Chemical inhomogeneities of flux grown rare-earth aluminate RAlO3 (R = La,Gd, Tb, Dy, Ho and Er) crystals

Results of scanning electron microscopy and energy dispersive X-ray analysi s of the microstructures on the surfaces of flux-grown crystals of RAlO3 (R = La, Gd, Tb, Dy, Ho and Er) an reported. The results of the microanalytic al characterisation of these crystals grown from PbO-PbF2 flux (with and wi thout additives) suggest their chemical imperfections due to crystallisatio n or precipitation of secondary phases in the growth of the major phase of RAlO3. The secondary phases include PbAl12O19 and Pb2OF2. Formation of othe r impurity phases mainly ROF, platinum free from or associated with flux co mponents (i.e., Pb2OF2) and a secondary phase (i.e., PbAl12O19) in the grow th of major phase RAlO3 are evidenced and the deposition of the former on t he growing crystals of the latter is explained to be taking place during eu tectic solidification. The nucleation mechanism proposed by Wanklyn and Wat ts (Mater, Res. Bull. 19 (1984) 711) applies generally to the flux growth o f RAlO3 crystals. The crystallisation of minor phases in the growth of a ma jor phase (viz., RAlO3) and formation of other impurity phases in the multi component system and the containing crucible involved in flux growth techni que, leading to inhomogeneity of crystal surfaces, are discussed. (C) 2000 Elsevier Science B.V. All rights reserved.