Two band analysis of normal state electrical resistivity of superconducting magnesium diboride with nano aluminium nitride addition

Superconducting magnesium diboride polycrystalline pellets containing 0, 0.5, 1, 3 and 5 wt% nano aluminium nitride are synthesized by solid state reaction. The prepared samples are characterized, using X-ray diffraction, field emission gun scanning electron microscope and high resolution transmission electron microscope. Structural analysis by X-ray diffraction indicates absence of any substitution for Mg or, B due to addition of nano aluminium nitride. Surface morphology of the samples displays random and well defined grains of various sizes. High resolution transmission electron microscopic images for aluminium nitride added magnesium diboride show presence of aluminium nitride nanoparticles between the grain boundaries and also on the surface. Temperature dependent electrical resistivity of the samples is measured between 20 and 300 K. The superconducting transition temperatures decrease from 38.0 to 36.0 K with addition of aluminium nitride nanoparticles in magnesium diboride. Resistivity data confirms improved connectivity of the grains for low level addition of aluminium nitride nanoparticles. Electrical resistivity of magnesium diboride without and with addition of nano aluminium nitride in the normal state has been analyzed in terms of conduction through σ and π bands of magnesium diboride and parameters, viz., scattering rates (γ_σ , γ_π ) and temperature coefficient of resistivity of both the bands are estimated. Our analysis confirms that major contribution to electrical conductivity comes from σ bands charge carriers in consistence with the 'dirty' nature of our samples. (author)