Raman spectrum of Li2B4O7

The Raman spectrum of lithium diborate (Li 2 B 4 O 7 ) has been recorded for the first time. After correction for polarisation leakthrough, the spectrum is consistent with group theoretical predictions. No anomaly is seen in the Raman spectrum from 100 to 400K or in the low-frequency dielectric constant from 150 to 350K. The anomalous elastic behaviour at around 300K thus remains unexplained. Some LO-TO splittings are observed for the polar modes. Tentative assignments for some modes in terms of internal vibrations of BO 4 tetrahedra and BO 3 planar triangles have been made. It is suggested that the loose binding of the lithium atom in a channel may be the reason for the highly anisotropic electrical resistivity observed.