Effect of Additives of Limited Solid Solubility on Ferroelectric Properties of Barium Titanate Ceramics

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Abstract
An experimental survey of additives to barium titanate shows that in addition to those which are readily soluble in the barium titanate lattice (class 1) and those which are insoluble (class 2) two other distinct classes of additive, with limited solid solubility (classes 3 and 4), can be distinguished. Class 3 additives give normal ferroelectric properties with particularly low electrical and mechanical losses, as exemplified by BaTiO3 2 mole % NiTiO3 for which, after aging, tan δ= 10−3 and 1/Q = 4 X 10−4. Experimental results indicate that the ferroelectric loss, in high and low fields, is hysteresis loss associated with domain boundary movement and that in class 3 materials the losses are low because the domain boundaries are in particularly stable positions. Class 4 materials have useful dielectric properties associated with a crystallite size between 0.1 and 1 μ. For example, BaTiO3.3 mole % NaNbO3 has ε= 3200 × 200 between 0°C. and 120°C. with tan δ= 3 X 10−2. The absence of a permittivity peak is attributed to a distribution of the Curie temperatures of individual crystallites and the enhanced permittivity at lower temperatures to inhibition of the spontaneous polarization by the mutual clamping, in the ceramic, of crystallites which are too small to divide into 90° domains.

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