Peculiarities of the local structure in new medium- and high-entropy, low-symmetry tungstates

Georgijs Bakradze; Edmund Welter; Alexei Kuzmin

doi:10.1016/j.jpcs.2022.111052

paper

Peculiarities of the local structure in new medium- and high-entropy, low-symmetry tungstates

arXiv:2210.16619 · doi:10.1016/j.jpcs.2022.111052

Abstract

New monoclinic ( $P 2$ / $c$ ) tungstates - a medium-entropy tungstate, (Mn,Ni,Cu,Zn)WO $_{4}$ , and a high-entropy tungstate, (Mn,Co,Ni,Cu,Zn)WO $_{4}$ - were synthesized and characterized. Their phase purity and solid solution nature were confirmed by powder X-ray diffraction and Raman spectroscopy. X-ray absorption spectroscopy was used to probe the local structure around metal cations. The atomic structures based on the ideal solid solution model were optimized by a simultaneous analysis of the extended X-ray absorption fine structure spectra at multiple metal absorption edges - five for (Mn,Ni,Cu,Zn)WO $_{4}$ and six for (Mn,Co,Ni,Cu,Zn)WO $_{4}$ - by means of reverse Monte Carlo simulations. In both compounds, Ni $^{2 +}$ ions have the strongest tendency to organize their local environment and form slightly distorted [NiO $_{6}$ ] octahedra, whereas Mn $^{2 +}$ , Co $^{2 +}$ , and Zn $^{2 +}$ ions have a strongly distorted octahedral coordination. The most intriguing result is that the shape of [CuO $_{6}$ ] octahedra in (Mn,Ni,Cu,Zn)WO $_{4}$ and (Mn,Co,Ni,Cu,Zn)WO $_{4}$ differs from that found in pure CuWO $_{4}$ , where a strong Jahn-Teller distortion is present: [CuO $_{6}$ ] octahedra become more regular with increasing degree of dilution.

Peculiarities of the local structure in new medium- and high-entropy, low-symmetry tungstates

Abstract

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