Variability of Young’s modulus and Poisson’s ratio of hexagonal crystals

In this paper, the variability of elastic characteristics (Young's modulus and Poisson's ratio) of hexagonal crystals has been studied. Analytic expressions for Young's modulus and Poisson's ratio are obtained. Stationary values for these elastic characteristics are found. Young's modulus has three stationary values, and Poisson's ratio has eight stationary values. Numerical analysis of these elastic characteristics for hexagonal crystals is given based on the experimental data from the Landolt-Bornstein handbook. Global extrema of Young's modulus and Poisson's ratio for hexagonal crystals are found. Crystals are found in which the maximum values exceeds the upper limit for isotropic materials.