Single-crystal IR spectroscopic investigation on fresnoite, Sr-fresnoite and Ge-fresnoite

• Published in: Vibrational spectroscopy Vol. 25; no. 2; pp. 185 - 195
• Main Authors: Mayerhöfer, Th.G, Dunken, H.H
• Format: Journal Article
• Language: English
• Published: Elsevier B.V 04.05.2001
• Subjects: Dielectric tensor; Fresnoite; Ge-fresnoite; IR-reflectance-spectroscopy; Single crystal; Sr-fresnoite; IR-reflectance-spectroscopy; Sr-fresnoite; Dielectric tensor; Single crystal; Fresnoite; Ge-fresnoite
• ISSN: 0924-2031; 1873-3697
• DOI: 10.1016/S0924-2031(01)00090-X

Single crystals of fresnoite (Ba 2TiSi 2O 8), the structural analogue Sr-fresnoite (Sr 2TiSi 2O 8) and the structurally similar Ge-fresnoite (Ba 2TiGe 2O 8) were investigated by FTIR-reflectance- (IRR-) and Raman-spectroscopy. The IRR-spectra were subjected to a complete dispersion analysis in order to evaluate the ε ̂ -tensor in the range of 100–2000 cm −1. The results were checked by Raman-spectroscopy. Ba-fresnoite was shown to contain a small amount (about 1–2%) of four co-ordinated Ti, represented by an oscillator at 749 cm −1. A 1-mode at 858 and 871 cm −1 are not mixed TO–LO-modes but simply pure TO and LO, respectively. Raman microscopy showed that the Sr-fresnoite single crystal contained small amounts of rutil, which could not be detected in the IRR-spectra. Because of the great similarity of the E ∥ c-spectra of Ba-, Sr- and Ge-fresnoite, the A 1-mode representing the oscillation of the short TiO-bond of the Ge-fresnoite has been assigned to a vibration at 797 cm −1.