Raman spectra of high-temperature incommensurate and superlattice phases of kliso4

We have measured the polarized Raman Spectra of single-crystal KLiSO4 from 293 K to above 980 K (melting is at ca. 996 K), with special attention paid to the phase transitions at 709 K, 743 K, and 948 K. The 943 K transition is one of three different commensurate-incommensurate transitions in this material at ambient pressures (KLiSO4, exhibits eight phases as T is varied at zero pressure). The 743 K transition is a lock-in; and that at 709 K reduces the size of the primitive unit cell upon cooling (this is unusual; upon cooling, structural phase transitions nearly always increase the primitive cell size or keep it unchanged). Our Raman spectra in the C66 ambient temperature phase agree with those of other workers, but in the upper incommensurate phase and in the “lock-in” superlattice phase we measure three A(TO) superlattice modes at 76, 117, and 545 cm-1, assigned as TA(K), LA(K), and TO(K), respectively, of the ambient hexagonal unit cell, plus an E1-symmetry superlattice mode at 520 cm-1.

Notes

Institute for Materials Analysis, Nanjing, China

University of Campinas, S.P., Brazil; University Puerto Rico, San Juan, P.R.