Thermal transport in (Y,Gd)Ba₂(Cu_1−xMn_x)₃O_7−δforx≤0.02

Abstract

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 Y- and 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 electron-like (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 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.

Specific heat and correlation between resistivity and thermoelectric power of GdBa2(Cu1−xMnx)3O7−δ HTSC system for x⩽0.02

“…However we observe drastic reduction of T C for the sample with x = 0.02 which is either due to potential scattering [17] or due to reduction in the carrier (hole) density (caused by Mn +k , k > 2 ions) [15]. In our earlier communication we have shown that the features of the thermoelectric power and thermal conductivity rule out the latter possibility [14]. The observed temperature dependence of the specific heat (C P ), of GdBa 2 (Cu 1Àx Mn x ) 3 O 7Àd for different x is described elsewhere [14].…”

“…In our earlier communication we have shown that the features of the thermoelectric power and thermal conductivity rule out the latter possibility [14]. The observed temperature dependence of the specific heat (C P ), of GdBa 2 (Cu 1Àx Mn x ) 3 O 7Àd for different x is described elsewhere [14]. The pristine sample (x = 0.0) shows a jump in C P of amount DC P = 5.7 mJ/gK.…”

“…Synthesis details and measurement techniques for thermopower and specific heat have already been described elsewhere [13,14]. …”

“…In this paper we present theoretical studies on the GdBa 2 (Cu 1Àx Mn x ) 3 O 7Àd superconducting system and highlight some important features of the specific heat (C P ) and thermoelectric power (S) [13,14] with a view to understand the role of Mn in GdBa 2 (Cu 1Àx Mn x ) 3 O 7Àd on the basis of the connections of its effects on the specific heat and thermoelectric power. The Mn +k ion (k = 2, 3, 4) is magnetic.…”

High Temperature Superconductors REBa2Cu3O7 (RE=Y, Gd and Eu) For Possible Thermo-electric Applications

“…They have shown that oxygen deficient samples show higher Z-values. However it is well-know that electrical conductivity, thermal conductivity and thermo-power strongly depend on nature of dopants and dopant concentration [8][9][10][11], thus, it would be interesting to explore other oxide superconductors where one can modify the stoichiometry and use suitable doping in order to achieve a fairly large value of Z.…”