PHASE-DIAGRAM OF MIXED LIK1-XRBXSO4 CRYSTALS

Neutron powder thermodiffractometry has been used to determine the pha se 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 transi tions as pure LiKSO4 crystal. The main effects of the presence of rubi dium ions in the potassium sites are seen in the variations of the cri tical temperatures and in the smearing of the first order transitions. We observed the narrowing of the region of the room temperature hexag onal phase with increasing Rb concentration. Its upper limit temperatu re decreases, while the lower one increases, favoring the trigonal pha se. 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.