Spectres d'absorption infrarouge de borates de terres rares

The infra-red spectra of either trivalent cations or rare-earth borates related to the calcite, the aragonite and the vaterite structures have been studied in the 1500-250 cm⁻¹ region.

The infra-red pattern given by the rare-earth borates of the YBO₃ type cannot be reconciled with a three-fold co-ordination, but instead points to a four-fold co-ordination of boron, a fact in contradiction with the alleged vaterite structure of these borates.

The low-frequency spectrum is strongly structure-dependent, and is clearly influenced by the co-ordination number of the trivalent cation. The strong band observed in this region may be assigned to a cation—oxygen vibration, or possibly (for the calcite or aragonite-type borates) to a libration of the borate anion. Some significant discrepancies between our results and some data recently published in the literature are found to be related to spurious effects, such as the granulometry of the sample and possibly orientation effects.