Influence of alloying and structural transition on the directional elastic and isotropic thermodynamic properties of wurtzite and layered hexagonal ScxAl1−xN crystals

Abstract

The structural, elastic, and basic thermodynamic properties of hexagonal Sc xAl1−xN crystals are calculated and discussed over the whole range of possible random alloys, including the transition from wurtzite to the layered hexagonal structure. Based on a review of lattice and internal parameters in combination with complete datasets of stiffness coefficients published in the literature, differing in the considered alloying intervals and the predicted structural transitions, changes in the crystal lattices caused by the substitution of aluminum by scandium atoms are discussed and illustrated. Crystal properties like the mass densities, average bond angles, and bond lengths are calculated, and the compliance coefficients, Young's modulus, shear modulus, Poisson's ratio, compressibility, and sound velocities are determined depending on the alloy composition and in relation to the orientation of crystal planes and axes. Particular attention is paid to the occurring directional anisotropies and the changes in structural and elastic properties in the alloy region of the structural transition between wurtzite and layered hexagonal Sc xAl1−xN crystals. The acoustic velocities determined are used to calculate basic thermodynamic properties such as the Debye temperature, heat capacity, and minimum heat conduction, as well as to evaluate both the influence of the alloying and the structural transition on these properties.