Frequency dependence of real (ε′) part of permittivity of CETCox for x = 0.00, 0.05 and 0.10 for T = 600 K.

In the present work, structural property of polycrystalline sample Ba0.97Bi0.02Ti0.9Zr0.05Nb0.04O3 (BBTZN) prepared by a molten-salt method were investigated.

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The La 0.7 Sr 0.25 K 0.05 MnO 3 (LSKMO 0.05 ) manganite compound was synthesized by the solid state reaction method. X-ray diffraction analysis revealed that this sample crystallizes in the distorted rhombohedral system with R3 ത c space group. Magnetic study showed a second order paramagnetic (PM)-ferromagnetic (FM) transition at Curie temperature T C = 332 K. In addition, isothermal measurements of magnetization allowed us, through thermodynamic Maxwell relations, to determine the magnetic entropy change (∆S M ). The maximum magnetic entropy change (∆S max ) and the relative cooling power (RCP) were found to be, respectively, 2.37 J/kg.K and 102 J/kg for a 2 T magnetic field change along with a negligible hysteresis loss, making of this material a promising candidate for magnetic refrigeration. In order to eliminate the drawbacks due to the use of multistep nonlinear fitting in a conventional manner, the field dependence of magnetic entropy change was applied to study the critical behavior. As expected, our results are consistent with the values derived for the 3D-Heisenberg model.

The perovskite sample La0.7Sr0.25Na0.05Mn0.7Ti0.3O3 (LSNM0.70T0.30) was produced via a solidstate route process. Impedance spectra of LSNM0.70T0.30 in the frequency interval [40Hz -1MHz] were studied at several temperatures [80K to 440 K]. The ac conductivity (ac) established that according to the Jonscher law. ac is described by Non-overlapping Small Polaron Tunneling model at low temperatures and Correlated Barrier Hopping model at high temperatures. From dc conductance analysis, conduction seems to be thermally activated, suggesting the existence of semiconductor process. Detailed investigation of impedance data revealed the non-Debye nature of the relaxation processes in the sample. In addition, Dielectric constant curves were applied to examine the relaxation dynamics of charge carriers. In fact, the Debye-like relaxation was performed on the basis of the polarization of spatial charges following Maxwell-Wagner model and Koop's phenomenological theory.

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