Optical investigations of LiKSO4 single crystals in the temperature range between 150 up to 730 K

Abstract

LiKSO4 (LPS) crystals show without a special thermal treatment a segment structure in the xy‐plane. These segments possess different values of optical activity along the c‐direction. Investigations of several LPS‐single crystals, grown under the same conditions, show that there are differences for the rotatory power (c‐direction) up to one order of magnitude. The crystals are probably built up from layers along the c‐axis additionally. After special thermal treatment a mosaic structure is obtained with components which exhibit an opposite rotatory power in direction of the hexagonal axis. Also the possibility of ferroelastoelectricity at room temperature is investigated. Below 190 and above 708 K there exists a threefold domain structure which can be changed by the aid of a mechanical external stress (compression). In both temperature regions a monodomain state is reached. So one can conclude that LPS is a ferroelastic crystal at temperatures T < 190 K and T > 708 K.

The absolute optical chirality of KLiSO4

“…1 shows, for such a crystal, a typical plot of the optical rotation down [00.1] (the optic axial direction) against wavelength measured with a precise polarimeter and a white-light source followed by a monochromator. The magnitudes shown here are within the range reported elsewhere, although slightly lower than the maximum reported [4.3 ° mm-~ for the Na D line by Sorge & Hempel (1986)]. A small crystal 0.98 (1)mm thick and of area 4 mm 2 was selected for further study• The optical rotation of this specimen along [00.1], as seen with a Schulz, Zucker & Frech, 1985) (2) white-light source and polarizing microscope, had been microscopic, the effect would have been to ~ 3.6 destroy the optical rotation.…”

“…These have been studied by X-ray and neutron diffraction as well as optically. It has been known for some time that the crystal is optically active with space group P63 (C 6) (Sorge & Hempel, 1986;Klapper, Hahn & Chung, 1987), although complex twinning often obscures the optical rotation.…”

Relation between the optical properties and structure of KLiSO4in the room-temperature phase

“…This large r explains the observation reported by Sorge & Hempel (1986) and by Klapper, Hahn & Chung (1987) that under a polarizing microscope the maximum brightness difference in domains with opposite gyrations is achieved with the polarizers slightly deviated (by about 5 ° ) from the crossed position.…”

“…It is worth noticing that, although p[100] is small, the relative effects of the optical activity with respect This gives r = 10-2 at room temperature, a value ten times larger than, for example, that of quartz (Moxon, 1990). This large r explains the observation reported by Sorge & Hempel (1986) and by Klapper, Hahn & Chung (1987) that under a polarizing microscope the maximum brightness difference in domains with opposite gyrations is achieved with the polarizers slightly deviated (by about 5 ° ) from the crossed position.…”

“…Since the relative amount of twins depends on the crystal growth conditions and thermal history of the sample, care must be taken when using experimental techniques that require single crystals. This explains, for example, differences higher than 100% in the optical-activity values reported by several authors (Bansal, 1984;Ivanov, 1985;Sorge & Hempel, 1986;Kleemann, Schfifer & Chaves, 1987;Klapper, Hahn & Chung, 1987).…”