Double Perovskites K2NbTaO6 and Rb2NbTaO6 from First-Principles: Towards Efficient Materials for Green Energy

TL;DR

This study uses first-principles calculations to analyze the structural, electronic, elastic, optical, and thermoelectric properties of double perovskites K2NbTaO6 and Rb2NbTaO6, highlighting their potential for green energy applications.

Contribution

It provides a comprehensive first-principles analysis of these double perovskites, revealing their stability and electronic properties relevant for energy-related applications.

Findings

Both compounds are mechanically stable but brittle.

They exhibit semiconducting behavior with band gaps around 2.6-2.8 eV.

Optical absorption occurs mainly in the UV region.

Abstract

The structural flexibility and multifunctional nature of double perovskite oxides make them attractive for applications requiring coupled optical, mechanical, and thermal performance. Using first-principles computations, this study examines the structural, electronic, elastic, optical, and thermoelectric stability of K2NbTaO6 and Rb2NbTaO6. The two compounds combine to form a cubic double perovskite structure with ordered Nb$^{5+}$ and Ta$^{5+}$ cations. The calculated elastic constants satisfy the Born stability criteria, confirming mechanical stability; however, both K2NbTaO6 and Rb2NbTaO6 exhibit brittle behavior according to Pugh's ratio, reflecting limited ductility. Semiconducting behavior is revealed by band structure analysis with energy gaps of 2.79 eV for K2NbTaO6 and 2.63 eV for Rb2NbTaO6. Optical spectra show noticeable absorption in the high-energy region near the UV, indicating relevance for theoretical studies of optoelectronic and photocatalytic processes, without implying practical device efficiency. Therm