6533b7cefe1ef96bd1257907

RESEARCH PRODUCT

Experimental and theoretical investigation of the stability of the monoclinicBaWO4-II phase at high pressure and high temperature

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description

In this work we report high-pressure (HP) and high-temperature (HT) ex situ and in situ experiments in ${\text{BaWO}}_{4}$. Starting from powder samples of ${\text{BaWO}}_{4}$, scheelite structure $(I{4}_{1}/a)$, we reached conditions of 2.5--5.5 GPa and 400--1100 K using a Paris-Edinburgh press. The quenched samples were characterized by x-ray diffraction and Raman measurements at ambient conditions. Depending upon the final $P\text{\ensuremath{-}}T$ conditions we found either the scheelite or the monoclinic ${\text{BaWO}}_{4}$-II $(P{2}_{1}/n)$ structure. We also performed HP-HT in situ Raman measurements in a single crystal of ${\text{BaWO}}_{4}$ using a resistive-heated diamond-anvil cell. The transition from scheelite to the ${\text{BaWO}}_{4}$-II phase was observed at 5 GPa for $T=621\text{ }\text{K}$. Ab initio lattice-dynamics calculations have been performed in order to characterize the vibrations of the ${\text{BaWO}}_{4}$-II phase. Finally we carried out in situ powder angle-dispersive x-ray diffraction synchrotron measurements on ${\text{BaWO}}_{4}$ compound following different $P\text{\ensuremath{-}}T$ paths, extending its measured phase diagram in the 2--6 GPa and 300--2000 K range.