Duplex n- and p-Type Chromia Grown on Pure Chromium: A Photoelectrochemical and Microscopic Study

Chromia grown on pure chromium at 900 °C for 30 min at an oxygen partial pressure p (O 2 ) of 10 −12 atm has been characterized using photoelectrochemical and electron microscopy techniques. This study reveals a duplex scale: n-chromia with equiaxis morphology in the internal part (~650 nm thick) and p-chromia with columnar morphology in the external part (~900 nm thick). Grain orientation maps also revealed the presence of a c-oriented chromia layer at the interface between the n- and the p-subscales. This 〈 0001 〉 textured layer was identified as the first-grown chromia layer. It means that internal n-equiaxis chromia grew by anionic transport governed by oxygen vacancy diffusion, whereas external p-columnar chromia layer grew outwards and was controlled by chromium vacancy diffusion.