Structure and spin-gap in the normal state of Y1−xCaxBa1.9Nd0.1Cu3Oy cuprates

Polycrystallized Y1−xCaxBa1.9Nd0.1Cu3Oy (YCBNCO) compounds with <f>x&les;0.40</f> were synthesized using standard solid state reaction technique. The structure for all samples was characterized by X-ray diffraction with Rietveld refinements. The transport properties for YCBNCO were measured by the standard four-probe method in the temperature range from 20 to 300 K. With the increase of Ca content, the variation of the superconducting transition temperature <f>Tc</f> can be divided into three regions: in the doping region I with <f>x&les;0.10</f>, <f>Tc</f> decreases sharply and linearly with <f>x</f>, which may relate to the competition between Ca2+ and Nd3+; in the region II with <f>0.10<x<0.25</f>, <f>Tc</f> deviates the fitting line; and in region III with <f>x&ges;0.25</f>, <f>Tc</f> decreases slowly with increasing Ca content,which may relate to the formation of the Ca-rich phase. The dependence of resistivity on temperature, and the relation of the structural parameters versus the content of Ca were discussed. The Ca content dependence of the spin-gap opening temperatures in the normal state for YCBNCO was investigated. [Copyright &y& Elsevier]