Unlike ordering of the octahedral B-site cations, ordering of the larger A-site cations in stoichiometric perovskites is rare. Herein the A- and B-site ordering characteristics of several double perovskites with AA'BB'O{sub 6} stoichiometry have been ...
Energy Citations Database
Large disorder effects due to size differences between A-site R3+ (R=La,Pr,Nd,Sm) and M2+ (M=Ca,Sr,Ba) cations have been found in magnetoresistive (R0.7M0.3)MnO3 perovskites. The ferromagnetic-metal-paramagnetic-insulator transition temperature Tm varies as Tm=Tm(0)-pQ2 due to strain fields resulting from ordered or disordered oxygen ...
NASA Astrophysics Data System (ADS)
... Abstract : Microstructure of ordered A-site perovskites has been studied by transmission electron microscopy and electron diffraction. ...
DTIC Science & Technology
In this paper we report results of structural, spectroscopic, and magnetic investigations of MgFe2O4 nanoparticles prepared by soft mechanochemical synthesis. MgFe2O4 nanoparticles crystallize in Fd3m space group with mixed cation distribution and reduced percentage of Fe3+ at tetrahedral (8a) sites. Discrepancy in the ...
Antimony substituted nickel ferrites Co x Ni5/3? x FeSb1/3O4 with x=0,1/3,1,4/3, and 5/3 were prepared by the common ceramic technique, and the single-phase structure was confirmed by x-ray powder diffraction.57Fe M�ssbauer spectra were recorded at 4.2 K with and without an applied magnetic field H long=60 kOe in order to determine the cation ...
Accurate oxygen-content analysis by means of a coulometric redox titration method specially devised for the purpose shows that as-synthesized (in 5% H2/Ar) samples of the recently reported novel solid oxide fuel cells anode material Sr2MgMoO6?? contain oxygen vacancies with a concentration of ??0.05. Oxygen contents and the resultant Mo-valence values are also analyzed for various A2MgMoO6?? ...
The structure of La(1/3)NbO3 is that of a perovskite with La3+ cations ordered into alternate layers of perovskite A-sites. This is the description of a tetragonal structure and yet the room-temperature structure shows an orthorhombic distortion. The structure of La(2/3)TiO3 shows similar features. It has been recognized only very ...
PubMed
... ABSTRACT (Maximum 200wcrs) Microstructure of ordered A-site perovskites has been studied by transmission electron microscopy and electron ...
The copper ferrite phase (Cu0.5 Fe2.5O4) has a spinel structure with copper normally occupying both the tetrahedral (A) site and the octahedral (B) site, depending on its valence. Theoretically, the material with all copper in the monovalent state and occupying the A-site of the spinet sublattice, will have a very high saturation magnetization of 7.5muB ...
The crystal structure of new A-site deficient La{sub 5/3}MgTaO{sub 6} perovskite was investigated by neutron, X-ray and electron diffraction. Neutron and X-ray powder diffraction spectra were refined in the monoclinic I2/m space group, with the parameters of the unit cell a=5.6304(2)A, b=5.6226(2)A, c=7.9434(2)A and {beta}=90.04(1){sup o}. This structural model presumes a ...
The crystal structure of new A-site deficient La5/3MgTaO6 perovskite was investigated by neutron, X-ray and electron diffraction. Neutron and X-ray powder diffraction spectra were refined in the monoclinic I2/m space group, with the parameters of the unit cell a=5.6304(2) �, b=5.6226(2) �, c=7.9434(2) � and ?=90.04(1)�. This structural model presumes a random ...
We have employed aliovalent A-site cation substitution, La{sup III}-for-Sr{sup II}, to dope the Sr(Fe{sub 0.5}Ta{sub 0.5})O{sub 3} perovskite oxide with electrons. Essentially single-phase samples of (Sr{sub 1-} {sub x} La {sub x} )(Fe{sub 0.5}Ta{sub 0.5})O{sub 3} were successfully synthesized up to x{approx}0.3 in a vacuum furnace at 1400 deg. C. The ...
Large disorder effects due to size differences between {ital A}-site {ital R}{sup 3+} ({ital R}=La,Pr,Nd,Sm) and {ital M}{sup 2+} ({ital M}=Ca,Sr,Ba) cations have been found in magnetoresistive ({ital R}{sub 0.7}{ital M}{sub 0.3})MnO{sub 3} perovskites. The ferromagnetic-metal{endash}paramagnetic-insulator transition temperature {ital T}{sub {ital m}} ...
The sintering behavior of Ca- and Sr-doped lanthanum manganite (the preferred SOFC cathode material) is highly dependent on the relative proportion of A and B site cations in the material. In general, A-site cation deficiency increases sintered density. The effect of additions of YSZ to lanthanum manganite (to expand the reactive ...
Accurate oxygen-content analysis by means of a coulometric redox titration method specially devised for the purpose shows that as-synthesized (in 5% H{sub 2}/Ar) samples of the recently reported novel solid oxide fuel cells anode material Sr{sub 2}MgMoO{sub 6-{delta}} contain oxygen vacancies with a concentration of {delta}{approx}0.05. Oxygen contents and the resultant Mo-valence values are also ...
The decomposition of the cubic perovskite-type oxide Ba(x)Sr(1-x)Co(0.8)Fe(0.2)O(3-delta) (BSCF) into hexagonal and cubic perovskite-type phases has been examined by means of Scanning Electron Microscopy (SEM), Transmission Electron Microscopy (TEM), Selected Area Electron Diffraction (SAED) and X-Ray Diffraction (XRD). SEM and TEM measurements reveal that the new hexagonal phase grows ...
Structural, magnetic, and transport properties of (La1-xNdx)0.8Na0.2MnO3(0<=x<=1) are studied. The system exhibits a rhombohedrally distorted perovskite structure for x<=0.2 and it converts to an orthorhombic structure for x>=0.4. Re-entrant ferromagnetic-type charge ordering transitions are observed in the narrow bandwidth samples (x>=0.8). For T>77K, the ...
Novel phenylpiperazine derivatives were developed in order to reversibly and irreversibly label the serotonin/sub 1a/ (5-HT/sub 1a/) binding site in the brain. 1-(2-(4-aminophenyl)ethyl)-4-(3-trifluoromethylphenyl)piperazine (PAPP) acts as a serotonin agonist in vivo and binds with high affinity and selectivity to the 5-HT/sub 1a/ site ...
Limited evidence to date suggests that acidic precipitation promotes leaching of nutrient cations from conifer foliage. In order to evaluate the relative contribution of the apoplast cation exchange complex and symplast nutrient pools to the leached ions,...
National Technical Information Service (NTIS)
Limited evidence to date suggests that acidic precipitation promotes leaching of nutrient cations from conifer foliage. n order to evaluate the relative contribution of the apoplast cation exchange complex and symplast nutrient pools to the leached ions, the magnitude of potentia...
EPA Science Inventory
Magnetite single crystals with Al, Ga and Ti substitutions were measured by means of 57Fe nuclear magnetic resonance (NMR) technique. Satellite structure of NMR spectra well above the Verwey temperature was detected and analyzed to obtain information on the distribution of substituting cations on iron sublattices. It was confirmed that Al and Ti enter iron octahedral B-sites. ...
The magnetic properties of RE0.7Ca0.3Mn0.95Fe0.05O3 perovskite with rare-earth cations (RE=Sm and Gd) were investigated by means of X-ray diffraction, M�ssbauer spectroscopy, and low temperature (4.2-266 K) magnetization measurements. Structural characterization of these compounds shows that they both have orthorhombic (Pbnm) structure. The M�ssbauer spectra show clear ...
... Accession Number : ADD256704. Title : Effect of Sn Substitution on Cation Ordering in (Zr(1-x)Sn(x))TiO4 Microwave Dielectric Ceramics. ...
... mechanisms in ferroelectric relaxors has been aided by the study of order-disorder of the cation arrangement in lead scandium tantalate, and the ...
This paper discusses a method that has been developed to study bulk lattice interdiffusion between calcium and strontium titanate by fabrication of a diffusion couple using cosintering. The measured interdiffusion coefficients, D(C), indicate that strontium impurity diffusion in calcium titanate occurs at a faster rate than calcium impurity diffusion in strontium titanate. These interdiffusion ...
