Preparation of Ca2Ti2O6 pyrochlore films by MOCVD

Abstract

Ca-Ti-O films were prepared on quartz substrates by MOCVD using the precursors of Ti(O-i-Pr)2(dpm)2 and Ca(dpm)2. The effects of deposition conditions on the crystal structure and microstructure of Ca-Ti-O films were investigated. The deposition temperatures (Tdep) were changed from 787 to 1187 K and the total pressures in the reaction chamber (Ptot) was kept at 0.8 kPa. The molar ratio of Ca to Ti precursors (RCa/Ti) was changed from 0.34 to 0.95. At temperatures higher than 1073 K, CaTiO3 perovskite films in a single phase were obtained. Mixtures of Ca2Ti2O6 in a pyrochlore structure and CaTiO3 in a perovskite structure were obtained at 787 to 1073 K and the content of Ca2Ti2O6 phase increased with decreasing RCa/Ti. Ca2Ti2O6 pyrochlore films in a single phase were obtained at Tdep = 1073K and RCa/Ti = 0.38. Ca2Ti2O6 is a face-centered cubic structure with a=0.990 nm. Pyrochlore showed a granular microstructure about 500 nm in grain size. The transmittance of the Ca2Ti2O6 films in a single phase was 50% to 70% in the wavelength range of 500 to 2500 nm. The band-gap of pyrochlore was about 3.3 eV that calculated by the transmittance. The permittivity of Ca2Ti2O6 films was about 100 from room temperature to 700K.