Effects of microstructure on the dielectric and piezoelectric properties of lead metaniobate

In an attempt to obtain dense PbNb2O6 ceramics, sintering experiments were conducted using starting powders with various particle sizes and different modifications (rhombohedral and orthorhombic structures). During sintering of rhombohedral powders, the phase transformation to the tetragonal phase promoted grain growth, resulting in poor densification. Sintering of orthorhombic powders, however, yielded dense ceramics through suppression of the phase transformation. Based on these results, ceramics with various densities and different microstructures were prepared, and their dielectric and piezoelectric properties were evaluated, The dielectric constant and Curie temperature were dependent on density, grain size, and crack density. Cracks and intragrain pores severely deteriorated the piezoelectric properties, Dense ceramics with the maximum coupling factors and piezoelectric strain constants were obtained by prolonged heating of a fine powder with orthorhombic structure.