Dielectric properties of spark plasma sintered (SPS) barium strontium titanate (BST) ceramics

Grain size can have a very important effect on the dielectric properties of ferroelectric ceramics through the interaction of domain structures and grain boundaries. In this work, Ba0.15Sr0.4TiO3 ceramics were fabricated to controlled grain sizes using a spark plasma sintering (SPS) technique which can produce dense ceramics at greatly reduced sintering temperatures and times. The microstructure and dielectric properties of SPS produced ceramics have been characterised and compared with those from conventional presureless sintered ceramics. The results show that SPS ceramics exhibit a duplex microstructure with 1-3 mum BST grains surrounded by submicron BT and ST grains. Consequently, they show a significantly diffused transition in permittivity and reduced dielectric losses in the ferroelectric region compared to conventionally sintered ceramics. This is believed to result largely from the large differences in grain sizes and domain structures. The mechanisms will be discussed in terms of domain walls contributions.