Phase stability of lanthanum orthovanadate at high-pressure

TL;DR

This study investigates the high-pressure phase transition of lanthanum orthovanadate (LaVO4) up to 12 GPa, revealing a monoclinic-to-monoclinic transition with increased density and altered electronic properties, using x-ray diffraction, Raman spectroscopy, and ab initio calculations.

Contribution

It provides detailed structural, vibrational, and electronic insights into LaVO4's phase transition under high pressure, combining experimental and computational methods.

Findings

Monoclinic-to-monoclinic phase transition occurs at 12 GPa.

High-pressure phase has doubled unit cell and increased density.

Pressure induces significant changes in electronic properties and color.

Abstract

When monoclinic monazite-type LaVO4 (space group P21/n) is squeezed up to 12 GPa at room temperature, a phase transition to another monoclinic phase has been found. The structure of the high-pressure phase of LaVO4 is indexed with the same space group (P21/n), but with a larger unit-cell in which the number of atoms is doubled. The transition leads to an 8% increase in the density of LaVO4. The occurrence of such a transition has been determined by x-ray diffraction, Raman spectroscopy, and ab initio calculations. The combination of the three techniques allows us to also characterize accurately the pressure evolution of unit-cell parameters and the Raman (and IR)-active phonons of the low- and high-pressure phase. In particular, room-temperature equations of state have been determined. The changes driven by pressure in the crystal structure induce sharp modifications in the color of LaVO4 crystals, suggesting that behind the monoclinic-to-monoclinic transition there are important changes of the electronic properties of LaVO4.