Pure (Na0.50K0.50)(0.95)(Li0.05Sb0.05Nb0.95)O-3 (NKNLS) and CuO doped NKNLS perovskite structured ferroelectric ceramics were prepared by the solid-state reaction method. x wt% of CuO (x = 0.2-0.8 wt%) was added in the NKNLS ceramics. X-ray diffraction patterns indicate that single phase was formed for pure NKNLS while a small amount of second phase (K6Li4Nb10O30 similar to 3%) was present in Cu2+ doped NKNLS ceramics. Dielectric anomalies around the temperatures of 120 degrees C and 350 degrees C have been identified as the ferroelectric-paraelectric transition (orthorhombic to tetragonal and tetragonal to cubic) temperatures for pure NKNLS compound. The electrical behavior of the ceramics was studied by impedance study in the high temperature range. Impedance analysis has shown the grain and grain boundary contribution using an equivalent circuit model. The impedance response in pure and Cu2+ doped NKNLS ceramics could be resolved into two contributions, associated with the bulk (similar to grains) and the grain boundaries. From the conductivity studies, it is found that activation energies are strongly frequency dependent. The activation energy obtained from dielectric relaxation data may be attributed to oxygen ion vacancies. (C) 2012 Elsevier Masson SAS. All rights reserved.

Inorganic pigments are substances that develop colour in organic solids such as ceramics and glazes, and are usually a complex mixture of oxides, and relatively low-cost. Their chromatic properties have been extensively studied, yet surprisingly the magnetic and electrical properties of these economic and common materials have been neglected, despite the fact many are based on ferrite spinels. Therefore, we investigated these properties in commercial black and brown pigments, to assess their potential as magnetic materials. The brown and black pigments were found to be spinel ferrites, with estimated formulas of Fe1.34Cr0.62Mn0.66Zn0.22Ni0.10Co0.06O4 and Fe1.02Cr0.97Co0.57Mn0.23Ni0.21O4, respectively. The brown pigment also contained a higher amount of SiO2 compared to the black pigment (similar to 7 mol% vs. similar to 2 mol%), which appeared as a second phase of crystalline quartz, and adversely affected its porosity, magnetisation and electrical ac conductivity, compared to the black pigment. However, both were very magnetic and very soft ferrites. The brown pigment had M-s=11.7 A m(2) kg(-1) and H-c of 1.5 kA m(-1), with a high electrical conductivity (sigma) of 4 x 10(-4)-7 x 10(-3) Omega(-1) m(-1) between 100 Hz and 1 MHz. The black pigment was equally magnetically soft, but had a much greater magnetisation and lower electrical conductivity, with M-s=18.7 A m(2) kg(-1), H-c=2.4 kA m(-1), and sigma=5 x 10(-6)-8 x 10(-5) Omega(-1) m(-1) between 100 Hz and 1 MHz. This work has revealed the potential hidden value of low-cost commercial inorganic pigments based on spinel ferrites as magnetic materials. This demonstrates their potential at low-cost alternative materials for applications such as in power supply transformers, switching materials and sensors, where soft magnetisation is especially important. (C) 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Lead-free particulate multiferroic composites of [0.94(Na0.5Bi0.5)TiO3-0.06 BaTiO3]:(Co0.6Zn0.4)( Fe1.7Mn0.3)O-4 were synthesized and magnetoelectric (ME) properties were studied. X-ray diffraction and microstructural studies indicated the formation of a two-phase composite system without any impurities. The shift of Raman modes corresponding to ferroelectric and ferrite phases was assigned to the induced strain amid the formation of a two- phase system, in relation to the fraction of each phase in the samples. A strong local piezoresponse and hysteresis loops observed for composites established the ferroelectric properties at a nanoscale. Magnetostriction measurements revealed values of lambda(11) = -10.4 and lambda(12) = 5.3 ppm and piezomagnetic coefficient d lambda(11)/dH = -0.0087 ppm Oe(-1) at 0.45 kOe for a composite with a ferrite concentration of 35 mol%. A maximum change of 18.5% in magnetization after electrical poling indicates a strong magnetoelectric response of the present composites followed by a direct ME coefficient of 8.2 mV cm(-1) Oe(-1). Our studies point to the fact that the present multiferroic composites having strong ME coupling are useful for lead-free electronic applications.

Gd-doped ceria (CGO) nanopowders were mixed with up to 1 mol% of Zn (as nitrate) to exploit the role of this dopant on sintering and electrical performance. All samples were prepared by two-step sintering schedules to try to combine the advantages of both effects on low-temperature densification. Structural and microstructural analyses were complemented with impedance spectroscopy (wide range of temperatures and oxygen partial pressures) and ion-blocking measurements. The combination of all data suggests that Zn is preferentially located in the grain boundary region, playing a significant role on sintering. Zn additions (I mol%) allowed for a 100 degrees C lower sintering temperature with respect to pure CGO. A marginal effect on the oxide-ion conductivity and a small enhancement (less than 20%) in n-type electronic conductivity was found between Zn-free and 1 mol% Zn-doped CGO. The removal of Zn from CGO after sintering is discussed. (C) 2013 Elsevier B.V. All rights reserved.

The oxygen tracer diffusion and surface exchange coefficients of Sr0.7Ce0.3MnO3-delta (SCM), measured by the O-18/O-16 isotopic exchange depth profile method with time-of-flight secondary-ion mass spectrometric analysis at 973-1123 K, are substantially higher than those of (La,Sr)MnO3-delta. Testing of model solid oxide fuel cells (SOFCs) with SCM cathodes, ceria-based protective interlayers and Ni-containing cermet anodes demonstrated a relatively good and stable performance. For 0.5 mm thick solid electrolyte membranes made of ZrO2- 10 mol% Sc2O3- 1 mol% Y2O3 and doped lanthanum gallate, the maximum power density at 1073 K was approximately 170 and 230 mW/cm(2), respectively, without microstructural optimization and surface modification of the electrodes. Compared to another promising family of SOFC cathode materials, (La,Sr)(Co,Fe)O3-delta, SCM exhibits significantly lower thermal and chemical expansion assessed by the controlled-atmosphere dilatometry. (C) 2013 Elsevier B.V. All rights reserved.

The thermal and chemical expansion of Ba0.5Sr0.5Co0.8Fe0.2O3-delta (BSCF) and SrCo0.8Fe0.2O3-delta (SCF) mixed ionic-electronic conductors were studied in combination with oxygen nonstoichiometry (delta) at 298-1223 K and p(O-2) = 10(-4) to 1.00 atm. In order to minimize the effects of phase separation or oxygen-vacancy ordering processes, the data were collected in dynamic cooling mode using dense ceramic samples. The procedure was justified by a very fast equilibration at given p(O-2) in high-temperature range demonstrated for ceramics samples with different specific surface area. The difference in nonstoichiometry of BSCF and SCF at temperatures >= 973 K was found to be <= 0.03 oxygen atoms per formula unit. BSCF demonstrates favorably smaller chemical expansion compared to SCF and many other mixed conductors, originating from smaller delta variations and larger unit cell less sensitive to temperature and nonstoichiometry changes. Excessive thermochemical expansion impedes however the use of BSCF in single-phase fuel cell cathodes and planar mixed-conducting membranes. (C) 2013 Elsevier Ltd. All rights reserved.

Randomly oriented Sr0.75Ba0.25Nb2O6 thin films have been deposited on Pt(111)/Ti/SiO2/Si substrates using a polymeric chemical method to study their physical properties. Refinements of the structure confirm the stoichiometry of the studied films. The relaxor behavior is evidenced by the dielectric measurements and Vogel-Fulcher analysis of the dielectric curves. Lowering the transition temperature (T-m) by about 100K and asymmetries in the local hysteresis loops well above T-m are discussed in terms of the existence of complex defects in thin films.

Pure BiFeO3 perovskite thin films have been prepared on Pt-coated silicon substrates by chemical solution deposition at temperatures below 500 A degrees C. Precursor solutions with and without Bi(III) excess have been used. Perovskite films without crystalline secondary phases, as detected by X-ray diffraction analysis, are obtained at the lowest temperature limit of 400 A degrees C. However, the scanning electron micrographs of these films show surface microstructures formed by well defined grains surrounded by a fine grained phase, suggesting the appearance of a volume fraction of crystals in an early stage of crystallization. The films prepared with Bi(III) excess have better defined ferroelectric hysteresis loops than those without any excess, especially for the films annealed at 400 A degrees C, which can be attributed to an improved connectivity of the ferroelectric phase. This together with the fact that leakage current densities in the films decrease with decreasing the processing temperature, make that the BiFeO3 films prepared with Bi(III) excess and annealed at 400 and 450 A degrees C can be poled at room temperature, obtaining an effective switching of the ferroelectric polarization with the electric field. Remanent polarization values of P-R similar to 10 and similar to 60 mu C/cm(2) with coercive fields of E-C similar to 205 and 235 kV/cm were obtained for the films prepared at 400 and 450 A degrees C, respectively. The demonstration of the functionality at room temperature of these low temperature processed undoped BiFeO3 thin films increases the interest in these materials for their integration in multiferroic devices.

A comparative microstructural study between Ni-Ce0.9Gd0.1O1.95 (Ni-CGO) anodes obtained from NiO-CGO nanocomposite powders prepared by in situ one-step synthesis and by mechanical mixture (two-step synthesis) of NiO and CGO powders is reported. The open porosity and microstructure of sintered and reduced pellets were investigated as a function of the citric acid content used as pore forming agent. Nanosized crystallites for the one-step and two-step routes were around 18 nm and 24 nm against 16 nm and 37 nm, for CGO and NiO, respectively. Overall results show that both routes provided suitable microstructures either for anode-support, or for functional anodes for solid oxide fuel cells (SOFCs), with more versatile characteristics in the case of the one-step route. The electrical characterization of selected NiO-CGO samples, carried out between 90 and 260 degrees C by impedance spectroscopy, confirms electrical percolation of both phases in the composites. However, based on combined microstructural and impedance data, it seems clear that the one-step processing route is the best approach to make SOFC anodes with improved performance. (C) 2012 Elsevier Ltd and Techna Group S.r.l. All rights reserved.

Composite electrodes based on several ceramic oxides were tested for their chemical compatibility and electrochemical performance in systems based on composite Gd-doped ceria + alkaline carbonate electrolytes. Reactivity tests performed at 700 degrees C (accelerated testing conditions), involving the ceramic electrode materials and one mixture of Na and Li carbonates, identified two promising perovskyte-type ceramics, LaCoO3 and La0.8Sr0.2Co0.2Fe0.8O3, as the most stable. Co-pressed and co-sintered cell assemblies (electrode/electrolyte/electrode) involving composite electrodes (perovskytes mixed with alkaline carbonates)were studied in detail by scanning electron microscopy and tested by impedance spectroscopy in air in the temperature range 300-600 degrees C. These tests showed the potential of these composite electrodes for intermediate temperature applications, clearly surpassing in performance standard Au electrodes, here used as reference. (c) 2012 Elsevier Ltd. All rights reserved.