Crystal structure of KLiSO4 at 200 K: a neutron diffraction study

Abstract

Abstract. M r = 142.10, trigonal, P3 lc, a = 5.129, c = 8.639 A, V= 196.82 A 3, z = 2, D x = 2.397 g cm -3, 2(neutron) = 1.176 A, gc = 0.74 cm -~, T-200 K. Refinement for the ordered structure with 593 reflections with (sin0)/;t_ 0.57 A -1 gave R(F 2) = 0.055. The study has revealed merohedral twinning of *CENG DRF/Sph-MDN 85x, 38041 Grenoble CEDEX, France.0108-2701/88/040592-04503.00 the crystal about (110), with twin components in nearly equal proportion, and large thermal vibration for the oxygens. Displacing the oxygens into three disordered positions gave a somewhat better R factor.

Phase transitions in between 1.5 K and 850 K: an infrared spectroscopic study

“…More recent measurements (Rajagopal et al 1991, Bhakay-Tamhane et al 1991 seem to support the trigonal P 31c phase below room temperature. In their neutrondiffraction study, Zhang et al (1988) showed that disorder in the orientation of the sulphate groups persists in this phase. Bansal and Roy (1984) proposed that this phase transition is due to the reorientation of one sulphate group in each unit cell (there are two formula units per unit cell in the trigonal and hexagonal structures).…”

Phase transitions in polar crystal RbLiCrO4

“…At room temperature RbLiCrO, belongs to pyroelectric class with the space group P31c (hereafter G3-phase). *-3 Positional atomic parameters of the RbLiCrO, structure, are similar to these of KLiSO, at 200 K. 5 The structure changes were found at T3 = 550 K, T2 = 606 and TI = 843 K. Under X-ray investigations of polycrystalline samples above 550 K a new phase (G2) has been found by appearance of the reflections of hh%l type with 1 = 2n + 1 forbidden in G3. Additional reflections appear by jump and sharply disappear on cooling the sample down to 542 K. The reflections 001 with 1 = 2n + 1 are absent in G2 as well as in G3 phases.…”