Synthesis, characterization, vibrational spectroscopy, and factor group analysis of partially metal-doped phosphate...

A simple precipitating method was used to synthesize effectively a partially metal-doped phosphate hydrate (Mn_0.9Mg_0.1HPO₄·3H₂O), whereas the thermal decomposition process of the above hydrate precursor was used to obtain Mn_1.8Mg_0.2P₂O₇ and LiMn_0.9Mg_0.1PO₄ compounds under different conditions. To separate the overlapping thermal decomposition peak, a deconvolution technique was used, and the separated peak was applied to calculate the water content. The factor group splitting analysis was used to exemplify their vibrational spectra obtained from normal vibrations of HPO₄^2-, H₂O, P₂O₇^4- and PO₄^3- functional groups. Further, the deconvoluted bending mode of water was clearly observed. Mn_0.9Mg_0.1HPO₄·3H₂O was observed in the orthorhombic crystal system with the space group of Pbca (D_2h¹⁵). The formula units per unit cell were found to be eight (Z = 8), and the site symmetric type of HPO₄^2- was observed as C_s. For the HPO₄^2- unit, the correlation filed splitting analysis of type C_3v - C_s - D_2h¹⁵ was calculated and had 96 internal modes, whereas H₂O in the above hydrate was symbolized as C_2v - C_s - D_2h¹⁵ and had 24 modes. The symbol C_2v - C_s - C_2h³ was used for the correlation filed splitting analysis of P₂O₇^4- in Mn_1.8Mg_0.2P₂O₇ (monoclinic, C2/m (C_2h³), Z = 2, and 42 modes). Finally, the symbol T_d - C_s - D_2h¹⁶ was used for the correlation filed splitting analysis of PO₄^3- in LiMn_0.9Mg_0.1PO₄ (orthorhombic, Pnma (D_2h¹⁶), Z = 4, and 36 modes).