Structural characterization and transport properties of the H Tc Bi 2Sr 2(Ca,Cd)Cu 2O 8+ δ glass-ceramic rods

Abstract

In this study, structural and transport properties including electrical resistance ( R– T) thermoelectric power ( S– T) and thermal conductivity ( κ– T), for the glass-ceramic rods of Bi 2Sr 2Ca 1− x Cd x Cu 2O 8+ δ with 0 ≤ x ≤ 0.8 were investigated. XRD and SEM-EDX investigations showed multiphase, complex and deformed structure in the Cd-substituted samples. An increase in the a-axis and decrease in the c-axis were obtained. All the samples showed metallic trend between 300 K and T c but the value of T c decreased significantly with increasing the Cd concentration in the system. The hole concentration per Cu was calculated by using Presland method and increased with increasing the substitution level. The thermoelectric power values, S, of the samples are obtained to be positive and found to increase almost linearly with decreasing temperature, reaching a maximum value around T c. With reducing temperature further, the thermoelectric power is found to fall rapidly to zero. Magnitude of S decreases with increasing the substitution level. The results obtained have been analyzed in terms of “ Two band model with linear T-term” and “ Xin's two band model”. An excellent agreement between Two band model with linear T-term and thermoelectric power data was obtained. The substitution has considerable effect on the thermal conductivity, κ. The magnitude of κ was suppressed when the Cd concentration was increased. A sharp rising was obtained just below T c in all the samples, suggesting that the impurities play an important role on heat transport due to increase of the electron–phonon-impurity scattering rate.