Peculiarities of temperature and field dependence of tunability in Ba0.6Sr0.4TiO3 ceramics with differing grain sizes

Study of the dielectric tunability and susceptibility, in a wide temperature range and at different bias fields, in Ba0.6Sr0.4TiO3 (BST) sol–gel derived ceramics of different crystallite sizes (between 1 and 6 μm), establishes two new regularities. The first one concerns the relative temperature of the maxima positions of the tunability and susceptibility. We show that the maximum in tunability is always at lower temperatures compared to the maximum in susceptibility. The second regularity tells that the electric field dependence of the susceptibility maximum temperature is always stronger than the one for the tunability maximum temperature. In small-size crystallite BST ceramics the temperature of susceptibility maximum starts changing only above a certain threshold field. Additionally, we discuss the nature of an extrinsic contribution to tunability in small-size crystallite BST ceramics.

► Tunability study in BST ceramics with different grain sizes revealed new regularities.
► The maximum in tunability n is always at lower temperatures than in permittivity ɛ.
► Field dependence of maximum temperature is always stronger for ɛ(T) than for n(T).
► Extrinsic contribution enlarges the values of tunability of small-size crystallites.
► This contribution is due to super-dipole moments related to small crystallites.