Lead-free antiferroelectric: xCaZrO3-(1 -x)NaNbO3 system (0 ≤x≤ 0.10).

This study demonstrates that antiferroelectricity can be stabilized in NaNbO(3) (NN) based ceramics by lowering the tolerance factor. Through consideration of the crystal chemistry via the Goldschmidt tolerance factor and polarizability, we show that simultaneous substitution of Zr(4+) and Ca(2+) ions in the Nb and Na sites, respectively, lowers the polarizability and tolerance factor of the (Na(1-x)Ca(x))(Nb(1-x)Zrx)O(3) (CZNN100x) solid solution, while maintaining charge neutrality. Structural investigations using both X-ray diffraction and transmission electron microscopy (TEM) indicated an enhancement of antiferroelectric (AFE) superlattice peaks with CaZrO(3) substitution. The TEM domain analysis revealed that only AFE domains existed in the CZNN4 and CZNN5 ceramics; in contrast, normal NN ceramics displayed coexistence of AFE and ferroelectric (FE) domains at room temperature. The CZNN100x (0.02 ≤x≤ 0.05) ceramics showed double polarization hysteresis loops, characteristic of reversible AFE↔FE phase transition switching. The field-induced polarization decreased drastically with increasing substitution, an effect of the decreases in tolerance factor. In addition, the AFE switching field was increased by the chemical substitution. First principles calculations are performed to obtain insights into the relative stability and coexistence of the AFE and FE phases in single domains. The large decrease of polarization in the CZNN system is explained by a modification of the relative stability of the relevant structures, which favours nonpolar-to-polar AFE transitions over polar-to-polar FE domain switching.

Size effect of barium titanate and computer-aided design of multilayered ceramic capacitors.

The size effect of BaTiO3 (BTO) is the most important issue to design multilayer ceramic capacitors (MLCCs) with high capacitance. In the size effect of BTO particles, the size dependence of dielectric permittivity related with the complex structure in BTO nano-particles. The grain size dependence of dielectric permittivity in BTO ceramics was due to the domain wall contribution. The core-shell structure played an important role in the size effect of dielectric layers in X7R-MLCCs. Computer simulation technique was developed to predict the limit of capacitance density of MLCCs produced by the current technology. Dielectric properties of MLCCs with different particle size of BTO were measured, and the data were analyzed using B-SPLINE fitting to predict dielectric permittivity at arbitrary temperatures and AC-fields. The dielectric properties of barium titanate grains smaller than 100 nm were predicted using least squares fitting of the B-SPLINE coefficients. It was found from the simulation that the use of barium titanate grains smaller than 80 nm did not give an advantage to increase the capacitance density as well as temperature stability of the MLCCs. The maximum capacitance was predicted for the 1608 (mm) chip size.