The effect of LaFeO 3 addition to Bi 1/2 (Na 0.78 K 0.22 ) 1/2 TiO 3 ceramics on the phase stability and macroscopic functional properties was investigated. Similarly to other chemical modifiers known in the literature, LaFeO 3 addition suppresses an electric-field-induced long-range ferroelectric order, giving rise to a giant unipolar strain of ∼0.3% at 2 mol% LaFeO 3 addition. Time-dependent changes in polarization and strain hysteresis loops both during successive electrical cycling and after removal of the electric field suggest that a specimen with 2 mol% LaFeO 3 consists of both ergodic and nonergodic phases, which is unique among the known relaxor materials.

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Abstract. Lead-free (K 0.38 Na 0.58 Li 0.04 )(Nb 0.86 Ta 0.10 Sb 0.04 )O 3 (KNLNTS) + x mol% Fe 2 O 3 (x = 0 ~ 1) ceramics were prepared by conventional solid state reaction technique. The effect of Fe 2 O 3 doping on the phase structure, microstructure and electrical properties of KNLNTS ceramics were studied. The addition of Fe 2 O 3 was found to be effective in enhancing densification of KNLNTS ceramics. When x = 0.3, the piezoelectric constant d 33 and planar piezoelectric coupling coefficient k p reached highest while maintaining a relatively high Curie point of 318 o C; d 33 =257 pC/N and k p =52 %, which suggests that the ceramics are promising for electromechanical transducer and actuator applications.

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The effects of CaZrO3 substitution on the crystal structure, electric field–induced strain, and piezoelectric properties of Bi0.5(Na0.78K0.22)0.5TiO3 ceramics have been investigated. The CaZrO3 substitution resulted in a transition from ferroelectric tetragonal to pseudocubic symmetry with relaxor characteristics, leading to degradations in the piezoelectric coupling coefficient, electromechanical quality factor, and piezoelectric coefficient d33. However, the electric field–induced strain was significantly enhanced by the CaZrO3-induced phase transition and reached a highest value of Smax/Emax = 617 pm/V when CaZrO3 content reached 3 mol%. The result supports a prediction that a large strain at the ferroelectric–relaxor transition region can be observed when the tolerance factor of the Bi-perovskite is decreased by the substitution of ABO3-type modifiers.