New progress in development of ferroelectric and piezoelectric nanoceramics

There has been great progress in the last decade in the synthesis of nanopowders with highly controlled size and size distribution. Meanwhile, the development of an unconventional pressureless two-step sintering strategy enabling densification without grain growth provides a novel technology suitable for commercial production of nanograin ceramics. The particular interest concerning bulk dense nanograin ceramics is the manifestation of ferroelectricity, which remains a fundamental issue to be understood and exploited. Combining the best powder synthesis and optimized two-step sintering, high-density barium titanate (BT) and related nanograin ceramics have been fabricated to allow for a detailed determination of the size effect on nanometer-scale ferroelectricity and piezoelectricity of fundamental and industrial interest. These include dense ceramics of undoped BT with an average grain size down to 5 nm, and of (1−x)BiScO₃−xPbTiO₃ (BSPT) solid solutions with an average grain size down to 10 nm. Here we review the fabrication methods of high-density BT and BSPT nanoceramics and the major findings of the size effect on their microstructure, phase transition and electrical properties. Robust ferroelectricity is demonstrated for the first time in 5 nm BT nanoceramics, while strong local piezoelectricity is present in 10 nm BSPT nanoceramics.