Optical vibrations of impurity and host ions in mixed crystals

Abstract

We reported a theoretical investigation of the ideal strengths, dynamical and thermodynamic properties of the CrB-type CaXIV (XIV = Si, Ge, and Sn) alkaline-earth metal compounds by employing density functional theory (DFT) and density functional perturbation theory (DFPT). The calculated ideal tensile strengths have the sequence of CaSi > CaGe > CaSn for these intermetallic compounds along the [100], [010], and [001] high-symmetry lines. The present results mean the tensile and shear abilities of CaSi are best, followed by CaGe and CaSn calcium-based compounds. Based on the linear response method within DFPT, the full phonon dispersion curves and the phonon densities of state of the CaXIV (XIV = Si, Ge, and Sn) intermetallic compounds are investigated systematically. Furthermore, the Raman-active and Infrared-active phonon modes at Г point of Brillouin Zone (BZ) center are assigned combining with the point group theory. Our calculated results indicate that three calcium-based compounds are all dynamically stable at ambient conditions. Additionally, within the calculated vibration phonon densities of states, the thermo-physical properties of three calcium-based compounds such as the vibration internal energy, Helmholtz free energy, the lattice entropy and the lattice heat capacity have been also obtained. These investigations serve for new references for further synthesis of various calcium-based alkaline-earth metal compounds.