Pressure-induced structural phase transition in $\mathrm{Li}{\mathrm{V}}_2{\mathrm{O}}_4$

Extended x-ray absorption fine structure analysis of $\mathrm{Li}{\mathrm{V}}_2{\mathrm{O}}_4$ at the vanadium $K$ edge under pressure is discussed. Changes in the absorption spectra at room temperature show that a structural phase transition is induced at high pressure. This phase transition can be attributed to a charge ordering, as it was observed in the isostructural compound $\mathrm{Al}{\mathrm{V}}_2{\mathrm{O}}_4$. The absorption spectra have been analyzed by considering the two models previously proposed for $\mathrm{Al}{\mathrm{V}}_2{\mathrm{O}}_4$. Our results indicate that the high pressure structure of $\mathrm{Li}{\mathrm{V}}_2{\mathrm{O}}_4$ is probably implying the formation of “vanadium molecules” in a geometrically frustrated crystal.

Figure 1

(Color online) Charge ordering structures of $\mathrm{Al}{\mathrm{V}}_2\mathrm{O}4$: (a) three-one type and (b) heptamer type.

Figure 2

(Color online) Selected absorption spectra of $\mathrm{Li}{\mathrm{V}}_2{\mathrm{O}}_4$ at the vanadium $K$ edge as a function of pressure.

Figure 3

(Color online) Radial distribution functions at different pressures.

Figure 4

(Color online) Fit of the Fourier transform of the $0.7\mathrm{GPa}$ data (amplitude and imaginary parts). Solid line: experiment, dotted line: fit.

Figure 5

(Color online) Fit of the Fourier transform of the $21.7\mathrm{GPa}$ data (amplitude and imaginary parts) using the structural values listed in Table . Solid line: experiment, dotted line: fit.

Figure 6

(Color online) Calculation of the first V-O distances and disorder terms for $\mathrm{Li}{\mathrm{V}}_2{\mathrm{O}}_4$ at various pressures, calculated within a single shell model.

Figure 7

(Color online) (a) Absorption spectra and (b) Fourier transforms at various pressures.

Figure 8

(Color online) (a) Derivative of the absorption spectra. (b) Disorder term for the first shell and amplitude of the absorption spectra derivative as a function of the applied pressure.