Elastic anisotropy and thermodynamic properties of iron tetraboride under high pressure and high temperature

First principles calculations are performed to investigate the elastic anisotropy and thermodynamic properties of the recently synthesized iron tetraboride (FeB4) under high pressure and high temperature. The obtained normalized crystal parameters dependence of the resulting pressure are in excellent agreement with experimental data. Young׳s modulus and shear modulus as a function of crystal orientations have been systematically investigated. The obtained results reveal that the FeB4 exhibits a pronounced elastic anisotropy and it is stiffest along [110] and the most compliant along [100] in response to tension or compression loading. Using a set of total energy versus volume obtained with the first-principles calculations, the quasiharmonic Debye model is applied to the study of the thermal and vibrational effects. The dependences of Debye temperature, Grüneisen parameter, heat capacity, and expansion coefficient on the temperature and pressure are systematically explored in the whole pressure range from 0 to 30 GPa and temperature range from 0 to 1800 K.