  Mechanical properties of zirconia polycrystals decrease drastically at high
temperature due to thermally activated grain boundary (GB) sliding, leading to
plastic or even super-plastic deformation. As GB sliding is a source of energy
dissipation in the material, mechanical loss measurements are well suited to
study such a mechanism. They reveal, in general, a mechanical loss peak, which
evolves into an exponential increase at higher temperature. When intergranular
glassy films or/and amorphous pockets are presented in polycrystalline
ceramics, the mechanical loss is globally higher and so is the creep rate. Here
we show that introducing carbon nanotubes in zirconia, in particular, reduces
drastically GB sliding and consequently the mechanical loss at high
temperature. The nanotubes were observed at the grain boundaries by
high-resolution transmission electron microscopy and were related to the
reduction of superplasic flow through the boundaries, which should improve the
material creep resistance.
