Thermally induced crystallization of mechanically alloyed Na0.5Bi0.5TiO3 and K0.5Bi0.5TiO3 piezoelectric ceramic nanopowders

Thermally induced crystallization of mechanically alloyed K0.5Bi0.5TiO3 and Na0.5Bi0.5TiO3 piezoelectric ceramic nanopowders was investigated. The raw materials with a distinct molar ratio were initially mixed and milled in a high-energy ball mill under air atmosphere at room temperature for 1 h. After the mechanical activation, the resultant powders were annealed between 500 and 700 °C for 1 h to crystallize the mechanosynthesized powders. The results show that the mode of the reaction was progressive and consists of two stages: (i) the decomposition of some reagents to oxides and (ii) the reaction of Bi2O3 and TiO2 with potassium and sodium oxides which led to the formation of fine powders. From the structural point of view, the crystallite size and lattice strain of K0.5Bi0.5TiO3 nanopowder were 30 nm and 0.427%, respectively, while the Na0.5Bi0.5TiO3 powder gave a crystallite size of 37 nm and lattice strain of 0.340%. In accordance with the TEM images, upon heat treatment at 700 °C, coalescence of the grains led to the appearance of relatively large grains, with cubic (55±10 nm) and spheroidal (75±15 nm) morphologies, for the K0.5Bi0.5TiO3 and Na0.5Bi0.5TiO3 powders, respectively.