Heat conductivity and thermopower of Nd 1−xSr xCoO 3 ceramic

Abstract

Nd 1− x Sr x CoO 3 polycrystals have been prepared in the compositional range 0< x<0.5. Magnetisation, resistivity, thermoelectric power (TEP) and heat conductivity have been measured. Metallic conduction (d ρ/d T>0) is observed for x>0.4. All other compounds show activated behaviour: d ρ/d T<0. A higher order transition is observed in the heat conductivity κ( T) and the thermopower S( T) of the base compound around T s=200 K which gradually smoothens out with increasing Sr-content. Specifically, we propose a low spin–low spin approach transition which involves phonons in a way similar to the dynamic Jahn–Teller effect.