Место издания:INŠTITUT ZA KOVINSKE MATERIALE IN TEHNOLOGIJE LJUBLJANA
Аннотация:Barium titanate (BaTiO3) based ceramics is widely used in electronic industry as material with extremely high dielectric permittivity up to thousands at room temperature1. In present work BaTiO3 powder was synthesized by thermovaporous method, which was industrially approved for other complex oxides obtaining2. The synthesis was carried out in water vapour at 350°C, 16 MPa for 0-24 hours using BaO and TiO2 (29% anatase and 71% rutile) as reagents. From XRD data the process lead to crystalline single-phase BaTiO3 regardless to its duration. The morphology of product studied by SEM depends on processing time and shows different shape of particles and grade of aggregation. Taking into account the requirements for BaTiO3 powder as raw material for ceramics (nano-sized, well-dispersed, sphere-shaped, uniform particles3,4), sample synthesized for 3 hours was chosen for ceramics preparation as it consists of 80-90 nm weekly aggregated sphere-shaped crystals. Two series of pellets were uniaxially pressed at 100, 150 and 200 MPa with 1% PVA. In appliance with literature the first series was sintered at 1300°C for 1 hour1. Density of obtained ceramics is 84-86% of theoretical value (6,01 g/cm3)5. Average grain size from SEM study is 170 nm. Microstructure includes micrometer-sized plates, formed due to recrystallization, and pores. Porosity causes low values of dielectric permittivity: at 20 Hz – 2 MHz it varies in ranges 84-68, 93-83, 120-82 for pellets pressed at 100, 150 and 200 MPa, respectively. For the second series of pellets sintering temperature lowered to 1200°C and sintering time increased to 5 hours in order to prevent recrystallization process and decrease the porosity. The density of as-prepared ceramics is about 94% of theoretical value and corresponds to improved dielectric properties.
