Unfinished business

Abstract

Some aspects of defect chemistry do not seem to be fully settled. One of these is the limits to the application of dilute solution thermodynamics, i.e. the equivalence of concentrations and thermodynamic activities. YBa 2Cu3O6+y will be used as an example where ideal behavior can be extended to defect concentrations in excess of 10%, far greater than the limits found for aqueous solutions. Another question is to what extent different parts of single phase materials can exhibit separate and different types of defect chemistry. SrBi2M2O9 (M = Nb+5 or Ta+5) with alternating layers having different compositions and structures, is a system in which the different layers appear to have somewhat independent defect chemistries. Copyright © 2010 MS&T'10®.