Transport and Defect Mechanisms in Cuprous Delafossites. 2. CuScO2 and CuYO2

The delafossite structure (ABO2) accommodates a wide range of transition and rare-earth cations on the B-site in combination with a short list of A-site cations. This paper reports the effects on defect chemistry and transport as a function of the B-site cation in copper-based delafossite materials, with CuScO2 and CuYO2 as examples. Large B-site cation delafossites exhibit small polaron conduction, a diffusion-limited conduction mechanism, with an activation energy approximately twice that of CuAlO2 (0.22 eV vs 0.14 eV, respectively). The mobility for these materials is found to be <1 cm2 V-1 s-1, further evidence of small polaron conduction. The majority defect species is highly dependent on the B-site cation, such that CuScO2 and CuYO2 are dominated by extrinsic defects (acceptor doping) and free oxygen interstitials, whereas off-stoichiometry dominates CuAlO2. Dopant solubility is shown to be 1% for bulk CuScO2 samples and lower in CuYO2.