Crystal Growth, Crystal Morphology and Surface Micromorphology of Type III KGd(PO3)4and KNd(PO3)4

Abstract

Type III KGd(PO3)4 (KGP) and KNd(PO3)4 (KNP) inclusion-free single crystals can be grown using the top seeded solution growth−slow cooling method without pulling even though the viscosity of the solution is high (around 16 Pa·s-1 near the crystallization temperature). Poisoning by impurities in the crystals was minimized by using the corresponding self-fluxes as solvent. We determined their main growth process by analyzing the typical micromorphologies that appeared on the surface of the as-grown faces. The crystal morphologies of KGP and KNP were identified using X-ray diffraction analysis. The external habit of the crystals appeared to be more symmetrical than it structurally was because, although KGP and KNP are monoclinic with space group P21, they have an almost cubic cell because their cell parameters are similar and the β angle is very close to 90°. We checked the chemical stability of KGP and KNP in basic and acid media. The distribution and geometry of structural defects were studied by analyzing the etch pits that appeared on the {100}, the {010}, and the {001} forms. The crystals cleaved parallel to {010} and {001}, so the surface micromorphology of both forms was studied. We determined the orientation, the density, and the height of the cleaved planes. We also characterized the local plastic deformation of KGP and KNP by measuring the microhardness on the {100}, {010}, and {001} forms using an indentation method.