First principles study and comparison of vibrational and thermodynamic properties of X Bi (X = In, Ga, B, Al)

In the present work, vibrational and thermodynamic properties of XBi ($X=B$, Al, Ga, In) compounds are compared and investigated. The calculation is carried out using density functional theory (DFT) within the generalized gradient approximation (GGA) in a plane wave basis, with ultrasoft pseudopotentials. The lattice dynamical properties are calculated using density functional perturbation theory (DFPT) as implemented in Quantum ESPRESSO (QE) code. Thermodynamic properties involving phonon density of states (DOS) and specific heat at constant volume are investigated using quasi-harmonic approximation (QHA) package within QE. The phonon dispersion diagrams for InBi, GaBi, BBi, and AlBi indicate that there is no imaginary phonon frequency in the entire Brillouin zone, which proves the dynamical stability of these materials. BBi has the highest thermal conductivity and InBi has the lowest thermal conductivity. AlBi has the largest and GaBi has the smallest reststrahlen band which somehow suggests the polar property of XBi materials. The phonon gaps for InBi, GaBi, BBi and AlBi are about 160 cm⁻¹, 150 cm⁻¹, 300 cm⁻¹, and 150 cm⁻¹, respectively. For all compounds, the three acoustic modes near the gamma point have a linear behavior. C _V is a function of $T^3$ at low temperatures while for higher temperatures it asymptotically tends to a constant as expected. (paper)