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1.
This paper reports on the refined compositions and crystal structures of two phases from the homologous series (Hg, M)(Sr, Pr)2(Pr, Sr)k-1CukO2k+2+ with k = 2 (Hg-1212) — (Hg0.44(2)Ce
0.31
4+
Cu0.25)(Sr0.90(3)Pr0.10)2(Pr0.52(3)Sr0.48)Cu2.00O7.00 (a = 3.8634(1), c = 12.2030(8) , space group P4/mmm) with k = 3 (Hg-1223) — (Hg0.29(1)
)(Sr0.67(2)Pr0.33)2(Pr0.61(2)Sr0.39)2Cu3.00O9.32(8) or (Hg0.29(1)
)(Sr0.61(4)Pr0.39)2(Pr0.51(4)Sr0.49)2Cu3.00O9.00 (with a fixed content of superstoichiometric oxygen O(4) in the phase) (
is a vacancy; a = 3.8294(9), b = 3.8567(6), c = 15.2763(44) , space group Pmmm). The implausibly high content of oxygen in the Hg-1223 phase (refinement I) is attributed either to O–O bond formation or to the possible presence of a minor amount of copper in a defect position of Hg; the inclusion of the latter in structure refinement leads to a better reproduction of the real structure but increases the R indices. The crystal-chemical analysis of the title phases and a comparison with the available data for analogous phases indicates that the composition of the crystallographic positions is related to structural features, in particular, to the coordinates of (Hg, M) and superstoichiometric oxygen, whose content depends on the degree of substitution of strontium ions by praseodymium ions. Reasons for the orthorhombic distortion of the Hg-1223 phase are discussed. The absence of superconductivity is explained by the nonoptimal formal charge (FC) of copper, which depends on the oxygen content in the phase. 相似文献
2.
In order to get insight in some of the yet unanswered questions about the formation process of the (Bi,Pb)2Sr2Ca2Cu3O10+ superconducting compound, coupled DTA-TG measurements have been performed in parallel with other techniques such as X-ray diffraction, Scanning Electron Microscopy and Energy Dispersive X-ray Microanalysis. The path leading to the formation of the (Bi,Pb)2Sr2Ca2Cu3O10+ compound, starting from coprecipitated oxalates powders was studied. The activation energy of some of the involved transformation processes were determined. Relationships between the differences induced in the DTA traces by various sample nominal compositions and the intergranular magnetic properties of the superconductor will be discussed. 相似文献
3.
The homogeneity ranges with respect to the content of metal components in air were determined for yttrium and holmium manganites, based on X-ray phase analysis data for homogeneous solid solutions and heterogeneous compositions with the general formula Ln2?x Mn x O3±δ (Ln = Y, Ho) prepared by ceramic synthesis procedure in air at 900–1400°C. The results were presented as fragments of the composition-temperature phase diagrams of the Ln-Mn-O (Ln = Y, Ho) systems in air. 相似文献
4.
《Solid State Sciences》2012,14(10):1458-1461
Single phase (Tl1−yCy)Ba2Ca3Cu4O12−δ (Tl1−yCy-1234) (y = 0, 0.25, 0.5 and 0.75) superconductor samples have been prepared by solid state reaction method. The FTIR absorption measurements have confirmed the substitution of carbon at thallium site in the charge reservoir layer, (Tl1−yCy)Ba2O4−δ. The electron micrographs of these samples have shown that the carbon substitution has improved the grain morphology of Tl0.75C0.25-1234 sample. The y = 0.25 was found to be the optimum carbon concentration to achieve higher superconducting transition temperature Tc[0] and improved grain morphology. The superconducting transition temperature of Tl0.75C0.25-1234 sample has been increased to 100 K whereas a decrease in the superconducting transition temperature of Tl1−yCy-1234 (y = 0.5 and 0.75) samples was observed. However, the magnitude of diamagnetism has been decreased in all the carbon substituted samples. 相似文献
5.
Matthias Weil Tamara Đorđević Christian L. Lengauer Uwe Kolitsch 《Solid State Sciences》2009,11(12):2111-2117
The previously uninvestigated atomic arrangements of six strontium arsenate(V) phases in the systems Sr-As-O-X (X = H, Cl) have been determined. Single crystals of Sr3(AsO4)2 and Sr5(AsO4)3Cl were grown from a borate and NaCl melt, respectively, whereas single crystals of α- and β-SrAs2O6 and of Sr5-(AsO4)3OH were obtained under hydrothermal conditions. Microcrystalline samples of Sr2As2O7 were prepared by solid-state reaction of As2O5 with SrCO3 and, alternatively, by thermolysis of SrHAsO4. Crystal structure determinations based on powder X-ray diffraction data using the Rietveld method (Sr2As2O7), and from single-crystal X-ray diffraction data (all other phases) revealed isotypism with known structure types (except β-SrAs2O6 which represents a new structure type). Sr3(AsO4)2 crystallizes in the K2Pb(SO4)2 structure type; Sr2As2O7 is isotypic with the high-temperature polymorphs of Ca2P2O7 and Sr2V2O7, but itself shows no polymorphism; Sr5(AsO4)3OH and Sr5(AsO4)3Cl crystallize with the hydroxylapatite and chloroapatite structure, respectively; SrAs2O6 is dimorphic. Like all other known MIIAs2O6 metaarsenates (M = Mn, Co, Ni, Sr, Pd, Cd, Hg, Pb), the α-polymorph crystallizes in the PbSb2O6 structure type, whereas the novel β-polymorph is the first example of a MIIAs2O6 superstructure with a doubled c-axis. Additional analytical methods using Raman spectroscopy and thermal analyses support the results of the X-ray structure work. 相似文献
6.
J.-C. Grivel 《Journal of Thermal Analysis and Calorimetry》2012,109(1):81-88
The thermal decomposition of Ho(III), Er(III), Tm(III) and Yb(III) propionate monohydrates in argon was studied by means of thermogravimetry (TG), differential thermal analysis (DTA), IR-spectroscopy and X-ray diffraction (XRD). Dehydration takes place around 90?°C. It is followed by the decomposition of the anhydrous propionates to Ln2O2CO3 (Ln?=?Ho, Er, Tm or Yb) with the evolution of CO2 and 3-pentanone (C2H5COC2H5) between 300 and 400?°C. The further decomposition of Ln2O2CO3 to the respective sesquioxides Ln2O3 is characterized by an intermediate plateau extending from approximately 500?C700?°C in the TG traces. This stage corresponds to an overall composition of Ln2O2.5(CO3)0.5 but is more probably a mixture of Ln2O2CO3 and Ln2O3. The stability of this intermediate state decreases for the lighter rare-earth (RE) compounds studied. Full conversion to Ln2O3 is achieved at about 1,100?°C. The overall thermal decomposition behaviour of the title compounds is similar to that previously reported for Lu(C2H5CO2)3·H2O. 相似文献
7.
8.
Dr. Aleksandra Mielewczyk-Gryń Dr. Sebastian Wachowski Dr. Kacper Dzierzgowski Iga Szpunar Dr. Judyta Strychalska-Nowak Prof. Tomasz Klimczuk Dr. Mirosław Sawczak Prof. Maria Gazda 《Chemphyschem》2023,24(1):e202200368
LaNb0.8M0.2O4-δ (where M=As, Sb, V, and Ta) oxides with pentavalent elements of different ionic sizes were synthesized by a solid-state reaction method. The vibrational properties of these oxides have been investigated. These studies revealed that the substituent element influences both Debye temperature value as well as the Raman active vibrational modes. Additionally, the low-temperature vibrational properties of LaNb0.8Sb0.2O4-δ have been determined to show the phase transition occurrence at 260 K which is lower than previously reported. 相似文献
9.
Dr. Wiktor Zierkiewicz Dr. Rafał Wysokiński Mariusz Michalczyk Prof. Steve Scheiner 《Chemphyschem》2020,21(9):870-877
The ability of the central M atom of the MCl3− anion, with M=Be, Mg, Ca, Sr, Ba, to engage in a noncovalent bond with an approaching nucleophile is gauged by ab initio methods. The N atom of pyridine forms a M⋅⋅⋅N bond with an interaction energy between 12 and 21 kcal mol−1, even though the π-hole above the M atom is not necessarily positive in sign. Despite a strong Coulombic repulsion between two anions, CN− is also able to approach the M atom so as to engage in a metastable complex that is higher in energy than the individual anions. The energy barrier separating this complex from its constituent anion pair is roughly 20 kcal mol−1. Despite the endothermic formation reaction energy of the CN−⋅⋅⋅MCl3− complex, the electron topology signals a strong interaction, more so than in pyridine⋅⋅⋅MCl3− with its exothermic binding energy. The dianionic complex is held together largely on the strength of interorbital interactions, thereby overcoming a repulsive electrostatic component. The latter is partially alleviated by the pyramidalization of the MCl3 unit which makes its π-hole more positive. The complex sinks below the separate monomers in energy when the system is immersed in an aqueous medium, with a binding energy that varies from as much as 20 kcal mol−1 for Be down to 1.2 kcal mol−1 for Ba. 相似文献
10.
Sakai Mamoru Wang Chengkun Okiba Takashi Soga Haruki Niwa Eiki Hashimoto Takuya 《Journal of Thermal Analysis and Calorimetry》2019,135(5):2765-2774
Journal of Thermal Analysis and Calorimetry - Structural phase transition behavior between orthorhombic and tetragonal in Ln2Ni1?xCuxO4+δ (Ln?=?Nd, Pr), which attracts... 相似文献
11.
《Solid State Sciences》2001,3(3):309-319
Single crystals of two lanthanide complexes, presenting similar formula Ln(H2O)x(C2O4)2 · NH4 with Ln=La, x=0 and Ln=Gd, x=1, have been prepared, in closed system at 200 °C. The gadolinium complex is bi-dimensional. A layer is built by the packing of the basic unit, [Gd(C2O4)]4. The gadolinium atoms are related only by bischelating oxalate ligands, the ammonium ion and the water molecule (bound to the gadolinium atom) are localized into the interlayer space. The lanthanum complex is tri-dimensional. The basic building unit remains approximately the same and the packing of these units form a layer. However, within these units, the lanthanum atoms are related by either an oxalate ligand or an edge. Moreover, an oxalate ligand assumes the connection between the layers. The ammonium ion is localized into two sets of intersecting channels. Pure phase of the gadolinium complex has been prepared at 100 °C and extended to some lanthanide elements, Eu…Yb. As the size of the lanthanide ionic radius is decreasing, it is noticeable that the a unit–cell constant follows an expansion pattern while the others two follow an usual contraction one. The thermal behavior of this family shows that the anhydrous compounds are obtained and that some water molecule is sorbed during the cooling. Thus, the anhydrous compounds present a relatively open-framework with some small micropores. 相似文献
12.
The equilibrium geometrical parameters and frequencies of the normal vibrations of Ln2Cl 7 ? ions (Ln = La and Lu) and the enthalpies of the dissociation reactions Ln2Cl 7 ? → Ln2Cl6 + Cl? and Ln2Cl 7 ? → LnCl3 + LnCl 4 ? were calculated at the MP2 and MP4 levels (with regard to single, double, triple, and quadruple perturbations). The basis set superposition errors were eliminated by using the counterpoise approach. The potential energy surface of the Ln2Cl 7 ? ions was found to reach a minimum for a configuration with three bridging and four terminal Cl atoms (symmetry C 2). The terminal fragments LnCl2 show almost free inherent rotation. The lanthanide compression of the interatomic Ln-Cl distances differed for the bridging and terminal Ln-Cl bonds. The calculated enthalpies of dissociation of the Ln2Cl 7 ? ions were compared with data from high-temperature mass spectrometry. 相似文献
13.
《Journal of solid state chemistry》2004,177(4-5):1072-1077
The coexistence of superconductivity and magnetic order seems to take place in the so-called ruthenate-cuprates (Ru-1212). A systematic study is carried out on crystal structure of the RuSr2RCu2O8−δ phases (R=Gd, Tb, Dy, Y, Ho, Er) synthesized under high pressure by X-ray powder diffraction. RuSr2RCu2O8−δ (R=Gd, Tb, Dy, Y, Ho, Er) has the Ru-1212-type structure of a tetragonal symmetry and the RuO6 octahedra rotate around the c-axis with an additional small rotation around an axis perpendicular to c. The DC-magnetization data establish that compounds with R=Gd, Y, Ho, Er exhibit ferromagnetic order below about 140 K, and the Meissner effect was observed at low temperature for R=Y compound. 相似文献
14.
Thermal and calorimetric studies were carried out on M(IO3)2·6H2O and M(IO3)2·6D2O forM
2+=Ca2+ and Sr2+, using DTA and DSC methods. The thermal behaviour of the ordinary and deuterated hydrates is outlined and the differences observed between them are discussed. The enthalpies of the phase transitions were determined. The H
f
o
for Ca(IO3)2·6H2O, Ca(IO3)2·6H2O(D2O) and Sr(IO3)2·6H2O(D2O) were calculated from the H
deh data and comments are made on the isotope effect observed.
Zusammenfassung Mittels DTA- und DSC-Methoden wurden Me(IO3)2·6H2O und Me(IO3)2·6D2O (mitMe 2+=Ca2+ und Sr2+) thermisch und kalorimetrisch untersucht. Es wird ein Überblick über das thermische Verhalten ordentlicher und deuterierter Hydrate gegeben, in dem auch die Unterschiede zwischen beiden diskutiert werden. Die Enthalpien der untersuchten Phasenumwandlungen wurden bestimmt. Aus den Daten für Hdeh wurde Hf von Ca(IO3)2·6H2O, Ca(IO3)2H2O(D2O) und Sr(IO3)2·6H2O(D2O) berechnet und Bemerkungen zum beobachteten Isotopeneffektes gemacht.相似文献
15.
The (Cu0.5Tl0.25Li0.25)Ba2Ca2Cu3?ySiyO10?δ (y = 0, 0.25 0.5, 0.75, 1.0, 1.25) superconductor samples have been prepared by solid-state reaction method. The critical temperature and as well as the magnitude of diamagnetism is increased up to Si concentration y = 1.0, however, from the doping level y = 1.25 a decrease in the critical temperature along with the vanishing of the diamagnetism was observed. The carrier’s in the conducting CuO2/SiO2 planes were optimized by carrying out post-annealing in oxygen and an increase in the critical temperature was observed in all Si doped samples. The doping efficiency of Cu0.5Tl0.5Ba2O4?δ charge reservoir layer in (Cu0.5Tl0.25Li0.25)Ba2Ca2Cu3?ySiyO10?δ (y = 0, 0.25 0.5, 0.75, 1.0, 1.25) samples is enhanced by doping Li+1 ion; as alkali metals are known to easily loose their outer most electron which could be supplied to CuO2/SiO2 conducting planes and would suppress the anti-ferromagnetism in the inner conducting planes. The FTIR absorption measurements have provided an indirect evidence of Si substitution at in CuO2 planes. 相似文献
16.
《Journal of Coordination Chemistry》2012,65(19):3363-3371
Two new banana-shaped tungstophosphates [M6(H2O)2(PW9O34)2(PW6O26)]17 ? (MII?=?NiII, CoII) incorporating two types of lacunary polyoxometalate units have been synthesized in aqueous solution and characterized by elemental analyses, IR, and UV spectra, and single-crystal X-ray diffraction. Structural analyses show that Na6H11[Ni6(H2O)2(PW9O34)2(PW6O26)]?·?32H2O (1) and Na7H10[Co6(H2O)2(PW9O34)2(PW6O26)]?· 31H2O (2) are generated from two tri-MII substituted B-α-[(MOH2)M2PW9O34] Keggin units connected by a hexavacant [PW6O26]11? Keggin fragment, leading to the MII-containing banana-shaped tungstophosphates. Magnetic properties of 2 show decrease of the molar magnetic susceptibility at higher temperatures results from spin-orbit coupling of CoII and antiferromagnetic interactions whereas the maximum at the lower temperatures is indicative of the ferromagnetic interactions within the trinuclear CoII spin cluster in the sandwich belt. 相似文献
17.
The phase stability, nonstoichiometry and point defect chemistry of polycrystalline Sr2FeMoO6?δ (SFMO) was studied by thermogravimety at 1000, 1100, and 1200 °C. Single-phase SFMO exists between ?10.2≤log pO2≤?13.7 at 1200 °C. At lower oxygen partial pressure a mass loss signals reductive decomposition. At higher pO2 a mass gain indicates oxidative decomposition into SrMoO4 and SrFeO3?x. The nonstoichiometry δ at 1000, 1100, and 1200 °C was determined as function of pO2. SFMO is almost stoichiometric at the upper phase boundary (e.g. δ=0.006 at 1200 °C and log pO2=?10.2) and becomes more defective with decreasing oxygen partial pressure (e.g. δ=0.085 at 1200 °C and log pO2=?13.5). Oxygen vacancies are shown to represent majority defects. From the temperature dependence of the oxygen vacancy concentration the defect formation enthalpy was estimated (ΔHOV=253±8 kJ/mol). Samples of different nonstoichiometry δ were prepared by quenching from 1200 °C at various pO2. An increase of the unit cell volume with increasing defect concentration δ was found. The saturation magnetization is reduced with increasing nonstoichiometry δ. This demonstrates that in addition to Fe/Mo site disorder, oxygen nonstoichiometry is another source of reduced magnetization values. 相似文献
18.
E. M. Limanski M. Piepenbrink E. Droste K. Burgemeister B. Krebs 《Journal of Cluster Science》2002,13(3):369-379
Two novel examples of sandwich type heteropolyanions were synthesized and characterized by X-ray crystal structure and elemental analysis as well as infrared spectroscopy. Na13[H3Cu4(H2O)2(CuW9O34)2]39H2O (1) and Na9K[Fe4(H2O)2(FeW9O34)2]32H2O (2) were prepared in aqueous solution by reaction of sodium tungstate with FeIII and CuII cations, respectively. 1 crystallizes in the monoclinic space group P21/n (a=13.054(3) Å, b=17.729(4) Å, c=20.998(4) Å, =93.50(3)°), while 2 is triclinic, space group P¯1 (a=12.316(2) Å, b=13.716(3) Å, c=14.925(3) Å, =99.36(3)°, =104.21(3)°, =101.55(3)°). Each anion consists of two [XW9O34]
n– moieties (X=FeIII, n=11 (1) and CuII, n=12 (2)) which can be described as -B-isomers of the defect Keggin anion. These units are linked via a belt of four FeIIIO6 or CuIIO6 groups. Two transition metal atoms fill their octahedral coordination sphere with one additional water ligand. 相似文献
19.
Valdecir Biondo Suzana Nóbrega de Medeiros Andrea Paesano Luis Ghivelder Bachir Hallouche João Batista Marimon da Cunha 《Solid State Sciences》2009,11(8):1444-1450
The Fex(Cr2O3)1?x system, with 0.10 ≤ X ≤ 0.80, was mechanically processed for 24 h in a high-energy ball-mill. In order to examine the possible formation of iron–chromium oxides and alloys, the milled samples were, later, thermally annealed in inert (argon) and reducing (hydrogen) atmospheres. The as-milled and annealed products were characterized by X-ray diffraction, Mössbauer spectroscopy, transmission electron microscopy and magnetization. The as-milled samples showed the formation of an Fe1+YCr2?YO4?δ nanostructured and disordered spinel phase, the α1-Fe(Cr) and α2-Cr(Fe) solid solutions and the presence of non-exhausted precursors. For the samples annealed in inert atmosphere, the chromite (FeCr2O4) formation and the recrystallization of the precursors were verified. The hydrogen treated samples revealed the reduction of the spinel phase, with the phase separation of the chromia phase and retention of the Fe–Cr solid solutions. All the samples, either as-milled or annealed, presented the magnetization versus applied field curves typical for superparamagnetic systems. 相似文献
20.
L. Gao 《Russian Journal of Coordination Chemistry》2014,40(3):138-142
Reaction of Hg(NO3)2 with 4 equivalent KI in water afford K2[HgI4]. By using K2[HgI4] as the precursor, three new heterobimetallic compounds [Ni(N-MeIm)6][HgI4] (I), [Co(N-MeIm)6][HgI4] (II), and [Cu(N-MeIm)6][HgI4] (III) have been characterized by elemental analysis, IR spectra, and the singlecrystal X-ray crystallorgraphy analysis. Three complexes are isomorphous and crystallized in monoclinic symmetry space group P21/c. The coordination around each center metal(II) atom is octahedral with six nitrogen atoms of N-MeIm ligand. Each structure contains one tetrahedral [HgI4]2? as an anion to balance the charge of the molecular. Thermogravimetry analysis indicates these complexes have the similar departure process and cyclic voltammogram exhibits a significant pair of redox peaks. 相似文献