Isomorphism and polymorphism of the compounds Li3PO4, Li3AsO4 and Li3VO4

The structural study of the compounds Li3PO4, Li3AsO4 and Li3VO4 has been made by X-ray powder diffractometry and i.r. absorption spectroscopy. In addition to a previously described structure, which has been found for Li3PO4 and Li3AsO4 only and must be considered as a high temperature form, a new, low-temperature form, has been found for Li3PO4, Li3AsO4 and Li3VO4. The following unit cell dimensions (in angstroms) have been deduced from X-ray powder patterns: {A table is presented}{A table is presented}. Both structures are extremely similar, and are characterized by four-fold co-ordination of lithium, as deduced from the study of the 6Li7Li isotopic shifts in the spectra. Vibrational interactions between some LiO4 stretching frequencies and the PO4, AsO4 or VO4 bending frequencies are revealed by abnormal 6Li7Li isotopic shifts. © 1967.