HIGH-PRESSURE SYNTHESIS AND STRUCTURE OF THE NEW SPINEL-RELATED SERIES LNCU(2)O(4) (LN=ND, GD, ER, LU, Y)

The new spinel-related series LnCu(2)O(4) (Ln = Nd, Gd, Er, Lu, Y) has been prepared at pressures of 40-100 kbar using a multianvil apparatus. The structure of these phases was determined for the case of NdCu2O4 by Rietveld profile analysis of X-ray powder diffraction data. NdCu2O4 is monoclinic, I2/a, a = 5.822(2) Angstrom, b = 9.695(3) Angstrom, c = 5.748(2) Angstrom, beta = 92.34-(2)degrees, and Z = 4. The NdCu2O4 structure can be derived from that of spinel, as the cations in both have the Cu2Mg-type arrangement. However, the metal coordination by oxygen in NdCu2O4 is unlike that in spinel, consisting of NdO8 polyhedra and square-coplanar CuO4. The structure is comprised of (CuO4)-O-II chains along (100) and (CuO4)-O-III chains along [001]. These are linked perpendicularly through the corners of CuO4 square planes, leading to an array of parallel pseudotetragonal tunnels in which the Nd cations reside. Superconductivity was not observed in any of the new LnCu(2)O(4) phases to 4 K.