Neue Hochdruckmodifikationen im RhF3-Typ bei Seltenerd-Trichloriden

Novel High Pressure Modifications of Rare Earth Trichlorides in the RhF₃-Type The results of high pressure investigations on Rare Earth trichlorides crystallizing with the AlCl₃-type arrangement under normal conditions are reported. In addition to the PuBr₃-type geometry, formed at higher pressures, a new structure type is found in a lower pressure range. This high pressure phase is isotypic with the RhF₃-type arrangement, which so far has only been found with fluorides. It is packed more efficiently and shows a slightly higher primary coordination due to the higher symmetry of the coordination polyhedra compared with that of the original AlCl₃-type structure. We present a model for the mechanism of transformation.     

Polymorphism and phase transformation in the dimethyl sulfoxide solvate of 2,3,5,6‐tetrafluoro‐1,4‐diiodobenzene

A new polymorph (form II) is reported for the 1:1 dimethyl sulfoxide solvate of 2,3,5,6‐tetrafluoro‐1,4‐diiodobenzene (TFDIB·DMSO or C₆F₄I₂·C₂H₆SO). The structure is similar to that of a previously reported polymorph (form I) [Britton (2003). Acta Cryst. E 59 , o1332–o1333], containing layers of TFDIB molecules with DMSO molecules between, accepting I…O halogen bonds from two TFDIB molecules. Re‐examination of form I over the temperature range 300–120 K shows that it undergoes a phase transformation around 220 K, where the DMSO molecules undergo re‐orientation and become ordered. The unit cell expands by ca 0.5 Å along the c axis and contracts by ca 1.0 Å along the a axis, and the space‐group symmetry is reduced from Pnma to P2₁2₁2₁. Refinement of form I against data collected at 220 K captures the (average) structure of the crystal prior to the phase transformation, with the DMSO molecules showing four distinct disorder components, corresponding to an overlay of the 297 and 120 K structures. Assessment of the intermolecular interaction energies using the PIXEL method indicates that the various orientations of the DMSO molecules have very similar total interaction energies with the molecules of the TFDIB framework. The phase transformation is driven by interactions between DMSO molecules, whereby re‐orientation at lower temperature yields significantly closer and more stabilizing interactions between neighbouring DMSO molecules, which lock in an ordered arrangement along the shortened a axis.     

混合稀土对A_2B_7型储氢合金结构和电化学性能的影响

采用感应熔炼方法制备了A2B7型La0.83-0.5x(Pr0.1Nd0.1Sm0.1Gd0.2)xMg0.17Ni3.1Co0.3Al0.1(x=0~1.66)储氢合金,并在He+Ar气氛和1 173 K下进行退火处理。通过X射线衍射(XRD)、扫描电子显微镜(SEM)和电化学方法,研究了混合稀土(Pr,Nd,Sm,Gd)替代La元素对合金物相结构和电化学性能的影响。合金相结构分析表明,混合稀土含量对合金组成和相结构有重要的影响,随混合稀土含量x的增加,合金中主相A2B7型(2H-Ce2Ni7型+3R-Gd2Co7型)相丰度逐渐增多,其中2H-Ce2Ni7型相丰度先增多后减少,3RGd2Co7型相丰度则逐渐增加,主相晶胞参数随x增加而减小。电化学结果表明,随混合稀土含量增加,放氢平台压逐渐升高,合金电极的最大放电容量和循环稳定性均呈先增大后减小的规律,其中x=0.4合金电极具有最高的电化学放电容量(389.8 mAh·g-1)和最佳的循环寿命(S100=91.30%);合金电极的高倍率放电性能(HRD)则随x的增加获得显著提高。适量的混合稀土替代量可显著改善合金电极的综合电化学性能。     

混合稀土对A2B7型储氢合金结构和电化学性能的影响

采用感应熔炼方法制备了A₂B₇型La_0.83-0.5x（Pr_0.1Nd_0.1Sm_0.1Gd_0.2）_xMg_0.17Ni_3.1Co_0.3Al_0.1（x=0~1.66）储氢合金,并在He+Ar气氛和 1 173 K下进行退火处理。通过X射线衍射（XRD）、扫描电子显微镜（SEM）和电化学方法,研究了混合稀土（Pr,Nd,Sm,Gd）替代La元素对合金物相结构和电化学性能的影响。合金相结构分析表明,混合稀土含量对合金组成和相结构有重要的影响,随混合稀土含量x的增加,合金中主相A₂B₇型（2H-Ce₂Ni₇型+3R-Gd₂Co₇型）相丰度逐渐增多,其中2H-Ce₂Ni₇型相丰度先增多后减少,3R-Gd₂Co₇型相丰度则逐渐增加,主相晶胞参数随x增加而减小。电化学结果表明,随混合稀土含量增加,放氢平台压逐渐升高,合金电极的最大放电容量和循环稳定性均呈先增大后减小的规律,其中x=0.4合金电极具有最高的电化学放电容量（389.8 mAh·g^-1）和最佳的循环寿命（S₁₀₀=91.30%）;合金电极的高倍率放电性能（HRD）则随x的增加获得显著提高。适量的混合稀土替代量可显著改善合金电极的综合电化学性能。     

A structure refinement of the high pressure modification BaI2-II

A high pressure phase BaI₂-II, which can be quenched and retained as a metastable form at ambient conditions, is reported. The structure has been determined by X-ray investigations using single crystals. BaI₂-II crystallizes in an anti-Fe₂P-type arrangement, space group $\text{P}\text{6}\text{2m, a = 9.142(6)}$Å, c = 5.173(3)Å, which is slightly denser than the PbCl₂-type structure found at normal pressure. Structural features of the two phases are discussed in comparison.     

Intrinsic symmetry of the AABb-type distribution

By taking an A_aB_b-type polymerisation as an example

1 Each unit has a functional groups of type A and b of type B.

, an intrinsic symmetry of the equilibrium number fraction distribution of species is revealed. The symmetry shows that the distribution is invariant under transformation between the variables which describe the total system and the variables which describe the sol. It results that, when the polymer quantities for the pre-gel regime are given, the corresponding quantities for the post-gel regime can easily be obtained. As an illustration, the k th radius of an A_aB_b-type polymerisation is discussed.     

A TEM, XRD, and crystal chemical investigation of oxygen/vacancy ordering in (Ba1−xLax)2In2O5+x, 0x0.6

A careful TEM and XRD study of the (Ba_1−xLa_x)₂In₂O_5+x, 0x0.6, ‘defect-perovskite’-type solid solution has been carried out. A well-defined structural phase transition is shown to occur between x=0.1 and 0.2 from the orthorhombic brownmillerite structure type on the low x side to a multiple twinned, tetragonal 1×1×2 perovskite-related superstructure phase on the high x side at x=0.2. This phase transition correlates with an important phase transition previously observed in electrical conductivity versus temperature measurements. The existence of additional satellite reflections close to the regions of reciprocal space was found to be typical of all (Ba_1−xLa_x)₂In₂O_5+x specimens, although their intensity relative to the parent Bragg reflections systematically reduces as x increases. As x increases beyond 0.2, the -type satellite reflections initially become weaker and rather more diffuse for x=0.3 before splitting into pairs of rather weak and somewhat diffuse incommensurate satellite reflections for x=0.4 and beyond. An interpretation in terms of oxygen vacancy ordering and associated structural relaxation is given. Additional structured diffuse scattering is also observed and a tentative explanation in terms of Ba/La ordering and associated local strain distortions put forward.     

Structural and electrochemical properties of high-capacity Ml-Mg-Ni-based hydrogen storage alloys

The Ml-Mg-Ni-based (Ml = La-rich mixed lanthanide) hydrogen storage alloy Ml_0.88Mg_0.12Ni_3.0-Mn_0.10Co_0.55Al_0.10 was prepared by inductive melting. The micro-structure was analyzed by XRD and SEM. The alloy consists mainly of CaCu₅-type phase, Ce₂Ni₇-type phase and Pr₅Co₁₉-type phase. The electrochemical measurements show that the maximum discharge capacity is 386 mAh/g, 16.3% higher than that of the commercial AB₅-type alloy (332 mAh/g). At discharge current density of 1 100 mA/g, high rate dischargeability is 62%, while that of the AB5-type alloy is only 45%. The discharge capacity decreases to 315 mAh/g after 300 charge/ discharge cycles, 81.5% of the maximum discharge capacity. __________ Translated from Journal of Xi’an Jiao Tong University, 2008, 42(3) (in Chinese)     

Phase composition and phase transformation in Bi(Sb,Nb,Ta)O4 system

In this work Bi(Sb_xNb_yTa_z)O₄ (x + y + z = 1) samples are prepared using mixed-oxide method. A pseudo-ternary phase diagram of Bi(Sb,Nb,Ta)O₄ system is given below the melting point. It is composed of a monoclinic phase region, an orthorhombic phase region and a monoclinic–orthorhombic co-existing phase region. In the orthorhombic phase region, the transformation from orthorhombic to triclinic phase is found to be sensitive to the composition and sintering temperature. Both the transformation from monoclinic to orthorhombic structure and the transformation from orthorhombic to triclinic structure have been studied by the cell parameters.     

Transformation of three-connected silicon nets in CaSi2

Up to 40 kbar and 1100°C, CaSi₂ is dimorphic. Trigonal/rhombohedral CaSi₂I (CaSi₂-type structure) with corrugated layers of three-connected Si atoms can be transformed by a high pressure-high temperature treatment into tetragonal CaSi₂II (α-ThSi₂-type structure) with a three-dimensional net of three-connected Si atoms. The silicon net of CaSi₂II is slightly distorted from the topologically simplest tetragonal three-dimensional three-connected net derived on a geometrical basis. In order to correlate crystal chemical with thermochemical data the transformation between both polymorphs of CaSi₂ has been studied at equilibrium and nonequilibrium conditions. The pressure-temperature phase diagram of CaSi₂ has been investigated by X-ray technique in quenched samples. From the slope of the equilibrium line and the change in molar volume the approximate values of the entropy and energy of transformation CaSi₂(I-II) have been determined ΔS = 3.2 e.u., ΔU = 4.9 kcal/mole. Under nonequilibrium conditions the transformation CaSi₂(II-I) yielded ΔH = ?4.2 kcal/mole at 500°C and ambient pressure in a DTA apparatus. Complete transformation of metastable CaSi₂II can be achieved within 5 min at a heating rate of 20°C/min. Due to the relatively high speed of transformation simple structural relations between both polymorphs of CaSi₂ are discussed.     

Realizing Complete Solid-Solution Reaction in High Sodium Content P2-Type Cathode for High-Performance Sodium-Ion Batteries

P2-type layered oxides suffer from an ordered Na⁺/vacancy arrangement and P2→O2/OP4 phase transitions, leading them to exhibit multiple voltage plateaus upon Na⁺ extraction/insertion. The deficient sodium in the P2-type cathode easily induces the bad structural stability at deep desodiation states and limited reversible capacity during Na⁺ de/insertion. These drawbacks cause poor rate capability and fast capacity decay in most P2-type layered oxides. To address these challenges, a novel high sodium content (0.85) and plateau-free P2-type cathode-Na_0.85Li_0.12Ni_0.22Mn_0.66O₂ (P2-NLNMO) was developed. The complete solid-solution reaction over a wide voltage range ensures both fast Na⁺ mobility (10⁻¹¹ to 10⁻¹⁰ cm² s⁻¹) and small volume variation (1.7 %). The high sodium content P2-NLNMO exhibits a higher reversible capacity of 123.4 mA h g⁻¹, superior rate capability of 79.3 mA h g⁻¹ at 20 C, and 85.4 % capacity retention after 500 cycles at 5 C. The sufficient Na and complete solid-solution reaction are critical to realizing high-performance P2-type cathodes for sodium-ion batteries.     

Reinvestigation of the Fe-rich part of the pseudo-binary system SrO–Fe2O3

The phase relations in the Fe-rich part of the pseudo-binary system SrO–Fe₂O₃ (>33 mol% Fe₂O₃) were reinvestigated between 800 and 1500 °C in air. A combination of microscopy, electron probe micro-analysis, powder X-ray diffraction and thermal analysis was used to determine phase relations, crystal structure parameters and phase transition temperatures. M-type hexagonal ferrite SrFe₁₂O₁₉ (85.71 mol% Fe₂O₃) is stable up to 1410 °C. No indication of a significant phase width was found; Sr₄Fe₆O_13±δ appears as a second phase in compositions with <85.71±0.2 mol% Fe₂O₃. Sr₄Fe₆O_13±δ itself is stable between 800 and 1250 °C. Two other hexagonal ferrites were found to exist at high temperatures only: W-type SrFe²⁺₂Fe³⁺₁₆O₂₇ is stable between 1350 and 1440 °C and X-type ferrite Sr₂Fe²⁺₂Fe³⁺₂₈O₄₆ between 1350 and 1420 °C, respectively, which is shown here for the first time. These findings in combination with previously published data were used to derive a corrected phase diagram of the Fe-rich part of the pseudo-binary system SrO–Fe₂O₃.     

Recent Progress of P2-Type Layered Transition-Metal Oxide Cathodes for Sodium-Ion Batteries

Sodium-ion batteries (SIBs) have attracted much attention due to their abundance, easy accessibility, and low cost. All of these advantages make them potential candidates for large-scale energy storage. The P2-type layered transition-metal oxides (Na_xTMO₂; TM=Mn, Co, Ni, Ti, Fe, V, Cr, and a mixture of multiple elements) exhibit good Na⁺ ion conductivity and structural stability, which make them an excellent choice for the cathode materials of SIBs. Herein, the structural evolution, anionic redox reaction, some challenges, and recent progress of Na_xTMO₂ cathodes for SIBs are reviewed and summarized. Moreover, a detailed understanding of the relationship of chemical components, structures, phase compositions, and electrochemical performance is presented. This Review aims to provide a reference for the development of P2-type layered transition-metal oxide cathode materials for SIBs.     

New aspects of the single phase aggregate model for oriented polymers

A reinvestigation of the single phase aggregate model (SPAM) of Ward applied to the elastic properties of uniaxially oriented polymers is presented. It is shown that the Voigt and the Reuss orientation average of elastic constants can be represented as a linear transformation in a 5-dimensional vector space. The corresponding transformation matrix can be diagonalized, showing that the eigenvalues of this transformation are the orientation parametersP ₀ =1,P ₂ andP ₄ . Taking advantage of this representation an easy test of applicability of the SPAM is proposed. Possibilities to evaluate the SPAM parameters are reviewed.     

Sulfur-Doped n-Type Diamond: Preparation and Electrochemical Properties

Films of sulfur-doped synthetic diamond are chemical-vapor-deposited using codoping with sulfur and boron. The sulfur in diamond is detected with particle-induced x-ray emission (PIXE), x-ray photoelectron spectroscopy (XPS), and secondary ion mass spectroscopy (SIMS). Electrochemical and thermoelectric measurements show that the sulfur-containing diamond films grown in gas phase lean in boron are n-type, whereas those grown with higher boron content are overcompensated, hence, p-type. Electrochemical properties of the n-type diamond films are studied for the first time using methods of electrochemical impedance, open-circuit photopotential, and voltammetric curves in Fe(CN)₆ ^3-/4- solutions. A mechanism of boron-stimulated sulfur incorporation into diamond and the nature of donors thus formed is discussed.     

The substituent effect on mesomorphic properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy)benzoates and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates

Abstract

The thermal properties of 4-octyloxyphenyl 4-(4-R-3-nitrobenzoyloxy) benzo-ates (1) and 4-(4-octyloxybenzoyloxy)phenyl 4-R-3-nitrobenzoates (2) have been examined, where R = hydrogen, halogens, alkyl and alkoxy groups. The derivatives of compound 1 incorporating hydrogen, halogens, methoxy and nitro groups show a smectic A phase having a bilayer arrangement, and the others with a long alkoxy group show the S_A phase with the monolayer arrangement. The derivatives of compound 2 incorporating halogens, and the nitro group show the S_A phase with the monolayer arrangement. The alkoxy derivatives show a smectic C phase as well as the nematic phase. The nitro group at the lateral position tends to increase the ratio of the S_A-N transition temperature to the N-I. The effect of the nitro group on the smectic properties has been discussed in terms of the structural and electrostatic nature of the nitro group.     

Polymorphie bei APd2X2-Verbindungen (A = Sr,Ba; X = As,Sb)

Polymorphism of APd₂X₂-Compounds (A = Sr, Ba; X = As, Sb) SrPd₂Sb₂ crystallizes at room temperature in the CaBe₂Ge₂-type structure (lattice constants see “Inhaltsübersicht”); a high-temperature modification with ThCr₂Si₂-type structure was obtained by quenching samples from above 730°C. The same structure was found for the high-temperature modification of BaPd₂As₂ which can be prepared by quenching from above 720°C. For (ThCr₂Si₂-structure) no phase transition could be observed.     

Crystallization of markoffian copolymers

An equilibrium theory is proposed for crystallization of (A, B) binary copolymers whose comonomeric unit sequences are statistically described by conditional pair probabilities P_AA, P_AB, P_BA, and P_BB. These are linked to the product of the reactivity ratios by r = r_Ar_B = (P_AAP_BB)/(P_ABP_BA). Three cases are considered here, (i) B units are rejected from the crystals, (ii) cocrystallization of A and B comonomeric units is possible in the full range of compositions within a single crystal structure (copolymer isomorphism), (iii) cocrystallization takes place either in a poly(A)-type or in a poly(B)-type structure, depending on composition (copolymer isodimorphism). For case (i) crystallization the theory demonstrates, according to expectation, that alternating copolymers (r = 0) produce the largest melting point depression, whereas in case (ii) they give rise to the smallest composition difference between the crystals and the liquid. The theory developed here further illustrates that for binary copolymers which are isodimorphic (case iii), a phase diagram is obtained similar to that for a classical binary system of small molecules.     

Evidence of network demixing in GeS2-Ga2S3 chalcogenide glasses: A phase transformation study

The information of phase transformation is attained by in situ XRD experiments leading to the knowledge of topological threshold in GeS₂-Ga₂S₃ glasses. The turning point of phase transformation behavior is demonstrated to be glasses containing 14-15 mol% Ga₂S₃. To interpret it a network demixing model is further improved and proposed for the structure of these ternary or quasi-binary chalcogenide glasses. For the nearest-neighbor coordination environment of glass with a transitional composition of 85.7 mol% (6/7) GeS₂·14.3 mol% (1/7) Ga₂S₃, six-coordinated [S₃Ga-X-GaS₃] units (X=S or None) are well isolated by the [GeS₄] structures, which contributes to the decreasing of precipitation of Ga₂S₃ crystals in (100−x)GeS₂-xGa₂S₃ (x≤14.3) glasses corresponding to the experimental evidence of the phase transformation behavior. This scenario of intermediate-range structural order, firstly, includes the arrangement of structural units which is consistent with and provides an atomistic explanation of the compositional evolution of phase transformation behavior in these glasses.     

Observation of the verwey transition in Fe3O4 by high-resolution electron microscopy

High resolution electron microscopy (HREM) of Fe₃O₄ has been carried out at temperatures near the Verwey transition (∼120 K) with a point resolution of 3 Å. Lattice fringes of both the high- and the low-temperature phases have been observed at these temperatures. The crystal symmetry of the low-temperature phase indicated by the lattice images is consistent with the result obtained by earlier diffraction studies. A series of lattice images showing the transition from the low-temperature phase (to the high-temperature phase) has been obtained. The transformation to the high-temperature phase occurs through the penetration of the high-temperature phase into areas of the low-temperature phase. A quick motion of domain boundaries in the low-temperature phase, which is consistent with almost instantaneous rearrangements of charge ordering, has been observed. The possibility of determining the ordered arrangement of Fe²⁺ and Fe³⁺ ions directly by HREM is discussed.