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arXiv · 2610.33457

First-Principles Investigation of the Structural, Electronic, Optical, Elastic, and Thermoelectric Properties of X2MoSeO6 (X = K, Rb, Cs)

Sha Ajharul Islam Forhat·Md. Rakibul Hasan Rakib·Md. Al Noman Ruhin·Md Tashfiq Bin Kashem
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Abstract

Understanding how alkali-metal substitution influences the coupled physical properties of molybdenum selenite oxides is essential for establishing their composition-structure-property relationships. Although the lighter members of the X2MoSeO6 family have been investigated, the heavier alkali-metal compounds remain comparatively unexplored, particularly regarding their integrated electronic, mechanical, optical, and thermoelectric responses. Here, a comprehensive first-principles investigation of X2MoSeO6 (X = K, Rb, and Cs) is presented using density functional theory and semi-classical Boltzmann transport calculations. The optimized structures exhibit progressive unit-cell expansion with increasing alkali-metal ionic size, while their indirect electronic bandgaps vary non-monotonically, reaching 2.646, 2.216, and 2.427 eV for K2MoSeO6, Rb2MoSeO6, and Cs2MoSeO6, respectively. All three structures satisfy the elastic stability criteria, with Hill-averaged bulk moduli increasing from 16.332 to 20.975 GPa across the series. K2MoSeO6 exhibits the strongest elastic anisotropy, whereas Rb2MoSeO6 possesses the highest static electronic dielectric constant (4.614) and maximum absorption coefficient (2.291*106 cm-1). Thermoelectric calculations reveal pronounced carrier-polarity-dependent behavior, with Rb2MoSeO6 attaining a positive Seebeck coefficient of 390.55e-6 V/K at 100 K and an electronic-only figure of merit (ZTe) of 7.286 at 300 K under the selected positive-Seebeck condition. By extending the investigation to the K-Rb-Cs series, this work establishes a comparative foundation for understanding and further exploring the functional characteristics of molybdenum selenite oxides.

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Sha Ajharul Islam Forhat, Md. Rakibul Hasan Rakib, Md. Al Noman Ruhin, Md Tashfiq Bin Kashem. 2026-10-24. First-Principles Investigation of the Structural, Electronic, Optical, Elastic, and Thermoelectric Properties of X2MoSeO6 (X = K, Rb, Cs). https://arxiv.org/abs/2610.33457

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