Processing and electrical properties of Pb0.6Ba0.4Nb2O6 ceramics

Lead barium niobate (PBN or PbxBa1-xNb2O6) is a promising tungsten bronze ceramic system that has a morphotropic phase boundary between the orthorhombic and tetragonal phases at x approximate to 0.63, where the spontaneous polarization (P-s approximate to 60-70 mu C/cm(2)) and other ferroelectric properties are known to be higher. However, even textured PBN60 ceramics have low P-s (similar to 23.9 mu C/cm(2)) and piezoelectric charge coefficient (d(33) approximate to 236 pC/N) as compared to the single crystal counterparts. The aim of this study is to control powder processing, green body formation, and sintering conditions to enhance both densification and electrical properties. Therefore, samples were prepared by tape casting methods using single phase PBN60 and reactive mixture of PbNb2O6 and BaNb2O6 powders. Three wt% excess PbO was found to be necessary for densification. Our results showed that undoped PBN60 ceramics reached P-s = 33 mu C/cm(2), d(33) = 305 pC/N, and had a T-c = 340-350 degrees C. These results are much higher than the reported values in the literature, which can be attributed to the careful ceramic processing such as tape casting (e.g., homogenous green structure), annealing (e.g., control of excess grain boundary phase), and liquid phase sintering (e.g., higher densification).