Sintering temperature dependent dielectric properties of Sr 0.50-x YxBa0.50 TiO3

Abstract

The polycrystalline Sr0.50Ba0.50TiO3 (SBTO) perovskite has been prepared by the standard solid state reaction technique, and is sintered at various sintering temperatures, Ts (1250, 1300, 1350 and 1400C) for six hours in air. The internal structure and the surface morphology are studied by X-ray diffraction method and optical microscopy, respectively. The X-ray diffraction analyses confirmed that the samples are of single-phase with cubic perovskite structure. Lattice parameters are calculated using the Nelson Riley function. The measured lattice constant, 0 a of SBTO is found around 3.960Å, which is almost independent of Ts. The optical micrographs of SBTO exhibit homogeneous microstructure and the average grain size (determined by the linear intercept method) increases with increase of Ts. The dielectric properties of these materials have been measured in the frequency range between 0.1 kHz-30 MHz. It is observed that the dielectric constant of SBTO increases and the loss tangent decreases with the increase of Ts at all frequency. The maximum dielectric constant, ε', of SBTO is around 1657 at 0.1 KHz for the sample sintered at 1400C while its loss tangent, tanδ marks as low as 0.013 at the same frequency at room temperature. The Sr atom is substituted by Y atom for the polycrystalline Sr0.50-xYxBa0.50TiO3 (SYBTO, x=0.0, 0.1, 0.2 and 0.3) by the standard solid state reaction technique, and the samples are sintered at two different temperatures, (Ts = 1250 and 1400C) for six hours in air. The various content of Y substitution on SYBTO shown a remarkable reduction of the tan δ while maintaining a high ε'. For the sintering temperature 1250ºC, the best dielectric properties of the SYBTO samples is Sr0.20Y0.30Ba0.50TiO3 exhibiting the tan δ 0.03 and ε' was 5252 at 10KHz. Similarly, for the sintering temperature 1400ºC, the best dielectric properties of the SYBTO samples is Sr0.20Y0.30Ba0.50TiO3 exhibiting ε' was 15616 and the tan δ 0.012 at 0.1 kHz . Impedance spectra of the SYBTO sintered at 1400ºC indicates that due to Y doping the resistivity of the grain boundary increases by an order of magnitude thereby decreasing the dielectric loss in these samples. These results indicate the suitable practical applications of the samples.