On the role of oxygen vacancies and lattice strain in the tetragonal to monoclinic transformation in alumina/zirconia composites and improved environmental stability

The aim of this paper is to clarify at the nanometer scale the relevant factors influencing the hydrothermal resistance to polymorphic transformation of alumina/zirconia composites, primary candidates for artificial joint applications. The topographic distribution of oxygen vacancies and lattice strain on the composite surface were visualized by means of cathodoluminescence spectroscopy and mapped as a function of exposure time in a thermally activated water vapor environment (i.e., simulating the exposure in human body). Systematically monitoring the optical activity of oxygen vacancies in both alumina and zirconia phases also revealed the effect of surface lattice strain accumulation on the kinetics of polymorphic transformation. From the presented data, an explicit role is evinced for surface oxygen vacancy formation in the alumina matrix, an important step in the complex cascade of mechanochemical events determining the superior environmental resistance of the composite.