Nanoscale Densification Creep in Polymer-Derived Silicon Carbonitrides at 1350°C

The measurement of axial and radial strains during uniaxial compression creep of SiCN shows the deformation to be entirely volumetric (as opposed to shear). Phenomenologically, the densification strain rate shows a good fit to an exponential stress dependence. This result is explained by the large volume of the diffusing molecular units in the oligomeric amorphous structure of SiCN, which causes the driving force to become nonlinear in stress. The size of the diffusing unit is estimated to be 1.2 nm.