S. Zemni

X-ray diffraction, magnetic and electrical properties in the manganites (La1-xNdx)0.7Sr0.3MnO3

Abstract In several series of samples (La1−xNdx)0.7Sr0.3MnO3 (0⩽x⩽1), we studied the evolution of structure, magnetic and electrical properties with x and the average ionic radius of the A site 〈rA〉, which systematically varied while keeping the ratio Mn3+/Mn4+ fixed. Based on the classical ceramic preparation method, the samples have perovskite-like structure with different degrees of distortion (rhombohedral and orthorhombic). With increasing Nd concentration, a systematic decrease in the ferromagnetic transition temperature (TC), the metal semi-conducting transition temperature (Tp) and the cell volume is observed. Meanwhile, the size of the resistivity ρ increases near TC. This phenomenon is interpreted as a gradual bending of the Mn–O–Mn bond angle, with decreasing 〈rA〉, which causes the narrowing of the electronic bandwidth and the effect of the A-site variance σ2.

Above room temperature complex impedance analysis of properties of La0.33Sr0.67Mn0.33Ti0.67O3±δ perovskite

ABSTRACT La0.33Sr0.67Mn0.33Ti0.67O3±δ perovskite was prepared by the standard solid state reaction at 1773 K. The sample crystallizes in the cubic structure. The electrical properties of the sample have been investigated above room temperature in 293–373 K range with varying frequency between 102 and 106 Hz using complex impedance analysis. The sample exhibit a metal–semiconductor transition temperature at TMS = 303 K. The conductance curves were well fitted by Jonscher power law G(ω) = Gdc + Aωn, which shows that with increasing temperature, the exponent (n) decreases below TMS, and increases above TMS. The activation energy deduced from the analysis of the conductance curves matches very well with the value estimated from the relaxation time indicating that relaxation process and electrical conductivity are attributed to the same defect. Nyquist plots of impedance show semicircle arcs for sample and an electrical equivalent circuit has been proposed to explain the impedance results.

Effect of iron doping at Mn-site on complex impedance spectroscopy properties of Nd0.67Ba0.33MnO3 perovskite

ABSTRACT The effect of Fe-doping at Mn-site on the structural and electrical properties of Nd0.67Ba0.33Mn1−xFexO3 (0 ≤ x ≤ 0.05) perovskites has been investigated. X-ray diffraction patterns show that the structural parameters change slightly due to the fact that the Fe3+ ions replacing the Mn3+ have similar ionic radius. The electrical properties of these samples have been investigated using complex impedance spectroscopy technique. a function of the frequency at different temperatures. When increasing the Fe-content, a decrease of dc conductivity was observed throughout the whole explored temperature range and the deduced activation energy values are found to increase from 128 meV for x = 0 to 166 meV for x = 0.05. The curves of the imaginary part of impedance (Z″) show the presence of relaxation phenomenon in our samples. The complex impedance spectra show semicircle arcs at different temperatures and an equivalent circuit of the type of Rg + (Rgb//Cgb) has been proposed to explain the impedance results.

The effect of cation radii on structural, magnetic and electrical properties of doped manganites La0.6-xPrxSr0.4MnO3

The effect of trivalent substitution into rare earth sites in La 0.6-x Pr x Sr 0.4 MnO 3 oxides has been studied. The structural, and magnetic properties of these compounds with a fixed Mn 3+ /Mn 4+ ratio of 3/2 are studied. X-ray diffraction patterns show that these compounds are rhombohedral (R 3 c) below x = 0.42 and become orthorhombic (Pbnm) above x = 0.42. The paramagnetic to ferromagnetic transition temperature T c decrease from 374K to 310K when decreases. The ionic radii variance σ 2 decreases with the increase of . The resistivity transition temperature T p decreases from 350 K to 280 K as Pr content increases.