Characterization of Barium Borate Frameworks Using Raman Spectroscopy.

Systematic micro-Raman scattering investigations have been carried out on Sm doped 2(BaO)-n(BO) matrices for n = 4, 5, 8, and 2(BaO)-(NaO)-9(BO) using the 364 nm excitation of an Ar laser. The Raman results have been compared with the known structures of barium tetraborate, barium pentaborate, barium octaborate, and barium sodium nonaborate. An excellent correlation has been found between the BO/BO composition ratios for each product and intensity ratios of the designated BO and BO Raman peaks. Furthermore, the Raman frequencies of both BO and BO groups undergo a systematic blueshift as n increases from four to nine. The shift results from a decrease of the B-O bond lengths for both BO and BO groups as the samples transition from the tetraborate to nonaborate structures. Linear relations (with negative slopes) have been determined between the measured Raman frequencies and B-O bond lengths in the frameworks.