Ca-substitution and O-doping effects in superconductingCu(Ba0.8Sr0.2

Abstract

Distinct calcium and oxygen doping effects were studied in the Cu͑Ba 0.8 Sr 0.2 ͒ 2 (Yb 1Ϫx Ca x )Cu 2 O 6ϩz (Cu-1212: P) system by means of neutron diffraction and superconducting quantum interference device experiments in the wide substitution ranges of 0рxр0.35 and 0ϽzϽ1. The effectiveness of the two different ways to introduce holes into the CuO 2 planes was compared both in respect to the capability to increase T c and in terms of the hole production as estimated from neutron-diffraction data via bond-valence-sum calculation. Oxygen doping was found to increase the hole concentration less efficiently, and further, at a certain hole concentration value higher T c values were obtained with calcium substitution than with oxygen doping. The two different hole-doping methods exhibited also different T c vs Cu-O bond length relations. As a conclusion, the possible roles of the hole distribution in the in-plane Cu-O bond and the flatness of the CuO 2 planes in determining the superconducting properties were recognized. ͓S0163-1829͑99͒06929-5͔

Application of Multivariate Data Analysis Techniques in Modeling Structure–Property Relationships of Some Superconductive Cuprates

“…3b) suggests that adding oxygen to the structure increases the hole concentration in the superconductive CuO plane through the hole-doping routes I and II. This is in accordance with the conclusions made for the Cu(Ba,Sr) (Yb,Ca)Cu O >X system based on neutron diffraction results (19), showing that incorporation of oxygen into the CuO X chain results in a shift of O(4) toward the CuO plane (route I) and Ba/Sr away from the in-plane O(2, 3) atoms (route II) as the oxidation proceeds. Substitution of trivalent Yb by divalent Ca in the Cu(Ba,Sr) (Yb,Ca) Cu O >X system was shown to increase the concentration of holes in the CuO plane by lengthening the e!ective (Yb,Ca)}O(2,3) bond length according to route III (19).…”

“…This is in accordance with the conclusions made for the Cu(Ba,Sr) (Yb,Ca)Cu O >X system based on neutron diffraction results (19), showing that incorporation of oxygen into the CuO X chain results in a shift of O(4) toward the CuO plane (route I) and Ba/Sr away from the in-plane O(2, 3) atoms (route II) as the oxidation proceeds. Substitution of trivalent Yb by divalent Ca in the Cu(Ba,Sr) (Yb,Ca) Cu O >X system was shown to increase the concentration of holes in the CuO plane by lengthening the e!ective (Yb,Ca)}O(2,3) bond length according to route III (19). In the PC analysis the e!ects of Ca(II)-for-RE(III) substitution at the Q site are explained mainly by the parameter V(Q), which is the average valence of the Q cation.…”

OK-edge and CuL23-edge XANES study on the concentration and distribution of holes in the(Pb2/Karppinen1, Kotiranta2, Yamauchi3 et al. 2001Phys. Rev. BSelf Cite214170View full textAdd to dashboardCite

“…In Fig. 4 10,24,28 and Bi 2 Sr 2 ͑Y 1Ϫx Ca x ͒Cu 2 O 8ϩ␦ ͑Bi-2212; ␦ decreases from 0.52 to 0.26 with an increase of x from 0 to 1͒. 20,25 In the case of the Bi-2212 system with a strongly oxygenated BiO 1ϩ␦ Ј -BiO 1ϩ␦ Ј charge reservoir, quite a high Ca substitution level is required for the appearance of superconductivity, i.e., xϷ0.5 ͑Fig.…”

XANES Study on the Generation and Distribution of Holes via Ca Substitution and O Doping in Cu(Ba0.8Sr0.2)2(Yb1−Ca )Cu2O6+

“…The present notation system for the atoms in the Cu(Ba,Sr) 2 (Yb,Ca)Cu 2 O 6+z structure follows that of Ref. (16) and is given in Fig. 1.…”

“…The oxygen content was varied in the range of 0rzr0:96 in the samples studied. Furthermore, the results for the layer-specific hole concentrations obtained for the Cu(Ba 0.8 Sr 0.2 ) 2 (Yb 1Àx Ca x )Cu 2 O 6+z system from the O K-edge XANES data are compared with the results of bond-valence-sum (BVS) calculations based on precise structural data obtained for the same sample powders from neutron powder diffraction (NPD) experiments (16). The present notation system for the atoms in the Cu(Ba,Sr) 2 (Yb,Ca)Cu 2 O 6+z structure follows that of Ref.…”