Chemical inhomogeneities of flux grown rare-earth aluminate RAlO 3 (R=La, Gd, Tb, Dy, Ho and Er) crystals

Abstract

Results of scanning electron microscopy and energy dispersive X-ray analysis of the microstructures on the surfaces of flux-grown crystals of RAlO 3 (R=La, Gd, Tb, Dy, Ho and Er) are reported. The results of the microanalytical characterisation of these crystals grown from PbO–PbF 2 flux (with and without additives) suggest their chemical imperfections due to crystallisation or precipitation of secondary phases in the growth of the major phase of RAlO 3. The secondary phases include PbAl 12O 19 and Pb 2OF 2. Formation of other impurity phases mainly ROF, platinum free from or associated with flux components (i.e., Pb 2OF 2) and a secondary phase (i.e., PbAl 12O 19) in the growth of major phase RAlO 3 are evidenced and the deposition of the former on the growing crystals of the latter is explained to be taking place during eutectic solidification. The nucleation mechanism proposed by Wanklyn and Watts (Mater. Res. Bull. 19 (1984) 711) applies generally to the flux growth of RAlO 3 crystals. The crystallisation of minor phases in the growth of a major phase (viz., RAlO 3) and formation of other impurity phases in the multicomponent system and the containing crucible involved in flux growth technique, leading to inhomogeneity of crystal surfaces, are discussed.