Standard enthalpy of formation of La2CoO4(cr)

The enthalpies of reactions of La₂CoO₄(cr) and CoCl₂(cr) with hydrochloric acid were measured with an isothermal-jacket calorimeter. The results obtained and the available literature data were used to calculate the standard enthalpy of formation of La₂CoO₄(cr) at 298.15 K, Δ_f H ^o = ?2179 ± 7 kJ/mol.     

Impurity diffusion of (141)Pr in LaMnO(3), LaCoO(3) and LaFeO(3) materials

The impurity diffusion of Pr(3+) in dense polycrystalline LaMnO(3), LaCoO(3) and LaFeO(3) was studied at 1373-1673 K in air in order to investigate cation diffusion in these materials. Cation distribution profiles were measured by secondary-ion mass spectrometry and it was found that penetration profiles of Pr(3+) had two distinct regions with different slopes. The first, shallow region was used to evaluate the bulk diffusion coefficients. The activation energies for bulk diffusion of Pr(3+) in LaMnO(3), LaCoO(3) and LaFeO(3) were 126 +/- 6, 334 +/- 68 and 258 +/- 75 kJ mol(-1), respectively, which are significantly lower than previously predicted by atomistic simulations. The bulk diffusion of Pr(3+) in LaMnO(3) was enhanced compared to LaCoO(3) and LaFeO(3) due to higher concentrations of intrinsic point defects in LaMnO(3), especially La site vacancies. Grain-boundary diffusion coefficients of Pr(3+) in LaCoO(3) and LaFeO(3) materials were evaluated according to the Whipple-Le Claire equation. Activation energies for grain-boundary diffusion of Pr(3+) in LaCoO(3) and LaFeO(3) materials were 264 +/- 41 kJ mol(-1) and 290 +/- 36 kJ mol(-1) respectively. Finally, a correlation between activation energies for cation diffusion in bulk and along grain boundaries in pure and substituted LaBO(3) materials (B = Cr, Fe, Co) is discussed.     

Behavior of (La,Sr)CoO3- and La2NiO4-based ceramic anodes in alkaline media: compositional and microstructural factors

The behavior of dense ceramic anodes made of perovskite-type (x = 0.30–0.70; y = 0–0.05; z = 0–0.20) and K₂NiF₄-type (Me = Co, Cu; x = 0–0.20) indicates significant influence of metal hydroxide formation at the electrode surface on the oxygen evolution reaction (OER) kinetics in alkaline solutions. The overpotential of cobaltite electrodes was found to decrease with time, while cyclic voltammetry shows the appearance of redox peaks characteristic of Co(OH)₂/CoOOH. This is accompanied with increasing effective capacitance estimated from the impedance spectroscopy data, because of roughening of the ceramic surface. The steady-state polarization curves of in the OER range, including the Tafel slope, are very similar to those of model Co(OH)₂–La(OH)₃ composite films where the introduction of lanthanum hydroxide leads to decreasing electrochemical activity. La₂NiO₄-based anodes exhibit a low electrochemical performance and poor stability. The effects of oxygen nonstoichiometry of the perovskite-related phases are rather negligible at high overpotentials but become significant when the polarization decreases, a result of increasing role of oxygen intercalation processes. The maximum electrocatalytic activity to OER was observed for A-site-deficient , where the lanthanum content is relatively low and the Co⁴⁺ concentration determined by thermogravimetric analysis is highest compared to other cobaltites. Applying microporous layers made of template-synthesized nanocrystalline leads to an improved anode performance, although the effects of microstructure and thickness are modest, suggesting a narrow electrochemical reaction zone. Further enhancement of the OER kinetics can be achieved by electrodeposition of cobalt hydroxide- and nickel hydroxide-based films. Dedicated to Professor Dr. Yakov I. Tur’yan on the occasion of his 85th birthday.     

粉末固相反应合成LaCoO3-δ动力学的等温热重实验研究

用等温热重分析方法在830℃、860℃和890℃研究了La2O3和Co3o4粉末反应合成LaCoO3-δ的动力学.用常见的固相反应动力学模型对实验所得的反应分数和反应时间关系进行拟合分析的基础上,综合考虑粉末固相反应的特征得出反应前期、中期和后期可能分别为随机形核一快速生长、界面化学反应及固态离子三维扩散控速.三个阶段的表观活化能分别为133.4±3.4、183.5±21.5和135.1±303kJ/mol.     

Electronic Band Structure and Madelung Potential Study of the Nickelates La(2)NiO(4), La(3)Ni(2)O(7), and La(4)Ni(3)O(10)

Tight-binding electronic band structures and Madelung potentials were calculated for La(2)NiO(4), La(3)Ni(2)O(7), and La(4)Ni(3)O(10) to examine why a metal-to-metal transition occurs in the nickelate Ln(4)Ni(3)O(10) (Ln = La, Nd, Pr). La(4)Ni(3)O(10) and La(3)Ni(2)O(7) are each found to have two hidden one-dimensional (1D) Fermi surfaces, which suggests that both compounds should possess a charge density wave instability. Factors leading to hidden 1D Fermi surfaces in the e(g) block bands of the nickelates were discussed.     

Synthesis and Structure of Ba3La2（BO3）4 Crystal

1 INTRODUCTION At present the researches on more efficient solid-state laser materials become more important for the rapid development of diode-laser pumped solid-state laser. More researches have been devoted to the double borate compounds RX3(BO3)4 (R = Y, La, Gd and X = Y, Al, Sc), some of which exhibit good chemical and physical properties[1～10]. The rare earth and alkali-halide double borates M3Ln2(BO3)4 (M = Ca, Sr, Ba and Ln = LaLu and Y) were reported in literatures[11…     

La2Pb(SiS4)2

Crystals of La₂Pb(SiS₄)₂, dilanthanum(III) lead(II) bis[tetrasulfidosilicate(IV)], were obtained from the La–Pb–Si–S system and structurally characterized using X‐ray single‐crystal diffraction. The La and Pb atoms are coordinated in bicapped trigonal prisms of S atoms, with the Si atoms in tetrahedra. An occupational disorder of the La and Pb centres was refined for one position in the structure. The bicapped trigonal prisms and tetrahedra share edges. A gap located 2.629 (1) Å from the sulfide anions was found around the coordination polyhedra, which makes La₂Pb(SiS₄)₂ a prospective material in crystal engineering. The Si and one S atom lie on a threefold axis.     

负载型La0.8Sr0.2CoO3燃烧催化剂中Co(Ⅱ)与载体γ-Al2O3的相互作用

一般认为稀土钙钛矿型La0.8Sr0.2CoO3是CO氧化、碳氢(HC)化合物完全氧化和NOx还原的良好氧化物催化剂.用复合硝酸盐溶液浸渍γ-Al2O3制取负载型催化剂La0.8Sr0.2CoO3/γ-Al2O3(LSC/γ-Al2O3),负载量15%(质量分数).采用XRD, TPR, BET和二甲苯完全氧化催化剂活性测试等手段,研究了CoAl2O4的形成过程,催化剂经750 ℃焙烧, Co(Ⅱ)已进入γ-Al2O3体相,并有大量的CoAl2O4尖晶石形成. 若在γ-Al2O3表面涂敷一层以MgAl2O4为主相的覆盖层,在一定程度上能够阻挡Co2+离子进入γ-Al2O3的晶格,并有效地生成出LSC活性相,提高了其完全氧化的催化活性.     

The association of urethane-polyethyleneoxide (HEUR) thickeners,as studied by NMR self-diffusion measurements

The concentration and molecular weight dependence of the self-diffusion coefficient (D _self) of associative polymers of HEUR-type in aqueous solution have been investigated using FT-PGSE-NMR technique. The idea of three-dimensional network formation as a result of aggregation of the hydrophobic end-groups of the polymer in junctions is supported through the observed dramatic lowering ofD _self with increased concentration. The network-formation efficiency depends on the polymer molecular weight as well as the hydrophobicity of the end-groups.A double logarithmic dependence of the self-diffusion coefficient versus concentration (c) has been observed:D _selfc ^–a1,a2 . The first exponent,a ₁, is valid at low concentration, <1% polymer per weight solution, and ranges from 0.5 to 1, whereas the second exponent,a ₂, describing systems of higher concentration, ranges from 2 to 2.7.     

Rotational diffusion of anisotropic-shaped colloidal particles in microgravity as studied by free-fall experiments

Rotational relaxation times (τ) and diffusion coefficients of ellipsoidal colloids of tungstic acid are studied in aqueous suspension in microgravity by free-fall experiments. τ values are evaluated from the relaxation traces of the optical transmittance of the suspension using the stopped-flow technique. Experimental errors at 0 G are small compared with those at 1 G, which is ascribed to lack of the movement of impurities in suspension such as quite small dust and bubbles and the convection of the suspension in microgravity. The limiting slopes of the relaxation curves in the plots of the transmittance against time at 1 G depend on the flow direction of the suspension in the flow cell, whereas those at 0 G remain zero irrespective of the flow direction. For more reliable diffusion coefficients are obtained in microgravity; however, the diffusion coefficients themselves are quite insensitive to gravity. Received: 10 November 1998 Accepted in revised form: 22 December 1998     

Rotational diffusion of tungstic acid colloids in microgravity as studied by aircraft experiments

 Rotational relaxation times (τ) of anisotropic tungstic acid colloids (3.24 μm in major axis) in aqueous suspension are measured in microgravity (0G), normal gravity (1G) and at 2G. The measurements at 0G and 2G are achieved by parabolic and circular flights, respectively. The limiting slopes of the relaxation curves in the plots of the transmitted light intensity against time are close to zero at 0G irrespective of the flow directions in the flow cell, whereas those at 1G and especially at 2G depend on the flow direction by the convection of the suspension and particle sedimentation. Experimental errors at the τ values at 0G are small compared with those at 1G and 2G, which is ascribed to the lack of movement of impurities in the suspension such as quite small air bubbles, which cannot be recognized with the naked eye, and the convection of the suspension in microgravity. More reliable rotational relaxation times are obtained in microgravity; however, the relaxation times themselves are quite insensitive to gravity. Theτ values observed are larger than those calculated from the particle size, which indicates the important contribution of the electrical double layers formed around the colloidal particles. Received: 22 February 2001 Accepted: 13 June 2001     

三元体系La(ClO4)3-BAPHDCA-H2O(30℃)的相平衡研究及La(BAPHDCA)2.(ClO4)3.4H2O的合成和表征

在30℃时采用等温溶度法研究了三元体系La(ClO4)3-BAPHDCA-H2O(BAPHDCA, N, N'-二安替比林-1, 6-己二酰胺)的相平衡, 绘制了体系的溶度图及饱和溶液的折光指数-组成图,发现并制备了未见文献报道的固液异组成三元化合物La(BAPHDCA)2(ClO4)3.4H2O。通过化学分析、元素分析、IR光谱、TG-DTG及X射线粉末衍射分析等对其进行了物理化学表征。     

Na2Li3CoO4, das Erste quaternäre Oxocobaltat(III) der Alkalimetalle

Na₂Li₃CoO₄, the First Quaternary Oxocobaltate(III) of the Alkali Metals For the first time we obtained Na₂Li₃CoO₄ by annealing intimate mixtures of Co₃O₄, Na₂O₂, and Li₂O [Co : Na : Li = 1 : 2.2 : 10.1; 760°C; 21 d; Ag-tube] in form of transparent red single crystals. Structure Refinement [four-circle diffractometer data; AED2; MoKα-radiation; 1016 I_o(hkl); R = 2.6%; R_w = 2.0%; space group Pnnm; Z = 4; a = 818.7(3), b = 799.4(2), c = 655.1(2) pm] confirms the isotypism to Na₂Li₃GaO₄ [2] and Na₂Li₃FeO₄ [3]. Mean Fictive Ionic Radii, MEFIR, Effective Coordination Numbers, ECoN, and the Charge Distribution were calculated. The isotypism of Na₂Li₃CoO₄ and Na₂Li₃GaO₄ is compared graphically.     

Study of the ionic conductivity of Ca6La4(PO4)2(SiO4)4F2 and Ca4La6(SiO4)6F2

In order to enhance our knowledge about the Ca_10−xLa_x(PO₄)_6−x(SiO₄)_xF₂ (0 ≤ x ≤ 6) series, whose chemical stability decreases as the substitution degree increases, Ca₆La₄(PO₄)₂(SiO₄)₄F₂ and Ca₄La₆(SiO₄)₆F₂ compounds were prepared through a solid-state reaction. Their ionic conductivity was measured by impedance spectroscopy. The results indicate that the conductivity increases with substitution, and fits the Arrhenius equation over the investigated temperature range. At high temperatures, a change in the activation energy has been observed, which has been related to the nature of the Ca/La–F bond, i.e. to the polarizability of lanthanum.     

Selenophosphate phase diagrams developed in conjunction with the synthesis of the new compounds K(2)La(P(2)Se(6))(1/2)(PSe(4)), K(3)La(PSe(4))(2), K(4)La(0.67)(PSe(4))(2), K(9-x)La(1+x/3)(PSe(4))(4) (x = 0.5), and KEuPSe(4)

Five new rare-earth metal polyselenophosphates have been synthesized by the reactive flux method and characterized by single-crystal X-ray diffraction: K(2)La(P(2)Se(6))(1/2)(PSe(4)) (I), K(3)La(PSe(4))(2) (II), K(4)La(0.67)(PSe(4))(2) (III), K(9-x)()La(1+)(x/3)(PSe(4))(4) (x = 0.5) (IV), and KEuPSe(4) (V). Compound I crystallizes in the monoclinic space group P2(1)/n with a = 9.4269(1) A, b = 7.2054(1) A, c = 21.0276(5) A, beta = 97.484(1) degrees, and Z = 4. Compound II crystallizes in the monoclinic space group P2(1)/c with a = 9.5782(2) A, b = 17.6623(4) A, c = 9.9869(3) A, beta = 90.120(1) degrees, and Z = 4. Compound III crystallizes in the orthorhombic space group Ibam with a = 19.0962(2) A, b = 9.1408(1) A, c = 10.2588(2) A, and Z = 4. Compound IV crystallizes in the orthorhombic space group Ccca with a = 18.2133(1) A, b = 38.0914(4) A, c = 10.2665(1) A, and Z = 8. Compound V crystallizes in the orthorhombic space group Pnma with a = 17.5156(11) A, b = 7.0126(5) A, c = 6.9015(4) A, and Z = 4. Optical band gap measurements show that compound V has an optical band gap of 1.88 eV. Solid-state Raman spectroscopy of compounds II-V shows the four normal vibrations expected for the (PSe(4))(3-) unit. The observation of compounds I-V in several reactions has allowed the creation of a quasi-quaternary phase diagram for potassium rare-earth-metal polyselenophosphates. This phase diagram can qualitatively be separated into three regions on the basis of the oxidation state of phosphorus in the crystalline products observed and takes the next step in designing solid-state compounds.