Investigation of phase transitions in LiK1-x(NH4)(x)SO4 mixed crystal

We present Raman scattering results on LiK1-x(NH4)(x)SO4 mixed crystal for temperatures between 100 and 300 K. We observed that in this temperature ra nge the crystal undergoes two different phase transitions, which we call Ba nsal and Tomaszewski phase transitions. The introduction of ammonium ions i n the potassium sites increases the C-6(6) --> C-3v(4) (Bansal) phase trans ition temperature and decreases the Tomaszewski phase transition temperatur e. Finally, the most impressive effect of the presence of ammonium impurity in the LiKSO4 structure is the decrease in the temperature hysteresis of B ansal phase transition and the almost complete destruction of hysteresis in the Tomaszewski phase transition, leading to a high temperature range of s tability of the trigonal phase. (C) 1999 Elsevier Science Ltd. All rights r eserved.