A theoretical lattice dynamics model and phonon dispersion measurements for CaSO₄(anhydrite)

X-ray diffraction and infrared spectroscopy of monazite-structured CaSO4 at high pressures: Implications for shocked anhydrite

“…7, Table 2), in accord with previous work e.g., [21]. The peaks above 1000 cm À1 are assigned to n 3 asymmetric stretching vibrations of the sulfate tetrahedra, while those between 590 and 675 cm À1 are assigned to n 3 asymmetric bending vibrations of the sulfate tetrahedra, each split by crystal field effects [19,20]. All observed modes of b-CaSO 4 increase in frequency with compression, although their pressure shifts are not well-determined in this study because of the limited stability range of this phase.…”

“…Moreover, the bonding properties of sulfate groups under compression have been a topic of considerable interest [16,17], and the degree to which the sulfate unit is distorted within the high-pressure monazite-structured phase remains uncertain. Although the ambient pressure vibrational spectra of anhydrite have been studied extensively [18][19][20][21], the infrared spectrum of CaSO 4 has not previously been measured at high pressure. We have thus conducted infrared spectroscopy of anhydrite at high pressure in conjunction with our X-ray diffraction measurements in order to constrain the shifts in bonding of the sulfate group associated with the phase transition to the monazite structure and the compression of the high-pressure phase.…”

Diffraction Methods and Crystal Structure Analysis

“…Both the acoustic and the optical phonon modes show reasonable agreement between the experiment and the model calculation (Schweiss et al 1987). The calculations were carried out based on a breathing shell model for (1) a purely ionic model with charges on all atoms and (2) a model which treats the SOIgroup as a whole as a rigid body neglecting internal vibrations.…”