Effects of spark plasma sintering on ferroelectricity of 0.8Bi3.15Nd0.85Ti3O12-0.2CoFe2O4 composite ceramic

The 0.8Bi3.15Nd0.85Ti3O12 (BNdT)-0.2CoFe2O4 (CFO) composite multiferroic ceramics have been fabricated by spark plasma sintering (SPS) at 850 °C. The relative density of as-sintered SPS ceramic reaches 97.4 (±0.3)%. The composites are composed of pure BNdT and CFO phases without any preferred c-orientation. The a-orientation preference is more obvious perpendicular to the pressure direction. The average grain-sizes of BNdT and CFO are 163 and 146 nm, respectively. The BNdT phase has more grains below 100 nm (∼20%). The super energy-dispersive X-ray analyses suggest no serious reaction between BNdT and CFO. The Raman spectrum verifies the nano-structure of the SPS ceramic via the broadening bands and peak shifts. The Curie temperature of the SPS ceramic declines to 560 °C with stabilized dielectric loss. The grain boundary resistance plays a dominant role on impedance above 700 °C. The remanent polarization approaches to 15.2 μC/cm2 (300 kV/cm) with lower coercive fields (−89/+95 kV/cm).