Author(s): Ahn, KH; Wu, XW; Liu, K; Chien, CL | Abstract: The effect of Fe doping (l20%) on the Mn site in the ferromagnetic ((Formula presented)) and the antiferromagnetic ((Formula presented)) phases of (Formula presented) has been studied. The same ionic radii of (Formula presented) and (Formula presented) cause no structure change in either series, yet conduction and ferromagnetism have been consistently suppressed by Fe doping. Colossal magnetoresistance has been shifted to lower temperatures, and in some cases enhanced by Fe doping. Doping with Fe bypasses the usually dominant lattice effects, but depopulates the hopping electrons and thus weakens the double exchange. © 1996 The American Physical Society.

Magnetic properties and colossal magnetoresistance of LaÑCaÖMnO3 materials doped with Fe

We have prepared LaCrO3 (LCO) and 10% Ir doped LCO samples by the solid state reaction method and studied the electrical modulus and the other dielectric properties of the samples by means of the impedance spectroscopy in the −100 °C to 100 °C range, with steps of 20 °C. It has been clearly observed that the dielectric properties change due to Ir doping. The absolute dielectric constant value of Ir doped LCO has decreased and this reduction was attributed to decreasing Cr6+ ions which may play a vital role in space charge polarization and charge hopping. A plateau region appeared in the temperature-dependent real electrical modulus M′ versus f curves of the pure LCO sample while almost no plateau region is visible in the Ir doped LCO sample. The temperature-dependent imaginary modulus M′′ versus f curves has two peaks at each temperature; one of the peaks is at low frequency and the other at the high frequency region, which shifts through higher frequency region with increasing temperature. This originates from free charge accumulation at the interface with the increase of the temperature. Furthermore, it has been seen that the Ir doped LCO sample has higher impedance and resistance values than the undoped LCO sample at the same frequency and temperature. This phenomenon was attributed to doped Ir ions behaving like a donor in LCO because LCO is a p-type compound. Moreover, the activation energy values of 0.224 eV and 0.208 eV for LCO and of 0.161 eV and 0.265 eV for the Ir doped LCO have been obtained from the slopes of the ρdc vs. (kT)−1 curves, respectively. Also the activation energies were calculated from the slopes of the fmax vs. (kT)−1 curves and the obtained results from low frequency region were in good agreement with ρdc vs. (kT)−1 ones.

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The electrical modulus and other dielectric properties by the impedance spectroscopy of LaCrO3 and LaCr0.90Ir0.10O3 perovskites

Green synthesis using cherry and orange juice and characterization of TbFeO3 ceramic nanostructures and their application as photocatalysts under UV light for removal of organic dyes in water

Fuel cells offer the possibility of zero-emissions electricity generation and increased energy security. We review here the current status of solid oxide (SOFC) and polymer electrolyte membrane (PEMFC) fuel cells. Such solid electrolyte systems obviate the need to contain corrosive liquids and are thus preferred by many developers over alkali, phosphoric acid or molten carbonate fuel cells. Dramatic improvements in power densities have been achieved in both SOFC and PEMFC systems through reduction of the electrolyte thickness and architectural control of the composite electrodes. Current efforts are aimed at reducing SOFC costs by lowering operating temperatures to 500–800 °C, and reducing PEMFC system complexity be developing ‘water-free’ membranes which can also be operated at temperatures slightly above 100 °C.

Fuel cell materials and components

Investigation of structural, morphological, optical, magnetic and dielectric properties of (1-x)BaTiO3/xSr0.92Ca0.04Mg0.04Fe12O19 composites

Exceptional properties such as dielectric, ferroelectric, piezoelectric, magnetic, catalytic, and photovoltaic of perovskite materials open new doors to many groundbreaking discoveries for unique device ideas. These materials properties are inherited from their crystal structures; therefore, the features can be tuned via varying details of the crystal structures. In the literature, LaCrO3 (LCO) is one those mostly examined perovskites for various purposes such as solid oxide fuel cells, catalytic converters, and sensors. In the present study, the band gap tuning of LCO was investigated via doping a transition element such as cobalt (Co), palladium (Pd), and iridium (Ir) into Cr atom. The synthesized doped and un-doped LCO powders were characterized by infrared spectra (IR) and X-ray diffraction (XRD). Scanning electron microscopy (SEM) was employed to study the surface topography of LCO and doped LCO thin films on silicon substrates. The band gaps of the LCO and doped LCO films were scrutinized using a UV–Vis spectrometer. Our study has shown that the band gap of LCO was successfully lowered from 3.4 eV to 2.66 eV and can be engineered via substitution at various mol% of transition elements (Co, Pd, Ir) onto B-site Cr atom in the LCO perovskite structure.

F.M. Coskun

Papers

The electrical modulus and other dielectric properties by the impedance spectroscopy of LaCrO3 and LaCr0.90Ir0.10O3 perovskites

Engineering the band gap of LaCrO3 doping with transition metals (Co, Pd, and Ir)

Os doped YMnO3 multiferroic: A study investigating the electrical properties through tuning the doping level

Frequency and temperature dependent electrical and dielectric properties of LaCrO3 and Ir doped LaCrO3 perovskite compounds

Electrical characterization of Ir doped rare-earth orthoferrite YbFeO3