Structure of YSr2Cu3−M O7+δ (MMo, W and Re) from single-crystal X-ray and powder-neutron diffraction substituent site preference and oxygen defect structure

MoxCu1−xSr2YCu2Oy (0.3≤x≤1) revisited: Superconductivity, magnetism and the molybdenum oxidation state

“…Site occupancy refinement for all samples indicates that the chemical substitution of the Mo ions for the Cu ions in CuYSr 2 Cu 2 O 7 À d is found to occur in both Cu sites in the structure but up to limited extent. We have determined that the majority of the Mo substitution in these samples occurs for copper in [Cu 1 ] chain sites in the 123-type parent structure, which is in a good agreement with Harlow et al [6]. The initial model used for our refinements is based on the structure proposed by Harlow et al [6] in which the chain site (Cu/Mo)-O 6 octahedron are rotated.…”

“…But these phases can be stabilized at ambient pressure by substituting Pb, Al, Ti, Fe, W, Mo, and Ga partially or completely for Cu in the chains [4]. Previous crystal structure studies on superconducting YSr 2 Cu 2.7 Mo 0.3 O 7 7 d are somehow controversial: Hu et al [5] found that the majority of the molybdenum substitution occurs at the square-pyramidal Cu2 site, while Harlow et al [6] found the opposite result by single crystal X-ray and neutron diffraction studies. They found that the majority of molybdenum substitutes the chain (Cu1) site and discussed the correlation between the copper valence and superconductivity by assuming a Mo 6 þ state.…”

Phase diagrams for the YBa2Cu3O7 family — ANNO 1996

“…The presence of the smaller Sr atoms stabilizes some degree of substitution by W as well as Mo and Re in the triple-perovsldte structure [655]. Based on PND structure determinations, it is argued that these high valent transition metals increase the bond valence of Cu, and therefore shorten the Cu-O distances in the cuprate network, by bringing additional oxygen atoms into the structure, which then suits the Sr size better {YSr2Cu2.sWo.207.13; P4/mmm; 380.36(3), 1151.13(8)} [655].…”

“…Based on PND structure determinations, it is argued that these high valent transition metals increase the bond valence of Cu, and therefore shorten the Cu-O distances in the cuprate network, by bringing additional oxygen atoms into the structure, which then suits the Sr size better {YSr2Cu2.sWo.207.13; P4/mmm; 380.36(3), 1151.13(8)} [655]. Also a replacement of a portion of Cu by substantially smaller atoms like AI has a similar effect in stabilizing Sr in the structure (and vice versa) [656,657].…”

Oxidation state and superconducting properties of Y1−xPrxSr2Cu2.85Re0.15O7+δ

“…[11][12][13][14] Although a large number of articles have appeared on the YPrBCO system, only a few reports are available on the Y 1Ϫx Pr x Sr 2 Cu 3Ϫy M y O 7ϩ␦ series. [15][16][17][18][19][20] In view of the importance and the interest on the understanding of the T c depression mechanism, in particular the detrimental effect of Pr on T c , we have undertaken the present study. Moreover, this is also an attempt to stabilize these metastable Sr-based 123 phases by Re, viz 3 , CuO, and ReO 3 .…”