Elastic Moduli of Single-Crystal CaSnO3 Perovskite, end-member of Megawite: Bridging Experimental and Computational Approaches

Megawite, a recently discovered perovskite-structured mineral with Ca(Ti_0.07, Sn_0.6, Zr_0.33)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.