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The crystal structure of (1−x)(Na0.5K0.5)NbO3-xCaTiO3 ceramics began to change from orthorhombic to tetragonal at x≥0.03, then became a morphotropic phase boundary in which both the orthogonal and tetragonal phases coexisted at 0.03<x<0.07, and was converted to tetragonal structure at x≥0.07. The Curie temperature decreased with increasing x and the specimen became a relaxor at x≥0.03. A dense microstructure with large grains was developed at 0.04<x<0.07 due to liquid phase sintering. The relative density, grain size, and liquid phase considerably influenced the piezoelectric properties of the specimens. High piezoelectric properties of d33=241, kp=0.41, and ε3T/εo=1316 were obtained from the 0.95NKN-0.05CT ceramics sintered at 1050 °C for 2 h, indicating that the 0.95NKN-0.05 ceramic is a good candidate material for lead-free piezoelectric ceramics.

E-field induced phase transformation and associated changes in dielectric/piezoelectric properties of 〈001〉-oriented rhombohedral 0.92Pb(Zn1/3Nb2/3)O3–0.08PbTiO3 crystals were investigated. The longitudinal strain level was found to abruptly increase at 20 kV/cm, corresponding to that where an induced phase appears within a multidomain matrix. Decreases in the dielectric constant (K3T∼4000 to 500), transverse coupling (k31∼70% to 50%) and transverse piezoelectric coefficient (d31∼−1100 to −200 pC/N) associated with the induced phase were the result of increased crystal anisotropy. By contrast, the thickness coupling (kT) increased from 53% at 0 kV/cm to 64% at 45 kV/cm, associated with this phase transition. The measured dielectric and piezoelectric properties found for the induced phase state were nearly identical to those of 〈001〉 poled tetragonal (1−x)PZN−xPT (x>0.1) crystals. Based on these results, it is evident that the symmetry of induced phase is tetragonal, 4 mm.

A crystalline (Na0.5K0.5)NbO3 (NKN) phase was formed for a film grown at 600°C, but a K5.75Nb10.85O30 (KN) second phase was also observed in this film. Formation of the KN phase was due to the evaporation of Na2O. A homogeneous NKN phase was developed in the film grown at 300°C and annealed at 800°C under a Na2O atmosphere. This film exhibited the following good electric and dielectric properties: a high dielectric constant of 237.4 with a dissipation factor of 0.93% at 100 kHz, a low leakage current density of 1.0 × 10−8 A/cm2 at 0.1 MV/cm2, and the high Pr and d33 values of 21.1 μC/cm2 and 64.5 pm/V, respectively.

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