Search results for "lanthanum"
showing 10 items of 78 documents
Photoelectrochemical properties of doped lanthanum orthoferrites
2013
Abstract LaFeO 3 powders doped with Sr (20 mol%) and Cu (0-10-20 mol%) were prepared by citrate auto-combustion synthesis and investigated in terms of crystal structure, morphology, surface area and optical properties. All powders showed photocurrent response in the form of a pasted and annealed electrode and as slurry electrode; the highest value was obtained for undoped orthoferrite calcined at 600 °C. Their physical–chemical properties were related to photoelectrochemical behaviour. The position of the quasi-Fermi level of electrons for all the photocatalysts calcined in the range 600–980 °C is about the same within experimental error (between −0.62 and −0.67 V with respect to Ag/AgCl re…
Relationship between domestic smoking and metals and rare earth elements concentration in indoor PM2.5
2018
Cigarette smoke is the main source of indoor chemical and toxic elements. Cadmium (Cd), Thallium (Tl), Lead (Pb) and Antimony (Sb) are important contributors to smoke-related health risks. Data on the association between Rare Earth Elements (REE) Cerium (Ce) and Lanthanum (La) and domestic smoking are scanty. To evaluate the relationship between cigarette smoke, indoor levels of PM2.5 and heavy metals, 73 children were investigated by parental questionnaire and skin prick tests. The houses of residence of 41 "cases" and 32 "controls" (children with and without respiratory symptoms, respectively) were evaluated by 48-hours PM2.5 indoor/outdoor monitoring. PM2.5 mass concentration was determi…
Electrode–Electrolyte Compatibility in Solid-Oxide Fuel Cells: Investigation of the LSM–LNC Interface with X-ray Microspectroscopy
2015
Ca:LaNbO4 (LNC) constitutes the last real breakthrough in high-temperature proton conductors, with better chemical and mechanical stability with respect to cerate and zirconate perovskites. However, the low amount of bivalent dopant that can be hosted in the LaNbO4 matrix poses a limit to the proton concentration in the electrolyte. Using synchrotron X-ray microspectroscopy, we investigated the compatibility of annealed LNC/LSM electrolyte/cathode bilayers for proton-conducting SOFCs. The element maps are complemented by microEXAFS and microXANES, giving information on the fate of different cations after diffusion. The X-ray microspectroscopy approach described here is applied for the first…
Substitution effects on the relaxor properties of lead magnesium niobate ceramics
1999
Abstract The temperature dependence of the dielectric permittivity is studied in different Pb(Mg⅓Nb⅔)O3 based ceramics, in which the ordered region size can be changed by introducing titanium or lanthanum ions. Both the relaxor behaviour and the nonlinear dielectric component are found to be dependent on the impurity content. Especially, the nonlinearity increases strongly as the material exhibits a more conventional ferroelectric behaviour, i.e. as the size of the polar clusters, which develop in the paraelectric matrix, increases.
Processing, basic characterization and standard dielectric measurements on PLZTx/65/35 (4 ≤x≤ 11) ceramics
2014
The influence of external stress (0–800 bar) on the dielectric properties of lead lanthanum zirconium titanate (PLZT) x/65/35 (4 ≤ x ≤ 11) ceramics was investigated. Applying uniaxial pressure leads to a change in the peak intensity of the electric permittivity (ϵ), in its frequency dispersion as well as in the dielectric hysteresis. The peak intensity of ϵ becomes broader and shifts to lower temperatures for PLZT x/65/35 with x = 4, 7, 9.75 and 11, with increasing pressure, on heating. It was concluded that applying uniaxial pressure induces an increase of Tm, and thus has a similar effect as the increase of the Ti ion concentration in the lead zirconium titanate (PZT) system. Results base…
Phase Stability of Lanthanum Orthovanadate at High Pressure
2016
The journal of physical chemistry / C 120(25), 13749 - 13762(2016). doi:10.1021/acs.jpcc.6b04782
Study of the spontaneous relaxor to normal ferroelectric phase transition in la-doped lead titanate
2000
Abstract Highly lanthanum doped lead titanate ceramics exhibit relaxor properties and undergo on cooling a subsequent spontaneous macroscopic phase transition. The dielectric response is strongly affected by chemical (copper) doping and is found to become independent of the applied ac field for temperatures lower than the phase transition one.
Electroluminescence of (Pb0.91La0.09)(Zr0.65Ti0.35)O3 relaxor ceramics
2013
Abstract Lanthanum doped lead zirconate titanate (PLZT) relaxor ceramics with (Pb 0.91 La 0.09 )(Zr 0.65 Ti 0.35 )O 3 composition exhibit a repolarization induced by electroluminescence (EL) with a pronounced discrete character of emission. It is established that this behavior is related to the reorientation of nanodimensional polar regions in a strong pulsed electric field in the vicinity of a smeared phase transition. The time and temperature dependences of the EL intensity are studied.
Crystallographic changes and thermal properties of lanthanum?strontium ferromanganites between RT and 700 �C
2005
Abstract X-ray powder diffraction was used to determine the crystallographic changes between room temperature (RT) and 700 °C of the (La 0.8 Sr 0.2 )(Mn 1− y Fe y )O 3± δ perovskites with y =0.2, 0.5, 0.8, 1 which can be considered as possible cathode materials for the ITSOFCs. For y =0.2, the rhombohedral symmetry was preserved in the whole temperature range. For y =1, a transition from orthorhombic to rhombohedral symmetry occurred at 290 °C. The compounds with y =0.5 and 0.8 were found to be diphasic at RT by combination of both rhombohedral and orthorhombic symmetries. They became only rhombohedral at 80 and 160 °C, respectively. This reversible transition is discussed in terms of iron …
Self-assembled monolayers based spintronics: from ferromagnetic surface functionalization to spin-dependent transport.
2016
Chemically functionalized surfaces are studied for a wide range of applications going from medicine to electronics. Whereas non-magnetic surfaces have been widely studied, functionalization of magnetic surfaces is much less common and has almost never been used for spintronics applications. In this article we present the functionalization of La2/3Sr1/3MnO3, a ferromagnetic oxide, with self-assembled monolayers for spintronics. La2/3Sr1/3MnO3 is the prototypical half-metallic manganite used in spintronics studies. First, we show that La2/3Sr1/3MnO3 can be functionalized by alkylphosphonic acid molecules. We then emphasize the use of these functionalized surfaces in spintronics devices such a…