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 S 0,300  = 186(2) GPa, K ′ S 0,300  = 7.2(6), (∂ K S 0,300 /∂ 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 AlO 6 octahedra and SiO 4 tetrahedra within the constituting phases.