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The Hugoniot elastic limit (HEL) is widely adopted as an important criterion for assessing the dynamic strength of materials, representing the transition stress from elastic to plastic response prior to failure under shock compression. Nano-polycrystalline diamond currently holds the highest HEL of 208 (±14) GPa. Here, we report a diamond-TiC composite (∼11.5 wt. % TiC) showing an ultrahigh HEL of at least 195 (±3.5) GPa, which is comparable to that of nano-polycrystalline diamond. All measured velocity profiles on the diamond-TiC free surface exhibited a single-wave structure at shock pressures of 48–195 GPa. Moreover, the measured Us–Up (shock wave velocity–particle velocity) relation can be linearly fitted, indicating no elastic–plastic transition or solid–solid phase transition up to a shock pressure of 195 GPa. The diamond-TiC composite's compression ratio was similar to that of TiC but significantly higher than that of diamond. These extraordinary dynamic responses are intrinsically attributed to the unique microstructure in which diamond polycrystals are encased in a TiC matrix, providing protection against yielding. Our findings not only developed a mechanically reliable, lightweight, and high-performance armor material at low synthesis costs, but also provided new insights into the shock compression behavior of diamond composites. [ABSTRACT FROM AUTHOR]

Pressure is the core of high-pressure science and technology, and the accuracy of pressure calibration is of much importance for high-pressure experiments and production. Although the pressure limit of the large volume press (LVP) continues to increase, there are no well solutions for in situ pressure calibration. In this study, using in situ high-pressure electrical performance measurement technology, two ideal calibration standard materials in powder conductors, cadmium phosphide (Cd3P2) and zinc telluride (ZnTe) with stable physical and chemical properties and obvious resistance change, are applied to pressure calibration in the LVP. In situ high-pressure synchrotron radiation x-ray diffraction was used to verify the phase transition pressure point of Cd3P2. The introduction of powder conductors for pressure calibration commits to establish a pressure system, which is safer, more stable to operate, and more accurate in experimental measurements for the LVP. [ABSTRACT FROM AUTHOR]

We report experimental determination of compressibility and thermoelasticity for CrN based on in situ high pressure/high temperature synchrotron x-ray diffraction measurements. The pressure-induced cubic-to-orthorhombic phase transition is observed at ∼ 5 GPa in high-quality CrN samples synthesized using a high pressure reaction route. Equation of state, bulk modulus and axial compressibility of this material are obtained by analysis of high pressure x-ray diffraction data collected at room temperature. Both cubic and orthorhombic phases have a similar bulk modulus value of 257 (5) and 262 (6) GPa, respectively. For orthorhombic CrN, the b-axis has the most axial incompressibility, which should be associated with magnetic properties. In addition, the isothermal equation of states is also determined at different temperatures of 300, 400, 600, 800, 1000, and 1200 K, respectively. Some of the important thermoelastic properties of cubic CrN are thus derived, including temperature derivative of bulk modulus ∂ K T / ∂ T = − 2.95 (5) × 10 − 2 G P a ⋅ K − 1 and volumetric thermal expansivity a T ≈ a 0 + a 1 ⋅ T where a0 = 1.95 (16)×10−5 K−1 and a1 = 4.39 (3)×10−9 K−1. [ABSTRACT FROM AUTHOR]

High‐pressure structural evolution of CeOCl, a lanthanide oxychloride, was investigated by in situ high‐pressure Raman scattering and first‐principles calculations. We report the novel observation of discontinuities in Raman wavenumber at the pressure of approximately 7 GPa, which are related to an isostructural phase transformation caused by an increase of Bader charge transfer from Ce to Cl and O. In addition, the mode‐Grüneisen parameters (of CeOCl) were given and discussed. This is helpful for us to better understand applications of the Ce‐based compounds. [ABSTRACT FROM AUTHOR]

The thermal insulation performance of cubic ZrO2-CaO solid solution (CSZ) (16 mol % CaO) and monoclinic ZrO2 (MZ) was investigated in a two-stage multi-anvil press under a pressure of 10 GPa and temperatures up to 1800°C through in situ temperature measurements with the same cell assembly. The results show that the cell temperatures with CSZ as the thermal insulator were always higher than that when thermal insulator was MZ at the same heating power, and the maximum deviation value was 600°C (50% higher) within the measurable range. These two materials were analyzed using X-ray diffraction (XRD), thermal conductivity measurement and scanning electron microscopy. It revealed that the point defects existed in CSZ dominated the thermal insulation performance at high pressure, the same as what at normal pressure. It was also found that the heating process was more controllable when using CSZ as thermal insulator under high pressure. [ABSTRACT FROM AUTHOR]

Nanophase materials have novel physical and chemical properties, differing from bulk materials. It is of exceptional interest to investigate the size effect on structural stability in nanocrystals. Here, we investigated pressure-induced phase transitions in nanosized Er2O3using angle-dispersive synchrotron X-ray diffraction up to 40.6 GPa. Nano-Er2O3has enhanced transition pressure and higher bulk modulus (K0) than its bulk counterparts. Amorphous Er2O3nanoclusters with traces of monoclinic phase are obtained upon compression. This is the first time that partial amorphous structure under compression was observed in nano-Er2O3, indicating a kinetic trapping of partial amorphous Er2O3on pressurizing. [ABSTRACT FROM AUTHOR]

Phase stability of Ti3SiC2 was studied under high pressure and high temperature using X-ray diffraction, scanning electron microscopy, and energy-dispersive X-ray spectroscopy. From the results obtained, the decomposition temperature of Ti3SiC2 decreases quickly against pressure, and the low temperature limits of phase segregation of the sample Ti3SiC2 lie between 1100°C and 1000°C, 1000°C and 900°C, 900°C and 800°C, under high pressures of 3, 4 and 5GPa, respectively. Ti3SiC2 decomposes to generate TiC, SiC, and TiSi x . On the basis of the experimental results, we suggest two decomposition models to explain the phase decomposition of Ti3SiC2 at high pressure and high temperature. [ABSTRACT FROM AUTHOR]

Abstract: Phase transitions of both α-BiNbO4 and β-BiNbO4 were investigated under high pressure and high temperature (HPHT) (0–5GPa and 300–1800°C, respectively) using X-ray diffraction (XRD), scanning electron microscope (SEM), and energy dispersive spectroscope (EDS). The stable regimes for the BiNbO4 phases were also determined. Experiments showed that both α-BiNbO4 and β-BiNbO4 could convert to a new high pressure phase HP-BiNbO4 above 3GPa, and the transition temperatures decreased with increasing pressures. Below 3GPa, β-BiNbO4 keeps stable up to 1800°C, while α-BiNbO4 converts to β-BiNbO4 when temperature is higher than 1150°C. By heating the metastable HP-BiNbO4 phase at room pressure, HP-BiNbO4 converts to α-BiNbO4 at 600°C. Above 1150°C, HP-BiNbO4 would transform to β-BiNbO4. Phase relationships of Bi2O3, Nb2O5, α-BiNbO4, β-BiNbO4 and HP-BiNbO4 were also summarized. [Copyright &y& Elsevier]

Abstract: High pressure in situ differential thermal analysis (DTA) was applied to study phase transitions of Na0.5Bi0.5TiO3 (NBT) up to 5GPa. DTA analysis at room temperature with pressure as the variable indicated NBT samples have two pressure induced phase transformations at about 0.7GPa and 2.5GPa respectively. Below 0.7GPa, two temperature induced phase transitions could be observed at around 220°C and 520°C as it was reported at ambient pressure. But under a pressure higher than 0.7GPa, these two temperature induced phase transitions would not happen. In situ electrical resistance measurements showed that the resistance of NBT changes smoothly, and the tendency is similar to that of electrical insulators like pyrophyllite. We suggest that the pressure induced phase transitions at 0.7GPa and 2.5GPa are both insulator to insulator phase transitions. [Copyright &y& Elsevier]

The development of neutron diffraction under extreme pressure ( P) and temperature ( T) conditions is highly valuable to condensed matter physics, crystal chemistry, materials science, and earth and planetary sciences. We have incorporated a 500-ton press TAP-98 into the HiPPO diffractometer at the Los Alamos Neutron Science Center (LANSCE) to conduct in situ high- P– T neutron diffraction experiments. We have developed a large gem-crystal anvil cell, ZAP, to conduct neutron diffraction experiments at high P. The ZAP cell can be used to integrate multiple experimental techniques such as neutron diffraction, laser spectroscopy, and ultrasonic interferometery. More recently, we have developed high- P low- T gas/liquid cells in conjunction with neutron diffraction. These techniques enable in situ and real-time examination of gas uptake/release processes and allow accurate, time-dependent determination of changes in crystal structure and related reaction kinetics. We have successfully used these techniques to study the equations of state, structural phase transitions, and thermo-mechanical properties of metals, ceramics, and minerals. We have conducted researches on the formation/decomposition kinetics of methane, CO2 and hydrogen hydrate clathrates, and hydrogen/CO2 adsorption of inclusion compounds such as metal–organic frameworks (MOFs). The aim of our research is to accurately map out phase relations and determine structural parameters (lattice constants, atomic positions, atomic thermal parameters, bond lengths, bond angles, etc.) in the P– T– X space. We are developing further high- P– T technology with a new 2000-ton press, TAPLUS-2000, and a ZIA (Deformation-DIA type) cubic anvil package to routinely achieve pressures up to 20 GPa and temperatures up to 2000 K. The design of a dedicated high- P neutron beamline, LAPTRON, is also underway for simultaneous high- P– T neutron diffraction, ultrasonic, calorimetry, radiography, and tomography studies. Studies based on high-pressure neutron diffraction are important for multidisciplinary sciences, particularly for theoretical/computational modeling/simulations. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a comprehensive study on phase transitions in LiAlO2 system at high pressures and temperatures (0.5–5.0GPa and 300–1873K, respectively), as well as the phase stability for polymeric phases of LiAlO2 in the studied P–T space by X-ray diffraction (XRD). Besides the previously described polymorphic hexagonal α-phase, orthorhombic β-phase and tetragonal δ-phase, a possible new phase of LiAlO2 was observed after the tetragonal γ-LiAlO2 sample was treated at 5.0GPa and 389K. The stable regimes of these high-pressure phases were defined through the observation of coexistence points of the polymeric phases. Our results revealed that LiAlO2 could experience structural phase transitions from γ-LiAlO2 to its polymorphs at lower pressures and temperatures compared to the reported results. Hexagonal α-LiAlO2 with highly (003) preferential orientation was prepared at 5.0GPa and 1873K. [Copyright &y& Elsevier]

An anvil-preformed gasket system has been developed to extend the pressure range for the widely used large volume cubic press without sacrificing the sample volume. The relationship of the sample chamber pressure versus press load for this system was calibrated at room temperature using transitions in Bi, Tl, and Ba. With similar sample volumes (8-11 mm in diameter and 8 mm in length), the anvil-preformed gasket system can generate pressures up to about 8.5 GPa, significantly higher than 6 GPa, which was generally the maximum pressure for the conventional anvil-gasket system. The details on the optimized design for the anvil-preformed gasket system are given in this note. [ABSTRACT FROM AUTHOR]

In the present work, the orthorhombic (α) BiNbO 4 have been investigated with the in-situ angle-dispersive x-ray diffraction (ADXRD) measurements under high pressure. Pressure-induced phase transition was observed in α-BiNbO 4 , and compressibility of the unit cell axes (a, b and c axes) of α-BiNbO 4 shows an anisotropic with pressure increasing. The phase transition routine and the effect of pressure in the phase evolution of BiNbO 4 were also explored. The results indicate that pressure-induced phase transition is reversible, in contrast, pressure and temperature-induced phase transition is irreversible in system of BiNbO 4 , but the phase remains stable without pressure. High pressure plays a critical role and provides a driving force for phase transition of BiNbO 4 . [ABSTRACT FROM AUTHOR]

The phase transition of PbNiO3 from LiNbO3 structure to the perovskite structure has been observed between 4.4 and 9.5 GPa, which was investigated by high-pressure synchrotron x-ray powder diffraction at room temperature. Compression behavior of the two phases has been analyzed, and the c axis is the soft direction for LiNbO 3-type PbNiO3. The bulk modulus of the LiNbO3-type PbNiO3 is K0=184(3) GPa, K0′=4.5(9), and the perovskite type is K0=166(8) GPa, K0′=4.9(8). [ABSTRACT FROM AUTHOR]

Abstract: We report phase transition and stability of MoS2 with and without the presence of sulfur melt under high-pressure and high-temperature conditions. Rhombohedral (3R) phase is found to be a high-temperature phase of MoS2 at high pressures. Excess sulfur melt catalyzes the hexagonal (2H) to rhombohedral (3R) phase transformation and lowers the conversion temperature by more than 280K. Boundary between 2H and 3R phases has been delineated with a negative slope. Based on experimental observations, sulfur-catalyzed 2H→3R transformation mechanisms are proposed involving atomic exchange between MoS2 and sulfur, which is different from the case of without excess sulfur that proceeds through rotation and translation of the S–Mo–S sandwich layers. [Copyright &y& Elsevier]

Abstract: Internal residual metal phases (mainly cobalt) were effectively removed from polycrystalline diamond compacts (PDCs) by electrolysis to improve their high temperature wear resistance. Through turning granite (dry cutting), we have checked the wear resistance of PDCs with different residual metal removal depth (RMRD). The relationship between the measured wear rate and RMRD was obtained, and the results showed that PDCs treated by electrolysis have a significant improvement in wear resistance. X-ray diffraction (XRD) and scanning electron microscopy (SEM) observation of PDCs'' wear surface indicated that diamond–graphite phase transformation occurs for the samples with residual metal phase. The wear mechanism is discussed, and our study suggests that the graphitization is the main wear process of PDCs with internal residual metal phases. [Copyright &y& Elsevier]

A widely investigated allotrope of germanium, metastable germanium (ST12 Ge), has garnered sustained interest for quite a few years since it has been applied as a potential semiconductor component owing to its optical properties. In this study, a large pure bulk sample of ST12 Ge was synthesized through secondary pressure induced phase transition. The structure and purity of the sample were characterized via a combination of powder X-ray diffraction, Raman scattering, and X-ray photoelectron spectroscopy. Moreover, its thermal stability and optical properties were investigated. The bandgap structure, Vickers hardness, Raman spectrum, and other properties under pressure, were systematically investigated via first principles calculations. • First, in this study, phase-pure ST12 Ge bulks were prepared through secondary pressure induced phase transition. • Second, the structure and purity of the sample have been studied. The thermal stability and optical properties were investigated in details. • Third, first-principle calculations were used to calculate the its bandgap structure, Vickers hardness, Raman spectrum and other properties under pressure. [ABSTRACT FROM AUTHOR]

Abstract: This work presents a comprehensive study on phase transition in NaGaO2 under high pressure and temperature (P–T) conditions. X-ray diffraction (XRD) was used to identify the phase composition of the recovered samples. Our results revealed that NaGaO2 could undergo a structural phase transition from orthorhombic - NaGaO2 to hexagonal - NaGaO2 under high pressure and temperature. The pressure–temperature phase boundaries of NaGaO2 were determined up to 5 GPa and 2073 K. The hexagonal - NaGaO2 sample recovered from higher pressure and temperature exhibited a highly (003) preferred orientation. Besides, a reversible transition from - to - NaGaO2 was observed above 473 K under normal-pressure condition. The high-pressure melting curve of NaGaO2, for the first time, was measured by using in-situ thermal measurement. [Copyright &y& Elsevier]

Abstract: We report on the in situ electrical resistance measurements of Ti2AlC under high pressure up to 6 GPa using four-probe method in a cubic large volume press. The resistance of Ti2AlC changes smoothly with pressure without sharp anomalies, which reveals no phase transformations. The resistivity decreases with increasing pressure. At pressures above 3.5 GPa, the resistivity decreases slowly with a pressure dependence of about . In addition, the resistivity was also measured at the process of decompression. The resistivity changes slowly with a pressure dependence of about at pressures above 2.5 GPa. These results are associated with the resistivity change with temperature and could confirm that the transition metal plays the dominant role in electrical transport. [Copyright &y& Elsevier]

• The formation mechanism of BC8-Si was studied using in situ synchrotron XRD. • Phase-pure bulk BC8-Si was prepared though secondary phase transition method. • The bulk sample provides an opportunity to study its intrinsic properties. Phase-pure bulk samples of silicon in the body-centered cubic structure (BC8-Si) were prepared via secondary phase transition method under high pressure and room temperature. The bulk samples of BC-Si, with diameter of 3 mm and thickness of 0.5 mm, were synthesized via high-pressure phase transitions of single crystal silicon using the large volume cubic press. The formation mechanism of phase-pure BC8-Si via phase transitions of normal single crystal silicon was investigated using in situ synchrotron X-ray diffraction. The phase-pure BC8-Si was observed through primary phase transition under hydrostatic high-pressure condition. However, the secondary phase transformation was needed to obtain the phase-pure BC8-Si sample at non-hydrostatic compression using the large volume cubic press. The structure and purity of bulk BC8-Si were verified using powder X-ray diffraction, Raman spectroscopy, and energy dispersive spectra. Our experimental results show that the secondary phase transformation method under high pressure is an effective way for phase-pure bulk sample preparation of BC8-Si, which provides an opportunity for further studies of its intrinsic physical properties. [ABSTRACT FROM AUTHOR]