Structural, electrical and thermal studies of Nb-doped manganites

X-ray diffraction (XRD), electrical resistivity ( ρ ) and thermal measurements of thermopower ( S ) , thermal conductivity ( κ ), and specific heat ( C P ) of Pr 0.7 Sr 0.3 Mn 1 − x Nb x O 3 ( 0 ≤ x ≤ 0.05 ) manganite samples are reported here. XRD and electrical resistivity measurements have been carried out up to 5% Nb-doping whereas thermal measurements are limited up to 3% Nb-doping as higher doped sample exhibits a large value of electrical resistivity. With Nb-doping the lattice volume increases, which indicates the occupancy of Mn+4 sites by Nb+5 and eventually results in generating more Mn + 3 Jahn Teller active (JT) ions. Nb doping also reflects its repercussion in the ρ (T) behavior where the insulator-metal transition temperature of the pristine Pr0.7Sr0.3MnO3 shifts to lower temperatures with increasing doping content. Based on the comparison of electrical resistivity and thermopower data, we establish that the strength of electron–phonon coupling increases with increasing Nb content. Thermal conductivity behavior κ (T) has been viewed in terms of the scattering of phonons by spin fluctuations and such a scenario has been corroborated with the specific heat data.