Structural freedom, topological disorder, and the irradiation-induced amorphization of ceramic structures

The susceptibility to irradiation-induced loss of long-range translational and orientational order during amorphization of crystalline solids, a process which usually amounts to topological disordering, can be understood on the basis of available structural freedom which depends on the redundancies present in structural connectivity. A surprisingly good correlation has been established between the critical accumulated energy deposited per atom - or displacements per atom (dpa) - required for amorphization during ion irradiation and the calculated structural freedom for the structure type irradiated over a wide range of non-metal structural types. These include AO, AO(2), A(2)O(3), ABO(3), ABO(4), A(2)B(2)O(7) and A(2)BO(4) compact structure types, in which weakest links can often be identified, as well as less-compact network structures. The present contribution specifically compares the order of-susceptibility to amorphization - in these more complex oxide structures and in the simpler network structures Si3N4, SiC, Be2SiO4, AlPO4, Si, SiO2, P2O5 and graphite - on the basis of structural connectivity and discusses the anomalous susceptibility of SiC.