Nanoscale densification creep in polymer-derived silicon carbonitrides at 1350 degrees C

The measurement of axial and radial strains during uniaxial compression cre ep of SiCN shows the deformation to be entirely volumetric (as opposed to s hear). Phenomenologically, the densification strain rate shows a good fit t o an exponential stress dependence. This result is explained by the large v olume of the diffusing molecular units in the oligomeric amorphous structur e of SiCN, which causes the driving force to become nonlinear in stress. Th e size of the diffusing unit is estimated to be 1.2 nm.