First-principles study of phase transition and elastic properties of XBi (X = Ce, Pr) compounds

The pressure-induced phase transitions of CeBi and PrBi compounds were investigated by using full-potential linearized augmented plane-wave (FP-LAPW) method. The calculations indicate that the transition pressure for CeBi compound from the NaCl-type (B1) structure to the body centered tetragonal (BCT) structure are 11.53 GPa from total energy (E)-volume (V) data and 6.48 GPa from equal Gibbs free energy (G). For PrBi compound, the same phase transition sequence occurred at 10.94 GPa obtained from the slope of the common tangent of E-V curves and 6.04 GPa from the equal G. The detailed structural changes during the phase transition were analyzed. From the elastic constants at zero pressure, we can conclude that B1 phase of XBi (X = Ce, Pr) compounds are mechanical stable, consistent with the experimental observations.