Estudo das transições de fase bansal e tomaszewski em cristais de LiKx(NH4)1-xSO4

Abstract

ln this work we investigate the normal vibrational modes of de LiKx(NRi)1-x SO4 (KLAS) by Raman scattering technique in the temperature range between 100 K and 300K. X- ray measurements points to a hexagonal structure (C/) to KLAS with two molecules per unit cell at room temperature. With Raman measurements it was possible to show that between 100 K and 300 K, by increasing the temperature, KLAS undergoes two phase transitions - one at 275 K, the Bansal transition, and another at 160 K, the Tomaszewski transition. ln the first transition KLAS goes to a trigonal structure (C3v4) and in the second phase transition, the structure is possibly orthorombic (C2/2). ln the first phase transition it was observed hysteresis effect, while in the second phase transition tht:re is no hysteresis effect. This means that the NHi ion is destroying the hysterese in the cristal of Li.KSO4, because in this material with no impurity the Tomaszewisk phase transition is observed with 21 K difference by increasing and decreasing the temperature.