Publications
Chem-prep PZT 95/5 for neutron generator applications : effects of lead stoichiometry on the microstructure and mechanical properties of PZT 95/5
The microstructure and mechanical properties of niobium-modified lead zirconate titanate (PNZT) 95/5 ceramics, where 95/5 refers to the ratio of lead zirconate to lead titanate, were evaluated as a function of lead (Pb) stoichiometry. Chemically-prepared PNZT 95/5 is produced at Sandia National Laboratories by the Ceramics and Glass Processing Department (14154) for use as voltage elements in ferroelectric neutron generator power supplies. PNZT 95/5 was prepared according to the nominal formulation of Pb{sub 0.991+x}(Zr{sub 0.955}Ti{sub 0.045}){sub 0.982}Nb{sub 0.018}O{sub 3+x}, where x (-0.0274 {approx}< x {approx}< 0.0297) refers to the mole fraction of Pb and O that deviated from the stoichiometric value. The Pb concentrations were determined from calcined powders; no adjustments were made to Pb compositions due to weight loss during sintering. The microstructure (second phases, fracture mode and grain size) varied appreciably with Pb stoichiometry, whereas the mechanical properties (hardness, fracture toughness, strength and Weibull parameters) exhibited modest variation. Specimens deficient in Pb, 2.74% (x = -0.0274) and 2.15% (x = -0.02150), had a high area fraction of a zirconia (ZrO{sub 2}) second phase on the order of 0.02. As the Pb content in solid solution increased the ZrO{sub 2} content decreased; no ZrO{sub 2} was observed for the specimen containing 2.97% excess Pb (x = 0.0297). Over the range of Pb stoichiometry most specimens fractured predominately transgranularly; however, 2.97% Pb excess PNZT 95/5 fractured predominately intergranularly. No systematic changes in hardness or Weibull modulus were observed as a function of Pb content. Fracture toughness decreased slightly from 1.8 MPa{center_dot}m{sup 1/2} for Pb deficient specimens to 1.6 MPa{center_dot}m{sup 1/2} for specimens with excess Pb. Although there are microstructural differences with changes in Pb content, the mechanical properties did not vary substantially. However, the average failure stress and fracture toughness for PNZT 95/5 containing 2.97% excess Pb decreased slightly. It is expected that additional increases in Pb content would result in further mechanical property degradation. The decrease in mechanical properties for the 2.97% Pb excess ceramics could be the result of a weaker PbO-rich grain boundary phase present in the material. If better mechanical properties are desired, it is recommended that PNZT 95/5 ceramics are processed by a method whereby any excess Pb is depleted from the final sintered ceramic so that near-stoichiometric values of Pb concentration are reached. Otherwise, a PbO-rich grain boundary phase may exist in the ceramic which could potentially be detrimental to the mechanical properties of PNZT 95/5 ceramics.