Title: First principle study of structural, elastic, electronic and optical properties of Pb_0.5Sn_0.5TiO₃ and Pb_0.5Sn_0.5Ti_0.5(Zr_0.5)O₃
Author(s):

	S.G. Kuma (Department of Physics, Wollega University, P.O.Box 395, Nekemte, Ethiopia),
	M.M. Woldemariam (Department of Physics, Jimma University, P.O.Box 378, Jimma, Ethiopia)

The structural, electronic, elastic and optical properties of tetragonal (P4mm) phase of Pb_0.5Sn_0.5TiO₃ (PSTO) and Pb_0.5Sn_0.5Ti_0.5(Zr_0.5)O₃ (PSTZO) are examined by first-principles calculations based on the density functional theory (DFT) using the pseudo-potential plane wave (PP-PW) scheme in the frame of generalized gradient approximation (GGA). We have calculated the ground state properties such as equlibrium lattice constants, volume, bulk modulus and its pressure derivative. From elastic constants, mechanical parameters such as anisotropy factor, elastic modulus and Poisson's ratio are obtained from the Voigt-Reuss-Hill average approximation. Rather than their averages, the directional dependence of elastic modulus, and Poisson's ratio are modelled and visualized in the light of the elastic properties of both systems. In addition, some novel results, such as Debye temperatures, and sound velocities are obtained. Moreover, we have presented the results of the electronic band structure, densities of states and charge densities. These results were in favourable agreement with the existing theoretical data. The optical dielectric function and energy loss spectrum of both systems are also computed. Born effective charge (BEC) of each atoms for both systems is computed from functional perturbation theory (DFPT). Finally, the spontaneous polarization is also determined from modern theory of polarization to be 0.8662 C/m² (PSTO) and 1.0824 C/m² (PSTZO).

Key words: DFT, PSTO and PSTZO, electronic, elastic and optical properties

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