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Manganites La0.93K0.07Mn1−x Cu x O3 ( 0.0 ⩽ x ⩽ 0.09 ) , prepared by the solid state reaction method at high temperature, were studied structurally and magnetically. The unit cell parameters, as well as bond length d ( Mn,Cu)-O   Å and the bond angle θ ( Mn,Cu)- O 1 -Mn , were determined from the Rietveld refinement of the x-ray diffraction patterns. The Fourier-transform infrared spectroscopy analysis shows that Cu2+ substitution induces variations in the vibration modes of the MnO6 octahedra. Magnetization vs. temperature M T at low magnetic field H=0 .01T were performed in the range

The polycrystalline La 0.65 Ca 0.25 Sr 0.1 MnO 3 manganite was prepared by the solgel method. Structural analysis showed that our compound is single-phase and crystallizes in the orthorhombic phase with a Pnma space group. A detailed analysis of the electrical and dielectric characteristics of La 0.65 Ca 0.25 Sr 0.1 MnO 3 was carried out in the frequency and temperature range by the impedance spectroscopy technique. The electrical property of our compound as electrical conductivity dc reveals the semiconductor behaviour of our sample. At high temperatures, the transport properties of our material are dominated by a thermally activated small polaron jumping mechanism and at low temperature are dominated by a Mott-variable range hopping process. The values of the activation energy have been determined from DC conductivity and impedance, and the same type of charge carriers has been found in the relaxation process and electrical conductivity. The conduction mechanism is governed by the grain boundary. The experimental impedance data of the sample were fitted using Z-view software, to allow modelling an electrical equivalent circuit. Keywords X-ray diffraction analysis • Electrical and dielectric properties • Solgel* A. J. M. Sales

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