Heteroepitaxy of rare-earth hexa-aluminates on sapphire

Abstract

We have grown epitaxial thin films of rare-earth hexa-aluminates on basal plane sapphire from liquid precursors. LnAl₁₁O₁₈ (Ln = Gd³⁺, Nd³⁺) films form via the reaction of a perovskite intermediate phase and the sapphire substrate according to LnAlO₃ + 5Al₂O₃ = LnAl₁₁O₁₈. Hexa-aluminate thin films with magnetoplumbite (MP) structure grow epitaxially with (0001)_mp ‖(0001)_s, 〈1120_mp‖〈1010〉_s orientation relationship. The a-axis of the film is rotated 30°with respect to the substrate. This rotation results in a smaller mismatch (∼1%) between the two oxygen sublattices. Thermodynamic and kinetic arguments pertaining to magnetoplumbite formation for the smaller Gd³⁺ cation are presented. These epitaxial thin films are likely to have application in higher temperature ion conduction, catalysis, fluorescence, and as laser host.