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1.
Since the discovery of superconductivity in Sr 2CuO 2F 2+δ there has been an increased interest in ternary oxide-fluorides. Sr 2CuO 2F 2+δ is prepared via low temperature ( T = 220 °C) reaction routes. Low temperature fluorination induces an interesting structural rearrangement in the parent compound Sr 2CuO 3, which is a one-dimensional material containing linear chains of vertex sharing CuO 4 squares along the crystallographic b axis. Upon fluorination, one oxide is substituted by two fluorides and Cu 2+ becomes octahedrally coordinated by four oxides and two fluorides. The fluorinated compound Sr 2CuO 2F 2+δ displays the T-type structure (La 2CuO 4). Insertion of excess fluorine, δ, also takes place and this fluorine occupies interstitial sites in the T structure. Although the starting material Ca 2CuO 3 is isostructural to Sr 2CuO 3, Ca 2CuO 2F 2+δ displays the T′ (Nd 2CuO 4) structure due to the smaller radius of Ca 2+ compared to that of Sr 2+. The alkaline-earth palladates with the general formula A2PdO3 (A = Ba, Sr) are isostructural with the A2CuO3(A = Ca, Sr) materials. We prepared the Ba2−xSrxPdO3 (x = 0–2) series and performed low temperature fluorination, which led to the synthesis of the series Ba2−xSrxPdO2F2+δ (0 ≤ x ≤ 1.5). All the compounds in the Ba2−xSrxPdO2F2+δ series show T′ structure (Ca2CuO2F2+δ). Similarities and differences with Sr2CuO2F2+δ and Ca2CuO2F2+δ will be discussed. 相似文献
2.
A method for predicting an analytical equation of state for polymer mixtures and blends from surface tension and liquid state density at normal (ordinary) temperature ( γn, ρn), as scaling constants, is presented. B2( T) follows a promising corresponding-states principle. Calculation of ( T) and b( T), the two other temperature-dependent constants of the equation of state, are made possible by scaling. As a result, γn and ρn are sufficient for determination of thermophysical properties of polymer mixtures and blends. We applied the procedure to predict liquid density of poly(ethylene glycol) (PEG-200) + 1-octanol solutions and poly(propylene glycol) (PPG) + poly(ethylene glycol) (PEG-200) blends at compressed state with temperature range from 298.15 to 338.15 K and pressures up to 40 MPa. In this work, the ISM EoS is extended to polymer mixtures and blends as well as pure case without proposing any mixing rule. 相似文献
3.
Hydrogen and fluorine addition reactions with C 28( Td) have been investigated by the density function theory method at B3LYP/6-31G level. The interaction potential between C 28( Td) and atom X (X=H and F) shows that there are three possible stable isomers of C 28( Td)X (X=H and F) and the average binding energy calculations suggest that C 28( Td)H 4 is the most stable hydrogen adduct among C 28( Td)H n ( n=1–28). Furthermore, by comparisons of the energy between C 28( Td)H and C 28( Cs)H we found that the former are more stable than the later, and the structural and energy analysis further indicate that C 28( Cs)H is only with a small distortion of C 28( Td)H symmetry. In addition, the transition states, as well as reaction pathways of X transfer reactions between different key points on C 28( Td) representative patch are given to explore the possible reaction mechanism. 相似文献
4.
A series of Ce xPr 1−xO 2−δ mixed oxides were synthesized by a sol–gel method and characterized by Raman, XRD and TPR techniques. The oxidation activity for CO, CH 3OH and CH 4 on these mixed oxides was investigated. When the value x was changed from 1.0 to 0.8, only a cubic phase CeO 2 was observed. The samples were greatly crystallized in the range of the value x from 0.99 to 0.80, which is due to the formation of solid solutions caused by the complete insertion of Pr into the CeO 2 crystal lattices. Raman bands at 465 and 1150 cm −1 in Ce xPr 1−xO 2−δ samples are attributed to the Raman active F 2g mode of CeO 2. The broad band at around 570 cm −1 in the region of 0.3 ≤ x ≤ 0.99 can be linked to oxygen vacancies. The new band at 195 cm −1 may be ascribed to the asymmetric vibration caused by the formation of oxygen vacancies. The TPR profile of Pr 6O 11 shows two reduction peaks and the reduction process is followed: . The reduction temperature of Ce xPr 1−xO 2−δ mixed oxides is lower than those of Pr 6O 11 or CeO 2. TPR results indicate that Ce xPr 1−xO 2−δ mixed oxides have higher redox properties because of the formation of Ce xPr 1−xO 2−δ solid solutions. The presence of the oxygen vacancies favors CO and CH 3OH oxidation, while the activity of CH 4 oxidation is mostly related to reduction temperatures and redox properties. 相似文献
5.
The radical copolymerization of (2,6-diphenyl) phenyl methacrylate (1) with methyl methacrylate in DMF with AIBN at 70°C has the reactivity ratios r1 = 0.071 and r2 = 1.42, from which Q1 = 1.45 and e1 = 1.20. The copolymers had Mns in the range of 10,000–40,000 and Tgs ranging from 406 to 480 K from which the hypothetical Tg for poly-1 was deduced as 500 K (227°C). Unlike 1, (2,6-diphenyl) phenyl acrylate could be polymerized to oligomers with Mn of the order of 2500. 相似文献
6.
The 127I NQR, IR absorption and Raman spectra of impurity-doped and mixed lithium iodate Li 1−xH xIO 3 crystals grown from water solutions with different LiIO 3/HIO 3 ratios were investigated depending on the content of the impurity hydrogen x. The NQR results suggested that, at small concentration of doping iodic acid x<0.22, the lattice dynamics of the crystal grown from water solution changes significantly though the crystal retains hexagonal symmetry. Spectroscopic studies are compatible with average hexagonal symmetry of the grown doped crystals. From the results of Raman studies at room temperature and 100 K, the concentration range of hydrogen dopant 0.22< x<0.36 was found where disordered solid solution crystals Li 1−xH xIO 3 are formed. 相似文献
7.
采用氧化还原法合成了层状锰氧化物(OL),并以OL为载体采用离子交换法制备了不同Cu负载量的Cu_x/OL催化剂。利用X射线衍射(XRD)、电子扫描电镜(SEM)、N_2吸附/脱附、H_2~-程序升温还原(H_2-TPR)、TG(热重)、X射线光电子能谱(XPS)、O_2-程序升温脱附(O_2-TPD)等技术对所制催化剂进行结构和织构表征,并对其催化氧化CO及乙酸乙酯活性进行了评价。结果表明,OL具有典型的层状锰氧化物结构,适量掺杂Cu对OL的结构和织构影响不大,但Cu的掺杂明显影响Cu_x/OL的还原性、氧移动性及催化剂表面Cu~(2+)/CuO、(Mn~(2+)+Mn~(3+))/Mn~(4+)和Oads/Olatt的比例。Cu_x/OL的催化性能与以上因素密切相关。在Cu_x/OL样品中,Cu_5/OL催化剂具有最佳的催化活性(CO催化氧化,T_(50)=70°C和T_(90)=100°C;乙酸乙酯催化氧化T50=160°C,T90=200°C)。同时,Cu_5/OL催化剂具有最佳的还原性能、氧移动性能和最多的Cu~(2+)、(Mn~(2+)+Mn~(3+))和表面吸附氧浓度。Cu_x/OL催化性能与铜锰之间相互作用、还原性和氧移动性能密切相关。 相似文献
8.
Scientific interest, technological promise and increased availability of highly enriched isotope have led to a sharp rise in the number of experimental and theoretical studies with isotopically controlled crystals. Isotope pure compounds are really the material of future mankind. LiH has a giant isotope effect. Therefore, this review in the first step is devoted to some peculiarities of exciton states in isotope pure and mixed crystals of LiH. Excitons are the energetically lowest excitations of the electronic system in an ideal, crystallized insulator (semiconductor) at zero temperature. It is a collective excitation which has the full translational symmetry of the crystal lattice. For the first time a systematic analysis of experimental results is presented of isotopic and chemical effects on the exciton states observed in LiH xD 1−x crystals of various isotopic (and chemical) composition (0≤x≤1) using low temperature optical and luminescence spectroscopy. LiH (LiD) is an direct band-gap material with an energy gap 4.992 (5.095) eV at low temperature. Substituting a light isotope with a heavy one (or H→F) increases the interband transition energy ( Eg) and the binding energy ( Eb) of the Wannier–Mott exciton as well as the magnitude of the longitudinal–transverse splitting. The nonlinear variation of Eg, Eb with the isotope (or F) concentration is due to the compositional disordering of the crystal lattice and is consist with the concentration dependence of line half-width in exciton reflection and luminescence spectra. The free exciton luminescence spectrum of the LiH (LiH xD 1−x, LiH xF 1−x; 0≤x≤1) crystals under optical (X-ray) excitations consists of a narrow zero-phonon line and its more wider 5LO replicas. At 100 % substitution of hydrogen by deuterium the energy shift of the maximum of zero-phonon line is the following: Δ E= En=1s(LiD)− En=1s(LiH)=95 meV. The shift of the emission line maximum of 2LO replica overlaps the energetical interval of ≤200meV. The nonlinear dependence of the free exciton luminescence (especially LiH xF 1−x (LiD xF 1−x)) intensity on the excitation density allows to consider these crystals as potential solid state lasers in the UV part of spectrum. It is shown that potential fluctuation due to compositional disorder of alloy have a strong effect on both the exciton broadening and the band-gap energy shift. The review closes with a brief discussion of the present and future applications of these crystals. 相似文献
9.
The effect of the type of epoxidized butadiene/styrene block copolymer [ESBS; linear (B/S) or radial (E(B/S) n), containing 0–27% of epoxy groups] on the thermal dehydrochlorination of poly (vinyl chloride) (PVC)-ESBS blends (ESBS content 10%) was investigated in the temperature range 170–180 °C, under a non-oxygen atmosphere. Thermal stability of the PVC-ESBS blends was estimated on the basis of induction time, t0, and maximum rate of hydrochloride emission, Vmax from the system. It was found that, for a similar degree of epoxidation of the SBS copolymer, the induction time i.e. the time after which emission of HCl begins, is longer in the series PVC < PVC-SBS < PVC-EB/S < PVC-E(B/S) n, and the same is true for thermal stability. However, the maximum rate of emission of HCl is lowest in the case of PVC-EB/S blends, in the range of molar ratios from 0.5 to 2.0 × 1 O−2. On the basis of the dependence Vmax = f( EB/ VC), it was found that there is a certain content of epoxidized butadiene (EB) units in a mixture which causes the optimum stability of poly (vinyl chloride) during heating. During thermal destruction of the PVC-ESBS blends, the HC1 evolved undergoes addition both to epoxy fragments and to double bonds. The degree of conversion of EB units in time t0 is 20% at 170 °C and 30% at 180 °C. The glass transition temperature, Tg, of PVC in the PVC-ESBS blends shifts towards higher temperatures by about 6–8 °C, proving the existence of crosslinking processes during moulding of the blends. The epoxidized butadiene/styrene radial block copolymer, E(B/S) n, is a better thermal stabilizer of PVC than the linear EB/S copolymer. 相似文献
10.
The Ag + photoreduction by graphitic carbon nitride(g-CN) materials in a high concentration of Ag + solution is reported, and a series of colorful Ag/g-CN composites is prepared and characterized. The chromatic change correlates to the carbon nitride materials synthesized at different heating temperatures(CN T, where T means heating temperature), taking advantage of the different photocatalytic activities of different CN T. The mechanism beneath this phenomenon is attributed to two factors:the particle size of Ag NPs and the coordinate effect of Ag NPs on CN T sheets. Interestingly, the multi-colors of Ag/g-CN composites display only on the CN T materials synthesized from heating melamine-cyanuric acid precursor, but not on the CN T from heating pure melamine. The color of the as-prepared Ag/g-CN composites can endure the corrosion of HNO 3 and ethanol, which shows a good chemical stability and may hint its application as chromophores. 相似文献
11.
Excess molar enthalpies HE and excess molar volumes VE have been measured, as a function of mole fraction x1, at 298.15 K and atmospheric pressure for the five liquid mixtures ( x11,4-C 6H 4F 2 + x2n-C lH 2l+2), l = 7, 8, 10, 12 and 16. In addition, HE and excess molar heat capacities CPE at constant pressure have been determined for the two liquid mixtures ( x1C 6F 6 + x2n-C lH 2l+2), l = 7 and 14, at the same temperature and pressure. The instruments used were flow microcalorimeters of the Picker design (the HE version was equipped with separators) and a vibrating-tube densimeter, respectively. The excess enthalpies of the five difluorobenzene mixtures are all positive and quite large; they increase with increasing chain length l of the n-alkane from HE(x1 = 0.5)/(J mol−1) = 1050 for l = 7 to 1359 for l = 16. The corresponding excess volumes VE are all positive and also increase with increasing l: VE(x1 = 0.5)/(cm3 mol−1) = 0.650 for l = 7 and 1.080 for l = 16. Interestingly, the excess enthalphies of the corresponding mixtures with hexafluorobenzene are only about 5% larger, whereas the excess volumes of (x1C6F6 + x2n-ClH2l+2) are roughly twice as large as those of their counterparts in the series containing 1,4-C6H4F2. Specifically, at 298.15 K HE(x1 = 0.5)/(J mol−1) = 1119 for (x1C6F6 + x2n-C7H16) and 1324 for (x1C6F6 + x2n-C14H30), and for the same mixtures VE(x1 = 0.5)/(cm3 mol−1) = 1.882 and 2.093, respectively. The excess heat capacities for both systems are negative and of about the same magnitude as the excess heat capacities of mixtures of fluorobenzene with the same n-alkanes (Roux et al., 1984): CPE(x1 = 0.5)/(J K−1 mol−1) = −1.18 for (x1C6F6 + x2n-C7H16), and −2.25 for (x1C6F6 + x2n-C14H30). The curve CPE vs. (x1 for x1C6F6 + x2n-C14H30) shows a sort of “hump” for x1 0.5, which is presumed to indicate emerging W-shape composition dependence at lower temperatures. 相似文献
12.
The equilibrium structures and relative stabilities of BN-doped fullerenes C 70−2x(BN) x ( x=1–3) have been studied at the AM1 and MNDO level. The most stable isomers of C 70−2x(BN) x have been found out and their electronic properties have been predicted. The calculation results show that the BN substituted fullerenes C 70−2x(BN) x have considerable stabilities, though they are less stable than their all carbon analog. For C 68BN, the isomers whose BN is located in the most chemically active bonds of C 70 (namely B and A) are among the most stable species, of which B is predicted to be the ground state. The stabilities of C 68BN decrease and the dipole moments increase with increasing the distance between the heteroatoms. For C 66(BN) 2, the lowest energy species is the isomer in which the B–N–B–N bond is formed; For C 64(BN) 3, the most stable species should have three BN units located in the same hexagon to form B–N–B–N–B–N ring. The ionization potentials and the affinity energies of the most stable species of BN-doped C 70 are almost the same as those of C 70 because of the isoelectronic relationship. The ionization potentials and affinity energies depend on the relative position of the heteroatoms in C 68BN, the chemical reactivities of the isomers whose heteroatoms are well separated should differ significantly from their all carbon analog. 相似文献
13.
MXene是一种新型的二维析氢催化材料,其表面容易被亲水基团O和OH混合覆盖。我们基于第一性原理计算的方法,研究了M_2XO_(2-2x)(OH)_(2x)(M=Ti,V;X=C,N)的析氢催化活性。计算结果显示,M_2XO_(2-2x)(OH)_(2x)的析氢催化活性与其表面OH覆盖率(X)密切相关。对Ti_2CO_(2-2x)(OH)_(2x)来说,OH覆盖率不超过1/3时,具有优异的析氢催化活性。对Ti_2NO_(2-2x)(OH)_(2x)、V_2CO_(2-2x)(OH)_(2x)和V_2NO_(2-2x)(OH)_(2x)来说,OH覆盖率分别达到4/9、1/3和5/9时,才具有最佳的析氢催化活性。接着,电荷分析显示OH覆盖率会显著影响M_2XO_(2-2x)(OH)_(2x)活性位点O基团的电荷量。最后,我们从态密度的角度揭示了析氢催化活性变化的原因,即活性位点O基团的氧化性随OH覆盖率的增大而被削弱。因此,本文提出了调节表面OH覆盖率来获取M_2XO_(2-2x)(OH)_(2x)最佳析氢催化活性状态的方法,这在工业制氢生产过程中具有重要的应用价值。 相似文献
14.
Ferrocenyl-1,2-diketones FcCOCOR, 3, [Fc = (C 5H 5)Fe(C 5H 4)] can be prepared by oxidation of acylferrocenes FcCOCH 2R or, more efficiently, by oxidation of the isomeric ketones FcCH 2COR, 2. The ketones 2 are in turn readily synthesized from the salt (FcCH 2PPh 3) +I − via the acylated salts [FcCH(COR)PPh 3] +I −. The haloacylferocenes FcCOCCl x H 3−x ( x = 1, 2, 3, of which the x = 2 example is synthetically equivalent to a diketone) are synthesized by Friedel—Crafts acylation of ferrocene using CCl xH 3−xCOCl/AlCl 3, but the reaction proceeds via two parallel pathways, one giving the normal acyl derivatives FcCOCCl xH 3−x and the other giving the reduced products FcCOCCl x−1H 4−x. Two diketones FcCOCOFc 3b and FcCOCOC 6H 4Ph 3c have been structurally characterised by single-crystal X-ray diffraction. 相似文献
15.
制备了V取代的磷钼酸H 3+xPMo 12-xV xO 40( x=0,1,2)及1-丁基-3-甲基咪唑溴盐离子液体([C 4mim]Br),并采用离子交换的方法制备了系列杂化材料([C 4mim]3+xPMo 12-xV xO 40, x=0,1,2);采用X射线衍射(XRD)、傅里叶变换红外光谱(FT-IR)、紫外-可见漫反射光谱(UV-Vis DRS)对所制备样品进行了表征;以H 2O 2为氧化剂,考察了所得样品催化苯羟基化制苯酚的活性。结果表明,和相应的离子液体及杂多酸相比,杂化材料的催化活性得到了很大的提高,尤其是催化剂[C 4mim] 5PMo 10V 2O 40,在优化后的条件下,苯的转化率可达到21%,苯酚的选择性在99%以上。而且,该催化剂具有很好的可重复使用性,连续使用五次后,苯的转化率和苯酚的选择性没有明显降低。 相似文献
16.
The Flory–Huggins interaction parameter χ( ri) is considered as dependent on the chain length of a polymer. Therefore, a modified free energy expression of Flory–Huggins theory is obtained for the polydisperse polymer solutions. Based on this modified free energy expression and the thermodynamics of Gibbs, the expression of spinodal for polydisperse polymer solutions is obtained. For a given χ( ri) according to de Gennes, the spinodals are calculated for polydisperse polymer solutions at different molecular weights and their distributions. It is found that all the interested variables rn, rw, rz and molecular weight distribution have an effect on the spinodal for polydisperse polymer solutions, where the effect of changing rw is much greater than that of changing rn, rz and molecular weight distribution. 相似文献
17.
We studied the isotope, pressure and doping effects on the pseudogap temperature T* by neutron spectroscopic experiments of the relaxation rate of crystal-field excitations in La 1.96−xSr xHo 0.04CuO 4 ( x = 0.11, 0.15, 0.20, 0.25) on the high-resolution time-of-flight spectrometer FOCUS at SINQ, PSI. We found clear evidence for the opening of a pseudogap in the underdoped regime at T*( x = 0.11) = (82.2 ± 1.2) K as well as in the overdoped and the heavily overdoped compounds at T*( x = 0.2) = (49.2 ± 0.7) K and at T*( x = 0.25) = (46.5 ± 0.5) K, respectively. Furthermore, we investigated the effect of oxygen isotope substitution on the pseudogap, the experiments revealed Δ T*( x = 0.11) = (21.3 ± 5.2) K and Δ T*( x = 0.2) = (4.5 ± 1.3) K. The application of hydrostatic pressure (0.8 and 1.2 GPa) on the optimally doped compound ( x = 0.15) results in a downward shift of d T*/d p = (−5.9 ± 1.6) K/GPa. 相似文献
18.
In this communication, we report on the synthesis and characterization of a series of compounds with the general composition Ce 1−xSr xO 2−x (0.0≤ x≤1.0), to establish a detailed phase relation in the CeO 2–SrO system. The X-ray diffraction (XRD) pattern of the each product was refined to determine the solid solubility and the homogeneity range. The solid solubility limit of SrO in CeO 2 lattice, under the slow cooled conditions, is represented as Ce 0.91Sr 0.09O 1.91 (i.e. 9 mol% of SrO). A careful delineation of the phase boundary revealed that the stoichiometric SrCeO 3, in fact, contains a little amount of CeO 2 also. The mono-phasic compound could be obtained at the nominal composition Sr 0.55Ce 0.45O 1.45. The nominal composition Sr 2CeO 4, under the heat treatment used in the present investigation, was a bi-phasic mixture of SrCeO 3 and SrO. No new ordered phases were obtained in this system. 相似文献
19.
The applicability of positron annihilation spectroscopy for chemical structural problems is demonstrated by two examples: For the swelling dynamics of an amphiphilic polymer network, very quick structural changes were indicated by positronium lifetime parameters at very low swelling ratios and a hydration mechanism was proposed accordingly. For the series [Fe xZn 1−x(propyltetrazole) 6](BF 4) 2( x=1, 0.6, 0.4, 0.1, 0), changes in the dynamic structure were revealed by positronium lifetime spectroscopy. For compounds of x>0, temperature-induced spin-crossover was detected. 相似文献
20.
We report on the infrared spectra of binary di-palmitoyl-phosphatidyl-ethanolamine-cardiolipin (DPPE 1−xCLP x) monolayers and multilamellar vesicles as a function of CLP molar fraction x and temperature T. These data, which clearly show the presence of, at least, two kind of lipid domains with different thermodynamic stability and ordering of the lipid acyl chains, are consistent with similar domains observed in Langmuir–Blodgett films of the same binary system. Infrared results suggest the presence of lateral phase separation phenomena both in the bilayers and in the monolayers build up with this binary lipid mixture. These results further support the hypothesis that, within these structures, DPPE 1−xCLP x molecules, for given values of x, are organized in a superlattice as shown by thermodynamic and AFM measurements. 相似文献
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