Isotropic Thermal Expansivity and Anisotropic Compressibility of ReB₂

We experimentally investigated some of the mechanical properties of ReB₂ under high temperature/pressure (T/P) conditions. High-T experiments (up to 600°C at 1 atm) were carried out in a high-T oven attached to a conventional x-ray diffractometer and high-P experiments (up to about 42 GPa at 25°C) were conducted in a diamond-anvil cell using synchrotron x-ray radiation. The high-T data for ReB₂ suggests a highly isotropic thermal expansivity, whereas the high-P data suggests a highly anisotropic compressibility.