REVISTA COLOMBIANA DE F ´ ISICA, VOL.38, No.3, 2006 THERMAL CONDUCTIVITY OF Ag AND Au DOPED YBCO SAMPLES J.E. Rodr´ ıguez 1 ,D. Cadavid 1 and A. Mari˜ no 1 1 Departamento de F´ ısica Universidad Nacioanl de Colombia Bogot´a,COLOMBIA (Recibido 09 de Sep.2005; Aceptado 20 de Jun. 2006; Publicado 04 de Oct. 2006) ABSTRACT We report measurements of thermal conductivity κ(T ) and electrical resistivity ρ(T ) on Ag and Au doped Y Ba 2 Cu 3 O 7-δ (YBCO) polycrystalline samples. The thermal conductivity shows a weak temperature dependence and its magnitude decreases with the doping level. By using the Wiedemann-Franz model (WF) we were able to determinate the relative contributions of charge carriers and lattice to total thermal conductivity. We discuss the role of doping level on both the point-defect scattering and the electronic structure in the normal-state of these YBCO compounds. Keywords: Thermal conductivity, Transport properties, YBCO compounds. RESUMEN Se reportan medidas de conductividad t´ ermica κ(T ) y resistividad el´ ectrica ρ(T ) en mues- tras policristalinas de Y Ba 2 Cu 3 O 7-δ (YBCO) dopadas con plata y oro. La conductivi- dad t´ ermica muestra una d´ ebil dependencia con la temperatura y su magnitud decrece con el nivel de dopado. Utilizando el modelo de Wiedemann-Franz (WF) fue posible determinar las contribuciones electr´ onica y fon´onica a la conductividad t´ ermica total. Se discute el papel del dopado sobre la estructura electr´onica de estos compuestos. Palabras claves: Conductividad T´ ermica, Propiedades de transporte, Compuestos de YBCO. 1 Introducci´on One of the most important properties to be researched in YBCO compounds is their ability to transport heat. Since they were discovered there has been an interest from both technological and theoretical view points to know how efficient the heat flow through them in their normal and superconducting states [1]. The YBCO compounds can be considered as a promissory thermoelectric material if their electrical and thermal properties are modified through proper changes in their chemical composition and oxygen content. From theoretical view point thermal conductivity provides important information about of charge carriers and phonons and mainly about the scattering processes between them. Thermal conductivity in the normal state presents two contributions, one of phonon character κ ph and the other one of electronic nature κ e . Hence, the total thermal con- ductivity can be written as: κ = κ e + κ ph (1) The phonon contribution can be described by the expression [2]: κ ph =(ω ph 0 + αT ) -1 (2) where ω ph 0 and αT are the thermal resistivity generated by phonon-defect scattering and phonon-phonon respectively. 1050