Physical properties of vacancy-ordered double perovskites K2TcZ6 (Z = Cl, Br) for spintronics applications: DFT calculations.

Vacancy-ordered double perovskites (DPs) are emerging materials for spintronics due to their stable structures and non-toxic properties. In this study, we conducted a comprehensive investigation into the role of 4d electrons in Tc to understand their impact on the ferromagnetic properties of K2TcY6 (Y = Cl, Br). We have employed a modified Back and Johnson potential to assess electronic and magnetic characteristics and utilized the BoltzTraP code to investigate thermoelectric effects. Experimental lattice constants confirmed the presence of stable structures and formation energy estimates affirmed their thermodynamic stability. The Heisenberg model and density of electron states (DOS) at the Fermi level provides insights into Curie temperature and spin polarization. The presence of ferromagnetism is evident in the density of states, reflecting the transition of electron spins that support the exchange mechanism. The study delves into how electron functionality influences the control of ferromagnetism, considering exchange constants, exchange energies, hybridization process and the crystal field energies. Moreover, the exploitation of magnetic moments from Tc to K and Cl/Br sites takes precedence in driving ferromagnetism by exchanging electron spins rather than forming magnetic clusters. Additionally, to explore the optical characteristics of the compounds, we investigated their optical absorption, dielectric constants and refractive index within the energy range of 0-10 eV, ensuring absorption across both the visible and ultraviolet regions. Finally, we delve into the impact of the thermoelectric effect on both thermoelectric performance and spin functionality, taking into account factors such as the Seebeck coefficient, power factor, and electronic conductivity.

First principles investigation of halide based Rb2NaGaZ6 (Z = Br, I) double perovskites for energy harvesting applications.

Extensive investigations have been conducted on the thermoelectric and optoelectronic characteristics of double perovskite compounds using the full potential linearized augmented plane wave (FP-LAPW) approach. Here we investigated Rb2NaGaZ6 (Z = Br, I) to explore its band structure, and electronic, optical and transport properties. Born's stability criteria have confirmed the mechanical stability of these compounds. Analysis of the elastic properties reveals their ductile nature, as indicated by a Poisson coefficient (υ) greater than 0.26 and a Pugh ratio exceeding 1.75 for Rb2NaGaZ6 (Z = Br, I). Computation of the bandgap values shows that both compositions possess a direct bandgap nature, with respective values of 2.90 eV and 1.25 eV. This suggests that substituting Br with I brings the band edges closer together, resulting in a decrease in the bandgap value. The optical properties are assessed based on the absorption coefficient, reflectivity, and dielectric constants. The thermoelectric properties, including thermal and electrical conductivities, power factor (PF), and figure of merit (ZT), are determined using the BoltzTrap code. The ZT values indicate that both compositions exhibit promising potential for various transportation applications.

Study of the Influence of Electron Spin in Ferromagnetism and Thermoelectric Characteristics of CdTm2Y4 (Y = S, Se) Spinels for Spintronic Applications.

The current study used full-potential methods to examine the ferromagnetic characteristics of CdTm2Y4(Y= S, Se) spinels; i.e., structural, elastic, electronic, and thermoelectric characteristics of these spinels have been explored for the first time. We used PBEsol-GGA for enthalpy of formation calculations to explain the stability of the ferromagnetic state and calculate the elastic constants and corresponding mechanical modules to reveal the ductile behavior of the materials. The mBJ potential is used instead of PBEsol-GGA to obtain more accurate and precise results of electronic and thermoelectric characteristics. Using mBJ potential leads to complete occupation of the bands in the materials and a clear interpretation of the density of states (DOS). The analysis of the electronic band structure and DOS reveals the stability of the ferromagnetic state in the analyzed materials as a result of p-d hybridization-based exchange splitting of Tm cations in the lattice. The calculations of thermoelectric efficiency are effective in evaluating the aptitude pertinence of the material in waste energy recovery systems and other technological applications. The thermal parameters of these materials are also analyzed to examine their thermal stability over a wide range of temperatures. The results of these calculations are essential for determining the suitability of the materials for use in spintronics-based devices and thermoelectric appliances as these devices rely heavily on the material's thermoelectric properties.