Effect of calcination conditions and excess alkali carbonate on the phase formation and particle morphology of Na0.5K0.5NbO3 powders

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 degrees 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 degrees C for 2 h. Primary particles in 5 mol% excess samples were cuboid, with maximum sizes of similar to 2.5 mu m. Equiaxed 0.3-0.4-mu m 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.