Grain size-driven effects on the functional properties in Ba 0.6 Sr 0.4 TiO 3 ceramics consolidated by spark plasma sintering
PATRU R. 1, STANCIU C. 2,3, SOARE M. 2,4, SURDU A. 2, TRUSCA R. 2, NICOARA A. 2, VASILE B. 2, BONI G. 1, AMARANDEI L. 1, HORCHIDAN N. 5, CURECHERIU L. 5, MITOSERIU L. 5, PINTILIE L. 1, PINTILIE I. 1, IANCULESCU A. 2
1 National Institute for Materials Physics, Atomistilor 405A, Magurele, Romania; 2 Polytechnics University of Bucharest, Faculty of Chemical Engineering and Biotechnologies, Department Oxide Materials Science and Engineering, Bucharest, Romania; 3 National Institute for Lasers, Plasma and Radiation Physics, Atomistilor 409, Magurele, Romania; 4 Institute of Physical Chemistry "Ilie Murgulescu", Romanian Academy, 202 Splaiul Independentei, Bucharest, Romania; 5 Faculty of Physics, Alexandru Ioan Cuza University of Iasi, Iasi, Romania
Dense and fine-grained Ba0.6Sr0.4TiO3 ceramics with submicronic grains sizes have been prepared using nanopowders synthesized via the sol-gel route (~69 nm particle size) and consolidated by Spark Plasma Sintering (SPS). The ceramic grain size varied from 214 nm to 74 nm by changing the sintering parameters. The grain size reduction from the submicron to the nanoscale range reflects in the functional properties of the sintered ceramics. Impedance spectroscopy analysis performed on the wide frequency and temperature ranges revealed diffused ferroelectric-paraelectric
phase transitions and low dielectric permittivity values at the Curie temperature (TC ~280 K), below 1000, for all of the sintered ceramics. Dielectric constant, tunability, polarization, and storage energy properties are gradually diminishing with the reducing grain size down to the nanoscale.
As a result of the very broad ferroelectric-paraelectric phase transformation, the polarization-field (P-E) measurements indicate the presence of switching well above TC . The observed properties of Ba0.6Sr0.4TiO3 nanostructured ceramics are interpreted by considering the interplay between the grain size reduction, the increasing role of low-permittivity grain boundaries in finer structures, and the diffuse character of the ferroelectric-to-paraelectric transformation. Raman
spectroscopy investigations pointed out the presence of polar nanoclusters above the Curie temperature. The grain size decrease affects the short-range polar order, but it seems more thermally stable for nanostructured ceramics.