Solubility Limit and Thermostructural Properties of Kagome Mg3V2(1– x )Nb2 x O8: A Joint Diffraction and Spectroscopic Study

Abstract

Modification of composition via solid solution can significantly improve the physical properties of materials. The crystallographic properties of the novel Mg3V2(1–x)Nb2xO8 solid solution were investigated by X-ray powder diffraction (XRPD) and spectroscopy. XRPD analysis confirms crystallization in the Cmca space group, corresponding to the kagome-staircase Ni3(VO4)2-type structure. Rietveld refinements reveal that Nb substitution induces a systematic increase in lattice parameters and unit cell volume. However, the lattice parameters remain constant for x > 0.04, indicating a solid solution limit of approximately x ∼ 0.04. Spectroscopic analysis further indicates tetrahedral coordination of Nb dopants, as evidenced by the characteristic energy positions and splitting of the Nb L3 edge spectra. High-temperature XRD studies (298–1273 K) revealed pronounced anisotropic thermal expansion. The volumetric thermal expansion coefficient increases from 19(2) MK–1 at 298 K to 40.6(5) MK–1 at 1273 K. Electronic structure calculations based on density functional theory yield a band gap of 3.57 eV, which is in good agreement with previously reported experimental data. The calculated Debye temperature (734 K) indicates high lattice rigidity. The observed trend in directional compressibility (a > c > b) correlates well with the experimentally measured anisotropic thermal expansion, confirming the a-axis as the most responsive under both thermal and mechanical conditions.