The un-doped and doped lead-free piezoelectric potassium sodium niobate (K0.5Na0.5NbO3, KNN) ceramics with different amounts of Mn were prepared. The decreased dielectric losses and the improved electrical properties were observed in the Mn-doped KNN ceramics. However, the variation of electrical properties with the Mn contents was not continuously. The 0.5 mol.% Mn-doped KNN ceramic shows the highest dielectric loss and the worst electrical properties. The KNN ceramics doped with less than and more than 0.5 mol.% Mn all show improved electrical properties. The change of lattice position of Mn ions in KNN ceramics was the main reason. When the Mn content is less than 0.5 mol.%, the Mn ions occupied the cation vacancies in A-site. When the Mn content is higher than 0.5 mol.%, the Mn ions entered B-site of KNN perovskite structure and formed the defect complexes (MnNb″−VO⋅⋅) and (MnNb′−VO⋅⋅−MnNb′). They both led to a lower defect concentration. However, When the Mn content is up to 1.5 mol.%, the electrical properties of KNN ceramic became degraded because of the accumulation of Mn oxides at grain boundaries.

We report high pyroelectricity in lead-free 0.5Ba(Zr0.2Ti0.8)O3–0.5(Ba0.7Ca0.3)TiO3 (BZT–50BCT) ceramics which were previously reported to exhibit high piezoelectricity. The pyroelectric coefficient measured by the Byer–Roundy method upon heating for dc-poled samples shows a high value of 5.84 × 10−4 C m−2 K−1 at 300 K, comparable to those of PZT-based ceramics and significantly higher than many other lead-free pyroelectric materials. The pyroelectric coefficient calculated from the remanent polarization versus temperature relationship obtained during a cooling process is 17.17 × 10−4 C m−2 K−1 at 300 K, which is considerably larger than the value obtained by the Byer–Roundy method. This difference is attributed to the thermal hysteresis of the rhombohedral–tetragonal phase transition between the heating and cooling processes.

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