Effect of composition and grain size on the transport and dielectric properties of BaTi1-xZrxO3 ceramics

Abstract

n this thesis we have studied the electrical and dielectric properties of ferroelectric BaTiO3 (BTO) and BaTi1-xZrxO3 (BTZ) solid solutions with x = 0.05, 0.10, 0.15, 0.20, 0.25 and 0.30. We have investigated the effects of different parameters on the electrical and dielectric properties of BTZ ceramics, such as the sintering temperature, the grain size, the sintering atmosphere and the Zr content in the materials. Nanocrystalline powders of BTO and BTZ ferroelectric materials have been prepared by a combination of solid state reaction and mechanical milling. The particle size of the synthesized materials is below 50 nm for all compositions. We have prepared dense ceramics of BTO and BTZ materials by two techniques; the conventional sintering (CS) and the spark plasma sintering (SPS) at different temperatures. Materials characterization by XRD shows that pure BTO ceramics have tetragonal structure at room temperature. In BTZ ceramics the crystal structure changes to cubic for x ≥ 0.10 and the lattice parameter increases with Zr+4 substitution into Ti+4 site due to the larger ionic radius of Zr+4. SEM results showed that coarsegrained ceramics with grain size in the micrometer range are obtained by the CS technique. The grain size was found to increase with increasing the sintering temperature. BTO ceramics for example has grain size of 1 – 2 m after sintering at 1250 ⁰C that increases to some 50 m at 1400 ⁰C. The grain size at same sintering temperature of BTZ ceramics decreases in general with increasing the Zr content. Nanoceramics of BTO and BTZ materials have been obtained by the SPS technique. All BTO and BTZ compositions have been spark plasma sintered at 1100 ⁰C for 10 min, and the grain size was found to decrease from 200 – 300 nm for BTO ceramics to about 100 – 200 nm for BTZ30 ceramics. With increasing the SPS temperature, the grain size increases and finally ceramics with micrometer grain size are obtained at 1400 ⁰C.