 5.0 GPa and 15.4 GPa under hydrostatic condition. Additionally, a 3.3 GPa of electronic transition accompanying by the rhombohedral to cubic NaCl-type transition was characterized by the variable-temperature electrical conductivity experiments. Upon decompression, the recoverable Raman spectra and resumable electrical conductivity suggested that the structural and electronic transitions of GeTe were reversible. The reversibility was further confirmed by the microscopic structural observations from high-resolution transmission electron microscopy, fast Fourier transform and atomic force microscopy.

First-principles study of structural phase transitions and metallization of XPSe3 (X = Fe, Mn) under high pressure

The pressure-induced structural phase transition and metallization of FePSe3 and MnPSe3 are investigated from ambient pressure to 40 GPa by first-principles calculation. FePSe3 and MnPSe3 undergo reversible structural transitions from R3¯ structure to C2/m structure and then to P3¯1m structure. The structural phase transitions of FePSe3 are at about 6 GPa and 13 GPa, while the pressure points are at approximately 13 GPa and 25 GPa for MnPSe3, reflecting from pressure-dependent enthalpy calculation, cell volume collapses, and sudden changes of lattice parameters. The computed metallization transition is also observed at around 8 GPa and 16 GPa owing to energy-band closure for FePSe3 and MnPSe3, respectively. The metallic character of XPSe3 is strengthened with increasing pressure based on the electronic energy band and electron density of states. The layer sliding of atoms is revealed using the P2-P3 atom pair of XPSe3 during structural phase transitions. The paper is conducive to considering the electronic structure and metallization of transition metal thiophosphates XPSe3-type family under extreme conditions.

Superconductivity beyond the Conventional Pauli Limit in High-Pressure CeSb_{2}.

We report the discovery of superconductivity at a pressure-induced magnetic quantum phase transition in the Kondo lattice system CeSb_{2}, sustained up to magnetic fields that exceed the conventional Pauli limit eightfold. Like CeRh_{2}As_{2}, CeSb_{2} is locally noncentrosymmetric around the Ce site, but the evolution of critical fields and normal state properties as CeSb_{2} is tuned through the quantum phase transition motivates a fundamentally different explanation for its resilience to applied field.