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1.
The crystal structures of Bi2.5Na0.5Ta2O9 and Bi2.5Nam-1.5NbmO3m+3 (m=3,4) have been investigated by the Rietveld analysis of their neutron powder diffraction patterns (λ=1.470 Å). These compounds belong to the Aurivillius phase family and are built up by (Bi2O2)2+ fluorite layers and (Am-1BmO3m+1)2- (m=2-4) pseudo-perovskite slabs. Bi2.5Na0.5Ta2O9 (m=2) and Bi2.5Na2.5Nb4O15 (m=4) crystallize in the orthorhombic space group A21am, Z=4, with lattice constants of a=5.4763(4), b=5.4478(4), c=24.9710 (15) and a=5.5095(5), b=5.4783(5), c=40.553(3) Å, respectively. Bi2.5Na1.5Nb3O12 (m=3) has been refined in the orthorhombic space group B2cb, Z=4, with the unit-cell parameters a=5.5024(7), b=5.4622(7), and c=32.735(4) Å. In comparison with its isostructural Nb analogue, the structure of Bi2.5Na0.5Ta2O9 is less distorted and bond valence sum calculations indicate that the Ta-O bonds are somewhat stronger than the Nb-O bonds. The cell parameters a and b increase with increasing m for the compounds Bi2.5Nam-1.5NbmO3m+3 (m=2-4), causing a greater strain in the structure. Electron microscopy studies verify that the intergrowth of mixed perovskite layers, caused by stacking faults, also increases with increasing m.  相似文献   

2.
The phase relations in the cross-section of the K2W2O7-K2WO4-KPO3 containing 15 mol% Bi2O3 were undertaken using flux method. Crystallization fields of K6.5Bi2.5W4P6O34, K2Bi(PO4)(WO4), Bi2WO6, KBi(WO4)2 and their cocrystallization areas were identified. Novel phase K6.5Bi2.5W4P6O34 was characterized by single-crystal X-ray diffraction: sp. gr. P−1, a=9.4170(5), b=9.7166(4), c=17.6050(7) Å, α=90.052(5)°, β=103.880(5)° and γ=90.125(5)°. It has a layered structure, which contains {K7Bi5W8P12O68} layers stacked parallel to ab plane and sheets composed by potassium atoms separating these layers. Sandwich-like {K7Bi5W8P12O68} layers are assembled from [W2P2O13] and [BiPO4] building units, and are penetrated by tunnels with K/Bi atoms inside. FTIR-spectra of K2Bi(PO4)(WO4) and K6.5Bi2.5W4P6O34 were discussed on the basis of factor group theory.  相似文献   

3.
Synthesis and Crystal Structure of Bi2ErO4I Bi2ErO4I was prepared by solid‐state reaction of stoichiometric mixture of BiOI, Bi2O3 and Er2O3. Bi2ErO4I is a new compound and the first bismuth rare earth oxide iodide. The crystal structure was determined by the Rietveldmethod (P4/mmm, a = 3,8896(6) Å, c = 9,554(2) Å, Z = 1). In this structure [M3O4]+‐layers are interleaved by single I‐layers. Er and Bi atoms of Bi2ErO4I are 8‐coordinated. The structure can be derived from the LiBi3O4Cl2‐structure type.  相似文献   

4.
Single crystals of [Bi2(Bi1.56K0.44)O3] K0.88(PO4)2 (I), [Bi10 (Bi0.5Cd0.5)8O16] (Bi0.6Cd0.8)2(PO4)8 (II), and [Bi18Zn10O21] Zn5(PO4)14 (III) are prepared by melting K2CO3 (or CdO or ZnO), Bi2O3, and (NH4)2HPO4 in a 1:1:2 molar ratio (open Au tube, 900—950 °C, 10 h).  相似文献   

5.
Bi5AgNb4O18 is a new phase, which was discovered during the phase equilibrium study of the Bi2O3-Ag2O-Nb2O5 system. Bi5AgNb4O18 was prepared at 750°C and is stable in air up to its melting temperature of 1160.1±5.0°C (standard error of estimate). Results of a Rietveld refinement using neutron powder diffraction confirmed that Bi5AgNb4O18 is isostructural with Bi3TiNbO9, Bi5NaNb4O18, and Bi5KNb4O18. The structure was refined in the orthorhombic space group A21am, Z=2, and the lattice parameters are a=5.4915(2) Å, b=5.4752(2) Å, c=24.9282(8) Å, and V=749.52(4) Å3. The structure can be described as the m=2 member of the Aurivillius family, (Bi2O2)2+ (Am−1BmO3m+1)2− (where A=Bi and B=Ag, Nb), which is characterized by perovskite-like (Am−1BmO3m+1)2− slabs regularly interleaved with (Bi2O2)2+ layers. The octahedral [NbO6] units are distorted with Nb-O distances ranging from 1.856(4) to 2.161(2) Å and the O-Nb-O angles ranging from 82.6(3)° to 98.5(3)°. These octahedra are tilted about the a- and c-axis by about 10.3° and 12.4°, respectively. Ag was found to substitute exclusively into the Bi-site that is located in the layer between the two distorted [NbO6] units. Although the Ag substitutes into the Bi-site with the Bi:Ag ratio of 1:1, the existence of a superlattice was not detected using electron diffraction. A comparison of (Bi2O2)2+(Am−1NbmO3m+1)2− structures (where A=Ag, Na, and K) revealed a relation between the pervoskite tolerance factor, t, and structural distortion. The reference pattern for Bi5AgNb4O18 has been submitted to the International Centre for Diffraction Data (ICDD) for inclusion in the Powder Diffraction File.  相似文献   

6.
The ferroelectric ceramics of Bi4Ti3O12, SrBi4Ti4O15, and lanthanum-doped Bi4Ti3O12-SrBi4Ti4O15 were synthesized, and their Raman spectra were investigated. La-doping resulted in the enlargement of remnant polarization of Bi4Ti3O12-SrBi4Ti4O15. The structure of the Bi2O2 layers and TiO6 octahedra of the intergrowth was found to be different from those of Bi4Ti3O12 and SrBi4Ti4O15. La3+ ions exhibit pronounced selectivity for the occupation of A site as La content is lower than 0.50, and tend to be incorporated into Bi2O2 layers when the La content is higher than 0.50. Lanthanum substitution brings about the structural phase transition in Bi4Ti3O12-SrBi4Ti4O15. The variation of ferroelectric property may be attributed to combined contribution from the decreasing of the oxygen vacancies, the relaxation of the lattice distortion, the destroying of the insulation and the space charge compensation effects of the Bi2O2 slabs.  相似文献   

7.
The influence of Bi2O3 particles size at the sub-micron scale on the thermal excitation threshold and combustion performance of nano-thermite systems was investigated. Three formulas were designed and prepared, Al(100 nm)/Bi2O3(170 nm), Al(100 nm)/Bi2O3(370 nm) and Al(100 nm)/Bi2O3(740 nm). The samples were characterized and tested by SEM, XRD, and DSC techniques. Electrical ignition and combustion experiments were performed. The results showed that with the increase of the particle size of Bi2O3, in the case of slow linear heating, the exothermic heat decreased (1051.2 J g−1, 527.3 J g−1 and 243.6 J g−1) and the thermal excitation threshold temperature increased (564.52 °C, 658.1 °C and 810.9 °C). Simultaneously, the state of the thermite reaction correspondingly changed to solid-solid, liquid-solid and liquid-liquid thermite reaction. In the case of rapid heating , the increase in particle size increased the excitation current (0.561A, 0.710A and 0.837A). During the combustion process, the thermite system with the smallest Bi2O3 particle size showed the largest combustion rate, and that with the largest particle size had the longest combustion duration.  相似文献   

8.
The glasses within composition as: (80 − x)V2O5/20Bi2O3/xBaTiO3 with x = 2.5, 5, 7.5 and 10 mol% have been prepared. The glass transition (Tg) increases with increasing BaTiO3 content. Synthesized glasses ceramic containing BaTi4O9, Ba3TiV4O15 nanoparticles of the order of 25–35 nm and 30–46 nm, respectively were estimated using XRD. The dielectric properties over wide ranges of frequencies and temperatures were investigated as a function of BaTiO3 content by impedance spectroscopy measurements. The hopping frequency, ωh, dielectric constant, ε′, activation energies for the DC conduction, Eσ, the relaxation process, Ec, and stretched exponential parameter β of the glasses samples have been estimated. The, ωh, β, decrease from 51.63 to 0.31 × 106 (s−1), 0.84 to 0.79 with increasing BaTiO3 respectively. Otherwise, the Eσ, increase from 0.279 to 0.306 eV with increasing BaTiO3. The value of dielectric constant equal 9.5·103 for the 2.5BaTiO3/77.5V2O5/20Bi2O3 glasses-ceramic at 330 K for 1 KHz which is ten times larger than that of same glasses composition. Finally the relaxation properties of the investigated glasses are presented in the electric modulus formalism, where the relaxation time and the respective activation energy were determined.  相似文献   

9.
The Fe3O4/TiO2/Bi2O3 composites were synthesized by a sol–gel method and used as improved photocatalysts for the degradation of methyl orange (MO) under simulated sunlight at room temperature. The as-prepared Fe3O4/TiO2/Bi2O3 composites were characterized by X-ray diffraction, transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and diffuse reflectance spectroscopy (DRS). TEM analysis reveals that the composite has a core–shell structure and diameters of Fe3O4 core is about 200 nm. DRS results reveal that all composites showed red shift in optical absorption. TiO2, Fe3O4, and Bi2O3 exist mainly as separate phases in the Fe3O4/TiO2/Bi2O3 composites based on XPS analysis. The photocatalytic degradation of MO with the prepared photocatalysts was studied under simulated sunlight illumination. Photocatalytic reactivity test indicated that the removal efficiency of MO with the Fe3O4/TiO2/Bi2O3 photocatalyst was higher than that of pure TiO2 and Fe3O4/TiO2. Recovery rate of Fe3O4/TiO2/Bi2O3 photocatalysts achieved 80 % after five times reuse.  相似文献   

10.
Syntheses, Crystal Structures, and Properties of Ln4Au2O9 (Ln = Nd, Sm, Eu) The compounds Ln4Au2O9 (Ln = Nd, Sm, Eu) have been prepared from amorphous Au2O3 · 2–3 H2O and Ln2O3 (Ln = Nd, Sm, Eu) via solid state reaction under elevated oxygen pressure adding KOH as mineralising agent. They are isostructural with La4Au2O9 (Nd4Au2O9: a = 11.9813(3), b = 6.1474(1), c = 11.9641(4); 453 powder intensities, Rp = 3.75%; Sm4Au2O9: a = 11.8689(4), b = 6.0360(1), c = 11.8469(4) Å; 812 unique reflections, R1 = 2.75%; Eu4Au2O9: a = 11.8241(3), b = 5.9922(1) Å, c = 11.8013(3) Å; 1315 unique reflections, R1 = 7.83%). The crystal structure of Nd4Au2O9 was refined from powder diffraction data. The structures of Sm4Au2O9 and Eu4Au2O9 were solved and refined from single crystal data. The isolated square planar AuO4 units are stacked as columns and are linked to each other by LnO7‐polyhedra. One of the oxygen atoms is exclusively connected to the trivalent lanthanides in tetrahedral geometry. Ln4Au2O9, Bi2CuO4, Bi2AuO5 and Bi4Au2O9 are closely related, structurally. The lanthanoid aurates decompose between 700 and 800 °C into Ln2O3, Au and O2. The effective magnetic moments 3.64 μB (Nd4Au2O9), 1.7 μB (Sm4Au2O9) and 3.3 μB (Eu4Au2O9) confirm that the lanthanides are trivalent. The UV/VIS absorption spectra can be interpreted at assuming free ions.  相似文献   

11.
Polycrystalline gaudefroyite‐type YCa3(CrO)3(BO3)4 with Cr3+ ions (3d3, S = 3/2) forming an undistorted Kagome lattice is prepared by reaction of a stoichiometric mixture of Y2O3, CaCO3, Cr2O3, H3BO3 in a KCl flux (Al2O3 crucible, 1000 °C, 1 d) followed by re‐grinding and further annealing (1000 °C, 2 d, 95% yield).  相似文献   

12.
The n=3 Aurivillius material Bi2Sr2Nb2.5Fe0.5O12 is investigated and combined structural refinements using neutron powder diffraction (NPD) and X-ray powder diffraction data (XRPD) data reveal that the material adopts a disordered, tetragonal (I4/mmm) structure at temperatures down to 2 K. Significant ordering of Fe3+ and Nb5+ over the two B sites is observed and possible driving forces for this ordering are discussed. Some disorder of Sr2+ and Bi3+ over the M and A sites is found and is consistent with relieving strain due to size mismatch. Highly anisotropic thermal parameters for some oxygen sites suggest that the local structure may be slightly distorted with some rotation of the octahedra. Magnetic measurements show that the material behaves as a Curie-Weiss paramagnet in the temperature range studied with no evidence of any long-range magnetic interactions. Solid solutions including Bi3−xSrxNb2FeO12, Bi2Sr2−xLaxNb2FeO12 and Bi2Sr2Nb3−xFexO12 were investigated but single-phase materials were only successfully synthesised for a narrow composition range in the Bi2Sr2Nb3−xFexO12 system.  相似文献   

13.
The title compounds are prepared by solid state reactions of Nd2O3 or La2O3, Fe2O3, M2O3 (M: Al, Ga, In), and excess Li2CO3 (alumina crucibles, 800 °C, 16 h).  相似文献   

14.
It was earlier found from nuclear quadrupole resonance (NQR) measurements and computer modeling that -Bi2O3, Bi3O4Br and mixed oxides Bi2O3· 2Al2O3, Bi2O3· 2Ga2O3, Bi2O3· 3GeO2, and 2Bi2O3· 3GeO2exhibit local ordered magnetic fields from 30 to 200 G. It thus follows that these compounds are not diamagnets in a conventional sence of the word. With the aim of revealing previously unknown magnetic properties in bismuth(III) oxide-based Main Group element compounds, the mixed bismuth–boron oxides 2Bi2O3· B2O3, 3Bi2O3· 5B2O3, and Bi2O3· 3B2O3were prepared and studied using 209Bi NQR. The quadrupole interactions of the 209Bi nuclei and their electronic environment were studied, the crystallochemical features of the compounds were discussed, and the conformity of the 209Bi results to the X-ray structure data was verified. The preliminary tests in the field of a permanent magnet showed that the resonance intensities increase in external magnetic fields, indicating that a magnetism of unknown nature develops in the titled compounds. It was found reasonable to continue studies of the magnetic properties of these compounds using single-crystal 209Bi NQR in external magnetic fields.  相似文献   

15.
通过水热法合成具有协同机制的三元复合材料Bi2Fe4O9/g-C3N4/UiO-66,研究表明三元复合光催化剂的催化活性要高于二元材料和纯材料。这主要是由于Bi2Fe4O9更易于和g-C3N4结合形成稳定的Z-scheme异质结结构,使三元复合材料增强了可见光响应能力,提高了电子-空穴分离能力,增强了空穴和电子的氧化还原能力。  相似文献   

16.
通过水热法合成具有协同机制的三元复合材料Bi2Fe4O9/g-C3N4/UiO-66,研究表明三元复合光催化剂的催化活性要高于二元材料和纯材料。这主要是由于Bi2Fe4O9更易于和g-C3N4结合形成稳定的Z-scheme异质结结构,使三元复合材料增强了可见光响应能力,提高了电子-空穴分离能力,增强了空穴和电子的氧化还原能力。  相似文献   

17.
Subsolidus phase relations have been determined for the Bi-Mn-Nb-O system in air (750-900 °C). Phases containing Mn2+, Mn3+, and Mn4+ were all observed. Ternary compound formation was limited to pyrochlore (A2B2O6O′), which formed a substantial solid solution region at Bi-deficient stoichiometries (relative to Bi2(Mn,Nb)2O7) suggesting that ≈14-30% of the A-sites are occupied by Mn (likely Mn2+). X-ray powder diffraction data confirmed that all Bi-Mn-Nb-O pyrochlores form with structural displacements, as found for the analogous pyrochlores with Mn replaced by Zn, Fe, or Co. A structural refinement of the pyrochlore 0.4000:0.3000:0.3000 Bi2O3:Mn2Ox:Nb2O5 using neutron powder diffraction data is reported with the A and O′ atoms displaced (0.36 and 0.33 Å, respectively) from ideal positions to 96g sites, and with Mn2+ on A-sites and Mn3+ on B-sites (Bi1.6Mn2+0.4(Mn3+0.8Nb1.2)O7, (?227), a=10.478(1) Å); evidence of A or O′ vacancies was not found. The displacive disorder is crystallographically analogous to that reported for Bi1.5Zn0.92Nb1.5O6.92, which has a similar concentration of small B-type ions on the A-sites. EELS spectra for this pyrochlore were consistent with an Mn oxidation between 2+ and 3+. Bi-Mn-Nb-O pyrochlores exhibited overall paramagnetic behavior with negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. At 300 K and 1 MHz the relative dielectric permittivity of Bi1.600Mn1.200Nb1.200O7 was ≈128 with tan δ=0.05; however, at lower frequencies the sample was conductive which is consistent with the presence of mixed-valent Mn. Low-temperature dielectric relaxation such as that observed for Bi1.5Zn0.92Nb1.5O6.92 and other bismuth-based pyrochlores was not observed. Bi-Mn-Nb-O pyrochlores were readily obtained as single crystals and also as textured thin films using pulsed laser deposition.  相似文献   

18.
New Sillenite-Type Compounds New sillenite-type compounds (Bi12(V3/4Na1/4)O20, Bi12MnO20, Bi12(Mn1/2Ge1/2)O20, Bi12(Mn3/4Na1/4)O20, Bi12(Mn2/3M1/3)O20 with M = Cu, Cd and Bi12(Mn1/2M1/2)O20 with M = B, Al, Co) were synthesized at 700–750°C in corundum crucibles. Lattice constants have been determined and UV/VIS spectra have been recorded.  相似文献   

19.
The present study investigates the effect of (yttrium, terbium) ions codoping on structural and optical properties of sodium bismuth titanate (Na0.5Bi0.5TiO3 or NBT) with the possible practical application as a multi-luminescence material in optoelectronic devices such as light-emitting diodes. The polycrystalline samples of Na0.5(Y/TbxBi1-x)0.5TiO3 (x = 0.00, 0.04, 0.06, and 0.08) were synthesized using solid-state reaction (mixed oxide) technique. Stoichiometric amounts of metal compounds (Na2CO3, Y2O3, Tb4O7, Bi2O3, and TiO2) were mixed via ball milling at 250 rpm for 2 h, and the ground powders were calcined at 700 °C for 2 h. The powders were pressed under uniaxial pressure of 6.87 MPa to obtain green pellets, which were later sintered at 1,000 °C for 2 h to obtain the Na0.5(Y/TbxBi1-x)0.5TiO3 samples. X-ray diffraction analysis suggests that the perovskite phase is established for all (Y3+, Tb3+)-codoped NBT compositions (x = 0.00–0.08). The presence of NBT functional groups was confirmed by Fourier transform infrared spectroscopy. Raman spectra indicate that (Y3+, Tb3+) ions induce minor changes to the crystal lattice structure, with no disturbance to the long-range order. X-ray photoelectron spectroscopy results reveal the presence of all the constituent elements in the NBT samples. Scanning electron microscopy confirms the polycrystalline nature of the samples with uniform distribution of multifacetted or nearly spherical grain structures. Transmission electron microscopy and selected area electron diffraction (SAED) images show the presence of nanocrystals in the samples. Ultraviolet diffuse reflectance spectroscopy (UV-DRS) and photoluminescence results illustrate that Na0.5(Y/TbxBi1-x)0.5TiO3 possess wider optical energy band gap (Eg = 3.23–3.27 eV) with promising luminescence applications in the optoelectronic industry.  相似文献   

20.
The two hitherto unknown compounds Bi14P4O31 and Bi50V4O85 were prepared by the direct solid-state reaction of Bi2O3 and (NH4)H2PO4 or V2O5, respectively. Bi14P4O31 crystallizes in a C-centred monoclinic symmetry (C2/c space group) with the unit-cell parameters: , , and β=93.63(1)° (Z=16). The symmetry of Bi50V4O85 is also monoclinic (I2/m space group) with lattice parameters of , , and β=90.14(1)° (Z=2). Both structures correspond to a fluorite-type superstructure where the Bi and P or V atoms are ordered in the framework. An idealized structural model is proposed where the structures result of the stacking of mixed atomic layers of composition [Bi14M4O31] and [Bi18O27] respectively. This new family can be formulated Bi18−4mM4mO27+4m with M=P, V and where the parameter m (0?m?1) represents the ratio of the number of [Bi14M4O31] layers to the total number of layers in the sequence. Bi14P4O31 corresponds to m=1 when Bi50V8O85 corresponds to m=1/3. In this last case, the structural sequence is simply one [Bi14V4O31] layer to two [Bi18O27] layers. As predicted by the proposed structural building principle, Bi14P4O31 is not a good ionic conductor. The conductivity at 650 °C is 4 orders of magnitude lower from those found in Bi46M8O89 (M=P, V) (m=2/3) and Bi50V4O85 (m=1/3).  相似文献   

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