Alkaline niobate nanocrystalline powders produced by high energy ball milling and their corresponding ceramics

Abstract

Alkaline niobate ceramic system having composition (Na0.5K0.5)NbO3(KNN) has attracted attention in recent time due to its potential for replacing the widely used but highly toxic lead-based PZT piezoelectric system. One possible way for further improving the piezoelectric properties of KNN is to prepare it from nanoscale powders. In the present work, Retsch PM100 planetary ball mill has been used as a high-energy ball mill for producing nanoscale powders of (Na0.5K0.5)NbO3. The milling speed of the mill was varied from 100 rpm to 400 rpm at an interval of 75 rpm, keeping the milling time fixed for 20 hours each. TEM micrographs reveal that increasing milling speed from 100 rpm results in a gradual reduction in particle size from 90 nm till a saturation value of about 5 nm at 400 rpm. XRD studies show the crystalline phase of all the milled powders to be of single phase perovskite structure with orthorhombic symmetry. With the increasing milling time, the crystalline structure of the milled KNN powders exhibits a decreasing trend in the unit cell volume with a tendency to transform from orthorhombic phase towards tetragonal phase. Ceramics were formed by sintering these nanocrystalline powders in closed crucibles at 1110°C for 3 hours. The ceramics were found to possess different dielectric properties at different frequencies. The study indicates that high-energy ball milling is an effective technique for producing KNN nanocrystalline powders having different particle sizes and properties that can subsequently influence the electrical properties of the resulting ceramics.