Elasticity of nanocrystalline kyanite at high pressure and temperature from ultrasonic and synchrotron X-ray techniques

Material properties, such as elasticity data at wide-ranging conditions of pressure and temperature, attract increasing attention for material and earth sciences. In particular, polycrystalline ceramics for next-generation photonic applications are nowadays fabricated by advanced syntheses techniques operating under elevated pressures and temperatures. Herein, the elastic properties of a synthetic transparent and reinforced aluminosilicate nanoceramic composed of triclinic kyanite with minor amounts of trigonal α-alumina crystals are investigated using in situ synchrotron X-ray diffraction and ultrasonic techniques at high-pressure (up to 11 GPa) and high-temperature (300-1500 K) conditions. This not only enables the determination of the equation of state (EoS) parameters by applying the pressure-volume-temperature (P-V-T) data to the high-temperature Birch-Murnaghan EoS but also yields the elastic moduli together with their P and T derivatives from the fit of the compressional and shear wave velocities to a finite strain EoS: K_S0,300 = 186(2) GPa, K′_S0,300 = 7.2(6), (∂K_S0,300/∂T)_P = −0.023(2) GPa K⁻¹, G_0,300 = 125(1) GPa G′_0,300 = 2.3(2), (∂G_0,300/∂T)_P = −0.017(1) GPa K⁻¹. On the basis of our acquired results, we propose to predict the elastic moduli of aluminosilicate ceramics by a linear function of the ratio of AlO₆ octahedra and SiO₄ tetrahedra within the constituting phases.