Local Distortions in Nanostructured Ferroelectric Ceramics through Strain Tuning

Ferroelectric materials are highly sensitive to grain size reduction because strain and ferroelectric polarization have a direct connection. Using 15 nm (Ba,Sr)TiO3 particles obtained by advanced supercritical synthesis and their densification by high‐pressure spark plasma sintering under air, reproducible and dense nanostructured ceramics are achieved. Taking advantage of the high pressure (up to 600 MPa) applied during the sintering step, the internal stress generated at the grain scale can be monitored to compensate for the particle surface stress due to size effect. Both the local dynamics observed by Raman scattering and the overall dielectric behavior consistently indicate a recovery of the ferroelectric properties as the sintering pressure is increased. This unique behavior shows that low‐temperature and high‐pressure processing enables designing nanostructured functional ceramics exhibiting original properties. Supercritical fluid synthesis is combined with high‐pressure densification by spark plasma sintering under air to produce highly densified nanostructured ferroelectric ceramics with grain sizes below 20 nm. Increasing the uniaxial pressure during the sintering step impacts the local structure and leads to an increase of the transition temperature. The process can be tuned to achieve desired ferroelectric properties.