With the purpose of fabricating ceramics where ferroelectric and magnetic order coexist, ceramics of Pb͑Fe 1/2 Nb 1/2 ͒O 3 have been prepared using the traditional ceramic method following three different routes. The first is a direct via starting from oxide reagents and the other two use different kinds of FeNbO 4 precursors with either monoclinic or orthorhombic structures. Crystallographic and surface morphological studies were carried out by the powder x-ray diffraction and scanning microscopy techniques. The presence of Fe 2+ , detrimental to the ferroelectric and magnetic performance, was evaluated by x-ray photoelectron spectroscopy. The samples showed no structural differences, uniformly distributed grains, a ferro-paraelectric transition temperature at 110°C and a normal diffuse phase transition ͑nonrelaxor behavior͒. Differences in the degree of diffuseness, densities and grain size were observed depending on the kind of precursor. Measurements of dc and ac electrical resistivity, dielectric constant and dielectric loss were made as functions of temperature from room temperature to 250°C, at different frequency values ͑between 20 Hz and 1 MHz͒. Four conduction mechanisms were identified: hopping charge corresponding to low temperatures, small polarons and oxygen vacancies conduction at intermediate temperatures, and intrinsic ionic conduction at high temperatures. The best set of values of dielectric loss and dielectric constant, from the ferroelectricity point of view, were obtained when the precursor with orthorhombic structure was employed.

The dielectric behavior of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained using the traditional ceramic method employing three different precursors was investigated by impedance spectroscopy in the temperature range of 200–300°C. This study was carried out by means of the simultaneous analysis of the complex impedance Z̃, electric modulus M̃, and admittance Ỹ functions from the measurements in the frequency range of 20Hz–1MHz. In correspondence to a previous structural, morphological, and temperature response study, appropriate microstructural and equivalent circuit models were established. Based on the brick layer model, three series of interconnected electrically distinct regions are considered: a conductive grain boundary layer, a capacitive grain boundary surface layer, and a resistive-ferroelectric bulk layer. Two conduction mechanisms were identified: a dielectric relaxation process due to localized conduction associated with the presence of oxygen vacancies and the nonlocalized conduction corresponding to long range conductivity associated with extrinsic mechanisms due, fundamentally, to Fe2+ presence. Both mechanisms were discerned to occur inside the grains and where the contributions of the grain boundary are neglected. Three conductivity components were deconvoluted: a longe range dc conductivity at the low frequency region, a capacitive behavior at higher frequencies, and a universal power law behavior in an intermediate-frequency region. Values of the activation energy corresponding to relaxation processes and dc conductivity were determined and excellent correlation with those obtained from the temperature response was found. A comparative analysis between the behaviors of each sample is presented.

Dielectric relaxation processes occurring near the ferroelectric-paraelectric phase transition of ferroelectromagnetic Pb(Fe1∕2Nb1∕2)O3 ceramics obtained by different precursors are discussed using microstructural and equivalent circuit modeling and the impedance spectroscopy technique. The frequency-temperature response was obtained from room temperature to 300°C and from 20Hzto1Mz. In correspondence with a previous structural, morphological, and temperature response study, appropriate microstructural, and equivalent circuit models were established. The frequency response study was carried out by means of the simultaneous analysis of the complex dielectric constant ε̃ and admittance Ỹ functions and the dielectric loss, tanδ. A strong absorption near the transition temperature region at a frequency around 1MHz is discussed and is attributed with relaxation processes associated with domain reorientation, domain wall (DW) motion, and the dipolar behavior of ferroelectric materials. Such processes were found to take place inside the grain, and their low characteristic frequencies are explained by clamping effects of the DW due to the thermally activated diffusion of oxygen vacancies. At frequencies before relaxation, the high polarization values are due to small polaron mechanisms associated with the presence of Fe2+. The relaxation processes are very much conditioned by the grain and domain sizes, the degree of deformation of the lattice and the crystallites, as well as the potential barriers in the grain boundaries. Values of the activation energy corresponding to the different relaxation processes were determined from fitting of experimental data, identifying thus the involved mechanisms, and an excellent agreement with those obtained from the temperature response [Raymond et al., J. Appl. Phys. 97, 084107 (2005)] was found. The relaxation processes studied here are an evidence of domain structure.

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