The impact of lanthanum doping on the microstructure and colossal permittivity in BaxSr(1-x)TiO3

In this work BaSrTiO₃ with three different Ba/Sr (45/55, 55/45 and 65/35) ratios and lanthanum doping concentrations of 0, 0.2, 0.4 and 0.6 ​mol.% were studied. Samples were fabricated through the mixed oxide route. The microstructures were analyzed and the phases of the compositions were defined by XRD. The increase in lanthanum doping had a pronounced decreasing effect on the grain size. The temperature dependent dielectric characteristics were measured between 0.1 and 1000 ​kHz in the temperature range of -68 – 150 ​°C. Colossal permittivity was found in all doped samples with a Ba/Sr ratio of 65/35 from which the 0.6 ​mol. % doping level of lanthanum showed the most promising characteristics with relative permittivity >48,000 and a dielectric loss ≤0.06 over the whole temperature range below 1 ​kHz. It was found that the relaxation of the colossal permittivity effect exhibited a frequency shift at the Curie temperature.