Control of Impurity Phase Segregation in a PdCrO${}_2$/CuCrO${}_2$ Heterostructure

Abstract

PdCrO${}_2$ films are synthesized on CuCrO${}_2$ buffer layers on Al${}_2$O${}_3$ substrates. This synthesis is accompanied by impurity phase segregation, which hampers the synthesis of high quality PdCrO${}_2$ films. The potential causes of impurity phase segregation were studied by using a combination of experiments and ab initio calculations. X-ray diffraction and scanning transmission electron microscopy experiments revealed impurity phases of Cu${}_x$Pd${}_{1-x}$ alloy and chromium oxides, Cr${}_2$O${}_3$ and Cr${}_3$O${}_4$, in PdCrO${}_2$. Calculations determined that oxygen deficiency can cause the impurity phase segregation. Therefore, preventing oxygen release from delafossites could suppress the impurity phase segregation. The amounts of Cr${}_2$O${}_3$ and Cr${}_3$O${}_4$ depend differently on temperature and oxygen partial pressure. A reasonable theory-based explanation for this experimental observation is provided.

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