Studies of structural and dielectric properties of lead-free perovskite K 0.5 Na 0.5 NbO 3 (KNN) ceramics obtained by the substitution of 5 at% of La and Ti for ions in the A-site and B-site, respectively, and sintered at different temperatures between 1100°C and 1190°C, are presented. X-ray diffraction patterns show the successful formation of an orthorhombic perovskite phase similar to that of pure KNN. The effect of doping and sintering temperature on the dielectric properties of the resulting ceramics is discussed. Simultaneous substitution of La and Ti into the KNN (KNNLaTi) causes a shift in the ferroelectricparaelectric phase transition temperature from that of pure KNN (420°C) to considerably lower ones (81 to 110°C) for the modified compounds. A particularly important result is the appearance of a single peak in the permittivity vs. temperature curve associated with the ferroelectric-paraelectric phase transition, where the KNNLaTi compound changes from orthorhombic to cubic structure, instead of the two reported for pure KNN. This transition exhibits the characteristics of a normal diffuse phase transition with an incipient relaxer behavior.

This study is focused in the conduction processes taking place in 0.6 wt % Gd doped lead zirconate titanate samples PbZr0.53Ti0.47O3:Gd (PZT53/47:Gd) in the vicinity of the morphotropic phase boundary. Doped samples show very large dielectric permittivity with respect to that of undoped ones near the transition temperature. The frequency dependent ac conductivity of PZT53/47:Gd ceramics was studied in the 30–450 °C temperature range. X-ray diffraction analyses indicate the incorporation of Gd atoms to the structure. The changes in the dielectric properties as functions of temperature of the doped samples are taken as additional evidence of the incorporation of Gd into the crystal structure. Gd acts as donor center promoting extrinsic n-type conduction. The ac conductivity behavior obeys Jonscher universal relation in the 100 Hz–1 MHz frequency range for temperatures between 30 and 300 °C. The measured conductivity values for Gd doped PZT53/47 are higher than those of pure PZT53/47. According to the correlated barrier hopping model, the preponderant conduction mechanism in the frequency-temperature response was recognized as small polarons hopping mechanism.

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