High temperature solution growth of perovskite Pb 2CoWO 6 single crystals

Abstract

Single crystals of the perovskite Pb 2CoWO 6 (PCW) of sufficient size and homogeneity for optical and X-ray characterizations have been grown in sealed Pt crucibles by a slow cooling method of high temperature solution growth using PbO as flux. The best growth conditions were found to be: (1) 1130 to 830°C as growth temperatures, (2) (1 − x)PCW + xPbO with x (in wt%) varying from 0.35 to 0.43 as starting compositions and (3) 0.3 to 0.4°C/h as cooling rates. The common problem of separating the grown crystals from the residual flux has been solved by a flux separation technique using a porous ceramic piece which sucked the liquid at the end of the growth process inside the sealed Pt crucible. The growth morphology of PCW was found to be related to the cooling rate of the growth solution. Quasi-cubic {100} crystals with small {111} faces were grown at a small cooling rate, whereas cubo-octahedral {111}+{100}; crystals at a higher cooling rate. The PbO concentration in the starting composition was shown to have no significant effect on the growth morphology of PCW. Growth mechanisms are discussed according to the results of some surface micromorphological observations. Growth spirals and growth layers were observed on the (100) surface, giving evidence of a layer growth mechanism. A higher cooling rate induced growth instability and brought on formation of hopper crystals which are difficult to be cut and polished into thin plates necessary for subsequent characterizations. Some results of a polarized light microscopy study of domains in transmitted light and of X-ray diffraction characterizations are summarized, showing the high quality of the grown crystals.