Grain-Boundary Enthalpies of Cubic Yttria-Stabilized Zirconia

The change in enthalpy with grain size of dense nanograined yttria-stabilized zirconia (YSZ) was measured by oxide melt solution calorimetry of cubic 10 YSZ and 15 YSZ dense nanograined ceramic samples prepared by spark plasma sintering of nanopowders. The derived grain-boundary enthalpies are 0.68 J/m(2) for 10 YSZ and 0.64 J/m(2) for 15YSZ, with an estimated uncertainty of about+0.13 J/m(2), arising mostly from the roughly +20% uncertainty in interface area calculated from the particle size distribution. These values are similar to a previous value of 0.73 +/- 0.19 J/m(2) for 8 YSZ, suggesting a possible weak concentration dependence (decrease of grain-boundary energy with increasing dopant concentration) that may not be outside experimental error. Previously published interface enthalpies of 0.6-1.0 J/m(2) for partially agglomerated nanopowders of 8, 10, and 12 YSZ, are in general agreement with the present data on densified nanoceramics. These data, taken together, suggest the ratio of surface to interface energy increases slightly with doping level, providing a slightly higher driving force for densification and pore elimination as the yttria content is increased.