Raman scattering and x-ray diffraction studies of CaSnO3 perovskite were performed under high-pressure conditions. This high-pressure study was motivated by a recent theoretical study predicting a phase transition in CaSnO3 from GdFeO3-type perovskite to CaIrO3-type structure occurred at 12 GPa. Despite no obvious structure change up to a pressure of 26 GPa based on the x-ray diffraction data, high pressure Raman measurements revealed that some Raman modes disappeared upon compression; either merging into neighboring bands or vanishing. The signals for these Raman peaks were recovered during decompression. The measured pressure derivative of Raman shift (∂ν/∂P) of CaSnO3 ranged from ∼1.29 to ∼4.35, up to 20 GPa. Due to the lack of lattice dynamic study for CaSnO3 perovskite, the mode symmetry for CaSnO3 was tentatively assigned based on the empirical relation among Ca-bearing perovskites. The pressure derivative of the Raman shifts was found to be related to their mode vibrations: modes related to Ca and O shifts had a strong pressure dependence compared with those associated with oxygen octahedral rotation.

The crust of Venus is composed of the low lying volcanic planitiae and the elevated, deformed tesserae. It is thought that the tesserae may be composed of silicic igneous rocks and that it may resemble proto-continental crust. The initial development of terrestrial continental crust is likely due to melting and deformation of primitive mafic crust via mantle-plume upwelling and collisional plate processes. Unlike Earth, the lithosphere of Venus is not divided into plates and therefore evolved continental crust, if present, developed primarily by melting of pre-existing mafic crust. Here, we report the results of high pressure equilibrium partial melting experiments using a parental composition similar to the basalt measured at the Venera 14 landing site in order to determine if silicic melts can be generated. It was found that at pressures of 1.5 GPa and 2.0 GPa and temperatures of 1080 °C, 1090 °C, and 1285 °C that tonalitic and granodioritic melts can be generated. The experimental results indicate that silicic rocks may be able to form in the crust of Venus providing the thermal regime is suitable and that the lower crust is basaltic. The implication is that the older, thicker regions of Venusian crust may be partially composed of silicic igneous rocks.

A suite of hydrous orthoenstatite crystals were synthesized at 5–7 GPa and 1100–1300 °C, corresponding to the mid upper mantle conditions in continental regions. The synthetic crystals presented a clear, inclusion-free, and euhedral form with a size range from 100 to a few hundred microns. The Al- and water content of crystals were less than 2 wt. % and ranging from ~500 ppm to 1000 ppm, respectively, characterized by Raman and IR spectroscopy, electron microscopy, and SIMS. The analysis shows that the capability of water incorporation for this suite of hydrous orthoenstatite is correlated to the Al-content in the crystal structure. To understand how the detailed crystal structure reflects the influence of water and Al, single crystal X ray diffraction analysis was performed for this suite of hydrous orthoenstatite. By comparing the results obtained at ambient conditions, we find that for low-level of Al-content, <2 wt. %, the Al³⁺ cation tends to occupy one of tetrahedral sites (TB) only. Analysis of the X ray diffraction results under high pressure indicates that the elasticity of orthoenstatites is insensitive to the presence of low-level water and Al. We use this finding to evaluate the velocity profile at the mid upper mantle of continental regions to compare with seismic observation. The comparison indicates that the cause of the low velocity zone in continental regions originates from the geotherm profile rather than the effect of water on the elasticity of mantle phases.

In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopic experiments of scottyite, BaCu₂Si₂O₇, were carried out in a diamond anvil cell up to 21 GPa at room temperature. X-ray diffraction patterns reveal four new peaks near 3.5, 3.1, 2.6 and 2.2 Å above 8 GPa, while some peaks of the original phase disappear above 10 GPa. In the Raman experiment, we observed two discontinuities in dν/dP, the slopes of Raman wavenumber (ν) of some vibration modes versus pressure (P), at approximately 8 and 12 GPa, indicating that the Si-O symmetrical and asymmetrical vibration modes change with pressure. Fitting the compression data to Birch–Murnaghan equation yields a bulk modulus of 102 ± 5 GPa for scottyite, assuming K_o′ is four. Scottyite shows anisotropic compressibility along three crystallographic axes, among which c-axis was the most compressible axis, b-axis was the last and a-axis was similar to the c-axis on the compression. Both X-ray and Raman spectroscopic data provide evidences that scottyite undergoes a reversible phase transformation at 8 GPa.

Megawite, a recently discovered perovskite-structured mineral with Ca(Ti0.07, Sn0.6, Zr0.33)O3, was identified in a xenolith. Its end members, CaTiO3, CaSnO3, and CaZrO3, represent GdFeO3-type perovskites (A2+B4+O3), which have garnered significant attention for their structural and physical properties. Among these, CaSnO3 stands out due to its exceptional optical and electrical properties, supported by its high physical and chemical stability. Despite its increasing applications, critical physical properties such as the elastic moduli (Cij) of single-crystal CaSnO3 have yet to be determined experimentally. Available data on CaSnO3 elasticity stems from polycrystalline measurements or computational predictions. This gap underscores the need for experimental determination of single-crystal elastic moduli better to understand its mechanical behavior and implications for future applications.Here, we report the elastic moduli of single-crystal CaSnO3 perovskite measured using Brillouin scattering at ambient conditions. Crystals of CaSnO3 were synthesized at 1200 °C over 24 hours from a starting mixture of CaCl2 and SnO2 in a 2:1 molar ratio. Four high-quality crystals were selected for Brillouin scattering measurements. Full elastic moduli were derived via least squares regression of sound velocity data against the Christoffel equation. The obtained values for the elastic moduli include longitudinal moduli (C11, C22, C33) ranging from 270 to 290 GPa, shear moduli (C44, C55, C66) between 90 and 98 GPa, and off-diagonal moduli (C12, C13, C23) ranging from 100 to 120 GPa. These measurements' aggregate bulk modulus, shear modulus, and sound velocities align well with previous polycrystalline results obtained through ultrasonic interferometry (Kung et al., 2001; Schneider et al., 2008).A key step in Brillouin scattering data analysis is the establishment of an initial Cij model. For a new material such as CaSnO3, setting up an effective starting model requires experience. In this study, the starting Cij model was derived from density functional theory (DFT) computations to serve the purpose. Elasticity and electronic ground states were calculated using the CASTEP code integrated within the Materials Studio software package. These calculations employed LDA, GGA, and mGGA functionals, with norm-conserving and ultrasoft pseudopotentials modeling electron-ion interactions. The computationally predicted Cij values served as the initial input for data fitting. The final best-fit Cij model was determined by minimizing residual differences across iterative fitting steps. The close agreement between experimental and computational results highlights the utility of computational predictions as a starting point for Brillouin scattering analyses.This study presents the first experimental determination of the elastic moduli for single-crystal CaSnO3 perovskite, supported by computational insights. The integration of experimental and computational approaches offers a robust framework for characterizing the mechanical properties of new materials. Our findings contribute to the broader understanding of perovskite materials, with implications for geosciences and advanced material applications.