The decomposition of praseodymium carbonate, carbonate hydrate, and hydroxy carbonate: An in situ study by High-Resolution Electron Microscopy

Abstract

High resolution electron microscopy (HREM) has been successfully used to study electron-induced chemical decompositions in the past few years. With HREM having near-atomic resolution, atomic-level details can provide insight into the mechanisms of solid state reaction. In this work the in situ decomposition of Pr2(CO3)3, Pr2(CO3)3·8H2O and PrCO3OH has been studied.The starting materials were prepared as described elsewhere. Samples for HREM were prepared by crushing the crystal fragments in an agate mortar and placing a drop of the suspended powder in absolute alcohol on a holey carbon film supported on a copper grid to provide a distribution of fine crystal flakes. The samples were then studied by using a JEOL 4000EX microscope operated at 400KV and fitted with double-tilt-lift stage. The current density on the specimen was varied by changing the size of condenser aperture and spot providing various amounts of irradiation and heat transfer.The decomposition reaction was rapid, hence it was not possible to get good HREM images of the starting material. Fig. 1a shows the diffraction pattern of the starting materials. Fig. 1b presents a sequence of images showing crystallization of (PrO)2CO3 (type II), growing from the edge inward.