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The presence of the van der Waals gap in layered materials creates a wealth of intriguing phenomena different to their counterparts in conventional materials. For example, pressurization can generate a large anisotropic lattice shrinkage along the stacking orientation and/or a significant interlayer sliding, and many of the exotic pressure-dependent properties derive from these mechanisms. Here we report a giant piezoresistivity in pressurized β′-In2Se3. Upon compression, a six-orders-of-magnitude drop of electrical resistivity is obtained below 1.2 GPa in β′-In2Se3 flakes, yielding a giant piezoresistive gauge πp of −5.33 GPa−1. Simultaneously, the sample undergoes a semiconductor-to-semimetal transition without a structural phase transition. Surprisingly, linear dichroism study and theoretical first principles modelling show that these phenomena arise not due to shrinkage or sliding at the van der Waals gap, but rather are dominated by the layer-dependent atomic motions inside the quintuple layer, mainly from the shifting of middle Se atoms to their high-symmetric location. The atomic motions link to both the band structure modulation and the in-plane ferroelectric dipoles. Our work not only provides a prominent piezoresistive material but also points out the importance of intralayer atomic motions beyond van der Waals gap. Lattice shrinkage is a dominating factor for the strain-induced change of the electronic properties in vdW layered materials. Here, the authors discover a piezoresistivity in pressurized β′-In2Se3, which originates from the intralayer atomic motions. [ABSTRACT FROM AUTHOR]

Due to their large bandgaps, multiferroic oxides, the promising candidates for overcoming the disadvantages of metal-halide perovskites as light absorbers, have so far very limited use in solar cell applications. Previous investigations demonstrate that high pressure represents an efficient tool for tuning the bandgap of multiferroic Mn3TeO6 (MTO). However, the underlying mechanism of the giant bandgap reduction discovered in MTO remains unclear, which critically prevents the design of next-generation light absorbers. In this study, we performed in situ x-ray diffraction analyses on the structure evolution of MTO upon compression and decompression, discovering a sequence of irreversible phase transitions R 3 ¯ →C2/c→P21/n. The experimental results, supported by electronic structure calculations, show the shortening of Mn–O–Mn bonding, and, to a lower extent, the decrease in connectivity of octahedra across the phase transition, explain the giant bandgap reduction of MTO. These findings will facilitate the design and synthesis of next-generation light absorbers in solar cells. [ABSTRACT FROM AUTHOR]

The pressure-induced structural transformations of CdS have been investigated using synchrotron x-ray diffraction in a diamond anvil cell up to 104 GPa and the density functional theory calculations. The x-ray diffraction experiments show that CdS is stable with the wurtzite-type structure at ambient conditions. The wurtzite-type phase transforms to NaCl-type structure at 3 GPa, which is followed by a second phase transition at 52.3 GPa. In the diffraction patterns, the peak-splitting is observed, indicating that the high-pressure phase appearing at 52.3 GPa is the Pmmn structure, rather than the Cmcm phase reported earlier. With increasing pressure, the lattice parameter a of the Pmmn phase increases abnormally, contrary to decrease of b and c axes. Our calculations reveal that the abnormal change of the a-axis could be related to the pressure-induced crystal structural change. The bulk modulus (B0), is 64.3(9) GPa for wurzite-type phase, 105(2) GPa for NaCl-type phase, and 54(4) GPa for the Pmmn phase, respectively. [ABSTRACT FROM AUTHOR]

The structural stability of cubic Ho2O3 under high pressure has been investigated by angle-dispersive x-ray diffraction (ADXD) in a diamond anvil cell up to 63.0 GPa at room temperature. The diffraction data reveal two structural transformations on compression. The structural transformation from a cubic to a monoclinic structure starts at 8.9 GPa and is complete at 16.3 GPa with a ∼8.1% volume collapse. A hexagonal phase begins to appear at ∼14.8 GPa and becomes dominant at 26.4 GPa. This high-pressure hexagonal phase with a small amount of retained monoclinic phase is stable up to the highest pressure of 63.0 GPa in this study. After release of pressure, the hexagonal phase transforms to a monoclinic structure. A third-order Birch-Murnaghan fit yields zero pressure bulk moduli (B0) of 206(3), 200(7) and 204(19) GPa and their pressure derivatives (B0') of 4.8(4), 2.1(4), 3.8(5) for the cubic, monoclinic and hexagonal phases, respectively. Comparing with other rare-earth sesquioxides, it is suggested that the transition pressure from cubic to monoclinic phase, as well as the bulk modulus of the cubic phase, increases with the decreasing of the cation radius of rare-earth sesquioxides. [ABSTRACT FROM AUTHOR]

High-pressure transformation and compression behavior of Gd2O3 were investigated using synchrotron radiation x-ray diffraction in a diamond anvil cell up to 44 GPa at room temperature. The structural transformation from a cubic to a monoclinic phase occurred during the sample precompression process. Phase transitions from both the cubic and the monoclinic polymorphs to a hexagonal structure were observed. The hexagonal phase was stable up to the highest pressure in this study and was not quenchable and transformed to a monoclinic phase after pressure release. The bulk moduli of Gd2O3 for the cubic, monoclinic, and hexagonal phases were obtained by fitting the compression data to the Birch–Murnaghan equation of state. Moreover, an anomaly of the hexagonal type Gd2O3 was observed. [ABSTRACT FROM AUTHOR]

We have designed and implemented a novel DLD for controlling pressure and compression/decompression rate. Combined with the use of the symmetric diamond anvil cells (DACs), the DLD adopts three piezo-electric (PE) actuators and three static load screws to remotely control pressure in accurate and consistent manner at room temperature. This device allows us to create different loading mechanisms and frames for a variety of existing and commonly used diamond cells rather than designing specialized or dedicated diamond cells with various drives. The sample pressure compression/decompression rate that we have achieved is up to 58.6/43.3 TPa/s, respectively. The minimum of load time is less than 1 ms. The DLD is a powerful tool for exploring the effects of rapid (de)compression on the structure of materials and the properties of materials. [ABSTRACT FROM PUBLISHER]

PbTe has been investigated using synchrotron X-ray diffraction (XRD) in a diamond anvil cell under quasi-hydrostatic pressures up to 50 GPa. Upon compression to 6.6 GPa, the initial NaCl phase transforms to an intermediate phase, which is confirmed to be an orthorhombic structure with a space group Pnma. At 18.4 GPa, the intermediate Pnma phase undergoes a phase transition to the CsCl structure. The systemic analysis of the crystal structures between the NaCl and intermediate phases indicates that the structure of the Pnma phase could be derived from the distortion of the NaCl structure. The bulk modulus of the CsCl phase isB0=52(2) GPa withV0=60.8(4) Å3andB′0=4.0 (fixed), slightly larger than the NaCl phase (B0=44(1) GPa) and the intermediate phase (B0=49(3) GPa). [ABSTRACT FROM AUTHOR]

• We realize the "zoom-in" high pressure analysis of metallofullerenes (Gd@C 82). • The "three-level" phase transition procedure are achieved through morpholine ligand. • The carbon cage and morpholine groups are conserved with anisotropic shrinkage. • New constructed bonds and the encaged metal's movement is found. • The charge-transfer principle is the beneath driving force for the phase transition. [Display omitted] Metallofullerenes present an ideal research object for developing new carbon structures with improved properties under high pressure. In this study, high pressure investigation is realized on metallofullerene derivatives (Gd@C 82 (morpholine) 7) by applying in situ synchrotron XRD, Raman, and IR spectroscopy, combined with high pressure density functional theory (DFT) calculations. The regulations of multi-configuration morpholine ligands avoid the direct collapse of the carbon cages commonly happened to fullerenes, making the fine structure transformation possible for the first time, including ligand configuration exchange, anisotropic shrinkage of cage, new constructed bonds, and even the encaged metal's movement with increasing pressure. The charge-transfer principle as the beneath driving force of structural transition is found. These findings demonstrate that multi-configuration ligand maps an innovative strategy for phase transition control of metallofullerenes under high pressure, thus providing deep insight, step by step, into the phase transition mechanism of these hybrid molecular systems on molecular level. [ABSTRACT FROM AUTHOR]

The pressure-induced phase transition of the hexagonal manganite ErMnO3 has been investigated using the synchrotron x-ray diffraction technique up to 57.6 GPa in a diamond anvil cell. The hexagonal structure exhibits anisotropic compression behavior. The bulk modulus (B0) is 168(3) GPa with B0′ = 4.0 (fixed). At room temperature, ErMnO3 undergoes a hexagonal-to-orthorhombic phase transition at ∼20.2 GPa, but coexists with the orthorhombic phase up to the highest pressure of 57.6 GPa. When laser-heated to 1500-2000 K, the hexagonal ErMnO3 transforms to a denser orthorhombic perovskite structure completely at ∼17 GPa, accompanied by ∼11% volume reduction. The distortion and tilts of the octahedra MnO6 in the orthorhombic structure decrease with increasing pressure. The bulk modulus of the orthorhombic structure is 214(4) GPa with B0′ = 4.0 (fixed), larger than that of the hexagonal structure. The orthorhombic structure ErMnO3 is stable at least up to ∼45 GPa and can be quenched. [ABSTRACT FROM AUTHOR]

Fluorite phase CeO2 is compressed non-hydrostatically up to 27 GPa using a diamond anvil cell until the transition to α-PbCl2 phase occurred. The compressive strength (t) of CeO2 as a function of pressure is determined by the line width analysis of the high pressure angle dispersive x-ray diffraction patterns. The strength of CeO2 increases quickly below 3.30 GPa and reaches a plateau region at high pressures. A procedure combined the line width analysis and the line shift analysis together, based on the non-hydrostatic data to obtain the corresponding lattice parameter under hydrostatic pressures, is proposed and applied to the case of CeO2 sample. The bulk modulus and its pressure derivative of fluorite phase CeO2 (K0 = 235 (18) GPa, K0′ = 3.67) are obtained by fitting the P-V results into Vinet equation of state. A discussion of the pressure dependence of α, which determines the relative weights of the isostress and isostrain conditions across the grain boundary in an actual case, is presented. [ABSTRACT FROM AUTHOR]

Despite extensive and systematic studies on pressure-induced phase transitions and superconductivity in sesqui-chalcogenide A 2 B 3 (A=Sb, Bi; B S, Se, and Te) compounds, the detailed transporting properties of Bi 2 S 3 have rarely been reported. Here, we discovered an unambiguous correlation between superconductivity and phase transitions in Bi 2 S 3 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 (T C) increased to around 7.3 K, which was accompanied by the amorphization of Bi 2 S 3 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. [Display omitted] • In this study, we probed the effect of pressure on the transport properties of Bi 2 S 3 in combination with structural studies using high-resolution synchrotron XRD, Raman spectroscopy, and resistance measurements. • We discovered an unambiguous correlation between superconductivity and phase transitions in Bi 2 S 3 under non-hydrostatic conditions, which has not been reported thus far. • 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 increased to around 7.3 K, which was accompanied by the amorphization of Bi 2 S 3 above 43 GPa. • Furthermore, the divergence between the theoretical calculations and experimental measurements showed that the above phase transitions had a critical effect on the electronic properties of this compound. [ABSTRACT FROM AUTHOR]

High-pressure transformation and compression behavior of Gd2O3 were investigated using synchrotron radiation x-ray diffraction in a diamond anvil cell up to 44 GPa at room temperature. The structural transformation from a cubic to a monoclinic phase occurred during the sample precompression process. Phase transitions from both the cubic and the monoclinic polymorphs to a hexagonal structure were observed. The hexagonal phase was stable up to the highest pressure in this study and was not quenchable and transformed to a monoclinic phase after pressure release. The bulk moduli of Gd2O3 for the cubic, monoclinic, and hexagonal phases were obtained by fitting the compression data to the Birch–Murnaghan equation of state. Moreover, an anomaly of the hexagonal type Gd2O3 was observed. [ABSTRACT FROM AUTHOR]

Abstract The order-disorder transition has long been viewed as an important key to study materials structures and properties. Especially, pressure-induced ordering attracted the intense research interest in the recent years. In the present work, the pressure-induced ordering phase transition (disordered-fcc to ordered-fcc structures) in a CoCrCuFeNiPr high-entropy alloy (HEA) was found by employing the in situ high-pressure energy-dispersive X-ray diffraction (EDXRD) technique. It is interesting to note that there exists a pressure-induced fast ordering transition at the pressure ranging from 7.8 GPa to 16.0 GPa, followed by a slow transition with the pressure increase up to 106.4 GPa. We suggest that this phenomenon is caused by the presence of some short-range-order (SRO) local structures in the CoCrCuFeNiPr HEA. These SRO structures can be regarded as embryos, which will develop into the ordered phase with increasing the pressure in the prototype materials. This pressure-induced ordering may provides a new technique for tuning structures and properties of HEAs. Highlights • The in situ high-pressure X-ray diffraction technique was used and the maximum applied pressures were up to 106.4 GPa. • The pressure-induced ordering phase transition was found in CoCrCuFeNiPr high-entropy alloy. • The elastic anisotropy of the ordering-fcc phase can be well described with the pressure-dependence of the lattice strain. [ABSTRACT FROM AUTHOR]

The distribution and degradation of antibiotic enoxacin in ferrihydrite-enoxacin and ferrihydrite-enoxacin-citrate coprecipitates phase transformation processes were investigated through combined experiments and theoretical calculations. Results indicated that the coprecipitates, including enoxacin and citrate, suppressed the transformation of coprecipitates into hematite. The proportions of hematite in ferrihydrite-enoxacin and ferrihydrite-enoxacin-citrate were 11.7% and 8.4% lower than that in pure ferrihydrite, respectively. Most enoxacin was degraded mainly through •OH generated from Fe(II)/Fe(III) intervalence changing and citrate promoted the degradation of enoxacin during the phase transformation process. The transformation products were less toxic than the enoxacin. Our results strongly suggest that the coprecipitation transformation of fluoroquinolones antibiotics and ferrihydrite may play a larger role in their environmental fate and effects. [Display omitted] • Coprecipitated enoxacin and citrate inhibited the transformation of ferrihydrite. • Enoxacin was degraded by.•OH generated from Fe(II)/Fe(III) intervalence changing. • Citrate promoted the degradation of enoxacin. • Most transformation products were less toxic than the parent enoxacin. [ABSTRACT FROM AUTHOR]

Abstract: The structural stability of cubic Dy2O3 under high pressure has been investigated using synchrotron radiation in a diamond anvil cell up to 49.0GPa. The diffraction data reveals the cubic phase undergoes two successive phase transitions on compression. The phase transition from a cubic to a monoclinic structure starts at 7.7GPa and is complete at 18.8GPa with a ~7.9% volume collapse. The monoclinic phase further transforms to a hexagonal phase starting at ~10.9GPa and the hexagonal phase becomes dominant at 26.6GPa. This high-pressure hexagonal phase with a small amount of retained monoclinic phase is stable up to the highest pressure of 49.0GPa in this study. After pressure release, Dy2O3 is a monoclinic structure. A third-order Birch–Murnaghan fit yields zero pressure bulk moduli (B 0) of 191(4), 179(9) and 231(22)GPa and their pressure derivatives (B 0′) of 2.8(7), 4.2(6), 3.5(6) for the cubic, monoclinic and hexagonal phases, respectively. Comparing with other rare-earth sesquioxides, we confirm that the transition pressure from cubic to monoclinic phase, as well as the bulk modulus of the cubic phase, increases with the decreasing of the cation radius of rare-earth sesquioxides. [Copyright &y& Elsevier]

In this study, we systematically studied the high pressure polymorphism phase transition process in the Fe 40 Mn 40 Co 10 Cr 10 multi-principal element alloy through the hexahedron pressure equipment and the high pressure synchrotron angle-dispersive x-ray diffraction technique. A mixture of face-center cubic (fcc) + hexagonal close packed (hcp) nanolaminate structure was observed for the samples after high pressure treatment at 5 GPa, through the hexahedron pressure equipment. Especially, the hcp lath interaction structure with a new secondary hcp phase at the intersection zone was discovered in the sample. Transmission Electron Microscopy (TEM) analysis revealed that the transition from fcc to hcp was accomplished by the glide of Shockley partial dislocations. In addition, the in-situ synchrotron angle-dispersive x-ray diffraction technique was carried out to detect the phase transition process of the Fe 40 Mn 40 Co 10 Cr 10 alloy up to 40.4 GPa. The lattice constant, atomic volumes, bulk modulus, and volume fraction of the fcc and hcp phase were obtained during compression and decompression. These results can expand our understanding of the structure evolution and properties of multi-principal element alloys under extreme conditions such as high pressure, which is contribute to the development of new metastable structural materials. • The polymorphism phase transition was observed in the non-equiatomic Fe 40 Mn 40 Co 10 Cr 10 HEA. • Hexahedron pressure equipment and high pressure synchrotron angle-dispersive XRD technique were used to explore the phase transition. • A dual-phase HEA with enhanced tensile property was obtained after high pressure treatment. [ABSTRACT FROM AUTHOR]

Abstract: The compression behavior of a natural haüyne has been investigated to about 8.1GPa at 300K using in situ angle-dispersive X-ray diffraction and a diamond anvil cell at High Pressure Experiment Station, Beijing Synchrotron Radiation Facility (BSRF). Over this pressure range, no phase change or disproportionation has been observed. The isothermal equation of state was determined for the first time. The values of V 0, K 0, and K′0 refined with a third-order Birch–Murnaghan equation of state are V 0=751.6±0.4Å3, K 0=49±1GPa, and K′0=3.3±0.3, respectively. [Copyright &y& Elsevier]