Three Mg-3(PO4)(2) polymorphs (Mg-3(PO4)(2)-I, II, III) were synthesized at high-pressure and high-temperature conditions. The structures and vibrational properties of Mg-3(PO4)(2) polymorphs were studied by X-ray diffraction (XRD), Raman spectroscopy, and density functional theory (DFT) calculations. The obvious different P-O stretching vibrational modes were experimentally observed for Mg-3(PO4)(2)-I, II, III. The calculated vibrational frequencies were in good agreement with measurements. All the observed vibrational modes for Mg-3(PO4)(2)-I, II, III were well assigned based on the calculations, which provided a support for investigating and comparing vibrational properties of three Mg-3(PO4)(2) polymorphs. (C) 2020 Elsevier B.V. All rights reserved.