First principles investigation on optoelectronic and thermoelectric response of nitrides cadmium novel zintl compounds AB2C2 (A=Mg, Ca, Sr, Ba; B = Cd and C= N)

Abstract

Novel materials for high efficiency advance devices are critical to investigate. Zintl compounds are widely explored in the recent years because of their direct narrow band gaps, higher optical conductivity and figure of merit required for optimal-optoelectronic and thermoelectric response respectively. Thus, in the current study, the structural, electronic, optical and thermoelectric properties of nitrides cadmium novel Zintl compounds AB2C2 (A=Mg, Ca, Sr, Ba; B=Cd and C= N) having trigonal structure are studied by full potential linearized augmented plane wave method based on density functional and Boltzmann transport theory. The main objective of this project is to provide novel thermo electrical data on Cd-based Zintl compounds, such as nitride cadmium-based compounds. To get the desire results, the exchange correlations with generalized gradient approximation were used to obtain the ground state structure parameters in these compounds. The computed lattice parameters and c/a -ratio increase from the top to down while the bulk-modulus B(GPa) decreases from top to bottom. The modified versions of the Beck-Johnson potential (TB-mBJ) predict that CaCd2N2, SrCd2N2, BaCd2N2 and MgCd2N2 compounds are semiconductors with narrow band gap of 0.18 eV, 0.21 eV, 0.84 eV and 0.07 eV respectively. Based on the optical properties a deep analysis of dielectric constant, refractive index, reflectivity and optical conductivity were carried. Across the entire temperature range, all the compounds exhibit a positive Seebeck coefficient, indicating P-type conduction. The direct energy band gap nature of these compounds with high conductivity in the visible region shows their suitability for optical applications. Also, the figure of merit of these compounds is close to unity which also speaks about the high efficiency for thermoelectric applications.