X-ray diffraction and vibrational-spectroscopy study of the structure of La₂Ti₂O₇

The compound La₂Ti₂O₇ was prepared by a liquid mix technique and examined at room temperature by x-ray diffraction, infrared absorption, and Raman spectroscopy. The examinations confirm and supplement the earlier observation by x-ray diffraction that La₂Ti₂O₇ crystallizes in the monoclinic structure without an inversion symmetry. The energy-shifts (cm⁻¹) that were observed in the vibrational spectra may be explained by a sixfold coordination for the titanium and a ninefold coordination for the lanthanum in the structure. This type of coordination satisfies Pauling's electrostatic valence rule regarding the electrostatic bond strengths at the shared anions.