Abstract
At ambient pressure the spinel $\mathrm{Li}{\mathrm{V}}_{2}{\mathrm{O}}_{4}$ is a metal with a heavy fermion ground state. However, under applied pressure a transition to an insulating, nonmagnetic state occurs. Powder x-ray diffraction has been used to study structural changes associated with this transition, and reveals that the ambient-pressure $Fd\overline{3}m$ spinel structure distorts to a monoclinic cell of $C2/m,C2$, or $Cm$ symmetry above 11 GPa at low temperatures. The changes of structure and properties provide evidence for orbital molecule formation in the cubic phase at high pressures and low temperatures that leads to long-range orbital molecule order in the monoclinic phase.
Highlights
Metal-insulator transitions often occur in systems with strongly correlated electrons and are highly sensitive to perturbations such as a change of temperature, chemical substitution, or the application of pressure [1]
In addition to changes of properties, which result from the localization and spin pairing of d electrons into V-V bonds, the formation of orbital molecules in these materials is associated with a structural distortion, as the distance between the bonded cations is typically shortened by several tenths of an Ångstrom
It was suggested that the intermediate region of the phase diagram exists because the transition between the metallic and insulating phases occurs gradually, through the development of insulating grains [5]
Summary
Metal-insulator transitions often occur in systems with strongly correlated electrons and are highly sensitive to perturbations such as a change of temperature, chemical substitution, or the application of pressure [1]. Subsequent optical measurements revealed a pressure-temperature phase diagram with three distinct regions—a low-pressure metallic phase and a high-pressure insulating one with markedly different, pressure-independent conductivities, separated by an intermediate region in which the change from metallic to insulating conductivity gradually occurs [4]. The magnetic behavior of LiV2O4 under pressure has been studied—7Li- and 51VNMR have revealed that the local-moment low-pressure phase gradually converts to a spin-singlet high-pressure one, and that this conversion starts to occur at pressures consistent with the metallic-intermediate phase boundary determined by the optical measurements [5]. In addition to changes of properties, which result from the localization and spin pairing of d electrons into V-V bonds, the formation of orbital molecules in these materials is associated with a structural distortion, as the distance between the bonded cations is typically shortened by several tenths of an Ångstrom. A distortion of the cubic F d3 ̄m structure of the metallic phase was reported on the basis of powder x-ray diffraction results,
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
