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1.
La1-xAxCoO3-δ (A = Sr, Ba) nanoparticles used as an inert anode in molten salts were characterized using phonon vibrations, and their compositions and morphologies were investigated. These nanoparticles were used for nanostructure fabrication of an inert anode to reduce oxide ion transportation. The singularity structure changes with increasing Sr ion content in La1-xSrxCoO3-δ nanoparticles showed a transient of spin state change from a low-spin state to intermediate- and/or high-spin states. The valencies of Co ion in La1-xSrxCoO3-δ were 3.2 and 3.3 for La0.8Sr0.2CoO3-δ and La0.6Sr0.4CoO3-δ, respectively, suggesting that oxygen defects were introduced by Sr ion doping in La1-xSrxCoO3-δ nanoparticles. In contrast, the valencies of Co ion in La1-xBaxCoO3-δ were 3.1 and 3.0 for La0.5Ba0.5CoO3-δ and La0.4Ba0.6CoO3-δ, respectively, suggesting that oxygen defects were introduced slightly by Ba ion doping in La1-xBaxCoO3-δ nanoparticles. The isotropic phonon vibrations of La1-xAxCoO3-δ nanoparticles were estimated using high-temperature synchrotron radiation X-ray diffraction measurements. Crystal anisotropy measurements of phonon vibrations indicated that the oxide ions diffused preferentially along the (a, b) plane in the La1-xSrxCoO3-δ crystal lattice and toward the c-axis direction in the La1-xBaxCoO3-δ crystal lattice. These results suggest that the oxide ion transportation was curtailed using layered nanoparticles to fabricate an inert anode. 相似文献
2.
New oxysilicates with the general formula ALa 3Bi(SiO 4) 3O and ALa 2Bi 2(SiO 4) 3O [ ACa, Sr and Ba] are synthesized and characterized. Powder X-ray diffraction of these silicates show that they are isostructural with BiCa 4(VO 4) 3O which has an apatite-related structure. Eu 3+ luminescence in the newly synthesized oxysilicates show broad emission lines due to disorder of cations. The relatively high intense magnetic dipole transition 5D 0→ 7F 1 points to a more symmetric environment. The photoluminescence results confirm that the compounds have apatite-related crystal structure. 相似文献
3.
Apatite-type lanthanum silicate (La 9.33Si 6O 26) has been attracting significant recent interest due to its high oxide ion conductivity. In this paper, synthesis and conductivity
data for a range of doped samples (Mg, Ca, Sr, Ba, B, Ga and Zn) are reported, in particular, to compare the effect of rare
earth vs Si site doping. The results show that Ga, B and Zn favour substitution on the Si site, while Ca, Sr and Ba favour
La-site substitution. Mg is shown to be an ambi-site dopant, substituting on either site depending on the starting composition.
The samples doped on the Si site show higher conductivities than comparable samples doped on the La site, providing further
support for the importance of the silicate network in the conduction process, as initially predicted by atomistic modelling
studies. For Ga doping on the Si site, the effect of varying the rare-earth size on the conductivities is also reported. 相似文献
4.
Heat capacity measurements were carried out on Pb 1-xLa xWO 4+x/2 ( x=0.2) and Pb 1-xLa 2x/3WO 4 ( x=0.2, 0.5) solid solutions prepared by sintering and mechanical alloying (MA) methods. For all the solid solutions, sintered
samples showed slightly larger heat capacity around 100 K in comparison with MA samples, which was presumably caused by the
excitation of mobile oxide ion motion. For sintered scheelite-type structured PbWO 4s, high-temperature synthesis introduced oxide ion interstitials even for the Pb 1-xLa 2x/3WO 4 system, which resulted in the excess heat capacity at low temperature for excitation. On the other hand, for the samples
prepared by room-temperature MA technique, oxide ion seemed to occupy the regular sites rather than interstitial ones and
excess heat capacities were not observed.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
5.
Polycrystalline samples of La 2MMnO 6 ( M = Co and Mg) were prepared by a combined gel‐combustion and high temperature reaction method. The samples were annealed in different oxygen partial pressure ( pO2) and characterized by powder XRD, SQUID magnetometry, ac impedance spectroscopy, and electron paramagnetic resonance techniques. Monoclinic ( P2 1/ n) and rhombohedral ( R$\bar{3}$ ) lattices were observed for La 2CoMnO 6 and La 2MgMnO 6, respectively. On annealing in inert atmosphere, La 2MgMnO 6 partially converted to monoclinic La 2CoMnO 6 type structure, whereas no structural change was observed in La 2CoMnO 6. Dielectric studies of La 2CoMnO 6 indicated relaxor like behavior with polaronic conduction, which systematically decreased with the increase in pO2 of the annealing atmosphere. Magnetic studies indicated multiple ferromagnetic phase transitions in La 2CoMnO 6 and a spin‐glass like phase transition in La 2MgMnO 6. The fraction of ferromagnetic phases of La 2CoMnO 6 was significantly dependent on the annealing environments. The variations of magnetic and dielectric properties of samples were related to the fluctuation of oxidation state of transition metal ions and oxygen vacancies in the samples. 相似文献
6.
The RCO
2
–
catalyzed n-butylaminolysis of 4-nitrophenyl acetate in chlorobenzene has been studied. Logarithms of the catalytic rate constants can be linearly correlated with Taft polar substituent constants for the R groups. Product analysis as well as the lack of steric hindrance by bulky R substituents indicate that the carboxylates act as general base catalysts.
- 4- . R. , R , . 相似文献
7.
High Resolution Electron Microscopy Investigations of La 2CeTaO 6Cl 3 and its Thermal Decomposition Product La 2Ce Ce TaO 6Cl 3?x The thermal decomposition of the hexagonal La 2CeTaO 6Cl 3 led to a mixed-valent product La 2CeCe TaO 6Cl 3?x with a complicated monoclinic structure. The detailed inspection shows two subunits A and B, which form the monoclinic unit cell by a ABAB sequence. The subunit A is almost identical to the hexagonal cell of the starting material while subunit B has additional Ln- and Cl-positions. For this reason, the main structure features of the monoclinic compound and the starting material are related, which is clearly seen in the electron microscopy investigations. As might be expected from the relationship between the subunits A and B one can observe defects in the monoclinic compound arising from the various possibilities of combining these building elements. We also found structure defects in the hexagonal starting material, which are caused by the presence of the subunit B. 相似文献
8.
Electroreduction kinetics of to anions at chemically etched (CHE) and electrochemically polished (EP) Bi(1 1 1) electrodes has been studied using rotating disc electrode method. The surface nanostructure of CHE Bi(1 1 1) and EP Bi(1 1 1) electrodes has been studied by in situ STM and the very different values of root mean squared roughness (Rms) have been obtained (1000 times higher for CHE Bi(1 1 1) (Rms 143 nm) than for EP Bi(1 1 1) (Rms 0.145 nm)). The influence of the nanoroughness of CHE Bi(1 1 1) on the current density, heterogeneous reaction rate constant and corrected Tafel plots (cTp) has been demonstrated. For CHE Bi(1 1 1) the more pronounced inhibition of electroreduction reaction at moderate negative surface charge density has been observed in comparison with EP Bi(1 1 1), caused by the differences in surface charge density and also in diffuse layer ψ0 potential drop values at crystallographically different homogeneous regions (planes) exposed at the surface of the macroheterogeneous polycrystalline CHE Bi(1 1 1) surface. The very low apparent transfer coefficient αapp obtained indicates the nearly activationless charge transfer mechanism for electroreduction at the CHE Bi(1 1 1) electrode similarly to EP Bi(1 1 1). However, αapp only very weakly depends on Rms for the Bi electrodes at high negative surface charge densities where the values of ψ0 potential are nearly equal for different planes at fixed electrode potential. At very high negative surface charge densities the cationic catalysis through the adsorbed ion pairs is possible. 相似文献
9.
Electroconduction of BaR 2F 8 crystals (R = Y 0.9Er 0.1, Y 0.5Yb 0.5, Er 0.945Tm 0.05Ho 0.005) with the structure -BaTm 2F 8 (monoclinic syngony, spatial group C2/ m) is studied at 323–1073 K. Effect of partial pyrohydrolysis on the conduction of Ba(Y, Er) 2F 8 single crystals is investigated. Anion conductivity of crystals of Ba(Y, Yb) 2F 8 and Ba(Er, Tm, Ho) 2F 8 is measured at high temperatures. To a first approximation, there is no change in the ion transport mechanism in these crystals at elevated temperatures. Charge carriers in BaR 2F 8 crystals are, most probably, fluorine vacancies, and the anion conductivity reaches 1–2 mS cm –1 at 1073 K. 相似文献
10.
Lanthanum Containing Silicates and Germanates as Halogen Apatites and Oxyapatites Halogen apatites M 4La 6(XO 4) 6Z 2 and oxyapatites M 2La 8(XO 4) 6O 2 have been prepared: M = Sr, Pb, Ba; X = Si, Ge, and Z = F, Cl. The lattice parameters are discussed. The i.r. active internal vibrations of the silicate ion are assigned. A translational vibration of the “free” oxide ions in the oxyapatites causes an intense absorption at about 400 cm ?1 (silicates) and 350 cm ?1 (germanates), resp. The products “M 3La 6(XO 4) 6” and “M 4La 6(XO 4) 6O” are mixtures of various phases. Their respective apatite phase is a solid solution between M 2La 8(XO 4) 6O 2 and the defect apatite M 4La 6(XO 4) 6O□. Its composition mostly approximates to M 2La8(XO 4) 6O 2, however. 相似文献
11.
Composites of cuprates of La(III) and Ba(II) were obtained by decomposing mixtures of oxalates of La(III), Ba(II) and Cu(II) prepared in 111 and 123 mol proportions respectively and sintering the oxide products at 1173 K. Reactions studied by TG, DTA and XRD techniques revealed the following features: (i) Decomposition of oxalates of La(III) and Ba(II) is drastically affected in mixtures. Decomposition temperature of organic part in the former (111) is shifted by 100 K while that of BaCO 3 in the case of latter (123) is shifted by 400 K towards lower temperature side. (ii) All exothermic peaks on DTA traces of both the mixtures are allotted to the decomposition of oxalates to Cu 2O, La 2O 2CO 3 and BaCO 3 phases while endothermic peaks around 863 and 1083 K are assigned for BaCuO 2 and La 2CuO 4 phases respectively in the case of former (111) and endothermic peaks at about 1068, 1136 and 1213 K are correlated with BaCuO 2, a composite of La 2O 3, La 2CuO 4 and La 0.5Ba 0.5CuO 3– (0.5) phases and LaBa 2Cu 3O 7– (0) phase respectively in the case of latter (123) and (iii) Lines of all cuprate compounds appear in XRD patterns of those samples preheated at temperatures 873 K. The following reaction is proposed in the case of 123 mixture:
Authors are deeply thankful to the Authorities of Department of Atomic Energy (DAE), Goverment of India, for providing the funds for research project and to Professor A. V. Phadke, Department of Geology, University of Poona, for the valuable discussion. 相似文献
12.
La 2M 3 II Mn 4O 12 (M = Mg, Ca, Sr, or Ba) manganites have been synthesized by ceramic technology from lanthanum oxide, manganese(III) oxide, and magnesium, calcium, strontium, or barium carbonate. X-ray powder diffraction shows that these compounds crystallize in cubic perovskite space group Pm3m. 相似文献
13.
Hydrogen powered solid oxide fuel cells (SOFCs) are of enormous interest as devices for the efficient and clean production of electrical energy. However, a number of problems linked to hydrogen production, storage and transportation are slowing down the larger scale use of SOFCs. Identifying alternative fuel sources to act as intermediate during the transition to the full use of hydrogen is, therefore, of importance. One excellent alternative is ammonia, which is produced on a large scale, is relatively cheap and has the infrastructure for storage and transportation already in place. However, considering that SOFCs operate at temperatures higher than 500 °C, a potential problem is the interaction of gaseous ammonia with the materials in the cathode, anode and solid electrolyte. In this paper, we extend earlier work on high temperature reactions of apatite electrolytes with NH 3 to the transition metal (Co) doped systems, La 9.67Si 5CoO 26 and La 10(Si/Ge) 5CoO 26.5. A combination of PXRD, TGA and XAFS spectroscopy data showed a better structural stability for the silicate systems. Apatite silicates and germanates not containing transition metals tend to substitute nitride anions for their interstitial oxide anions, when reacted with NH 3 at high temperature and, consequentially, lower the interstitial oxide content. In La 9.67Si 5CoO 26 and La 10(Si/Ge) 5CoO 26.5 reduction of Co occurs as a competing process, favouring lower levels of nitride-oxide substitution. 相似文献
14.
Electrochemical Synthesis of Perovskites in the System K/Ba/Pr/Bi/O An easy procedure for the synthesis of well crystalline samples of (K,Ba)(Pr,Bi)O 3 is provided by anodic oxidation of melts consisting of Ba(OH) 2 / KOH / Pr(NO 3) 3 / Bi(NO 3) 3, at comparatively low temperatures of about 220 °C. We have explored the influence of different parameters like temperature, potential of the working electrode, and composition of the electrolyte. Chemical and thermal analyses were performed. Products obtained at different experimental conditions revealed different Ba/K and Pr/Bi ratios with a large homogeneity range. X‐Ray powder diffraction and single crystal structure analyses of K xBa 1?xPr yBi 1?yO 3 proved these compounds to be cubic perovskites. Barium and potassium ions are disordered occupying the A‐sites while praseodym and bismuth ions share the B‐sites or are ordered, as indicated by a doubling of the lattice parameter. The composition x and y can independently be altered. XPS analysis and physical properties are reported and discussed. 相似文献
15.
The ternary germanide Mg 5.57Ni 16Ge 7.43 (cubic, space group Fmm, cF116) belongs to the structural family based on the Th 6Mn 23-type. The Ge1 and Ge2 atoms fully occupy the 4 a ( mm symmetry) and 24 d ( m.mm) sites, respectively. The Ni1 and Ni2 atoms both fully occupy two 32 f sites (.3 m symmetry). The Mg/Ge statistical mixture occupies the 24 e site with 4 m.m symmetry. The structure of the title compound contains a three-core-shell cluster. At (0,0,0), there is a Ge1 atom which is surrounded by eight Ni atoms at the vertices of a cube and consequently six Mg atoms at the vertices of an octahedron. These surrounded eight Ni and six Mg atoms form a [Ge1Ni 8(Mg/Ge) 6] rhombic dodecahedron with a coordination number of 14. The [GeNi 8(Mg/Ge) 6] rhombic dodecahedron is encapsulated within the [Ni 24] rhombicuboctahedron, which is again encapsulated within an [Ni 32(Mg/Ge) 24] pentacontatetrahedron; thus, the three-core-shell cluster [GeNi 8(Mg/Ge) 6@Ni 24@Ni 32(Mg/Ge) 24] results. The pentacontatetrahedron is a new representative of Pavlyuk's polyhedra group based on pentagonal, tetragonal and trigonal faces. The dominance of the metallic type of bonding between atoms in the Mg 5.57Ni 16Ge 7.43 structure is confirmed by the results of the electronic structure calculations. The hydrogen sorption capacity of this intermetallic at 570 K reaches 0.70 wt% H 2. 相似文献
16.
Summary The initial stages of oxidation of clean (110), (100), and (111) oriented -NiAl single crystals, with and without Pt doping (50 nm), were followed at 973 K using LEED and AES. Upon oxidation, Al 2O 3 is selectively formed. On NiAl (110) a complex surface structure is observed which according to Jäger et al. [13] is a duplex oxide structure similar to - or -Al 2O 3. On the (100) face, submicroscopic facetting occurs during oxidation. For the (111) oriented sample the hexagonal structure remains and only an increased background intensity for the LEED pattern is observed for the oxidized surface. After Pt doping, the phenomena observed for the Pt-free sample are not significantly changed. However the following differences exist: 1. the formation of the Al 2O 3 oxide is more difficult for the (110) and (111) samples but Pt doping facilitates facetting and oxide formation on the (100) oriented sample; 2. sputtering of the oxide layers on Pt-doped samples is retarded in all cases, a very stable and dense oxide seems to be formed which adheres well; 3. Pt seems to hinder the Al diffusion to the unoxidized surface of the samples. 相似文献
17.
The synthesis of nanosized manganites LaMnO 3 and La 1–xK xMnO 3, where x = 0.1, 0.15, 0.185, by low-temperature extraction-pyrolytic method was shown to be promising. Temperature and field dependences for the specific magnetization of the obtained specimens were studied. The dependence of magnetic characteristics on the concentration of doping potassium ion in the studied lanthanum manganites was revealed. 相似文献
18.
Crystal structure and electron density in the apatite-type ionic conductor La 9.71(Si 5.81Mg 0.18)O 26.37 have been investigated at 302, 674 and 1010 K by Rietveld refinement and a whole-pattern fitting approach based on the maximum-entropy method (MEM) using synchrotron X-ray powder diffraction data. Second harmonic generation measurements indicated that the space group of this material is centrosymmetric. Among the possible hexagonal groups P6 3/ m, P6 3 and the former is correct for La 9.71(Si 5.81Mg 0.18)O 26.37. Rietveld refinements suggested an oxygen interstitial site (0.03,0.15,0.85) near the hexagonal axis. MEM analyses revealed that the Si 0.97Mg 0.03 atom has covalent bonds with four adjacent oxygen atoms to form a tetrahedron. The oxygen O4 atom located at the 2 a site (0.0,0.0,1/4) exhibited large atomic displacement parameters along the c axis and electron density mapping also indicated the wide distribution consistent with migration of oxygen ions in this direction. 相似文献
19.
Incorporation of gallium into the perovskite lattice of La 0.3Sr 0.7CoO 3–
leads to increasing unit cell volume and to decreasing thermal expansion, total conductivity and oxygen permeability. At 973–1223 K, the oxygen permeation fluxes through La 0.3Sr 0.7Co 0.8Ga 0.2O 3–
ceramics with 96.5% density are determined by the bulk ionic conduction and surface exchange rates. The total conductivity of La 0.3Sr 0.7Co 0.8Ga 0.2O 3–, predominantly p-type electronic, exhibits an apparent pseudometallic behavior due to oxygen losses on heating, whereas the
p(O 2) dependencies of the conductivity and Seebeck coefficient suggest a small-polaron mechanism of hole transport. The average thermal expansion coefficients in air are 15.9×10 –6 K –1 at 360–710 K and 27.9×10 –6 K –1 at 710–1030 K. On decreasing oxygen pressure down to 4–30 Pa at 973–1223 K, perovskite-type La 0.3Sr 0.7Co 0.8Ga 0.2O 3–
transforms into a brownmillerite-like modification, whose electrical properties are essentially p(O 2) independent. Further reduction results in the decomposition of the brownmillerite into a multiphase oxide mixture at
p(O 2)=8×10 –10–3×10 –4 Pa, and then in the segregation of metallic cobalt. Due to surface-limited oxygen transport, La 0.3Sr 0.7Co 0.8Ga 0.2O 3–
membranes are, however, kinetically stable under an air/CH 4 gradient up to 1223 K. The conversion of dry methane in model membrane reactors increases with oxygen permeation flux and temperature, but yields high CO 2 concentrations (>90%), indicating a dominant role of complete CH 4
oxidation on the membrane surface. 相似文献
20.
Based on the EHMO approach, the band structures for the Y? Ba? Cu? O superconductors doped by La were calculated. The influence of the partial substitutions of La for Y and Ba in YBa 2CU 3O y on its electronic structures was investigated. The results demonstrate that the La doping at the Ba site has a great effect on the electronic structures of the Y? Ba? Cu? O superconductors, whereas the change in the band structures caused by the La doping at the Y site is very small. The increase in the oxygen content caused by the La doping results in an increase in the densities of states at Ef, N( Ef), for La 1+x Ba 2?xCu 3O y, but the increase in N( Ef) cannot compensate the decrease caused by the La doping at the Ba site. In addition, the 2D Cu? O planes are much more sensitive to the change in N( Ef) than are the 1D Cu? O ribbons, which implies an important role of the 2D Cu? 0 planes in the Y? Ba? Cu? O superconducting system, regardless of whether La substitutes for Y or for Ba. © 1995 John Wiley & Sons, Inc. 相似文献
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