Theoretical Study of Compressibility and Thermoelasticity of LaNi_5-xAl_x (x=0.3, 0.5 and 1.0)

The compressibility, the temperature dependence of bulk modulus, the pressure dependence of normalized volume V/V₀, thermal expansion coefficient and Debye temperature of LaNi_5-xAl_x compounds are successfully obtained using the first-principles plane-wave pseudopotential (PW-PP) method, the EOSFIT6.0 software and the quasi-harmonic Debye model. The rapid decrease of relative lattice constant a/a₀ shows that the deformation is easier in directions normal to the c-axis than that along it. The relationships between bulk modulus B and pressure at different temperatures are also analysed. It is found that the bulk modulus B increases monotonically with increasing pressure. Moreover, the pressure dependences of thermal expansion and Debye temperature are also successfully obtained. The calculated results are in agreement with the experimental data.