Infrared Lattice Spectra of Rare-Earth Stannate and Titanate Pyrochlores

The ir lattice spectra of six rare-earth stannates and six rare-earth pyrochlores have been recorded. A factor-group analysis has been performed on the Oh7–Fd3m space group. The analysis predicts seven F1u ir-active modes, and A1g, Eg, and 4 F2g Raman-active modes. All the 7 predicted F1u transverse optic modes have been observed. The highest-frequency band in each spectrum correlates with the unit-cell volume of the crystal; however, the stannate data appear to be anomalous with the previously reported rare-earth garnet data.