This site can explain everything pertaining to the strengths of ceramics, first an excerpt then the site:

Abstract The key features of the processes underlying the failure of ceramics are considered for a wide temperature range. The brittleness and high-temperature plasticity of ceramics are correlated with their crystal chemistry. The general issues related to the strength of ceramics are treated in terms of synergetics, which deals with the spatiotemporal ordering and self-organization in nonequilibrium systems. The strength of ceramics is shown to be governed by its structure on different scales-from atomic to macroscopic. The conclusion is drawn that, in the strict sense, strength is not a property of the material; rather it characterizes its quality.

* http://www.springerlink.com/content/lf6yr4pjf5wmh425/