First-principles calculations of vibrational and optical properties of half-Heusler NaScSi
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ORIGINAL PAPER
First-principles calculations of vibrational and optical properties of halfHeusler NaScSi I Kars Durukan* and Y Oztekin Ciftci Department of Physics, Faculty of Science, Gazi University, 06500 Ankara, Turkey Received: 22 September 2019 / Accepted: 09 June 2020
Abstract: Ab initio calculation of the structural, mechanical, dynamic, thermodynamic, electronic, and optical properties of cubic half-Heusler compound NaScSi have been reported using density functional theory. Generalized gradient approximation has been used as the exchange and correlation potential for investigating these properties. The lattice constant, bulk modulus, the first pressure derivative of bulk modulus, and band gap of NaScSi have been calculated and compared to the previous XScSi (X = Na, Li, Ag, K) studies. The band structure and corresponding density of states have also been determined and analyzed. The elastic properties of the compound, calculated by the strain–stress method, satisfy the mechanical stability conditions for a cubic structure. According to the data obtained from the vibration properties, the compound is also stable dynamically. Additionally, heat capacity, entropy, and free energy of NaScSi have been calculated by using the phonon frequencies. The optical investigation of the compound shows high reflectivity in the UV region of the photon energy. Keywords: Half-Heusler compounds; Electronic properties; Optical properties; NaScSi
1. Introduction Heusler compounds have been studied both experimentally and theoretically [1–4] since they were discovered. These compounds are an intermetallic class consisting of three elements in 1:1:1 (half-Heusler) or 2:1:1 (full-Heusler) stoichiometric ratios. In full-Heusler alloys, X is usually a transition metal, such as Cu, Fe, Ni, Co, Ru; Y is usually Mn, Cr, or V; and Z can be Al, Ga, Ge, Si, Sn in L21 structure [5]. For half-Heusler alloys, the general formula is XYZ, where X can be a transition or alkali metal element, Y is another transition metal element, typically Mn or Cr, and Z is a member of the group IV element or a pnictide [6]. The full-Heusler compound can crystallize in the L21 structure (space group Fm-3m with Cu2MnAl prototype structure with or space group F-43m with Hg2CuTi prototype structure), while the half-Heusler can crystallize in the C1b structure (space group F4-3m with MgAgAs prototype structure) [7, 8]. Heusler compounds are generally magnetic intermetallic with face-centered cubic crystal structure. A lot of Heusler
*Corresponding author, E-mail: [email protected]
compounds show properties relevant to spintronics such as magnetoresistance, Hall effect, ferro-, anti-ferro-, and ferrimagnetism, half- and semi-metallicity, semiconductivity with spin filter’s ability, superconductivity, and topological band structure [9]. Due to their electronic structure indicating half-metallicity, Heusler compounds exhibit significant research topics such as magneto-caloric, thermoelectric, and magnetic shape memory effects [9, 10]. On the other hand,
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