A thorough study of the vibrational dynamics of xenotime YPO4 and, its isomorphs, pretulite ScPO4 single crystals, with tetragonal zircon-structure, was carried out by means of an integrated approach consisting of both polarized micro-Raman scattering spectroscopy and first-principles calculations. Polarized Raman scattering experiments were performed at room temperature either in the 180◦ or in the 90◦ geometry on both samples under different crystal orientations set by a micromanipulator. For the first time, all the 12 independent components of the polarizability tensor, expected on the basis of the group theory for both YPO4 and ScPO4, were selected in turn and assigned in symmetry. In particular, it was possible to unambiguously identify a B1g mode peaked at 316 cm−1 in YPO4, and two B1g modes peaked at 350 cm−1 and 677 cm−1 in ScPO4, respectively, all of them never reported before. These observations were corroborated by the results of first principles calculations, based on density-functional theory in the generalized gradient approximation, performed to determine Raman and infrared vibrational modes. In fact, an excellent agreement between computational and experimental results has been found.
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