Thermal transport in (Y,Gd)Ba₂(Cu_1-xMn _x)₃O_7-δ for x≤0.02

Thermal conductivity κ(T) and thermoelectric power S(T) studies on (Y,Gd)Ba₂(Cu_1-xMn_x)₃O _7-δ (x≤0.02) superconductors are presented here. Thermal conductivity for all the samples exhibits a hump below the superconducting transition temperature T_c. The peak height of the hump decreases with the Mn content in both the Y-and Gd-based systems, barring GdBa ₂(Cu_0.99Mn_0.01)₃O _7-δ. The peak height reduction in the Gd-based cuprates is much faster (∼onefourth) compared to the Y-based samples. The thermoelectric power (TEP) of the Y-based samples for x≤0.0075 is electron-like (up to ∼140K) 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 electron-or 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.