Thermal transport in ( Y , Gd ) Ba 2 ( Cu 1 − x Mn x ) 3 O 7 − δ for x 0 . 02

Thermal conductivity κ(T ) and thermoelectric power S(T ) studies on (Y,Gd)Ba2(Cu1−xMnx)3O7−δ (x 0.02) superconductors are presented here. Thermal conductivity for all the samples exhibits a hump below the superconducting transition temperature Tc. The peak height of the hump decreases with the Mn content in both the Yand Gd-based systems, barring GdBa2(Cu0.99Mn0.01)3O7−δ. The peak height reduction in the Gd-based cuprates is much faster (∼one fourth) compared to the Y-based samples. The thermoelectric power (TEP) of the Y-based samples for x 0.0075 is electronlike (up to ∼140 K) whereas it turns to hole-like even at x = 0.005 for the Gd-based system. On the basis of the structure of the thermal conductivity hump, and of the electronor hole-like nature of the thermopower, it has been argued that, in the Y-based system up to x = 0.0075, Mn produces qualitatively the same effect as Gd in the Gd-based system. An analysis of the thermal conductivity data in terms of lattice theory, and the TEP data in terms of a narrow-band picture, has been made to invoke the role of Mn in these systems. Boundary scattering, point defects and sheet-like faults (from κ(T ) data analysis) and chemical potential (from S(T ) data analysis) support different roles of Mn for x 0.0075 and x > 0.0075.