Particle size effects on the processing of textured PMN-PZT ceramics

Current generation textured ceramics synthesized for piezoelectric applications are generally processed by a shear-inducing technique, such as tape casting, which orients anisotropically shaped particles to seed templated grain growth and maximize the piezoelectric (d(ij)) coefficient. This work explores how changes in particle size distribution during ball milling of slurries impacts slurry rheology, texture fraction after thermal processing, and piezoelectric coefficient (d(33)) of the final, sintered ceramic. While ball milling (>72 h) of slurries did have the positive effect of further reducing the median particle size, unfortunately the slurry was observed to change from shear-thinning to shear-thickening in the shear rate range that is produced in a tape casting environment. The slurry's shear-thickening behavior at extended mill times was found to be reversible by using additional dispersant in the slurry composition, which ultimately resulted in textured ceramics with Lotgering factors ranging from 0.94 to 0.97 and piezoelectric coefficient d(33) enhancements as high as 764-807 pC/N. This work highlights the importance of careful control over slurry composition and rheology to maximize template alignment during casting needed to produce high-quality textured piezoelectric ceramics.