Magnetic and Mössbauer studies of LixMyV1−yS2 (M=FeorCr)

Abstract

We report magnetic and Mössbauer studies of the lithium intercalation compounds ${\mathrm{Li}}_x{M}_y{\mathrm{V}}_{1-y}{\mathrm{S}}_2$, where we have $M=\mathrm{Fe}\mathrm{or}\mathrm{Cr}$, and we have $x<~1$ and $y<~\frac{1}{2}$ for Fe or $y<~1$ for Cr. In some cases, the valence and magnetic state of the transition metals can be determined unambiguously from these data. When we have $M=\mathrm{Fe}$ and $x=0\mathrm{}$ (no Li), the Fe is divalent and low spin ($S=0\mathrm{}$), and some compensating pentavalent V must be produced according to ${\mathrm{Fe}}_y^{2+}{\mathrm{V}}_{2y}^{5+}{\mathrm{V}}_{1-3y}^{4+}{\mathrm{S}}_2$. When $x=1\mathrm{}$ (fully lithiated) the Fe remains divalent and low spin only at low-Fe concentrations ($y\lesssim 0.1$) but some of the V atoms develop a magnetic moment. At higher-Fe concentrations ($x=1\mathrm{}$, $y\gtrsim \frac{1}{4}$) some of the Fe atoms also develop a moment. These latter materials are quite complicated. Similar results are observed when $M=\mathrm{Cr}$; i.e., no moments are observed at $x=0\mathrm{}$, but at $x=1\mathrm{}$ moments appear probably associated with the Cr atoms. In either case ($M=\mathrm{Fe}\mathrm{or}\mathrm{Cr}$) phase transitions apparent in pure ${\mathrm{Li}}_x\mathrm{V}{\mathrm{S}}_2$ are suppressed by the cation substitution.