Vibrational spectra and the ferroelectric phase transition of colemanite

Abstract

Abstract. The infrared and far infrared (10-4000 cm-1) polarized, single crystal reflectivity of the calcium borate mineral colemanite, CaB30~(OH)3"HzO, have been measured at room temperature and at several temperatures below the ferroelectric phase transition at approximately 270 K. Over the entire frequency range studied, only minor spectral changes are seen at the ferroelectric phase transition.

Infrared reflectance of single-crystal jarandolite, CaB3O4(OH)3

“…Bands in the range 1240À1371 cm À1 correspond to asymmetric stretching of the BO 3 group, bands at 700À800 cm À1 correspond to symmetric s t r e t c h i n g o f B O 4 t e t r a h e d r a a n d a t 350À600 cm À1 to bending modes of BO 4 tetrahedra and the BO 3 triangle. Below this frequency, bands in the far-IR range correspond (Malinko et al, 2004), reflection spectra of colemanite (Gallup and Coleman, 1990) and results from this study with band assignment.…”

“…The second group of peaks in the range 1240À1460 cm À1 is stronger forẼ E|| c c polarization and weaker, but noticeable, forẼ E\c c. These bands were attributed to asymmetric stretching vibrations of the BO 3 group, which were also noted in the absorption spectra of jarandolite by Malinko et al (2004), and assigned as stretching vibrations of BÀO bonds in BO 3 groups. Bands at similar values (~1400 cm À1 ) were noted and assigned as BO 3 asymmetric stretching by Gallup and Coleman (1990) for colemanite and also by Grice et al (1996) for penobsquisite in the range 1300À1400 cm À1 .…”

“…By showing both polarizations in one graph we can obtain a better view of the characteristic bands, enabling easier assignment and comparison with the absorption bands determined by Malinko et al (2004). This spectral range also corresponds to that measured for colemanite by Gallup and Coleman (1990), allowing easier comparison. The band frequencies for these three spectra are also given in Table 3.…”

“…In addition to the strong peaks, a number of smaller peaks and shoulders can be noted in the jarandolite spectra for both polarizations. Bands near 1160 and 650 cm À1 were assigned by Gallup and Coleman (1990) as out-of-plane and in-plane bending modes of BO 3 . Also, Weir (1966) questioned the inclusion of bands just below 1200 cm À1 as part of the asymmetric stretching of BO 3 and considered that they may arise from BÀOH bending modes.…”

“…origin as the one made for brucite (Lutz et al, 1994;Braterman et al, 2006) is very complex. Assignments of some vibrational modes of jarandolite can be achieved by comparison with the spectra of related borates, including colemanite and fabianite (Weir, 1966;Gallup and Coleman, 1990;Guo et al, 2000).…”