STRUCTURAL FREEDOM, TOPOLOGICAL DISORDER, AND THE IRRADIATION-INDUCEDAMORPHIZATION OF CERAMIC STRUCTURES

The susceptibility to irradiation-induced loss of long-range translati onal and orientational order during amorphization of crystalline solid s, 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 accumulate d energy deposited per atom - or displacements per atom (dpa) - requir ed for amorphization during ion irradiation and the calculated structu ral 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), AB O(4), A(2)B(2)O(7) and A(2)BO(4) compact structure types, in which wea kest links can often be identified, as well as less-compact network st ructures. The present contribution specifically compares the order of- susceptibility to amorphization - in these more complex oxide structur es and in the simpler network structures Si3N4, SiC, Be2SiO4, AlPO4, S i, SiO2, P2O5 and graphite - on the basis of structural connectivity a nd discusses the anomalous susceptibility of SiC.