Ceramic materials Ba(1 − x)SrxTiO3 for electronics — Synthesis and characterization

Ceramics (Ba1 − xSrx)TiO3, (BST) with x = 0.25; 0.35; 0.40; 0.50; 0.60; 0.75; 0.90 were prepared by sintering method from BaCO3, SrCO3 and TiO2 of high purity (99.98%). The solid-state reaction was employed to obtain pure and doped BST ceramic samples. In order to improve the sintering process the following additives were added: 1.0 wt.% MgO and 1 wt.% MnO2. The sintering treatment was performed in the temperature range 1200 to 1260 °C, for 2 h. Archimedean method was used for ceramic density measurements, which was found to depend linearly on strontium content: ρ(x) = 5.42–0.88 · x, (g/cm3). SEM, EDX and XRD methods were used for sample characterization. Morphology, pores and grain size distribution of both pure and doped ceramics were investigated by SEM analysis. A bimodal grain distribution could be observed in pure BST for x ≤ 0.25, whereas a uniform one was noticed for doped samples of x = 0.25. Well faceted grains of ∼ 5 μm size, could be seen for x = 0.75 samples. Pores size has grown with the increase of Sr content. X-ray diffraction patterns have shown a dominant perovskite structure and some other minor phases. Dielectric permittivity and loss were investigated at 1 kHz, in the temperature range − 150 to + 150 °C, at a pace of ∼ 2 °C /min. Sharp transitions, with higher peaks values of permittivity were noticed with the increase of the sintering temperature. A shift of the Curie points to lower values was noticed with the increase of Sr content, according to the equation: Tc = 127.4 − 331 ∙ x. Measured at room temperature, in the frequency range of ∼ 1 GHz, permittivity was found to increase and losses to decrease with the sintering temperature. For x ≤ 0.35 permittivity of the samples, being in the ferroelectric phase could not be measured in microwave domain at room temperature. Our results point to important application of these BST compositions for microwave devices.