共查询到20条相似文献,搜索用时 31 毫秒
1.
Igor Presniakov Gérard M. Demazeau Alexey Baranov 《Journal of solid state chemistry》2004,177(10):3324-3332
Mössbauer spectroscopy has been applied for studying local environment of 57Fe and 119Sn probe atoms within tin-doped Sr2Fe1.98Sn0.02O5+x (x?0.02) ferrite with the brownmillerite-type structure. 57Fe Mössbauer spectra indicate no appreciable local distortions induced by the tin dopant atoms. The 119Sn spectra recorded below the magnetic ordering temperature (TN) can be described as a superposition of two Zeeman sextets, which indicate that Sn4+ dopant ions are located in two non-equivalent crystallographic and magnetic sites. The observed hyperfine parameters were discussed supposing Sn4+ cations to replace iron cations in the octahedral (SnO) and tetrahedral (SnT) sublattices. It has been supposed that Sn4+ cations being stabilized in the tetrahedral sublattice complete their nearest anion surrounding up to the octahedral oxygen coordination “SnT4+”. Annealing of the Sr2Fe1.98Sn0.02O5+x in helium flux conditions at 950°C leads to formation of divalent Sn2+ cations with a simultaneous decrease of the contribution for the SnT4+ sub-spectrum. The parameters of combined electric and magnetic hyperfine interactions of the 119Sn2+ sub-spectrum underline that impurity atoms are stabilized in the sp3d-hybrid state in the oxygen distorted tetragonal pyramid. The analysis of the 119Sn spectra indicates a chemical reversibility of the processes SnT2+?SnT4+ within the tetrahedral sublattice of the brownmillerite-type ferrite. 相似文献
2.
M. AllixD. Pelloquin F. StuderN. Nguyen A. WahlA. Maignan B. Raveau 《Journal of solid state chemistry》2002,167(1):48-58
Two new Sr-rich “1201”-type oxides, Bi0.4Sr2.5Cr1.1O4.9 and Bi0.4Sr2.5Fe1.1O5 have been synthesized. These compounds, intergrowths of double rock-salt layers with single perovskite layers, show a 1:1 ordering between (Bi,M) and Sr species within the intermediate rock-salt layer [Bi0.4M0.1Sr0.5O]. The XANES study shows that bismuth is mainly trivalent, whereas iron is mixed valent containing 50% Fe3+ and 50% Fe4+ (also confirmed by Mössbauer), and chromium could be a mixture of Cr3+ and Cr6+ sitting in the perovskite and rock-salt-type sites, respectively. Both compounds exhibit antiferromagnetic interactions. The Cr-phase is a strong insulator, whereas the Fe-phase exhibits a semi-conductor-like resistivity whose value at room temperature is close to that of isotypic cobaltite. 相似文献
3.
Teresa Berrocal José L. Pizarro María I. Arriortua 《Journal of solid state chemistry》2006,179(6):1659-1667
Fe2(AsO4)F has been synthesized under mild hydrothermal conditions in the form of single crystals. The compound crystallizes in C2/c monoclinic space group with the unit cell parameters a=13.214(1), b=6.623(1), and β=116.90(2)° with Z=8. The crystal structure consists of a three-dimensional framework constructed by two kinds of chains, A and B, with 50% of population. In the chains, the environments for the iron(II) cations show penta- and hexa-coordination. The chains establish an angle of approximately 120° between them. The disordered fluoride anions in these chains given rise to [Fe(1)O4F(1)0.5(F(2)0.5)2] and [Fe(2)O4(F(1)0.5)2F(2)0.5] edge-shared polyhedra in which the fluoride anions have occupancy factors of 50% over two distinct crystallographic sites. The IR spectrum shows the characteristic bands of the (AsO4)3− groups. From the diffuse reflectance spectrum a Dq parameter of 650 cm−1 has been calculated for the Fe(II) d6 high spin cation. The Mössbauer spectrum in the paramagnetic state shows a doublet that has been fitted, according to the existence of two crystallographically independent iron environments, with two Lorentzian doublets. Magnetic measurements performed between room temperature and 5 K exhibit a maximum at 22.6 K, characteristic of antiferromagnetic interactions with a estimated “J”-exchange parameter of −1.2 K. 相似文献
4.
The alkali sodium ferrate (IV) Na4FeO4 has been prepared by solid-state reaction of sodium peroxide Na2O2 and wustite Fe1−xO, in a molar ratio Na/Fe=4, at 400°C under vacuum. Powder X-ray and neutron diffraction studies indicate that Na4FeO4 crystallizes in the triclinic system P−1 with the cell parameters= a=8.4810(2) Å, b=5.7688(1) Å, c=6.5622(1) Å, α=124.662(2)°, β=98.848(2)°, γ=101.761(2)° and Z=2. Na4FeO4 is isotypic with the other known phases Na4MO4 (M=Ti, Cr, Mn, Co and Ge, Sn, Pb). The solid solution Na4FexCo1−xO4 exists for x=0-1 and we have followed the evolution of the cell parameters with x to determine the lattice parameters of the triclinic cell of Na4FeO4. A three-dimensional network of isolated FeO4 tetrahedra connected by Na atoms characterizes the structure. This compound is antiferromagnetic below TN=16 K. At 2 K the magnetic cell is twice the nuclear cell and the magnetic structure is collinear (μFe=3.36(12) μB at 2 K). This black compound is highly hygroscopic. In water or on contact with the atmospheric moisture it is disproportionated in Fe3+ and Fe6+. The Mössbauer spectra of Na4FeO4 are fitted with one doublet (δ=− 0.22 mm/s, Δ=0.41 mm/s at 295 K) in the paramagnetic state and with a sextet at 8K. These parameters characterize Fe4+ high-spin in tetrahedral FeO4 coordination. 相似文献
5.
6.
The solid solution of YMn1−xFexO3 (x=0.0, 0.1, 0.2, 0.3, 0.5, 1.0) was synthesized from the citrate precursor route. The hexagonal crystal structure related to YMnO3 was stable for x?0.3. Rietveld refinement was carried out on the composition for x=0.3 and was refined to a major hexagonal phase (∼97%) with 3% of orthorhombic Y(Fe/Mn)O3 phase. The a-axis lattice constant increases and the c-axis lattice constant decreases with x for x?0.2. The increase in the c-axis lattice constant at x=0.3 could be due to the doping of significant amount of d5 ion (high spin Fe3+ ion) in a trigonal bipyramidal crystal field. The detailed structural, magnetic and dielectric properties are discussed. 相似文献
7.
Siân E. Dutton Fernande Grandjean Moulay T. Sougrati Emma Winstone 《Journal of solid state chemistry》2009,182(7):1638-5922
A polycrystalline sample of Pr18Li8Fe4RuO39 has been synthesized by a solid state method and characterized by neutron powder diffraction, magnetometry and Mössbauer spectroscopy; samples of Pr18Li8Fe5−xMnxO39 and Pr18Li8Fe5−xCoxO39 (x=1, 2) have been studied by magnetometry. All these compounds adopt a cubic structure (space group , a0∼11.97 Å) based on intersecting 〈111〉 chains made up of alternating octahedral and trigonal-prismatic coordination sites. These chains occupy channels within a Pr-O framework. The trigonal-prismatic site in Pr18Li8Fe4RuO39 is occupied by Li+ and high-spin Fe3+. The remaining transition-metal cations occupy the two crystallographically-distinct octahedral sites in a disordered manner. All five compositions adopt a spin-glass-like state at 7 K (Pr18Li8Fe4RuO39) or below. 相似文献
8.
Seung-Joo KimIgor Presniakov Gerard Demazeau Konstantin PokholokAlexey Baranov Alexey SobolevDenis Pankratov Nikolay Ovanesyan 《Journal of solid state chemistry》2002,168(1):126-133
Nickelates ANiO3 (A=Pr, Nd, Sm, Lu, Y, Tl) containing Mössbauer probe 57Fe atoms were synthesized. In the case of nickelates with larger rare earth (A=Pr, Nd, Sm) the Mössbauer spectra confirm that ferric ions are located in single type of crystallographic positions. On the contrary, the spectra of ANi0.98Fe0.02O3 with small cations (A=Lu, Y, Tl) can be described as a superposition of two sub-spectra which indicate that 57Fe probe atoms are simultaneously stabilized in two non-equivalent crystallographic positions. These results have been interpreted in terms of partial charge disproportionation of Ni3+ cations associated with the electronic localization in monoclinic distorted Lu, Y, Tl nickelates. The modification of 57Fe spectra for TlNi0.98Fe0.02O3 as a function of temperature has shown that this charge disproportionation occurs in varying degrees, corresponding to the charge states Fe(3+σ)+ and Fe(3−σ′)+. On the contrary, the spectra for Lu and Y nickelates show that charge variation (σ,σ′) for dopant Fe(1) and Fe(2) cations does not depend on temperature. 相似文献
9.
E.V. Tsipis M.V. Patrakeev Y.V. Pivak P. Gaczyński V.V. Kharton 《Journal of solid state chemistry》2007,180(6):1902-1910
The oxygen deficiency of iron-substituted nickelates Ln4Ni2.7Fe0.3O10−δ (Ln=La, Pr) with the orthorhombic Ruddlesden-Popper structure was studied by thermogravimetric analysis and coulometric titration in the oxygen partial pressure range 6×10−5 to 0.7 atm at 973-1223 K. In air, the non-stoichiometry values vary in the relatively narrow ranges (2.4−4.2)×10−2 for La- and (0.01−2.0)×10−2 for Pr-containing compositions, increasing with temperature. Due to the smaller size of praseodymium cations, Pr4Ni2.7Fe0.3O10−δ exhibits a substantially lower thermodynamic stability in comparison with La4Ni2.7Fe0.3O10−δ and La4Ni3O10−δ, although the oxygen content in Pr4Ni2.7Fe0.3O10−δ lattice is higher. The partial substitution of iron for nickel has no essential effect on the low-p(O2) stability limit corresponding to the transition of Pr4Ni3O10−δ into K2NiF4-type Pr2NiO4+δ. On the contrary, doping of La4Ni3O10−δ with iron decreases the oxygen vacancy concentration and shifts the phase stability boundary towards lower oxygen chemical potentials, suggesting a stabilization of the transition metal-oxygen octahedra in lanthanum nickelate lattice. The Mössbauer spectroscopy showed that the predominant state of iron cations, statistically distributed between the nickel sites, is trivalent. 相似文献
10.
Vladislav V. Kharton Joao C. Waerenborgh Sergey O. Yakovlev Piotr Gaczyński Aleksey A. Yaremchenko Victor V. Samakhval 《Journal of solid state chemistry》2006,179(4):1273-1284
Aluminum incorporation in the rhombohedrally distorted perovskite lattice of (La0.5Sr0.5)1−xFe1−yAlyO3−δ (x=0-0.05, y=0-0.30) decreases the unit cell volume and partial ionic and p-type electronic conductivities, while the oxygen nonstoichiometry and thermal expansion at 900-1200 K increase on doping. The creation of A-site cation vacancies has an opposite effect on the transport properties of Al-substituted ceramics. The maximum A-site deficiency tolerated by the (La,Sr)(Fe,Al)O3−δ structure is however limited, close to 3-4%. The Mössbauer spectroscopy revealed progressive localization of electron holes and a mixed charge-compensation mechanism, which results in higher average oxidation state of iron when Al3+ concentration increases. The average thermal expansion coefficients of (La0.5Sr0.5)1−xFe1−yAlyO3−δ are (12.2-13.0)×10−6 K−1 at 300-900 K and (20.1-30.0)×10−6 K−1 at 900-1200 K in air. The steady-state oxygen permeability (OP) of dense Al-containing membranes is determined mainly by the bulk ionic conductivity. The ion transference numbers at 973-1223 K in air, calculated from the oxygen permeation and faradaic efficiency (FE) data, vary in the range 1×10−4-3×10−3, increasing with temperature. 相似文献
11.
A series of spinel compounds with composition CuFe0.5(Sn(1−x)Tix)1.5S4 (0≤x≤1) is analysed by X-ray diffraction, measurements of magnetic susceptibilities and 57Fe Mössbauer spectroscopy. All samples show a temperature-dependent equilibrium between an electronic low spin 3d(t2g)6(eg)0 and a high spin 3d(t2g)4(eg)2 state of the Fe(II) ions. The spin crossover is of the continuous type and extends over several hundred degrees in all samples. The Sn/Ti ratio influences the thermal equilibrium between the two spin states. Substitution of Sn(IV) by the smaller Ti(IV) ions leads to a more compact crystal lattice, which, in contrast to many metal-organic Fe(II) complexes, does not stabilise the low spin state, but increases the residual high spin fraction for T→0 K. The role played by antiferromagnetic spin coupling in the stabilisation of the high spin state is discussed. The results are compared with model calculations treating the effect of magnetic interactions on spin state equilibria. 相似文献
12.
Phases formed by the reduction of compounds of the type La0.5Sr0.5MO3 (M=Fe, Co) have been characterized by means of temperature programmed reduction, X-ray powder diffraction, 57Fe Mössbauer spectroscopy and Fe K-, Co K-, Sr K-, and La LIII-edge X-ray absorption spectroscopy. The results show that treatment of the material of composition La0.5Sr0.5FeO3 (which contains 50% Fe4+ and 50% Fe3+) at 650 °C in a flowing 90% hydrogen/10% nitrogen atmosphere results in the formation of an oxygen-deficient perovskite-related phase containing only trivalent iron. Further heating in the gaseous reducing environment at 1150 °C results in the formation of the Fe3+-containing phase SrLaFeO4, which has a K2NiF4-type structure, and metallic iron. The material of composition La0.5Sr0.5CoO3 is more susceptible to reduction than the compound La0.5Sr0.5FeO3 since, after heating at 520 °C in the hydrogen/nitrogen mixture, all the Co4+ and Co3+ are reduced to metallic cobalt with the concomitant formation of strontium- and lanthanum-oxides. 相似文献
13.
Jesús Canales-Vázquez João C. Waerenborgh Jorge R. Frade 《Journal of solid state chemistry》2004,177(9):3105-3113
A study of the structure of FeIV CaTi0.4Fe0.6O3−δ is presented and compared to data on the FeIII counterparts. The powder XRD pattern was dominated by a simple cubic perovskite unit cell; however, some small peaks indicated an orthorhombic distortion. All peaks could be indexed using a space group analogous to the FeIII phase Ca3TiFe2O8. From HRTEM the strong cubic peaks are well explained by the superposition of three equivalent and mutually perpendicular orthorhombic unit cells. TEM analysis further revealed a microdomain structure consisting of disordered intergrowths of CaTiO3- and Ca3TiFe2O8-like phases. Mössbauer spectra show that ca. 4% of the Fe cations are in the 4+ oxidation state. Results suggest that the Fe4+ cations are associated with octahedral coordination and hence are associated with the CaTiO3-like regions, transition regions between the CaTiO3- and Ca3TiFe2O8 intergrown phases and the domain boundaries. Structural models for the intergrowths are proposed based on HRTEM image simulations. 相似文献
14.
Fe4(P2O7)3 was prepared from Fe(PO3)3 and FePO4 at 940°C under oxygen. The unit cell is monoclinic, space group P21/n, with a=7.389(2) Å, b=21.337(1) Å, c=9.517(2) Å, β=90(1)°, and Z=4. The crystallographic structure has been determined from a single crystal through direct methods and difference Fourier synthesis and refined to R=0.10 (Rw=0.09). The three-dimensional framework is built up from Fe2O9 clusters of two face-sharing octahedra, linked by bent diphosphates P2O7 (P-O-P∼156°). Fe4(P2O7)3 is antiferromagnetic below TN=50 K. The magnetic structure has been determinated by means of powder neutron diffraction. There are four antiferromagnetic iron sublattices corresponding to the four crystallographically distinct iron atoms. The magnetic moments are antiferromagnetically coupled inside the Fe2O9 dimers, in agreement with the Goodenough rules. They are parallel to the c axis and have 4.55(5) μB value at 1.7 K. The magnetic interactions are discussed. Mössbauer spectra are fitted with four doublets and sextuplets in the paramagnetic and antiferromagnetic states, respectively. Their rather high isomer shifts are explained by the inductive effect. 相似文献
15.
We have synthesized samples in the system BaTi1−xFexO3−x/2 with x=0.1−0.6 at temperatures of 1200-1300°C under reducing conditions of oxygen fugacity. After drop quenching, samples were characterized using the electron microprobe, X-ray diffraction and Mössbauer spectroscopy. All samples were hexagonal with a 6H-BaTiO3 type structure. Mössbauer spectroscopy showed all iron to be present as Fe3+, occurring in octahedral and pentahedral sites. Analysis of area ratios indicates that oxygen vacancies are distributed randomly over O1 sites, and that a random distribution of Fe and Ti cations over M1 and M2 sites is consistent with the data. No evidence for ordering of oxygen vacancies was found. Results are consistent with conductivity results, which show generally increasing ionic conductivity with increasing oxygen vacancy concentration. 相似文献
16.
The structure, the energetics and the internal redox reactions of La0.7Sr0.3FexMn1−xO3 have been studied in the complete solid solution range 0.0<x<1.0. High temperature oxide melt drop solution calorimetry was performed to determine the enthalpies of formation from binary oxides and the enthalpy of mixing. There is a noticeable change in the energetics of the solid solution near x=0.7, which is due to the growing concentration of Fe4+ at higher Fe/(Fe+Mn) ratio. The balance between different valences of the transition metals, Mn and Fe, is the main factor in determining the energetics of the La0.70Sr0.30FexMn1−xO3 solid solution. 相似文献
17.
L.K. ElbouaananiB. Malaman R. Gérardin B. Ouladdiaf 《Journal of solid state chemistry》2002,164(1):71-80
Fe3P5SiO19 has been prepared by solid state reaction of Fe(PO3)3, FePO4, and SiO2 at 1000°C. The structure has been determined from a single crystal through direct methods and difference Fourier synthesis and refined to R=0.052. The unit cell is hexagonal, space group P63, with a=14.4804(8) Å, c=7.4256(2) Å, and Z=4. The three-dimensional framework is built up from [Fe2O9] units of two faces sharing octahedra and Si2O7 disilicates linked by PO4 tetrahedra. Fe3P5SiO19 is isotypic with V3P5SiO19. Fe3P5SiO19 is antiferromagnetic below TN=35 K. The magnetic structure has been determined by means of powder neutron diffraction methods: the magnetic moments are antiferromagnetically coupled inside the [Fe2O9] units, in agreement with the Goodenough rules. These units are linked to each other through several Fe-O-P-O-Fe super-superexchange pathways and form antiferromagnetic [001] rows. The moment direction lies in the (001) plane (μFe=4.56(5) μB at 2 K). There is a competition between the intra- and interunits interactions which all are antiferromagnetic and cannot be simultaneously satisfied without frustration. Mössbauer spectra are fitted with two doublets and two sextuplets in the paramagnetic and antiferromagnetic states, respectively. Their rather high isomer shifts are explained by the inductive effect. The magnetic interactions are discussed. 相似文献
18.
Antimony silicate glasses, of general formula xSb2O3·(1−x)SiO2 (0.1≤x≤0.78), have been prepared by melt-quenching and their structures studied using 29Si MAS NMR spectroscopy, 121Sb Mössbauer spectroscopy and Raman spectroscopy. Oxidation during melting gives rise to Sb5+ in concentrations, which increase linearly with x to give a value of ∼10% when x=0.78. 121Sb Mössbauer spectra show Mössbauer shifts and quadrupole splittings consistent with Sb3+ in a [:SbO3] trigonal pyramid, similar to that in crystalline Sb2O3. A broad band in the Raman spectrum at ∼410 cm−1 is due to the vibrations of such a unit. The dependence of the silicon Qn speciation on x can be interpreted by the formation of Sb-O-Sb links possibly to form rings of 4 [:SbO3] units such as are found in valentinite. 相似文献
19.
Qian Zhao Huan Yan Ping Liu Yingyi Yao Yudong Wu Jian Zhang Hengxuan Li Xiaoqun Gong Jin Chang 《Analytica chimica acta》2016
Here, we report an ultra-sensitive and colorimetric sensor for the detection of Fe3+ or Cu2+ successively using glutathione-functionalized Au nanoclusters (GSH-AuNCs). For GSH-AuNCs can catalytically oxidize peroxidase substrates, such as 3, 3′, 5, 5′-tetramethylbenzidine (TMB), colored products are formed in the presence of H2O2. While upon the addition of Fe3+ or Cu2+ into the GSH-AuNCs-TMB-H2O2 system, diverse color and absorbance of the system was obtained due to the self oxidation of Fe3+ and the inhibition of peroxidase-like activity of GSH-AuNCs. With the introduction of ethylene diamine tetraacetic acid (EDTA) or ammonium fluoride (NH4F) to GSH-AuNCs-TMB-H2O2+Cu2+ system or GSH-AuNCs-TMB-H2O2+Fe3+ system respectively, a restoration of color and absorbance of system was realized. On the basis of above phenomenon, a colorimetric and quantitative approach for detecting Fe3+ and Cu2+ was developed with detection limit of 1.25 × 10−9 M and 1.25 × 10−10 M respectively. Moreover, the concentration of Fe3+ and Cu2+ in human serums was also accurate quantified by this method. So this design strategy realized the simple and simultaneous detection of Fe3+ and Cu2+, suggesting significant potential in clinical diagnosis. 相似文献
20.
A.P. Kazin M.N. Rumyantseva V.E. Prusakov I.P. Suzdalev A.M. Gaskov 《Journal of solid state chemistry》2011,184(10):2799-2805
This work is devoted to a detailed analysis of the interconnection between composition, cation distribution and acidic properties of the surface of nanocrystalline ferrites NixZn1−xFe2O4 obtained by aerosol pyrolysis. The detailed analysis of the Mössbauer spectra allows us to determine the distribution of cations between tetrahedral and octahedral positions in spinel structure. Depending on samples composition, the tetrahedral positions can be occupied by only Fe3+ cations (inverse spinel, x≥0.4) or by Fe3+ and Zn2+ cations (mixed spinel, x=0, 0.2). Increasing the nickel concentration in the ferrite leads to decrease in the number of strong acid centers on the surface. It was found that the decrease in the contribution of strong surface acid sites leads to an increase in sensory sensitivity of the ferrite towards ammonia. For ethanol detection an inverse relationship between sensor signal and surface acidity was observed. 相似文献