Structural, dielectric and optical properties of barium strontium sodium niobate (Sr_0.7Ba_0.3)₂NaNb₅Oi ₁₅ single crystals

Barium strontium sodium niobate (Sr₀₇Ba_0.3) ₂NaNb₅O₁₅ (SBNN70) crystals were grown by the Czochralski method. X-ray energy dispersive spectrometry showed that SBNN70 crystals have a stoichiometric composition nearly identical to the starting materials. X-ray diffraction of crushed powder indicated that the SBNN70 crystals are orthorhombic with a = 1.2748nm, b = 1.1402nm and c = 0.3898 nm. The measured temperature dependence of dielectric constants showed strongly anisotropic relaxor behaviour. The Curie temperature of the SBNN70 crystals is 186.7°C, which is 116°C higher than that of the (Sr_xBa _1-x)₅Nb₁₀O₃₀ (SEN) crystal. The transmissivity and refractive index of [001] oriented SBNN70 single crystals were measured, and a deep energy level of 3.54 eV was found. The SBNN70 crystal has better than 70% optical transmittance for wavelengths above 500 nm. The refractive index of SBNN70 is 2.004 at 632.8 nm, which is lower than 2.3117 for SEN crystals.