Structural properties and Raman spectra of columbite-type NiNb$_{2-x}$V$_x$O$_6$ synthesized under high pressure

TL;DR

This study investigates the structural parameters and Raman spectra of NiNb$_{2-x}$V$_x$O$_6$ compounds synthesized under high pressure, revealing how vanadium substitution affects local structure and vibrational properties.

Contribution

First comprehensive structural and vibrational analysis of NiNb$_{2-x}$V$_x$O$_6$ with high-pressure synthesis, including the first Raman spectrum of NiV$_2$O$_6$-Pbcn polymorph.

Findings

Vanadium substitution influences local structural environment.

V atoms favor increased oxygen symmetry around nickel.

Vanadium distribution in the solid solution is non-homogeneous.

Abstract

The complete set of structural parameters of the new series of compounds NiNb$_{2-x}$V$_x$O$_6$ ($0\leq x \leq 2$) with the unusual columbite-type structure is presented here. In the samples containing vanadium, this crystalline structure was stabilized by synthesis in conditions of high pressure and high temperature. Here we report here the first Raman spectrum for the NiV$_2$O$_6$-\textsl{Pbcn} polymorph and extend the list of the previously observed modes for the NiNb$_2$O$_6$. The evolution of the vibrational Raman spectrum produced when the vanadium is substituted for niobium along the series is also presented and discussed. This evolution is interpreted by taking into account the changes in the local structural environment of the niobium/vanadium atoms and its influence over the nickel-oxygen bonds around them. The presence of vanadium atoms favors an increase of the symmetry in the arrangement of oxygen atoms around the nickel-ones; in counterpart, the vanadium is in an octahedral environment which is more distorted than that of the niobium. Because of these apparently subtle differences, the homogeneous distribution of vanadium in the solid solution NiNb$_{2-x}$V$_x$O$_6$ is not possible.