Optical properties of c-axis oriented Ba₂NaNb₅O₁₅ thin films formed by electron cyclotron resonance plasma sputtering

Thin films of Ba₂NaNb₅O₁₅ (BNN) with (001) orientation were formed on sapphire (0001) substrates by electron cyclotron resonance plasma sputtering using ring shaped targets. The thin films were obtained at a substrate temperature of 773 K using a target of Ba : Na : Nb= 1.2 : 1.2 : 5.0 composition. The surface of BNN thin films was flat. The thickness of BNN thin films was estimated to be 7.2 μm. The absorption edge of BNN films was about 310 nm. The transmittance in the wavelength between 400 and 2500 nm was more than 75%. The refractive index of the film was estimated to be 2.25-2.34 at 1100 to 2500 nm.