Lead-free piezoceramics with giant strain in the system Bi0.5Na0.5TiO3-BaTiO3-K0.5Na0.5NbO3.: II.: Temperature dependent properties

The temperature dependence of the dielectric and ferroelectric properties of lead-free piezoceramics of the composition (1-x-y)Bi0.5Na0.5TiO3-xBaTiO(3)-yK(0.5)Na(0.5)NbO(3) (0.05 <= x <= 0.07, 0.01 <= y <= 0.03) was investigated. Measurements of the polarization and strain hystereses indicate a transition to predominantly antiferroelectric order when heating from room temperature to 150 degrees C, while for 150 < T < 200 degrees C both remnant polarization and coercive field increase. Frequency-dependent susceptibility measurements show that the transition is relaxorlike. For some samples, the transition temperature T-d is high enough to allow mostly ferroelectric ordering at room temperature. These samples show a drastic increase of the usable strain under an external electric field just after the transition into the antiferroelectric state at high temperatures. For the other samples, T-d is so low that they display significant antiferroelectric ordering already at room temperature. In these samples, the usable strain is relatively stable over a wide temperature range. In contrast to T-d, the temperature T-m of the transition into the paraelectric high-temperature phase depends far less on the sample composition. These results confirm that the high strain in this lead-free system is due to a field-induced antiferroelectric-ferroelectric phase transition and that this effect can be utilized in a wide temperature range. (c) 2008 American Institute of Physics.