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We have studied BaWO under compression at room temperature by means of x-ray diffraction and Raman spectroscopy. When compressed with neon as a pressure-transmitting medium (quasihydrostatic conditions), we found that BaWO transforms from its low-pressure tetragonal structure into a much denser monoclinic structure. This result confirms our previous theoretical prediction based on ab initio calculations that the scheelite to BaWO-II transition occurs at room temperature if kinetic barriers are suppressed by pressure. However, our experiment without any pressure-transmitting medium has resulted in a phase transition to a completely different structure, suggesting nonhydrostaticity may be responsible for previously reported rich polymorphism in BaWO. The crystal structure of the low- and high-pressure phases from the quasihydrostatic experiments has been Rietveld refined. Additionally, for the …