Transport and Defect Mechanisms in Cuprous Delafossites. 2. CuScO<INF>2</INF> and CuYO<INF>2</INF>

The delafossite structure (ABO<INF>2</INF>) 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 CuScO<INF>2</INF> and CuYO<INF>2</INF> as examples. Large B-site cation delafossites exhibit small polaron conduction, a diffusion-limited conduction mechanism, with an activation energy approximately twice that of CuAlO<INF>2</INF> (0.22 eV vs 0.14 eV, respectively). The mobility for these materials is found to be &lt;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 CuScO<INF>2</INF> and CuYO<INF>2</INF> are dominated by extrinsic defects (acceptor doping) and free oxygen interstitials, whereas off-stoichiometry dominates CuAlO<INF>2</INF>. Dopant solubility is shown to be 1% for bulk CuScO<INF>2</INF> samples and lower in CuYO<INF>2</INF>.