Dielectric properties of BaTiO3–NaNbO3 composites

The barium titanate (BaTiO3) is a ferroelectric material with a perovskite structure. BaTiO3 was largely studied because of its electric properties: ferroelectricity, positive temperature coefficient and piezoelectricity. Generally, BaTiO3 is doped with small amounts of impurities to modify its properties and to widen the number of potential applications. Ceramic samples with composition (1−x) BaTiO3 +xNaNbO3 (where x=0–10 mol%) were prepared by calcinations from appropriate mixture of BaCO3, TiO2, Na2CO3 and Nb2O5. The calcined powder was sintered at temperature range 1400–1500 °C. Dielectric measurements and electron microscopy analysis were made for samples characterisations. The addition of NaNbO3 to BaTiO3 causes a considerable change in the microstructure of the sample, i.e. grain growth inhibition and increase in both density and dielectric constant. It was found that Nb substitutes Ti in the BaTiO3 lattice while Na segregates in grain boundaries or into a shell structure. This kind of additive makes the dielectric constant flat in a wide temperature range. A good stability with frequency and a maximum dielectric strength of 65 kV/cm was also achieved.