title: Correlation of structural, magnetic and transport properties with the tolerance factor in a low-doped La(0.875)Sr(0.125-x)Ca(x)MnO(3), (0 ≤x≤0.125) system: cross-over from Mott to Shklovskii-Efros variable range hopping conduction.
abstract: Samples of the low-doped manganite La(0.875)Sr(0.125-x)Ca(x)MnO(3) (0≤x≤0.125) have been synthesized and the effect on the structural, magnetic and transport properties of decreasing the tolerance factor by replacing larger Sr(2+) ions with smaller Ca(2+) ions are reported. For samples with x≥0.0625, a concentration (x) dependent structural transition (rhombohedral ([Formula: see text]) to orthorhombic (Pnma)) has been detected at room temperature and the Curie temperature T(C) is found to decrease with increased Ca doping level. For samples with x≤0.0625, a narrow metallic region exists and the corresponding insulator to metal transition temperature T(MI) decreases with increasing Ca content, i.e. decreasing tolerance factor. In the paramagnetic region, x dependent crossover from Mott variable range hopping (Mott-VRH) to Shklovskii-Efros variable range hopping (SE-VRH) occurs as the Ca content increases. The thermoelectric power (TEP) of the samples increases substantially, varying inversely with the tolerance factor. These results are analysed from the consideration of increased bending of the Mn-O-Mn bond with the decrease of the average ionic radius of the A-site element [Formula: see text] and the tolerance factor t, which causes narrowing of the bandwidth, decrease of mobility of e(g) electrons and weakening of the double exchange (DE) interaction associated with the substitution of Ca.
authors.affiliation: Department of Solid State Physics, Indian Association for the Cultivation of Science, Kolkata-700032, India.
authors.forename: Esa
authors.initials: E
authors.lastname: Bose
authors.forename: S
authors.initials: S
authors.lastname: Karmakar
authors.forename: B K
authors.initials: BK
authors.lastname: Chaudhuri
authors.forename: S
authors.initials: S
authors.lastname: Pal
authors.forename: C
authors.initials: C
authors.lastname: Martin
authors.forename: S
authors.initials: S
authors.lastname: Hébert
authors.forename: A
authors.initials: A
authors.lastname: Maignan