Sodium‐potassium niobate [Na0.5K0.5NbO3] powders were prepared following the conventional mixed oxide method. An orthorhombic XRD pattern, consistent with single‐phase Na0.5K0.5NbO3, was obtained after calcination at 900°C for 6 h. Introducing 5 mol% excess Na2CO3 and K2CO3 into the starting mixture allowed milder calcination conditions to be used, for example 800°C for 2 h. Primary particles in 5 mol% excess samples were cuboid, with maximum sizes of ∼2.5 μm. Equiaxed 0.3–0.4‐μm particles were formed for non‐excess powders, and also for powders prepared with 1 and 3 mol% excess alkali carbonates. The results suggest liquid formation during calcination of the excess 5‐mol% starting powders.

No abstract

Lead‐free piezoelectric ceramics in the system 0.95Na0.5K0.5NbO3–0.05LiTaO3 were modified with ≤1 mol% MnO. Maximum densities occurred at a sintering temperature of 1050°C. Characteristic changes in the relative intensity of X‐ray diffraction peaks were consistent with Mn ions substituting on the perovskite lattice to produce a change from orthorhombic to a mixture of tetragonal and orthorhombic phases. Grain growth during secondary recrystallization was also affected, leading to increased grain sizes. The dielectric constant increased from ∼600 in unmodified ceramics to ∼1040 in ceramics prepared with 0.5 mol% MnO.

Electrically conductive epoxidized natural rubber filled with conductive carbon black was prepared. The AC conductivity ( σAC), dielectric constant ( ɛ′), loss factor (tan δ*) and dynamic mechanical properties of the composites were studied. It was found that the epoxide groups in epoxidized natural rubber molecules positively contributed to AC conductivity, dielectric constant, and tan δ* of the composites. Especially, the composite with epoxidized natural rubber containing 50% mol epoxide (epoxidized natural rubber–50) showed better electrical and dynamic mechanical properties than the composites with epoxidized natural rubber–25 or NR. The effects of conductive carbon black loading level on electrical conductivity and dielectric constant of the epoxidized natural rubber–50/conductive carbon black composites was also studied. The percolation threshold was found at very low content of conductive carbon black at volume fraction of 0.07 with the critical exponent value 2.04. Furthermore, the glass transition temperatures of epoxidized natural rubber–50/conductive carbon black composites were higher than those of epoxidized natural rubber–25/conductive carbon black or NR/conductive carbon black composites, and increased with conductive carbon black content.