“CaCu2O3”—a nonstoichiometric compound: structural disorder and magnetic properties

In the compounds MgCu2O3 and CaCu2O3 the Cu and O atoms are connected topologically in the same way as in the fascinating spin-ladder compound SrCu2O3. In contrast to the latter, the Cu—O—Cu bonding angle corresponding to the “rungs” is significantly less than 180° in MgCu2O3 and CaCu2O3. As a consequence, the magnetic susceptibility is quite different compared with that of SrCu2O3. Single-phase samples of CaCu2O3 revealed a deficiency of Ca, a balancing excess in Cu, and an oxygen deficiency corresponding to Ca1−xCu2+xO3−δ. The excess Cu atoms, which are located near the Ca sites, are in the 3d10 state. The deficiency of oxygen causes a Curie term in the magnetic susceptibility due to the interruption of Cu—O—Cu bonds. From the overall behavior of the susceptibility an antiferromagnetic ordering at a Néel temperature of about 27 K is concluded.