Grain core and grain boundary electrical/dielectric properties of yttria-doped tetragonal zirconia polycrystal (TZP) nanoceramics

Bulk samples of nanocrystalline tetragonal zirconia polycrystal (TZP), with 3 mol.% Y₂O₃, were fabricated over a range of average grain sizes (16-70 nm) by partial sintering. The samples were measured using AC-impedance spectroscopy over a range of temperatures, and porosity-corrected electrical results were interpreted in terms of microstructural models. Whereas the conventional brick layer model (BLM) significantly overestimated the specific grain boundary conductivity at the nanoscale, our recently developed nano-Grain Composite Model (n-GCM) allowed accurate determination of local grain boundary and grain core conductivities, grain boundary dielectric constants, and electrical grain boundary widths. Grain core effective dielectric constants were also separately measured on microcrystalline samples over a range of temperatures for use in the n-GCM analysis. It was found that TZP exhibits an enhanced local grain boundary conductivity at the nanoscale, but the enhancement is insufficient to improve the total conductivity. Rather, total conductivity decreased with decreasing grain size. Results were compared with those for nanocrystalline yttria-stabilized zirconia (8 mol.% Y₂O₃, YSZ).