Eur. Phys. J. B (2017) 90: 254
https://doi.org/10.1140/epjb/e2017-80508-6

Regular Article

Ab initio study of phonon dispersion and thermodynamic properties of pure and doped pyrites

¹ Department of Physics, Federal University of Agriculture, PMB 2240, Abeokuta, Nigeria
² Physics with Electronics Unit, Moshood Abiola Polytechnic, PMB 2210, Abeokuta, Nigeria
³ National Institute for Theoretical Physics, Mandelstam Institute for Theoretical Physics, School of Physics University of Witwatersrand, Johannesburg, Wits 2050, South Africa
⁴ Department of Computer Science, Federal University of Agriculture, PMB 2240, Abeokuta, Nigeria

^a e-mail: adebayo@daad-alumni.de

Received: 6 September 2017
Received in final form: 26 October 2017
Published online: 18 December 2017

Abstract

Pyrites (FeS₂) are solid minerals that are found abundantly in Nigeria and are easy to prepare in laboratories. In this work, FeS₂ is studied extensively in its pure state as well as when iron is substitutionally doped with zinc and calcium at concentrations of 0, 0.25, 0.5, 0.75 and 1. Using density functional theory, the eectronic, dynamic and thermodynamic properties were calculated. The results revealed that the lattice parameters and bulk modulus increases with increasing concentration and the obtained values are in agreement with available experimental and theoretical values. Though pyrite, when doped with zinc, obeys Vegard’s law, doping with calcium revealed pronounced deviation from this law. The calculated band structures showed that FeS₂ has an indirect band gap whose size decreases after introducing zinc while doping with calcium increases the band gap. The phonon dispersion of the end members FeS₂ and ZnS₂ indicate that the systems are dynamically stable while CaS₂ is dynamically unstate. Also, the thermodynamic properties of the pure and doped pyrites were calculated and the ranges of temperature at which the lattice and electronic degrees of freedom contribute to the specific heat capacity are presented.