Measurement of raman polarization anisotropy in gyrotropic crystals

Vibrational Origin of the Thermal Stability in the Highly Distorted α-Quartz-Type Material GeO2: An Experimental and Theoretical Study

“…28,29,31,32,34,36 Only Avakyants et al and Kaindl et al have reported A 1 symmetry for this mode. 30,24 Similarly, if the mode located around 212 cm −1 was correctly assigned by Scott in his second paper, 29 some authors still have used his first assignment and have thus assigned this mode as A 1 . 31,32 The z(xz)z ̅ polarization configuration was used to activate only the transverse optical E modes.…”

“…29 Despite important errors, these results were for a long time considered to be reliable, although the identification of the E lines was based exclusively on analogies with α-quartz. In the late 1980s, a significant improvement in the Raman mode assignments was reported by Avakyants et al; 30 however, this work went largely unnoticed and many experimental and theoretical Raman spectroscopy studies continued to use the mode assignments of Scott and coworkers. 31−36 In order to clarify this long-standing debate, polarized Raman spectroscopy measurements were performed on high-quality, water-free α-quartz GeO 2 single crystals, and the results were compared with state-of-the-art first-principles calculations.…”

“…Furthermore, even if Avakyants et al succeeded in detecting the E lines around 260 cm −1 the E (TO) mode was incorrectly located at a higher frequency than the A 1 (TO2) mode. 30 Kaindl et al have also assigned the mode at ∼960 cm −1 to a longitudinal E (LO), whereas it is actually a transverse mode. 24 Finally, the eight longitudinal E (LO) modes are obtained with the incident and scattered light propagating perpendicular to the Y face of a GeO 2 single crystal and with the incident and scattered polarization along the x-and z-axis respectively (Figure 3c).…”

“…Despite important errors, these results were for a long time considered to be reliable, although the identification of the E lines was based exclusively on analogies with α-quartz. In the late 1980s, a significant improvement in the Raman mode assignments was reported by Avakyants et al; however, this work went largely unnoticed and many experimental and theoretical Raman spectroscopy studies continued to use the mode assignments of Scott and co-workers. − …”

Thermodynamic properties of the α-quartz-type and rutile-type GeO2 from first-principles calculations

“…6 Nevertheless, at this stage, the metastability of the a-quartz phase remains poorly understood. Although several studies on the lattice dynamics of the a-quartz-type and rutile-type GeO 2 can be found in the literature, 7,[13][14][15][16][17][18] few studies are devoted to understand their thermodynamic properties. Entropy and heat capacity at constant-pressure have been measured 50 years ago at low temperatures by King 19 (a-quartz phase) and Counsell et al 20 (rutile phase), while, more recently, Richet 21 has completed these measurements up to the high temperature range.…”