Liquid-phase sintering of PZT ceramics

Lead zirconate titanate (abbreviated as PZT) ceramics are of considerable commercial importance for a host of piezoelectric and pyroelectric applications. Conventionally, many PZT ceramics are sintered at temperatures above 1250°C. Such extreme temperatures are undesirable due to the increased energy consumption, limitation of electrode material and evaporation of volatile components. A liquid-phase sintering aid incorporating Cu2O and PbO is presented which demonstrates a reduction in the required sintering temperature of these ceramics. This new aid is described with particular reference to a commercial PZT, termed Pz26, used industrially for its optimised piezoelectric properties. Pz26 has a composition near the morphotropic phase boundary and possesses a tetragonal crystalline structure. Typically this material is sintered between 1260 and 1300°C for 1 h to achieve the required densification. With the inclusion of sintering aid, sintered densities comparable to those obtained by conventional sintering are achieved at only 800°C. The optimum weight percentage of sintering aid varies for different ceramic materials, particle sizes, morphology and the desired sintering temperature. However, with standard “mixed-oxide” produced Pz26 powder and with a median particle size in the range 1.6–1.7 μm, a value of 5 wt.% allows sintering at 800°C, according to densification, dielectric and piezoelectric measurements (ϵ=873, tan δ=1.13 %, kp=43.1%). When finer grained powder is used (d0.5=1.1 μm), improved properties (ϵ=960, tan δ=1.04%, kp=51.7%) are obtained for an addition of 3 wt.% sintering aid and a sintering temperature of 850°C.