Phase diagram of mixed LiK1-xRbxSO4 crystals

Neutron powder thermodiffractometry has been used to determine the phase diagram of LiK1-x RbxSO4 mixed crystals (x less than or equal to 0.50), between 50 and 800 K. We observed that, in this temperature range, these crystals undergo practically the same sequence of phase transitions as pure LiKSO4 crystal. The main effects of the presence of rubidium ions in the potassium sites are seen in the variations of the critical temperatures and in the smearing of the first order transitions. We observed the narrowing of the region of the room temperature hexagonal phase with increasing Rb concentration. Its upper limit temperature decreases, while the lower one increases, favoring the trigonal phase. The low-temperature ferroelastic phase is absent for crystals with Rb concentration higher than c.a. 0.30. (C) 1998 Elsevier Science Ltd. All rights reserved.