Hole doping and superconductivity characteristics of the s=1, 2 and 3 members of the (Cu,Mo)-12s2 homologous series of layered copper oxides

Superconductivity characteristics have been systematically evaluated for a two-CuO2-plane copper oxide system, (Cu,Mo)-12s2, upon increasing the number of fluorite-structured layers, s, between the two CuO2 planes. Essentially single-phase samples of (Cu0.75Mo0.25)Sr2YCu2O7+δ (s=1s=1), (Cu0.75Mo0.25)Sr2(Ce0.45Y0.55)2Cu2O9+δ (s=2s=2) and (Cu0.75Mo0.25)Sr2(Ce0.67Y0.33)3Cu2O11+δ (s=3s=3) were synthesized through a conventional solid-state route in air. To make the samples superconductive an additional high-pressure oxygenation (HPO) treatment was required. Such treatment (carried out at 5 GPa and 500 °C in the presence of 75 mol% Ag2O2 as an oxygen source to maximize the Tc) compressed the crystal lattice for the three members of the (Cu0.75Mo0.25)-12s2 series equally, i.e., by 0.01 Å for the a parameter and by 0.07 Å for the c parameter per formula unit. From both Cu L-edge and O K  -edge XANES spectra the s=1s=1 sample was found to possess the highest overall hole-doping level among the HPO samples. Accordingly it exhibited the best superconductivity characteristics. With increasing s, both the Tc (s=1s=1: 88 K, s=2s=2: 61 K, s=3s=3: 53 K) and Hirr values got depressed, being well explained by the trend of decreasing CuO2-plane hole concentration with increasing s as revealed from O K-edge XANES spectra for the same samples. Hence, the present results do not suggest any significant (negative) impact on the superconductivity characteristics from the gradually thickened fluorite-structured block itself.

Graphical abstractCrystal structures of the first three members of the (Cu,Mo)-12s2 homologous series of superconductive copper oxides.Figure optionsDownload full-size imageDownload as PowerPoint slide