Superconducting cuprates with ladder-type structure

Structural units of cuprates in natural Cu-oxysalts

“…As a whole, the copper±oxygen structural units in copper oxysalt minerals correspond to the classi®cation scheme (Leonyuk et al, 1998) developed for synthetic cuprates grown from melts and¯uxes or obtained as a result of solid-state reactions. However, there are some speci®c features in the structure of minerals, which will be analyzed below.…”

“…In most synthetic cuprates, the structural category of isolated (Cu, O) complexes was represented by isolated squares and by the combination of different isolated units (Leonyuk et al, 1998). In copper oxysalt minerals, the isolated Acta Cryst.…”

“…In this respect, a structural similarity of copper±oxygen compounds with well investigated silicates and borates allowed the separation of the individual class of cuprates (Leonyuk et al, 1997), as the salts of hypothetical copper acids. The structural classi®cation scheme for cuprates was developed (Leonyuk et al, 1998). Therefore, the fourfold coordination of Cu atoms is assumed to indicate the role of copper as acid-forming element by analogy with Si, B etc.…”

“…(ii) All cuprates considered in the previous classi®cation scheme ( Leonyuk et al, 1998) were grown from the melt, while oxysalts, both natural and synthetic, were usually formed under a hydrothermal process. Therefore, a separation of cuprates among oxysalts would allow one to reveal the dependence of particular structural features on the type of crystallization.…”

“…In the present work, the structures of copper oxysalt minerals are analyzed and classi®ed on the basis of the previous classi®cation scheme for cuprates (Leonyuk et al, 1998). The results of magnetic susceptibility measurements performed recently (Maltsev et al, 2001) were analyzed from the viewpoint of the developed extended structural classi®-cation scheme.…”