K. Ruck

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

Abstract 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 Neel temperature of about 27 K is concluded.

Structural and electrical properties of La{sub 2{minus}x}Ca{sub x}NiO{sub 4+{delta}} (0 {le} x < 0.4) with regard to the oxygen content {delta}

Monophasic samples of La{sub 2{minus}x}Ca{sub x}NiL{sub 4+{delta}} were prepared in the range between 0 {le} x < 0.4. Their electrical and structural properties were investigated with regard to the excess oxygen {delta}. Except for the orthorhombic phase with x = 0.1 and {delta} = {minus}0.01, all members of the system with higher excess of oxygen or calcium are tetragonal with space group I4/mmm. At temperatures below 300 C, the compounds are thermally activated semiconductors; in the range of higher temperatures, the electrical properties are influenced by oxygen exchange, which depends on the calcium doping level.