Preferred orientations and microstructures of lanthanum phosphate films prepared via laser chemical vapor deposition

Abstract

In this study, the vapor-phase growth of lanthanum phosphate (LaPO4 monazite) films having preferred orientations on polycrystalline alumina substrates was demonstrated via laser chemical vapor deposition using metal-organic precursors. The effects of the laser power densities and oxygen (O2) partial pressure on the crystal orientations, microstructures, and textures of the LaPO4 films were investigated. Monoclinic LaPO4 monazite was grown at laser power densities of 62–96 W cm−2 (deposition temperatures of 1075–1120 K) and an O2 partial pressure of 257 Pa. The (111¯)-oriented LaPO4 films with small pyramidal facets of less than 1 μm in sizes and large platelets were grown at laser power densities lower than 85 W cm−2. The preferred orientation of the monoclinic LaPO4 changed from (111¯) to (101¯) as the laser power density was increased to 95 W cm−2, at which large platelets inclined from the substrate surface were formed. Deposition with a reduced O2 partial pressure of 200 Pa induced the growth of highly (111¯)-oriented LaPO4 films with small pyramidal facets, which comprised (001), (100), and (010) faceted planes. At a low O2 partial pressure of 133 Pa, (100)-oriented LaPO4 films with platelet grains vertically grown from the substrate were formed. The deposition rates of the LaPO4 films were as high as 58.6 μm h−1.