Vibrational characteristics of aluminum-phosphate compounds by an experimental and theoretical approach.

Aluminum phosphates are materials with relatively wide potential applications in many industries. The vibrational features of selected compounds were established on Raman and infrared spectroscopy. The experimentally determined spectra are compared to those calculated by ab initio methods. This gives a unique possibility of a proper assignment of the experimental spectral features to specific modes of vibration. In the results, it was evidenced that the spectra are characterized by two specific intense bands in the mid- and high-frequency range due to the P-O-P and P-O bonds in [PO4] tetrahedron vibrations. The position of the high-frequency band is related to the number of bridging oxygen atoms connecting [PO4] tetrahedrons in the unit cell. Additionally, the differences in the spectra were evidenced as a result of different polymorphic forms of the selected compounds. Therefore, the results may be useful in determining the phase composition of polyphase materials or structural features of aluminum-phosphate glasses and glass-ceramic materials.