Subsolidus phase relations and crystal structures of R-Ca-Cu-O (R=Nd, Sm, Gd, Tm) systems

The subsolidus phase relations of R2O3-CaO-CuO ternary systems (R=Nd, Sm, Gd, Tm) have been investigated by X-ray powder diffraction. All samples were synthesized at about 950 deg. in air. There exists a ternary compound Ca14-xRxCu24O41 (x = 4 for R=Nd, Gd and x = 5 for R = Sm) and a ternary solid solution Ca2+xR2-xCu5O10 (R=Nd, Sm, Gd, Tm) with a wide composition range Δx of about 0.6. The compound Ca14-xRxCu24O41 possesses a layered orthorhombic structure and is isostructural to Sr14-xCaxCu24O41. The lattice parameters a and c of the compound are basically independent of the ionic radius of R, while the lattice parameter b and unit-cell volume V decrease substantially with the decrease of the ionic radii of R. The Ca2+xR2-xCu5O10 solid solution is isostructural to Ca2+xY2-xCu5O10, the structure of which is based on an orthorhombic ''NaCuO2-type'' subcell containing infinite one-dimensional chains of edge-shared square planar cuprate groups crosslinked by the layered cations Ca and R that locate in the inter-chain tunnels