Fig. 4.

Conceptual depiction of Cu1–Mo plane. As described in the text, the Mo is clustered into domains 12 to 20 unit cells (= 20 to 30 Mo atoms) in size, in which it can exert its preference for a distorted octahedral geometry, allowing the Cu1 to be in its preferred square geometry with its two Oaps. The disorder at the interfaces that results in some interstitial O out of this plane and the minimized contribution of the Mo–Cu pairs with bridging O caused by the strain from the average Mo–O distances being longer than the Cu–O ones is not fully shown. The alteration of the directions of the Cu–O chains at the Mo clusters result in the average tetragonal symmetry.