Grain Size‐Dependent Properties of Dense Nanocrystalline Barium Titanate Ceramics

Abstract

The grain size influence on the dielectric relaxation and nonlinear dielectric properties of BaTiO 3 ceramics with grain size in the range of (92Ä936) nm densified by Spark Plasma Sintering (SPS) from ultrafine powders were investigated. The progressive reduction of the Curie temperature and of the effective permittivity results from a combination of intrinsic size effects and low-permittivity grain boundary layer. A model of dielectric cylindrical cavities was employed in order to calculate intrinsic effective permittivity values in GHz range. An interesting feature is the presence of a thermally activated Debyelike relaxation in the ferroelectric state of ceramics with grain size above 300 nm, with activation energies of 0.45-0.49 eV, which seems to be related to the domain walls forced motion under the applied field. By diminishing grain size, a progressive reduction of the ferroelectric nonlinear character was obtained, reaching a macroscopic non-switching character and a linear permittivity versus field dependence for the finest ceramics (grain size of 90-100 nm) until very high values of the applied field. The observed behavior supports the idea of frozen polarization induced by pinning centers as due to a large number of grain boundaries and charged defects in the fine structures.

Preparation and properties of La doped PZT 90/10 ceramics across the ferroelectric–antiferroelectric phase boundary

“…1). Since the reducing of both porosity [29] and ceramic grain size normally causes a reduction of material constants as result of a "dilution" effect [30], it means that much higher permittivity values can still be achieved around this composition, by optimising the sintering strategy for a better densification. In the present work, we preferred to maintain the same sintering parameters for all the compositions, in order to describe the role of La 3þ addition only.…”

Study of the role of porosity on the functional properties of (Ba,Sr)TiO 3 ceramics

“…BT and its solid solutions are lead-free ferroelectrics with a wide range of permittivity varying from a few hundreds to thousands, depending mainly on the doping level, microstructural characteristics, density and grain size, temperature range and applied field [7][8][9][10][11]. Ba 1Àx Sr x TiO 3 (BST) solid solution is one of the most favorable electronic materials due to its composition-dependent Curie temperature in a large temperature range and excellent electrical properties.…”

Functional properties of Sm2NiMnO6 multiferroic ceramics prepared by spark plasma sintering

“…The samples were polished and than annealed at 700°C for 24h in order: (i) to minimize the concentration of the oxygen vacancies originated by the reducing conditions of the SPS process; (ii) to remove possible surface carbon contamination and (iii) to relieve the residual stresses arising either from the SPS process or from polishing [24].…”