Origin of high piezoelectric activity in ferroelectric (K0.44Na0.52Li0.04)-(Nb0.84Ta0.1Sb0.06)O3 ceramics

We study the temperature dependence of dielectric constant (K) and spontaneous polarization (P-s) in the range of -95-200 degrees C. Cubic (C)-tetragonal (T) and T-orthorhombic (O) transitions are observed at 264 and 25 degrees C, respectively. The Curie-Weiss temperature of C-T transition is 249 degrees C, indicating it is first order. X-ray data indicate T-O phase coexistence at 25 degrees C. A singularity in P-s at 25 degrees C and a T-O phase coexistence spanning 25-31 degrees C was observed, wherein P-s increases from 17x10(-2) C/m(2) at 31 degrees C to 23x10(-2) C/m(2) 25 degrees C. The transition at 25 degrees C appears diffusionless and polymorphic with martensite start and finish temperatures of 31 and 25 degrees C, respectively. The maximum in d(33) is 345 pC/N and is attributed to the instability at 25 degrees C, where P-s and K show singularity. (c) 2008 American Institute of Physics.