Structural, electrical and thermal studies of Nb-doped Pr_0.7 Sr_0.3 Mn_{1 - x} Nb_x O₃ (0 ≤ x ≤ 0.05) 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 O₃ (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 Pr_0.7Sr_0.3MnO₃ 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.