Structural changes in Fe-doped SrSnO3 perovskites during thermal analysis

Perovskite-type strontium stannate, SrSnO₃, is of technological interest because of its potential applications. In the present work, Fe(III)-doped SrSnO₃ perovskites were synthesized using Sn metal and the polymeric precursor method, derived from the Pechini method. Thermogravimetric evaluations in N₂ and O₂ atmospheres were performed to evaluate the possible formation of oxygen vacancies resulting from Fe(III) doping. The X-ray diffraction patterns showed the formation of an orthorhombic structure with high crystallinity after calcination at 1,073 K. The first thermal analysis, in a N₂ atmosphere, led to the partial elimination of strontium carbonate and hydroxyl groups, while the thermal analysis in an O₂ atmosphere led to an increase in the mass, indicating O₂ adsorption on the lattice, which could be related to the presence of Fe(III) and Fe(IV) in the perovskite structure. Moreover, the thermal analysis changed the symmetry of the iron-doped perovskites.     

Visible light photocatalytic reduction of water using SrSnO3 sensitized by CuFeO2

SrSnO_3–δ, prepared in sealed ampoules, crystallizes in the perovskite structure. The band gap is directly allowed at 3.93 eV. The conductivity was found to change markedly and occurs by polaron hopping with activation energy of 0.22 eV. The thermal variation of the thermopower indicates an electron mobility μ_{e 300K} = 3.15∙10^–6 cm²∙V^–1∙s^–1), thermally activated. The capacitance measurement shows a linear behavior from which a flat band potential of –0.20 V_SCE and an electronic density of 5.56∙10¹⁸ cm^–3 were determined. The conduction band edge (–4.32 eV/–0.42 V_SCE) lies below the H₂O/H₂ level. Accordingly, SrSnO_3–δ can be used for water photoreduction when combined with the delafossite CuFeO₂ as sensitizer. Translated from Teoreticheskaya i éksperimental’naya Khimiya, Vol. 45, No. 3, pp. 160-166, May-June, 2009.     

Crystallization kinetics of amorphous Fe75-xCuxSi9B16

In this work the influence of Cu admixtures on the crystallization process of amorphous Fe-Si-B alloys is studied, based on measurements of differential thermal calorimetry of the series Fe_75-xCu_xSi₉B₁₆ (x=0, 1, 2, 2.8 and 3.5) during their heating with different heating rates. The first crystallization stage can not be traced for any of the amounts of Cu content examined, while the second stage is observed only when the Cu content is 1 at%. The activation energy as estimated with Kissinger's method for the third crystallization stage has a mean value of 326 kJ mol^-1 and with the isoconversional Flynn, Wall and Ozawa method is almost constant when 0.05<a<0.6 and exhibits a small monotical decrease when a>0.6. The main crystallization peak can not be described by means of a single JMA-type function. This revised version was published online in August 2006 with corrections to the Cover Date.     

Effect of Fe2O3 Content on the Local Structure and Crystallization Mechanism of Calcium Gallate Glasses

⁵⁷Fe Mössbauer and FT-IR of 60CaO·(40-x)Ga₂O₃·xFe₂O₃ glasses revealed that Fe(III)O₄ tetrahedra occupy substitutional sites of Ga(III)O₄ tetrahedra. The activation energy for crystallizaation (E _a) obtained from DTA study decreases distinctly from 8.9 to 4.8 eV with an increase in the Fe₂O₃ content. In the case of 40CaO·(60-x)Ga₂O₃·xFe₂O₃ glasses, a week doublet due to Fe(II)O₄ tetrahedra or Fe(III)O₆ octahedra was observed in addition to Fe(III)O₄ tetrahedra. The E _avalue decreases gradually from 7.1 to 5.6 eV with an increasing Fe₂O₃ content. These results indicate that a large amount of Fe₂O₃ in the network structure is favorable for the crystallization of calcium gallate glass, since it reduces the chemical bond strength.     

Annealing and Crystallization of Fe40Ni40P14B6 Glassy Alloy. A DSC study

In this paper a DSC study is reported of the behavior of Fe₄₀Ni₄₀P₁₄B₆ alloy produced by rapid quenching. The experimental results show that relaxation phenomena can be studied directly from the DSC curves. From these experiments, the spread of the E _c values in the literature is attributed to differences in the quenching rates and the presence of variable number of quenched-in nuclei. It is also shown that the microstructure (number and size of crystals) of the non-isothermally devitrified metallic alloy changes with the heating rate; this is a consequence of the shift of crystallization temperatures and, therefore, of the change of the ratio of nucleation and crystal growth rates. This revised version was published online in July 2006 with corrections to the Cover Date.     

Differential thermal study of FeO and Fe3O4

Two batches of wüstite were produced from a stoichiometric mixture of Fe and Fe₂O₃ by sealing in steel tubes in vacuum and helium, respectively, and igniting the first tube at 1300° for 21 hours and the second one at 1200° for 34 hours. There were two exothermic peaks on the DTA curves of both samples at 345 and 545 to 700° due to surface oxidation of FeO to Fe₃O₄ followed by bulk oxidation of FeO to Fe₃O₄ and of Fe₃O₄ to-Fe₂O₃. The last two reactions gave rise to a dual (or twin) peak for coarse material but one peak in the case of fine material, indicating that the two reactions occurred concurrently for fine material. Similar investigations on both fine and coarse magnetites showed only two exothermic peaks which corresponded to surface and bulk oxidation, respectively. This result confirms the previous observations that coarse magnetite converts to-Fe₂O₃ by surface oxidation followed by bulk oxidation.

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Zusammenfassung Es wurden zwei Serien von Wüstit aus einem stöchiometrischen Gemisch von Fe und Fe₂O₃ in versiegelten Stahlröhren unter Vakuum bzw. Helium durch 21 stündiges Erhitzen bei 1300° bzw. 34 Stunden bei 1200° dargestellt. Die DTA-Kurve wies bei beiden Proben zwei exothermische Spitzen auf, bei 345° bzw. bei 545° bis 700° auf, die der oberflächlichen Oxydation von FeO zu Fe₃O₄ bzw. der vollständigen Oxydation von FeO zu Fe₃O₄ bzw. Fe₃O₄ zu-Fe₂O₃ entsprechen. Die beiden letzten Reaktionen verursachten eine Zwillingsspitze im Fall von grobem Material, hingegen eine einzige Spitze bei feinem Material. Diese Reaktionen verlaufen also im letzten Fall gleichzeitig. Ähnliche Versuche mit grobem und feinem Magnetit zeigten nur zwei, der oberflächlichen und massiven Oxydation entsprechenden exothermischen Spitzen. Dieses Ergebnis unterstützt die früheren Beobachtungen, daß grober Magnetit durch oberflächliche und darauffolgende vollständige Oxydation in-Fe₂O₃ überght.

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Résumé On a préparé deux séries de wüstite à partir d'un mélange stoechiometrique de Fe et Fe₂O₃ dans des tubes scellés d'acier sous vide rsp. en hélium. Un tube a été chauffé pendant 21 heures chez 1300° l'autre chez 1200° pendant 34 heures. On observe dans les courbes d'ATD des deux séries d'échantillons deux pics exothermiques chez 345° et de 545° jusqu' à 700° dûs à l'oxydation superficielle de FeO en Fe₃O₄ suivie par l'oxydation de la masse de l'échantillon de FeO en Fe₃O₄ rsp. de Fe₃O4 en-Fe₂O₃. Les deux réactions dernières donnent pour un produit à gros grains, un pic double, et pour un produit à grains fins un pic simple indiquant que dans le dernier cas deux réactions concurrentes eurent lieu. Pareilles investigations avec magnétite grossière et fine n'ont montré que deux pics exothermiques correspondant à l'oxydation superficielle et dans la masse. Ces resultats confirment les observations antérieures de la transformation de magnétite grossière en-Fe₂O₃ par oxydation superficielle suivie d'oxydation dans la masse.

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Fe Fe₂O₃ . , 1300° 21 ., — 1200° 34 . 345° 545–700°, FeO Fe₃O₄ Fe₃O₄ -Fe₂O₃. , . , . , , . , -Fe₂O₃ , .

     

Fe2+/Fe3+ based MOIFs + dye interaction study: Thermodynamic and kinetic analysis estimated through spectrophotometrically

Herein, the interaction study of organic dyes with newly reported metal organic ionic frameworks (MOIF) based on [Fe(CN)₆]^3-/[Fe(CN)₆]^4-/[Fe(CN)₅NO]^2- and cetylpyridinium cation, investigated through spectrophotometric method. Measurements were carried out at 303.15, 308.15 and 313.15 K where interaction found to be decreased with increase in temperatures. The 60–90% maximum interaction was noted for [Fe(CN)₅NO]^2- based MOIF with all chosen dyes at 303.15 K inferring the high interaction ability associated with dissymmetry of this MOIF due to presence of different ligands. The oxidation state and hydrophilicophobic domains of MOIFs have been found accountable for the stronger interaction where Fe²⁺ with high hydrophobicity was found more interacting as compared to Fe³⁺ with less hydrophobicity. The activation parameters ΔG⁰, ΔH⁰ have been found greater for MOIFs and methylene blue dye systems due to stronger interaction of their hydrophobic domains. The ΔS⁰ noted greater for [Fe(CN)₅NO]^2- based MOIF showing the impact of availability of interacting sites and distortion in symmetry. The isotherm analysis has inferred about the maximum uniform distribution of binding energy, favorability of interaction, interaction capacity and intensity, was associated with methylene blue and MOIFs systems. The positive slope (2.303/K) of a plot of log(A_o/A_t) vs t (time) inferred the first order kinetic of MOIF and chosen dyes.     

Theoretical study of NH3 adsorption on Fe(110) and Fe(111) surfaces

With the aim of understanding the nature of the interactions between organic molecules and metal surfaces, the adsorption of NH3 onto model Fe(110) and Fe(111) surfaces has been studied with use of the molecular orbital and density functional theories. B3LYP calculations have revealed that the on-top site is most suitable for adsorption of NH3 both on Fe(110) and on Fe(111). Mulliken population analysis in terms of the MO's of the two fragment systems suggested that electron delocalization from NH3 to the Fe surface should play a key role in the adsorption. Then, our transformation scheme of fragment orbitals has demonstrated that the electron delocalization is represented well only by a pair of interaction orbitals. The NH3 molecule provides the occupied interaction orbital bearing a close resemblance to the highest occupied (HO) MO, whereas the Fe surface prepares the paired unoccupied orbital that is localized at the adsorption site and overlaps in-phase with the orbital of NH3. Not only the lowest unoccupied (LU) MO but also other unoccupied MO's have been shown to participate significantly in the interaction. The reason the on-top site is the most preferable position for NH3 attack has been elucidated by investigating the interaction orbitals.     

Thermal decomposition of Fe2(SO4)3: Demonstration of Fe2O3 polymorphism

The mechanism of the thermal decomposition of Fe₂(SO₄)₃ in air has been studied at different temperatures (520-700 °C) using mainly ⁵⁷Fe Mössbauer spectroscopy. Iron(III) oxides with corundum (), bixbyite (), spinel () and orthorhombic () structures were identified as solid products of this conversion. A significant influence of the heating temperature on the decomposition mechanism and on the phase composition of reaction products was found.     

Fe/Dy非晶多层膜晶化反应的热力学及动力学研究

由Miedema半经验公式计算出了Fe Dy二元系自由能图以揭示Fe Dy非晶多层膜的晶化本质。晶化受热力学和动力学两种因素控制 ,Fe,Dy晶态自由能低于初始非晶态 ,提供了晶化的热力学驱动力 ,而形核势垒及临界晶核尺寸控制了晶化反应的相选择 ,因而中等温度退火时先出现Fe晶粒 ,继而Dy晶粒 ,不出现金属间化合物。     

经Fe(NO3)3处理的Fe3O4纳米微粒分析

Fe3O4纳米微粒是一种制备磁性液体的重要组成部分。但Fe3O4纳米微粒不稳定,极易氧化成γ-Fe2O3,其磁化强度也会明显降低[1-2]。铁氧体还易为酸溶解,化学反应式为:MFe2O4 8H M2 2Fe3 4H2O式中M为Fe、Co、Mn等二价金属。在Massart法制备酸性离子型磁性液体的方法中,采用了Fe(NO     

Synthesis of Fe3O4, Fe2O3, Ag/Fe3O4 and Ag/Fe2O3 nanoparticles and their electrocatalytic properties

Two important iron oxides:Fe3O4 and Fe2O3,as well as Fe3O4 and Fe2O3 nanoparticles mingling with Ag were successfully synthesized via a hydrothermal procedure.The samples were confirmed and characterized by X-ray diffraction(XRD),and X-ray photoelectron spectroscopy(XPS).The morphology of the samples was observed by transmission electron microscopy(TEM).The results indicated Fe3O4,Fe2O3,Ag/Fe3O4 and Ag/Fe2O3 samples all were nanoparticles with smaller sizes.The samples were modified on a glassy carbon electrode and their elctrocatalytic properties for p-nitrophenol in a basic solution were investigated.The results revealed all the samples showed enhanced catalytic performances by comparison with a bare glassy carbon electrode.Furthermore,p-nitrophenol could be reduced at a lower peak potential or a higher peak current on a glassy carbon electrode modified with Ag/Fe3O4 or Ag/Fe2O3 composite nanoparticles.     

Crystallization behaviour of Fe−(Nb,Cu)−Si−B metallic glasses

The crystallization behaviour and Curie temperatures of Fe?(Nb,Cu)?Si?B metallic glasses were studied by means of differential scanning calorimetry (DSC), thermomagnetic gravimetry (TMG) and X-ray diffraction. The agreement between the DSC and TMG results was complete. For all Fe?Si?B amorphous alloys, two-peak crystallization was observed with the primary crystallization of α-Fe(Si) followed by eutectic crystallisation. The effects of Cu and Nb additions on the crystallization behaviour and on the activation energies for each stage of the crystallization process of Fe?Si?B glass were investigated.     

Fe2O3/Al2O3氧载体制备方法的研究

采用溶胶-凝胶法、共沉淀法、水热合成法、低热固相合成法、机械混合法、燃烧合成法和冷冻成粒法制备铁基氧载体Fe₂O₃/Al₂O₃,并通过物理和化学表征手段来筛选和优化制备方法和制备工艺。对煅烧后的氧载体进行硬度测试,结果表明,溶胶-凝胶法、共沉淀法、机械混合法、燃烧合成法和冷冻成粒法制备的氧载体硬度较高;载体的X射线衍射(XRD)谱图表明,各种制备方法均能制得物相组成为Fe₂O₃/Al₂O₃的氧载体,且随着煅烧温度的提高、煅烧时间的延长,氧载体的结晶度、晶体粒径逐渐增大,煅烧温度1 200℃的氧载体的机械性能、晶体结构、晶相组成更稳定。借助化学吸附仪的程序升温还原(TPR)实验表征氧载体的反应活性,并计算氧载体活性度。综合物理和化学表征实验结果表明,最优制备方法为溶胶-凝胶法和冷冻成粒法。     

The L Spectrum of Fe and Fe3O4

The intensities of the Fe L lines/bands l = L₃M₁, η = L₂M₁, α_1,2 = L₃M_4,5, β₁ = L₂M₄, and β_3,4 = L₁M_2,3 were measured for pure Fe and Fe₃O₄ using a TAP crystal as the dispersing element. The energy of the exciting electrons, E₀, was varied in the range 5 ≤ E₀ ≤ 25 keV. For pure Fe the following results were obtained. The net peak height ratio Ll/Lα remains relatively constant with varying E₀ at approximately 14%. The E₀ dependence of Lη is similar to that of Ll, although Lη is less intense than Ll by a factor of 7. Lβ₁/Lα decreases from 20% for E₀ = 5 keV to about 5% for 25 keV. Lβ_3,4 behaves like Lβ₁ but is weaker by a factor of 15. For Fe₃O₄ a much weaker intensity of Lα was observed which can be partially explained by its stronger absorption. Again, the E₀ dependence of Ll and Lη is similar with Ll/Lα = 19% and Lη/Lα = 4%. Lβ₁ and Lβ_3,4 show a comparable E₀ dependence. Lβ₁/Lα decreases from 50% for E₀ = 5 keV to 34% for 25 keV. Lβ_3,4 is weaker than Lβ₁ by a factor of about 25. The observed E₀ dependence of the different lines was used to estimate a set of mass absorption coefficients. Our value for Lα in Fe agrees well with other data which were deduced from variable E₀ measurements but differs considerably from data given by Heinrich and Henke.     

Vibration frequencies of Ca3Fe2Si3O12 andradite: an ab initio study with the CRYSTAL code

The vibrational spectrum of Ca3Fe2Si3O12 andradite is calculated at the Gamma point by using the periodic ab initio CRYSTAL program that adopts an all-electron Gaussian-type basis set and the B3LYP Hamiltonian. The full set of frequencies (17 IR active, 25 Raman active, and 55 inactive modes) is calculated. The effect of the basis set on the calculated frequencies is discussed. The modes are characterized by direct inspection of the eigenvectors and isotopic substitution. The present calculations permit us to clarify some of the assignment problems raised by experiments. The mean absolute differences of the various modes with respect to the available experimental IR and Raman data are as small as 9 and 5 cm(-1), respectively.     

水分辅助对无机钙钛矿CsPbI3薄膜结晶的影响

利用水分辅助晶粒溶解重结晶策略提高全无机铯铅碘钙钛矿(CsPbI₃)薄膜的质量, 探究了退火过程中不同湿度条件对薄膜结晶质量的影响, 并从形貌结构、 缺陷复合以及光伏性能等方面进行了研究. 结果表明, 相比于相对湿度(RH)为0%组CsPbI₃薄膜明显的晶界空隙, 适当的湿度退火有助于晶粒间更致密地结合, 晶界的减少进而可抑制载流子非辐射复合; 湿度过大则会形成较粗糙的表面形貌, 影响界面接触. 实验结果表明, 7%RH下CsPbI₃薄膜中缺陷明显减少, 非辐射复合得到抑制, 载流子寿命增加; 光伏性能测试结果显示, 开路电压(V_oc)和填充因子(FF)显著增大, 并获得了15.28%的光电转换效率(PCE).