Raman spectroscopic study of

The dielectric constant of polycrystalline LiH2PO4 has been measured between 297 and 17 K. No marked changes were observed over this range, indicating that the room-temperature orthorhombic phase persisted up to 17 K. Raman spectra of polycrystalline LiH2PO4 were also measured at 297, 200, and 70 K in the frequency shift region of 15–4000 cm−1 with Raman-active vibrational modes naively assigned to low-frequency (0–300 cm−1) external and high-frequency (300–4000 cm−1) internal modes. In addition to the internal modes of the PO4 tetrahedra, the internal modes of the LiO4 tetrahedra spectroscopically manifested themselves between 390–500 cm−1. This frequency range overlaps those of ν 2 (PO4) and ν 4 (PO4). The LiH2PO4O–H vibrational frequencies were in good agreement with crystallographic reports that there are two types of hydrogen bonds: intermediate (long bonds) and strong (short bonds).