High-pressure dynamic, thermodynamic properties, and hardness of CdP₂

Using a pseudopotential plane-waves method, we calculate the phonon dispersion curves, thermodynamic properties, and hardness values of α-CdP₂ and β-CdP₂ under high pressure. From the studies of the phonon property and enthalpy difference curves, we discuss a phase transform from β-CdP₂ to α-CdP₂ in a pressure range between 20 GPa and 25 GPa. Then, the thermodynamic properties, Debye temperatures, and heat capacities are investigated at high pressures. What is more, we employ a semiempirical method to evaluate the pressure effects on the hardness for these two crystals. The results show that the hardness values of both α-CdP₂ and β-CdP₂ increase as pressure is increased. The influence mechanism of the pressure effect on the hardness of CdP₂ is also briefly discussed.