R-site varied series of RBaCo2O5.5 (R2Ba2Co4O11) compounds with precisely controlled oxygen content

The entire family of carefully oxygen-adjusted RBaCo₂O_5.5 or R₂Ba₂Co₄O₁₁ (R=Y, Ho-La) double-perovskite oxides is systematically investigated for the lattice parameters, A-site cation disorder, and characteristic physical properties, i.e. the metal-insulator transition, ferromagnetic transition and so-called metamagnetic transition. With increasing size of the R constituent, the lattice parameters start to deviate from the linear behavior, indicating partial oxygen/vacancy and A-site cation disorder for the largest Rs of Nd, Pr and La. Both the metal-insulator transition and the two magnetic transitions are found to be highly sensitive to even minor deviations from the ideal 5.5 oxygen stoichiometry, thus underlining the importance of proper oxygen-content adjustment.     

Novel perovskite-related barium tungstate Ba11W4O23

Ba₁₁W₄O₂₃ was synthesized at 1300 °C, followed by quenching with liquid nitrogen. The crystal structure, which was known to be cryolite-related but has remained unclear, was initially determined by single-crystal X-ray diffraction for the isostructural Ru-substituted compound Ba₁₁(W_3.1Ru_0.9)O_22.5, which was discovered during exploratory synthesis in the Ba-Ru-O system. The structure of Ba₁₁W₄O₂₃ was refined by a combined powder X-ray and neutron Rietveld method (Fd-3m, a=17.1823(1) Å, Z=8, R_p=3.09%, R_wp=4.25%, χ²=2.8, 23 °C). The structure is an example of A-site vacancy-ordered 4×4×4 superstructure of a simple perovskite ABO₃, and it may be written as (Ba_1.75□_0.25)BaWO_5.75□_0.25, emphasizing vacancies on both metal and anion sites. The local structure of one of two asymmetric tungsten ions is the WO₆ octahedron, typical of perovskite. The other tungsten, however, is surrounded by oxygen and anionic vacancies statistically distributed over three divided sites to form 18 partially occupied oxygen atoms (∼30% on average), represented as WO_18/3. The A-site cation-vacancies are ordered at the 8a (, , ) site in between adjoining WO_18/3 polyhedra which form 1-D arrangements along [110] and equivalent directions. In situ high-temperature XRD data have shown that the quenched Ba₁₁W₄O₂₃ at room temperature is isostructural to the high-temperature phase at 1100 °C.     

Investigation on double perovskite Ba4Ca2Ta2O11

The structure, conductivity and water uptake of the oxygen-deficient perovskite-type compound Ba₄Ca₂Ta₂O₁₁ have been investigated. Ba₄Ca₂Ta₂O₁₁ crystallizes in the cryolite structure (cubic, Fm3m SG) with a = 8.4508(2) Å, under dry air. The compound can be partially hydrated up to a maximum water content of approximately 0.52 mol H₂O per mol Ba₄Ca₂Ta₂O₁₁. In moist air, the structure symmetry becomes monoclinic (C2/m) and the temperature dependence of total conductivity shows a different behavior because of changes in transport mechanism. Three regions can be observed as a function of temperature. For the low temperature range 200–400 °C, the protonic conduction is prevailing with an activation energy E_A = 0.85 eV. In the intermediate temperature range (400–600 °C), O²⁻ anionic and protonic conductions are mixed with an activation energy E_A = 0.45 eV and in the third region, for temperatures above 600 °C, O²⁻conduction is prevailing with an activation energy E_A = 0.85 eV.     

Oxygen fugacity for stoichiometric magnetite Fe3O4-hercinite FeAl2O4 solid solutions

The Frenkel defect model is applied to determine the oxygen fugacity that corresponds to the preparation of magnetite-hercinite solid solutions with an exact 4:3 oxygen:cation ratio. The result are presented in graphic form for .     

Crystal and Magnetic Structures of Ba4Mn3O10

A polycrystalline sample of Ba₄Mn₃O₁₀ has been prepared and characterized by X-ray diffraction (290 K), neutron diffraction (290, 80, 5 K) and magnetometry (5≤T(K)≤1000). At 290 K the compound is paramagnetic and isostructural with Ba₄Ti₂PtO₁₀. Mn₃O₁₂ trimers, built up from MnO₆ octahedra, are linked through common vertices to form corrugated sheets perpendicular to the y-axis of the orthorhombic unit cell (Space group Cmca, a=5.6850(1), b=13.1284(1), c=12.7327(1) Å); Ba atoms occupy the space between the layers. On cooling, the magnetic susceptibility shows a broad maximum at ∼130 K, and a sharp transition at 40 K. Neutron diffraction has shown that long-range antiferromagnetic order is present at 5 K but not at 80 K, although magnetometry at 5 K has revealed a remanent magnetization (0.002 μ_B per Mn) which is below the detection limit of the neutron experiment.     

氮掺杂MnCo2O4/N-KB的制备及氧还原催化性能

以Mn(Ac)_2和Co(Ac)_2作为前驱体,导电碳Ketjenblack (KB)作为负载碳源,采用水解-水热法制备氮掺杂的MnCo_2O_4/N-KB催化剂材料,对其结构特征和碱性溶液中氧还原反应的催化性能进行表征,并进一步分析其氧还原反应活性。结果表明:MnCo_2O_4/N-KB催化剂的形态是KB骨架上生长纳米级MnCo_2O_4,并且在N-KB和MnCo_2O_4之间形成化学耦合,产生协同作用,有效提高了MnCo_2O_4/N-KB催化剂的氧还原活性。MnCo_2O_4与N-KB的质量比为1∶9时,MnCo_2O_4/N-KB催化剂在O_2饱和0.1mol·L~(-1)KOH溶液中对氧还原反应的电催化性能最佳,反应的极限电流密度为5.7 mA·cm~(-2),半波电位接近0.81 V,电子转移数为4。在相同负载量下,MnCo_2O_4/N-KB催化剂相比商用Pt/C(电流密度5.2 mA·cm~(-2),半波电位0.83 V)有着更高的极限电流密度和耐久性。     

Thermoelectric properties of the AA′3B4O12-type ordered perovskite oxides

The perovskite transition-metal oxide ABO₃ has been extensively studied in various areas in solids. While the B ion determines the electronic properties, e.g., ferroelectricity, ferromagnetism, and superconductivity, the A site has been regarded as a “back-seat player” to change the doping level or the bandwidth. However, in the ordered perovskite oxide AA′₃B₄O₁₂, the A site order is closely related to the peculiar electronic states. In CaMn₃Mn₄O₁₂, the unusually small bandwidth justifies to extrapolate the transport data to the high-temperature limit, and in CaCu₃Ru₄O₁₂, a novel heavy-fermion state is realized through the Cu–O–Ru interaction.     

LiNi0.49Mn1.49Y0.02O4的合成及其电化学性能研究

应用柠檬酸辅助溶胶-凝胶法.合成了Y3+掺杂的尖晶石LiNi0.49Mn1.49Y0.02O4材料.XRD、循环伏安、恒流充放电和交流阻抗测试结果表明,Y3+的掺杂能提高LiNi0.5Mn1.5O4的倍率和循环性能.在电压区间3.5～4.9V,1C倍率下,其初始放电比容量为114.9 mAh.g-1,100次循环后放电比容量仍可达113.0 mAh.g-1,容量保持率为98.3%.掺杂Y3+能减小材料界面阻抗.     

Synthesis, crystal structure and magnetic properties of the Sr2Al0.78Mn1.22O5.2 anion-deficient layered perovskite

A new layered perovskite Sr₂Al_0.78Mn_1.22O_5.2 has been synthesized by solid state reaction in a sealed evacuated silica tube. The crystal structure has been determined using electron diffraction, high-resolution electron microscopy, and high-angle annular dark field imaging and refined from X-ray powder diffraction data (space group P4/mmm, a=3.89023(5) Å, c=7.8034(1) Å, R_I=0.023, R_P=0.015). The structure is characterized by an alternation of MnO₂ and (Al_0.78Mn_0.22)O_1.2 layers. Oxygen atoms and vacancies, as well as the Al and Mn atoms in the (Al_0.78Mn_0.22)O_1.2 layers are disordered. The local atomic arrangement in these layers is suggested to consist of short fragments of brownmillerite-type tetrahedral chains of corner-sharing AlO₄ tetrahedra interrupted by MnO₆ octahedra, at which the chain fragments rotate over 90°. This results in an averaged tetragonal symmetry. This is confirmed by the valence state of Mn measured by EELS. The relationship between the Sr₂Al_0.78Mn_1.22O_5.2 tetragonal perovskite and the parent Sr₂Al_1.07Mn_0.93O₅ brownmillerite is discussed. Magnetic susceptibility measurements indicate spin glass behavior of Sr₂Al_0.78Mn_1.22O_5.2. The lack of long-range magnetic ordering contrasts with Mn-containing brownmillerites and is likely caused by the frustration of interlayer interactions due to presence of the Mn atoms in the (Al_0.78Mn_0.22)O_1.2 layers.     

B-site ordered perovskite LaSrMnNbO6: Synthesis, structure and antiferromagnetism

LaSrMnNbO₆ has been synthesized by high temperature solid state reaction under 1% H₂/Ar dynamic flow. The structure is determined by Rietveld refinement of the powder X-ray diffraction data. It crystallizes in the monoclinic space group P2₁/n with the unit cell parameters: a=5.69187(12), b=5.74732(10), c=8.07018(15) Å and β=90.0504(29)°, which were also confirmed by electron diffraction. The Mn²⁺ and Nb⁵⁺ ions, whose valence states are confirmed by X-ray absorption near-edge spectroscopy, are almost completely ordered over the B-site (<1% inversion) of the perovskite structure due to the large differences of both cationic size (0.19 Å) and charge. The octahedral framework displays significant tilting distortion according to Glazer’s tilt system a⁻b⁻c⁺. Upon heating, LaSrMnNbO₆ decomposes at 690 °C under O₂ flow or at 775 °C in air. The magnetic susceptibility data indicate the presence of long-range antiferromagnetic ordering at T_N=8 K; the experimentally observed effective paramagnetic moment, μ_eff=5.76 μ_B for high spin Mn²⁺ (3d⁵, S=5/2) is in good agreement with the calculated value (μ_calcd=5.92 μ_B).     

高性能Ce0.35Zr0.55Y0.1O1.95稀土储氧材料的研究

The oxygen storage material (OSM) Ce_0.35Zr_0.55Y_0.1O_1.95 was prepared by co-precipitation routine and studied by means of TEM, XRD, XPS, BET, H₂-TPR and oxygen storage capacity (OSC) measurements. The results indicated that this material possessed plenty of Ce³⁺ and lattice oxygen vacancy (percentage of Ce³⁺ was 59.6%) and high cerium atom utilization ratio (80.04%). The porous material was with an average BET surface area of 97 m²·g^-1 and pore volume of 0.26 mL·g^-1. After aged at 1 000 ℃ in air for 5 h, the sample still possessed plenty of Ce³⁺ and lattice oxygen vacancy (percentage of Ce³⁺ was 57.1%), and showed high cerium atom utilization ratio (78.25%), and high thermal stability.     

Analysis of (NH4)2SO4/(NH4)H2PO4 mixtures by thermogravimetry and X-ray diffraction

(NH₄)₂SO₄ and (NH₄)H₂PO₄ are the principal components in the powder material used in fire extinguishers. In this paper the mutual influence in their thermal decomposition is investigated by thermogravimetry. Two methods for the quantification of both salts in mixtures (NH₄)₂SO₄/(NH₄)H₂PO₄ are proposed. The first employs thermogravimetry and is based on the measurement of the mass fraction in the 500-550 °C interval, once (NH₄)₂SO₄ has totally decomposed to yield gaseous products. The second uses some selected peaks in the X-ray diffractogram.     

Synthesis and spectral characteristics of Sr2Y8(SiO4)6O2: Eu polycrystals

Spectral-luminescent characteristics of Sr₂Y₈(SiO₄)₆O₂: Eu powder crystal phosphor with the apatite structure and high-intensity luminescence of Eu³⁺ ions have been studied. The charge state of europium in the samples has been characterized by means of X-ray L₃-adsorption spectroscopy. It was established that Eu³⁺ forms two types of optical centers. Besides, luminescence of Eu²⁺ions was found. Reduction Eu³⁺→Eu²⁺ was considered, which may be due to vacancy formation in the 4f crystal lattice position and to negative charge transfer by this vacancy to two ions. Thus, in the silicate lattice there exist inhomogeneously distributed oxygen-deficient centers, which are responsible for nonradiative transfer of excitation energy to Eu³⁺ and Eu²⁺ ions. To study electron-vibrational interactions in the crystal phosphor samples, their IR and Raman spectra were examined. In the luminescence spectrum of Eu²⁺, a series of low-intensity bands caused by interaction of the 4f⁶5d state of Eu²⁺ with silicate lattice vibrations was observed.     

Syntheses and characterizations of complex perovskite oxynitrides LaMg1/3Ta2/3O2N, LaMg1/2Ta1/2O5/2N1/2, and BaSc0.05Ta0.95O2.1N0.9

The following complex oxynitride perovskites have been prepared: LaMg_1/3Ta_2/3O₂N, LaMg_1/2Ta_1/2O_5/2N_1/2, and BaSc_0.05Ta_0.95O_2.1N_0.9. Synchrotron X-ray powder diffraction analyses show that LaMg_1/3Ta_2/3O₂N and LaMg_1/2Ta_1/2O_5/2N_1/2 are isostructural to the oxide La₂Mg(Mg_1/3Ta_2/3)O₆ (space group P2₁/n), whereas BaSc_0.05Ta_0.95O_2.1N_0.9 has a simple cubic symmetry similarly to BaTaO₂N. The orderings of octahedral cations are markedly diminished in the above oxynitrides, as compared with the related oxides such as La₂Mg(Mg_1/3Ta_2/3)O₆ and Ba₂ScTaO₆. The optical band gaps are similar for the homologous compositions, LaMg_1/3Ta_2/3O₂N, LaMg_1/2Ta_1/2O_5/2N_1/2 and LaTaON₂ (1.9 eV), and BaSc_0.05Ta_0.95O_2.1N_0.9 and BaTaO₂N (1.8 eV), while the absorption edges become broader for the complex derivatives. As revealed from the impedance spectroscopic analysis, the oxynitrides have clearly different dielectric components from those of comparable oxides containing Ta⁵⁺. Impedance spectroscopy reveals interesting capacitor geometry in BaSc_0.05Ta_0.95O_2.1N_0.9 in which the semiconducting oxynitride grains are separated by insulating secondary phases. Most notably BaSc_0.05Ta_0.95O_2.1N_0.9 has a bulk component with a high relative permittivity (κ=7300) and the grain boundary component with an even higher κ.     

Crystal growth of a novel oxygen-deficient layered perovskite: Ba7Li3Ru4O20

Single crystals of both Ba₇Li₃Ru₄O₂₀ and Ba₄NaRu₃O₁₂ were grown from reactive molten hydroxide fluxes. Ba₇Li₃Ru₄O₂₀ is a 7L-layer perovskite-related phase resulting from the stacking of six [AO₃] layers and one oxygen deficient [AO₂] layer, thereby creating LiO₄ tetrahedra in addition to the LiO₆ octahedra and face-sharing Ru₂O₉ bi-octahedra formed from the [AO₃] layers. The compound crystallizes in the space group with a=5.7927(1) Å and c=50.336(2) Å, Z=3. Ba₄NaRu₃O₁₂ crystallizes in the space group P6₃mc with lattice parameters of a=5.8014(2) Å and c=19.2050(9) Å, Z=2. Ba₄NaRu₃O₁₂ is identical to a previously reported neutron refinement structure. The magnetic properties of Ba₇Li₃Ru₄O₂₀ are also reported.     

New transparent conductors with the M7O12 ordered oxygen-deficient fluorite structure: from In4Sn3O12 to In5.5Sb1.5O12

A new transparent conductor, containing pentavalent antimony, In_4+xSn_3−2xSb_xO₁₂, has been synthesized for 0?x?1.5. The latter exhibits an ordered oxygen-deficient fluorite structure with an ordered distribution of Sb⁵⁺ and In³⁺/Sn⁴⁺ species in the octahedral and seven-fold coordinated sites, respectively. More importantly, it is shown that the electronic conductivity of this transparent conducting oxide (TCO) at room temperature, is one order of magnitude larger for x=1 (In₅SnSbO₁₂) than for x=0 (In₄Sn₃O₁₂) and it turns to a semi-metallic behavior in contrast to In₄Sn₃O₁₂ which is a semi-conductor. The potential of this new material, as TCO, is also shown by its reflectance spectra, similar to In₄Sn₃O₁₂, involving only a small increase of the optical bandgap, by 0.15 eV.     

Synthesis and structure of three manganese oxalates: MnC2O4·2H2O, [C4H8(NH2)2][Mn2(C2O4)3] and Mn2(C2O4)(OH)2

Three manganese oxalates have been hydrothermally synthesized, and their structures determined by single-crystal X-ray diffraction. MnC₂O₄·2H₂O (I) is orthorhombic, P2₁2₁2₁, , , , , Z=4, final R, R_w=0.0832, 0.1017 for 561 observed data (I>3σ(I)). The one-dimensional structure consists of chains of oxalate-bridged manganese centers. [C₄H₈(NH₂)₂][Mn₂(C₂O₄)₃] (II) is triclinic, , , , , α=81.489(2)°, β=81.045(2)°, γ=86.076(2)°, , Z=1, final R, R_w=0.0467, 0.0596 for 1773 observed data (I > 3σ (I)). The three-dimensional framework is constructed from seven coordinate manganese and oxalate anions. The material contains extra-framework diprotonated piperazine cations. Mn₂(C₂O₄)(OH)₂ (III) is monoclinic, P2₁/c, , , , β=91.10(3)°, , Z=1, final R₁, wR2=0.0710, 0.1378 for 268 observed data (I>2σ (I)). The structure is also three dimensional, with layers of MnO₆ octahedra pillared by oxalate anions. The hydroxide group is found bonded to three manganese centers resulting in a four coordinate oxygen.     

Oxygen non-stoichiometry of Ln4Ni2.7Fe0.3O10−δ (Ln=La, Pr)

The oxygen deficiency of iron-substituted nickelates Ln₄Ni_2.7Fe_0.3O_10−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, Pr₄Ni_2.7Fe_0.3O_10−δ exhibits a substantially lower thermodynamic stability in comparison with La₄Ni_2.7Fe_0.3O_10−δ and La₄Ni₃O_10−δ, although the oxygen content in Pr₄Ni_2.7Fe_0.3O_10−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 Pr₄Ni₃O_10−δ into K₂NiF₄-type Pr₂NiO_4+δ. On the contrary, doping of La₄Ni₃O_10−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.