Two-step sol–gel method for preparing MgO–MnO2–B2O3–Li2O co-added core-shell structural Ba0.55Sr0.40Ca0.05TiO3 powders and the dielectric properties of the composite ceramics

Abstract

The Ba0.55Sr0.4Ca0.05TiO3–MgO (BSCT–MgO) composite powders possessing core-shell structure, small particle size and high specific surface area were prepared by the novel two-step sol–gel method which was based on the citric acid (CA)–ethylene glycol (EG) system. In this experiment, the Ba0.55Sr0.40Ca0.05TiO3 (BSCT) powders were firstly synthesized by chemical co-precipitation method. MgO [(MgO/BSCT)mass = 1] and MnO2 [(MnO2/BSCT)mole = 0.01] were added into the BSCT powders in the first sol–gel step. 1.5 wt% B2O3–Li2O as sintering aids was added into the composite powders during the second sol–gel step. The BSCT–MgO composite powders were detected to have a perfect core-shell structure which was detected by the transmission electron microscope. Perovskite BSCT and periclase MgO were confirmed to exist in the BSCT–MgO composite powders according to the X-ray diffraction patterns. The Ba0.55Sr0.4Ca0.05TiO3–MgO (BSCT–MgO) composite ceramics that synthesized with the core-shell powders were sintered at 1,000 °C for 2 h. According to the scanning electron microscope images, the grain sizes of BSCT and MgO in the BSCT–MgO composite ceramics were in the range of 0.5–2.0 μm and 1.0–2.5 μm, respectively. The dielectric constant of the BSCT–MgO composite ceramics was 210 and the dielectric loss was 0.0012 when tested at 1 MHz, room temperature. The BSCT–MgO composite ceramics were expected to be a promising candidate for applying as phase shifters or tunable components, etc, in the microwave field.