Doping induced phase transition, elastic, electronic, vibrational and thermal properties of LiBeA_1—xSb_x (A= P and As)

ABSTRACT

Phase transition, elastic, electronic, vibrational and thermal properties of ${\mathrm{L}\mathrm{i}\mathrm{B}\mathrm{e}\mathrm{A}}_{1-x}{\mathrm{S}\mathrm{b}}_x$ (A = P and As) are investigated via performing ab-initio calculations combined with the virtual crystal approximation (VCA) and the quasi-harmonic Debye model. Our total energy results show that ${\mathrm{L}\mathrm{i}\mathrm{B}\mathrm{e}\mathrm{A}\mathrm{s}}_{1-x}{\mathrm{S}\mathrm{b}}_x$ and ${\mathrm{L}\mathrm{i}\mathrm{B}\mathrm{e}\mathrm{P}}_{1-x}{\mathrm{S}\mathrm{b}}_x$ undergo a phase transition from the ${\mathrm{C}\mathrm{u}}_2\mathrm{S}\mathrm{b}$ (P4/nmm) phase to the polar LiGaGe (P$6_{3}mc$) one beyond antimony concentration of x = 0.21 and 0.36, respectively. The calculated elastic constants show that the studied alloys are mechanically stable and they also exhibit abrupt discontinuities at the transition concentrations. From Poisson's ratio and the B/G ratio, both alloys are brittle. Our results indicate that the studied alloys are semiconductors and the gap value decreases as Sb concentration increases. The calculated phonon dispersion curves for different antimony concentrations have positive frequencies. The phonon frequencies at the zone centre for the Raman-active and infrared-active modes are predicted for the ${\mathrm{C}\mathrm{u}}_2\mathrm{S}\mathrm{b}$ and the LiGaGe structures for different antimony concentrations. The value of the polarisation is almost constant for different values of concentration. The variations of thermal expansion coefficient (α), bulk modulus (B), Debye temperature (${\mathrm{\Theta }}_D$), heat capacities at constant volume (C${}_v$) and the $Gr\ddot{u}neisen$ parameter (γ) as a function of pressure and temperature were all obtained and analysed in detail.

KEYWORDS:

• Ab initio calculations
• phase transitions
• electronic properties
• lattice dynamics
• thermodynamic properties

Acknowledgments

Part of this work is performed at the High Performance Computing Center of the University 8 mai 1945 Guelma, Algeria.

Disclosure statement

No potential conflict of interest was reported by the author(s).