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δ-AlOOH is regarded as a potential water carrier that is stable in the Earth’s lower mantle down to the core-mantle boundary along the cold slab geotherm; thus, knowledge of its structural evolution under high pressure is very important for understanding water transport in the Earth’s interior. In this work, we conducted Raman scattering and luminescence spectroscopic experiments on δ-AlOOH at pressures up to 34.6 and 22.1 GPa, respectively. From the collected Raman spectra, significant changes in the pressure dependence of the frequencies of Raman-active modes were observed at ~8 GPa, with several modes displaying softening behavior. In particular, the soft A1 mode, which corresponds to a lattice vibration of the AlO6 octahedron correlated to OH stretching vibrations, decreases rapidly with increasing pressure and shows a trend of approaching 0 cm−1 at ~9 GPa according to a quadratic polynomial extrapolation. These results provide clear Raman-scattering spectroscopic evidence for the P21nm-to-Pnnm structural transition. Similarly, the phase transition was also observed in the luminescence spectra of Cr3+ in both powder and single-crystal δ-AlOOH samples, characterized by abrupt changes in the pressure dependences of the wavelength of the R-lines and sidebands across the P21nm-to-Pnnm transition. The continuous decrease in R2-R1 splitting with pressure indicated that the distortion of the AlO6 octahedron was suppressed under compression. No abnormal features were clearly observed in our Raman or luminescence spectra at ~18 GPa, where the ordered symmetrization or fully centered state with hydrogen located at the midpoint of the hydrogen bond was observed by a previous neutron diffraction study. However, some subtle changes in Raman and luminescence spectra indicated that the ordered symmetrization state might form at around 16 GPa.

Mineral dehydration in the subduction zone enormously affects Earth’s geodynamics and the global geochemical cycles of elements. This work uses Raman spectroscopy and X-ray diffraction to investigate the dehydration process of antigorite under compression and shear loading conditions in a rotational diamond anvil cell (RDAC) at room temperature. In order to compare the shear effects, T301 stainless steel and Kapton plastic are applied as the gasket materials. In the experiment using a high-strength T301 stainless steel gasket, two new broad OH-stretching peaks of H2O and H3O2− appear at 3303 and 3558 cm−1, respectively, at 1.7 GPa. The original sharp OH-stretching peaks of antigorite at 3668 and 3699 cm−1 remain, while the central pressure is increased to 8.0 GPa, and the largest pressure gradient is about 2.5 GPa in the sample chamber. In another experiment with a low-strength gasket of Kapton plastic, two new OH-stretching broad peaks of H2O and H3O2− also start to appear at 3303 and 3558 cm−1, respectively, at a lower pressure of 0.3 GPa, but the original sharp OH-stretching peaks of antigorite at 3668 and 3699 cm−1 almost completely vanish as the central pressure reaches 3.0 GPa, with the largest pressure gradient at around 4.8 GPa. The comparison between the two experiments shows that antigorite is easier to dehydrate in the chamber of a Kapton plastic gasket with a larger gradient of shear stress. However, its axial compression stress is lower. The high-pressure Raman spectra of MgO2(OH)4 octahedron and SiO4 tetrahedron in the low wavenumber zones (100–1200 cm−1) combined with the micro-beam X-ray diffraction spectrum of the recovered product strongly support the structural breakdown of antigorite. This investigation reveals that the water-bearing silicate minerals have strong shear dehydration in the cold subduction zone of the plate, which has important applications in predicting the physical and chemical properties of subduction zones and deducing the rate of plate subduction.

Understanding the structural behavior of double perovskites plays a pivotal role in optimizing their optical, electrical, and magnetic properties, especially when the effects of external parameters...

The presence of the van der Waals (vdW) 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 vdW 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 \(\beta \text{’}\)-In2Se3. Upon compression, a six-orders-of-magnitude drop of electrical resistivity is obtained below 1.2 GPa in \(\beta \text{’}\)-In2Se3 flakes, yielding a giant piezoresistive gauge \({\pi }_{P}\) 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 vdW 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. Our work not only provides a prominent piezoresistive material but also points out the importance of intralayer atomic motions beyond vdW gap.

Crystals usually grow by attachment of ions or atoms to seed crystals. The explorations two decades ago showed that oriented attachment, an aggregation-based crystal growth, can be an alternative process in nanocrystal solutions. However, oriented attachment is thought to be not operative in solids as the rotational alignment is not favored in the absence of a liquid medium. Here, we report the unusual grain growth of nickel nanoparticles during calcination. The nickel nanocrystals calcined at 600 °C were coarsened by nearly two folds, much larger than the coarsening amount at lower and higher temperatures, which suggests that directional growth based on oriented attachment wins out over the classical crystal growing mechanism at a certain temperature. Varied temperature transmission electron microscope (TEM) observation confirmed the oriented attachment behavior in the growth of nanocrystals. This finding reshapes our view on the mechanism of grain growth at the nanoscale and helps us to better design the synthesis and application of nanomaterials.

This study reports the discovery of Yilan crater, a newly identified impact structure in northeast China. The crater has a rim-to-rim diameter of 1.85 km, and is located in Yilan County of Heilongjiang Province. The latitude and longitude coordinates of the crater are 46°23′03″N and 129°18′40″E, respectively. The crater lies in a low mountainous and hilly area of the southwest border of the Xiaoxinganling mountain range. Most of the crater is covered with dense forests. Geotectonically, the area belongs to the eastern Central Asian Orogenic Belt where strong tectonic and magmatic activities have occurred since the late Proterozoic. The crater was entirely formed within the bedrock of Cretaceous granite and appears as a bowl-shaped structure. Approximately one-third of the southern part of the crater rim has been significantly eroded and mostly removed; otherwise, most of the crater rim is well preserved. In a panoramic view, the crater appears as an unclosed ring mountain surrounding a circular depression, and it has steep walls and a relatively flat floor. The crater rim raises approximately 70–120 m above the surrounding terrain. The maximum elevation of the crater rim over the present crater floor is approximately 150 m. Most of the crater rim is composed of granite impact breccia varying from granules to boulders in size. The crater’s interior has been filled by a large amount of granite impact breccia at the bottom and lacustrine deposits at the top. The target rock of granite contains abundant quartz. This study investigated the planar deformation features (PDFs) in the quartz, which is one of the commonest shock metamorphic features in numerous terrestrial impact structures. For the investigation, granite impact breccia was collected from the crater floor. Most of the samples were made into polished thin sections for identifying the PDFs in quartz. Some fine-grained fragments of quartz were also collected from the samples for observation and analysis. The crystallographic orientations of the quartz PDFs were observed on a 4-axis universal stage under an optical microscope. No PDFs in quartz were observed in the quartz of large granite breccia fragments, but many PDFs appeared in the quartz of the fine-grained samples. One to four sets of PDFs in quartz were observed. The forms of the PDFs with Miller indices, such as (0001), { 10 1 ¯ 1 } and { 10 1 ¯ 3 }, were indexed. The observed multiple sets of PDFs in quartz provide unambiguous evidence of shock-metamorphism and confirm an impact origin of the structure. The topographic and structural features of the crater, as well as the occurrences of crater-filled materials (impact breccia and lacustrine deposits), characterize a bolide impact site. Based on 14C dating of the lacustrine deposits from the crater floor, the Crater Lake disappeared approximately 10 ka ago; this disappearance can be related to the loss of crater rim in the southern part of the crater. The large-scale absence of the crater rim cannot be explained by tectonic activity, normal weathering, or erosional process, and must correspond to directional erosion caused by a specific exogenic geological process after the formation of the impact crater. The geologic agent, mechanism, and history of the strong erosion of the crater rim require further investigation. The Yilan crater is the second confirmed impact structure in a large country (China) with an area of 9.6 million square kilometers.

The high-pressure behavior of manganese diselenide MnSe2 was investigated by synchrotron angle-dispersive X-ray diffraction (ADXRD) and infrared reflection spectroscopy equipped with a diamond-anvil cell. It was found that MnSe2 with a pyrite-type structure undergoes a transformation into a disordered intermediate phase at ~ 12.5 GPa, with a ground state composed of an arsenopyrite-type structure, as confirmed by laser-heating treatment. The pyrite to arsenopyrite phase transition was found to be coupled to a large collapse in the unit-cell volume (∆V ~ 19%) and an electronic transition from a high-spin to low-spin state for manganese cations (Mn2+). With a fixed value for the pressure derivation of the bulk modulus K' = 4, fitting of the pressure–volume data to a second-order Birch–Murnaghan equation of state yielded isothermal bulk modulus values of K0 = 56.1(9) GPa and K0 = 93.1(4) GPa for the pyrite-type and arsenopyrite-type phases, respectively. The measured infrared reflectivity (Rsd) for MnSe2 showed a drastic increase at pressures between 13 and 20 GPa, but became insensitive to pressure under further compression, implying a pressure-induced transition from an insulator to metallic state.

In situ X-ray diffraction and Raman scattering experiments using a diamond anvil cell revealed that Im-3-type KSbO3 remains stable up to 40.5 GPa with a bulk modulus K0 = 101.6 (7) GPa. Rietveld st...

Significance The presence of extra reducer was thought to be essential for producing natural diamonds from reduction of carbonates. The present study of the Xiuyan meteoritic crater, however, finds natural diamond formation via a subsolidus self-redox of a ferromagnesian carbonate during shock compression to 25–45 GPa and 800–900 °C without melting, fluid, and another reductant. The ability of carbonate to produce diamond by itself implies that diamond would be a very common mineral in the lower mantle where the carbonates are abundant and pressures and temperatures are sufficiently high., Formation of natural diamonds requires the reduction of carbon to its bare elemental form, and pressures (P) greater than 5 GPa to cross the graphite–diamond transition boundary. In a study of shocked ferromagnesian carbonate at the Xiuyan impact crater, we found that the impact pressure–temperature (P-T) of 25–45 GPa and 800–900 °C were sufficient to decompose ankerite Ca(Fe2+,Mg)(CO3)2 to form diamond in the absence of another reductant. The carbonate self-reduced to diamond by concurrent oxidation of Fe2+ to Fe3+ to form a high-P polymorph of magnesioferrite, MgFe3+2O4. Discovery of the subsolidus carbonate self-reduction mechanism indicates that diamonds could be ubiquitously present as a dominant host for carbon in the Earth’s lower mantle.

The compression behavior of zircon-type DyVO4 has been investigated in a diamond anvil cell by angle-dispersive X-ray diffraction (ADXRD) at high pressures up to 36.4 GPa. Under quasi-hydrostatic compression with argon as the pressure transmitting medium, DyVO4 underwent a sluggish zircon-to-scheelite phase transformation that started at approximately 8.0 GPa and was completed at 15.3 ± 0.9 GPa. The scheelite-type phase remained stable at pressures up to 25.3 GPa and during the process of decompression to ambient conditions, implying that the zircon-to-scheelite transformation is irreversible. Fitting the pressure-volume data using the third-order Birch-Murnaghan equation of state yielded a bulk modulus B 0 = 129 (7) GPa and a pressure derivative of bulk modulus B ′ = 3.4 (4) for the zircon-type phase, and B 0 = 184 (10) GPa and B ′ = 5.3 (8) for the scheelite-type phase. When compressed in a methanol-ethanol (4:1) pressure transmitting medium, DyVO4 was transformed into the scheelite-type phase at a pressure of 8.8 ± 1.1 GPa and then transformed into a fergusonite-type phase at 21.3 ± 1.6 GPa. The scheelite-to-fergusonite transformation was reversible during decompression. Our study indicates that DyVO4 under compression experiences a sequential zircon-scheelite-fergusonite phase transformation and that the scheelite-fergusonite transformation is sensitive to nonhydrostatic conditions.

The comprehension of structural behaviors in double perovskites is crucial for their functional optimization, especially when applying external regulations. Here, to inquire about potential structures with better magnetic performance, high-pressure phase transformation in double perovskite Ba2SmBiO6 was first investigated up to 50 GPa via in situ high-pressure x-ray diffraction and Raman spectroscopy. A pressure-induced phase transition from cubic Fm-3m to orthorhombic Pnma is discovered at 4.8 GPa, accompanied by the splitting of the diffraction peaks. Above 19.8 GPa, the new phase becomes distorted as shown by the peak recombination and broadening. The variation of Raman spectra also confirms the formation and distortion of the high-pressure phase during compression, through the evolution of Bi–O stretching, Bi–O bending, octahedral rotation, and Ba-sites translation modes. The analysis of tilt angles and distortion factor evinced that the octahedral BiO6 tilting is the key factor for the phase transition occurrence. Based on the Mulliken populations analyses, the Bi–O bonds undergo a covalent-ionic-antibonding transition across the phase transition under compression. Our exploration of the phase transition mechanism guides the modulation of the magnetic and electronic properties under extreme conditions.

Nanoceramics may have different structural and physical properties compared to their coarse-grained counterparts. Here, we report the high-pressure study of micro- and nano-crystalline MgAl2O4 in order to examine the effect of particle size on the structural stability. A reversible pressure-induced phase transition (cubic to tetragonal) is observed in MgAl2O4 nanocrystals under non-hydrostatic pressure at room temperature, in contrast to the previously reported structural transition of MgAl2O4 at high pressure and high temperature. It is also found that the compressed MgAl2O4 microcrystals do not fracture further below 60 nm, suggesting a plastic deformation mechanism transition. MgAl2O4 with a grain size above ∼60 nm exhibits normal cracking behaviors, but shows metal-like plastic deformation behaviors below this critical size. It is implied that combined ductility and strength can be achieved in nanoceramic MgAl2O4.

Herein, we report the intriguing electrical transport and structural properties of compressed Alq3, which is an extensively used electron transport material in OLEDs. The bulk resistance (Rb) of Alq3 increases with uploading pressure, but drops markedly when the uploading pressure is above 8.6 GPa. In contrast, the grain boundary resistance (Rgb) varies smoothly below 16.4 GPa. With further compression, both Rb and Rgb increase with the amorphization of Alq3. The pressure-induced amorphization is found to be reversible at a low density amorphous state, while it is irreversible at a higher density state. Interestingly, XRD measurements indicate no structural transition at ∼8.0 GPa. The variation of Rb is found to be synchronous with the blue-shift of the Al–oxine deformation mode, which rationalizes the anomalous changes of Rb. The Al–oxine interaction is believed to be also significant in the electrical transport properties of dense Alq3, which provides insight into the correlation between its structural changes and electrical transport properties.

Nanocrystalline magnesium aluminate was synthesized with the coprecipitation method. Its growing behaviors as a function of temperature were studied with synchrotron X-ray diffraction (XRD) and Raman spectroscopy. It is found that the particle growth was greatly inhibited at temperatures below 1000 °C due to the hydroxide precursor reactants. Above 1000 °C, magnesium aluminate nanoparticles start to grow fast. After two hours annealing at 1200 °C, the grain size changes by multiple folds, suggesting that oriented attachment may occur. Above 1200 °C, the grain size changes in various directions are much smaller than the average grain size, indicating the oriented attachment mechanisms become inactive in the growth of MgAl2O4 nanoparticles with sizes larger than 42 nm.

The high-pressure minerals of reidite and coesite have been identified in the moderately shock-metamorphosed gneiss (shock stage II, 3545GPa) and the strongly shock-metamorphosed gneiss (shock stage III, 4555GPa), respectively, from the polymict breccias of the Xiuyan crater, a simple impact structure 1.8km in diameter in China. Reidite in the shock stage II gneiss displays lamellar textures developed in parental grains of zircon. The phase transformation of zircon to reidite likely corresponds to a martensitic mechanism. No coesite is found in the reidite-bearing gneiss. The shock stage III gneiss contains abundant coesite, but no reidite is identified in the rock. Coesite occurs as acicular, dendritic, and spherulitic crystals characteristic of crystallization from shock-produced silica melt. Zircon in the rock is mostly recrystallized. The postshock temperature in the shock stage III gneiss is too high for the preservation of reidite, whereas reidite survives in the shock stage II gneiss because of relatively low postshock temperature. Reidite does not occur together with coesite because of difference in shock-induced temperature between the shock stage II gneiss and the shock stage III gneiss.

In a hydrostatic pressure environment condition and in manual milling, respectively, investigations of PbWO4-III (P21 /n) have been performed by X-ray diffraction and Raman scattering techniques. Experiments found that PbWO4-III keeps its monoclinic structure under hydrostatic pressures with the sample’s anisotropic compressibility up to 14.6 GPa, but transforms to PbWO4-I (I41 /a) in a grinding process. The stability and variability of PbWO4-III depending on the strain states were also explored by first-principles calculations of elasticity. Calculations show PbWO4-III has an anisotropic compressibility and a ductile nature with increasing pressure up to 15 GPa.

The pressure effects on plastic deformation and phase transformation mechanisms of materials are of great importance to both Earth science and technological applications. Zircon-type materials are abundant in both nature and the industrial field; however, there is still no in situ study of their deformation behavior. Here, by employing radial x-ray diffraction in a diamond anvil cell, we investigate the dislocation-induced texture evolution of zircon-type gadolinium vanadate (${\mathrm{GdVO}}_{4}$) in situ under pressure and across its phase transitions to its high-pressure polymorphs. Zircon-type ${\mathrm{GdVO}}_{4}$ develops a (001) compression texture associated with dominant slip along $⟨100⟩{001}$ starting from 5 GPa. This (001) texture transforms into a (110) texture during the zircon-scheelite phase transition. Our observation demonstrates a martensitic mechanism for the zircon-scheelite transformation. This work will help us understand the local deformation history in the upper mantle and transition zone and provides fundamental guidance on material design and processing for zircon-type materials.

A new cubic perovskite polymorph of PbGeO 3 (Phase II) was synthesized by laser heating in the diamond-anvil cell (DAC) at the pressure of 36 GPa. Fitting the Birch-Murnaghan equation of state against its observed P-V data yields a bulk modulus K 0 of 196(6) GPa and the volume V 0 of 56.70(13) A 3 when K 0 ′ is assumed being 4. After the pressure is released, the PbGeO 3 Phase II changes gradually into an amorphous phase, which contains mainly fourfold-coordinated germanium. It indicates that the PbGeO 3 Phase II with a GeO 6 octahedron framework transforms to a GeO 4 tetrahedron network during the amorphization. The existence of PbGeO 3 cubic perovskite Phase II at high pressures indicates that the polarized character of the Pb 2+ ion induced by its 6 s 2 lone pair electrons would be totally reduced in the environment of major silicate perovskites inside the lower mantle, and thus the Pb atom would substitute the Ca atom to enter the CaSiO 3 perovskite.

BaWO4-II has been synthesized at 5 GPa and 610 degrees C. Its high pressure behavior was studied by in situ synchrotron X-ray diffraction measurements at room temperature up to 17 GPa. BaWO4-II retains its monoclinic structure. Bulk and axial moduli determined by fitting a third-order Birch-Murnaghan equation of state to lattice parameters are: K-0 = 86.2 +/- 1.9 GPa, K-0(a) = 56.0 +/- 0.9 GPa, K-0(b) = 85.3 +/- 2.4 GPa, and K-0(c) = 146.1 +/- 3.2 GPa with a fixed K' = 4. Analysis of axial compressible modulus shows that the a-axis is 2.61 times more compressible than the c-axis and 1.71 times more compressible than the b-axis. The beta angle decreases smoothly between room pressure and 17 GPa from 93.78 degrees to 90.90 degrees.

The 1.8 km-diameter Xiuyan crater is an impact structure in northeastern China, exposed in a Proterozoic metamorphic rock complex. The major rocks of the crater are composed of granulite, hornblendite, gneiss, tremolite marble, and marble. The bottom at the center of the crater covers about 100 m thick lacustrine sediments underlain by 188 m thick crater-fill breccia. A layer of polymict breccia composed of clasts of granulite, gneiss, hornblendite, and fragments of glass as well as clastic matrix, occurs near the base, in the depth interval from 260 to 295 m. An investigation in quartz from the polymict breccia in the crater-fill units reveals abundant planar deformation features (PDFs). Quartz with multiple sets of PDFs is found in clasts of granulite that consist of mainly quartz and feldspar, and in fine-grained matrix of the impact-produced polymict breccia. A universal stage was used to measure the orientation of PDFs in 70 grains of quartz from five thin sections made from the clasts of granulite of polymict breccia recovered at the depth of 290 m. Forty-four percent of the quartz grains contain three sets of PDFs, and another 40% contain two sets of PDFs. The most abundant PDFs are rhombohedron forms of pf10 12g, xf10 13g ,a ndr=zf10 11g with frequency of 33.5, 22.3, and 9.6%, respectively. A predominant PDF form of f10 12g in quartz suggests a shock pressure >20 GPa. The occurrence of PDFs in quartz from the polymict breccia provides crucial evidence for shock metamorphism of target rocks and confirms the impact origin of this crater, which thus appears to be the first confirmed impact crater in China.

The well-preserved 1.8-km-diameter Xiuyan crater is located in the low mountain-hill region of the northern part of Liaodong Peninsula of northern China. Recently, a 307-m-deep borehole at the centre of crater became available. After penetrating 107 m lacustrine sediments, a breccia lens about 188 m in thickness was encountered. The crater-fill breccia is deposits of rock clasts and fragments more or less shock-metamorphosed. The features of geological structure and stratigraphic configuration within the crater, shock-melted rocks, and PDFs in quartz found in the basement rocks close to the crater rim and in the crater-fill breccia provide clear evidence for an impact origin of the Xiuyan crater.

To achieve early diagnosis for inheritable hearing loss and determine carrier rate of deafness causing gene mutations in order to provide information for premarital, prenatal and postnatal genetic counseling.A total of 17 000 dried heel blood spots of normal newborns in Chengdu were collected with informed consent obtained from their parents. Genomic DNA was extracted from dried blood spots using Qiagen DNA extraction kits. Microarrays with 9 common mutation loci of 4 deafness-associated genes in Chinese population were used. Nine hot mutations including GJB2 (35delG, 176del16, 235delC and 299delAT), GJB3 (538CT), SLC26A4 (IVS 7-2AG, 2168AG), and mitochondrial DNA 12S rRNA (1555AG, 1494CT) were detected by PCR amplification and microarray hybridization. Mutations detected by microarray were verified by Sanger DNA sequencing.Of the 17 000 new-borns, 542 neonates had mutations of the 4 genes. Heterozygous mutations of GJB2, at 235delC, 299delAT, and 176del16 were identified in 254, 55, and 15 newborns, respectively. Two newborns had homozygous mutation of GJB2, 235delC. Heterozygous mutations at 538CT of GJB3, 2168AG and IVS 7-2AG of SLC26A4 were found in 23, 17 and 128 newborns, respectively. For mutation analysis of mitochondrial DNA 12S rRNA, 1494CT and 1555AG were homogeneous mutations in 4 and 42 neonates, respectively. In addition, 6 complexity mutations were detected, which demonstrated that one newborn had heterozygous mutations at GJB2 235delC and SLC26A4, IVS7-2AG, one had heterozygous mutation GJB2 235delC and 12S rRNA homogeneous mutation, 1555 AG, one heterozygous mutations at GJB2, 299delAT, and GJB3, 538CT, one at GJB2, 299delAT and 12S rRNA, 1555 AG, two at GJB2, 299delAT, and SLC26A4, IVS7-2AG. All mutations as above were confirmed by DNA sequencing.The total mutation carrier rate of the 4 deafness genes is 3.19% in healthy newborns at Chengdu. Mutations of GJB2 and SLAC26A4 are major ones (86.5% of total). The mutation rate of mitochondrial DNA 12S rRNA is 2.71‰, which may have deafness induced by aminoglycoside antibiotics. Newborn screening for mutation of genes related to hereditary deafness plays an important role in the early detection and proper management for neonatal deafness as well as genetic counseling for premarital, prenatal and postnatal diagnosis.

When cubic PbCrO 3 perovskite (Phase I) is squeezed up to ∼1.6 GPa at room temperature, a previously undetected phase (Phase II) has been observed with a 9.8% volume collapse. Because the structure of Phase II can also be indexed into a cubic perovskite as Phase I, the transition between Phases I and II is a cubic to cubic isostructural transition. Such a transition appears independent of the raw materials and synthesizing methods used for the cubic PbCrO 3 perovskite sample. In contrast to the high-pressure isostructural electronic transition that appears in Ce and SmS, this transition seems not related with any change of electronic state, but it could be possibly related on the abnormally large volume and compressibility of the PbCrO 3 Phase I. The physical mechanism behind this transition and the structural and electronic/magnetic properties of the condensed phases are the interesting issues for future studies.

In this article, we present the abnormal compression and plastic behavior of germanium during the pressure-induced cubic diamond to β-tin structure transition. Between 8.6 GPa and 13.8 GPa, in which pressure range both phases are co-existing, first softening and followed by hardening for both phases were observed via synchrotron x-ray diffraction and Raman spectroscopy. These unusual behaviors can be interpreted as the volume misfit between different phases. Following Eshelby, the strain energy density reaches the maximum in the middle of the transition zone, where the switch happens from softening to hardening. Insight into these mechanical properties during phase transformation is relevant for the understanding of plasticity and compressibility of crystal materials when different phases coexist during a phase transition.

We report an anomalous phase transition in compressed In2Se3. The high-pressure studies indicate that In2Se3 transforms to a new isosymmetric R-3m structure at 0.8 GPa whilst the volume collapses by ∼7%. This phase transition involves a pressure-induced interlayer shear glide with respect to one another. Consequently, the outer Se atoms of one sheet locate into the interstitial sites of three Se atoms in the neighboring sheets that are weakly connected by van der Waals interaction. Interestingly, this interlayer shear glide changes the stacking sequence significantly but leaves crystal symmetry unaffected. This study provides an insight to the mechanisms of the intriguing isosymmetric phase transition.

Nearly all displacive transitions have been considered to be continuous or second order, and the rigid unit mode (RUM) provides a natural candidate for the soft mode. However, in-situ X-ray diffraction and Raman measurements show clearly the first-order evidences for the scheelite-to-fergusonite displacive transition in BaWO4: a 1.6% volume collapse, coexistence of phases, and hysteresis on release of pressure. Such first-order signatures are found to be the same as the soft modes in BaWO4, which indicates the scheelite-to-fergusonite displacive phase transition hides a deeper physical mechanism. By the refinement of atomic displacement parameters, we further show that the first-order character of this phase transition stems from a coupling of large compression of soft BaO8 polyhedrons to the small displacive distortion of rigid WO4 tetrahedrons. Such a coupling will lead to a deeper physical insight in the phase transition of the common scheelite-structured compounds.

Raman spectrum and angle-dispersive x-ray diffraction (ADXD) measurements have been performed to investigate the effects of high temperature on the high-pressure behavior of bulk CeO 2 . A phase transformation of CeO 2 from fluorite to PbCl 2 -type structure occurs at 12.0 GPa and is completed at 14.2 GPa after the sample is heated, and the phase transition pressure decreases by nearly 20 GPa compared with that at room temperature. On decompression, the high-pressure phase of CeO 2 remains down to 2.2 GPa, and it changes back to a cubic structure at ambient conditions. At a pressure of 22.1 GPa, a 6.4% lattice volume difference between the fluorite and PbCl 2 -type structures was observed. The lattice volume of fluorite phase obtained in the areas that have been heated is about 1% less than that obtained in the areas that have not been heated. Besides prompting the phase transition of CeO 2 , high temperature also anneals the sample and leads a small reduction in lattice volume of the fluorite phase. The zero-pressure bulk modulus of the fluorite phase of CeO 2 after annealing is calculated to be about 200 GPa with an assumed pressure derivative of four, which is smaller than that of former x-ray diffraction experiments at room temperature.