Origin of diffuse electron scattering in yttria-cubic-stabilized zirconia single crystals with 24-32 mol% yttria

Transmission electron microscopy (TEM) of yttria (Y2O3)-cubic-stabilized zirconia with an yttria content between 24 and 32 mol% reveals diffuse electron scattering. Analysis of the diffuse intensity maxima in electron diffraction patterns recorded with the incident electron beam along < 112 > (c) or < 110 > (c) zone axes suggest that they originate from incipient microdomains of the 'delta phase', a superstructure with the composition Zr3Y4O12. A compound with this composition has been observed before, however, for Y2O3 concentrations substantially higher (40 mol% or greater) than in our case. The microdomains are probably platelets and must have a diameter of less than 10 nm, rendering them hard to detect in TEM images. A part from the delta phase, we have considered two other superstructures to explain the experimental observations, the pyrochlore type phase Zr2Y2O7 and the structure of the C-type rare-earth oxide Y2O3. However, our data allow us to rule out these superstructures as the main source of diffuse electron scattering.