共查询到20条相似文献,搜索用时 31 毫秒
1.
Yassine Bessekhouad Yamina Gabes Aissa Bouguelia Mohamed Trari 《Journal of Materials Science》2007,42(15):6469-6476
CuMnO2 is prepared via Cu+ → Li+ exchange in molten copper (I) chloride. It crystallizes in a monoclinic structure (SG C2/m) where the MnO6 octahedra elongation is ascribed to the Yahn–Teller (Y–T) effect of Mn3+ ions. From chemical analysis, the oxide is more accurately formulated as CuMnO2.01. Above 250 °C, it undergoes a reversible transition to spinel Cu
x
Mn3−x
O4 and beyond 940 °C it converts back to Cu1.1Mn0.9O2. Extrapolation of high-temperature magnetic data indicates T-intercept θ
p of −450 K and an effective moment of 5.22 μB, consistent with strong antiferromagnetism in the basal plans and high spin (HS) configuration Mn3+. This value is slightly larger than that of the spin only moment, a behavior ascribed to Cu2+ originating from oxygen insertion. As prepared, CuMnO2 displays p-type conductivity with an activation energy of 0.16 eV. Most holes generated upon band gap excitation are trapped
on Cu+ ions and the conduction occurs by small polarons hopping between neighboring sites. The linear increase of thermopower for
Cu1.05Mn0.95O2 with temperature indicates a hole mobility μ300 K (3.5 × 10-6 cm2 V−1 s−1) thermally activated. CuMnO2 is made p- and n-type and the difference in the carriers mobilities is attributed to different oxygen polyhedra. The title
oxide, characterized photo electrochemically, exhibits a pH-insensitive flat band potential (+0.13 VSCE). The valence band, located at 5.3 eV below vacuum, is made up of Cu 3d orbital. As application, the powder showed a good
performance for the H2-photo evolution.
相似文献
Mohamed TrariEmail: |
2.
S. M. Rao J. K. Srivastava M. K. Wu B. H. Mok C. L. Chen M. C. Ling H.-L. Liu Y. Y. Chen J. C. Ho 《Journal of Superconductivity and Novel Magnetism》2011,24(4):1249-1262
We report here SQUID (magnetization) measurements, along with supporting specific heat, Raman, SEM (scanning electron microscope),
EDX (energy dispersive X-ray) and XRD (X-ray diffraction) measurements, on Cu-doped and undoped double perovskite Sr22+Y3+Ru5+O62-\mathrm{Sr}_{2}^{2+}\mathrm{Y}^{3+}\mathrm{Ru}^{5+}\mathrm{O}_{6}^{2-} (abbreviated as SrY2116) system grown as single crystal using high-temperature solution growth technique. These measurements
show the undoped system to be a nonmetallic (insulating) spin glass (SG) and the ∼5–30% Cu-doped (i.e. Cu-concentration/(Cu + Ru-concentration)
∼5–30%) system to be a spin glass superconductor (SGSC) with T
c (critical temperature) ∼28–31 K and superconducting volume fraction, f
sc∼2.2–9%. To mention, similar measurements done on undoped and Cu-doped BaY2116 and BaPr2116 systems show for them the same
(SG, SGSC) behaviors. However they show a decrease in T
c and f
sc when diamagnetic Y3+ ions are replaced by Pr3+ spins, presumably due to enhanced internal pair breaking, and also decreased Cu–O–Cu overlap, owing to Pr3+ presence; these phenomena are known to exist in the Pr123 compound, PrBa2Cu3O7−δ
(δ∼0), due to ∼10% of Pr3+ ions having tendency to occupy Ba2+ sites. Measurements done on undoped and Cu-doped SrHo2116 show similar SG and SGSC properties. Further, the undoped and Cu-doped
SrY2116 crystals grown by hydrothermal growth technique (i.e., grown using lower temperature and high pressure) show same
behaviors. From these investigations it can be said that the undoped Ru-double perovskites (A2BB′O6, B′=Ru) are SG systems and that Cu-doped Ru-double perovskites (A2BB′O
δ
, δ∼6, B′=Ru1−x
Cu
x
, 0<x≲0.3) are SG superconductors (SGSCs). Results are discussed. 相似文献
3.
CdGa2S4 single crystals have been grown from a presynthesized source material by closed-tube iodine vapor transport, and their X-ray
dosimetric properties have been studied. Their X-ray sensitivity coefficient K ranges from K = 1.26 × 10−11 to 1.39 × 10−10 A min/(V R) at effective X-ray hardnesses V
a = 25–50 keV and dose rates E = 0.75–78.05 R/min, and increases with X-ray dose. The K(V
a) curve has a negative slope, in contrast to the K(E) curve. The photocurrent-dose curves of the CdGa2S4 single crystals demonstrate that the steady-state X-ray photocurrent is a power-law function of X-ray dose rate: ΔI
E,0 ∼ E
α
. With increasing V
a, the slope of the curves sharply decreases and α approaches unity. 相似文献
4.
Tianxiang Zhou Shanshan Mo Shuangli Zhou Wujun Zou Yingliang Liu Dingsheng Yuan 《Journal of Materials Science》2011,46(10):3337-3342
A quick and facile microwave method has been employed to prepare Mn3O4/worm-like mesoporous carbon (Mn3O4–MC) composites. Structural and morphological characterizations of worm-like mesoporous carbon and Mn3O4–MC composites have been carried out using X-ray diffraction, transmission electron microscopy, N2 adsorption–desorption, and electrochemical measurement. Cyclic voltammograms demonstrate that the Mn3O4–MC composites perform improved capacitive behavior at the range of −0.8~0.2 V (vs. Hg/HgO electrode) with reversibility.
The Mn3O4–MC composite electrode possesses an enhanced specific capacitance of 266 F g−1 at a sweep rate of 1 mV s−1. 相似文献
5.
Josef Jirák Ladislav Koudelka Jaroslav Pospíšil Petr Mošner Lionel Montagne Laurent Delevoye 《Journal of Materials Science》2007,42(20):8592-8598
Glasses of the ternary system ZnO–Bi2O3–P2O5 were prepared and studied in two compositional series 50ZnO–xBi2O3–(50 − x)P2O5 and (50 − y)ZnO–yBi2O3–50P2O5. Two distinct glass-forming regions were found in the 50ZnO–xBi2O3–(50 − x)P2O5 glass series with x = 0–10 and 20–35 mol.% Bi2O3. All prepared Bi2O3-containing glasses reveal a high chemical durability. Small additions of Bi2O3 (∼5 mol.%) improve thermal stability of glasses. All glasses crystallize on heating within the temperature range of 505–583 °C.
Structural studies by Raman and 31P MAS NMR spectroscopies showed the rapid depolymerisation of phosphate chains within the first region with x = 0–15 and the presence of isolated Q0 phosphate units within the second region with x = 20–35. Raman studies showed that bismuth is incorporated in the glass structure in BiO6 units and their vibrational bands were observed within the spectral region of 350–700 cm−1. The evolution of properties and the spectroscopic data are both in accordance with a network former effect of Bi2O3. 相似文献
6.
We have synthesized materials based on a silver titanium phosphate with partial substitution of tri-, tetra-, or pentavalent
cations for titanium: Ag1±x
Ti2−x
M
x
(PO4)3 (M = Nb5+, Ga3+) and AgTi2−x
Zr
x
(PO4)3. The materials have been characterized by X-ray diffraction and impedance spectroscopy and have been shown to have small
thermal expansion coefficients. Their ionic conductivity has been determined. Silver ions in these materials are difficult
to replace with protons. 相似文献
7.
Sv. Ivanova E. Zhecheva D. Nihtianova R. Stoyanova 《Journal of Materials Science》2011,46(22):7098-7105
XRD-pure Li4Mn5O12 spinels are obtained below 600 °C from oxalate and acetate precursors. The morphology consists of nanometric particles (about
25 nm) with a narrow particle size distribution. HRTEM and electron paramagnetic resonance (EPR) spectroscopy of Mn4+ are employed for local structure analysis. The HRTEM images recorded on nano-domains in Li4Mn5O12 reveal its complex structure. HRTEM shows one-dimensional structure images, which are compatible with the (111) plane of
the cubic spinel structure and the (001) plane of monoclinic Li2MnO3. For Li4Mn5O12 compositions annealed between 400 and 800 °C, EPR spectroscopy shows the appearance of two types of Mn4+ ions having different metal environments: (i) Mn4+ ions surrounded by Li+ and Mn4+ and (ii) Mn4+ ions in Mn4+-rich environment. The composition of the Li+, Mn4+-shell around Mn4+ mimics the local environment of Mn4+ in monoclinic Li2MnO3, while the Mn4+-rich environment is related with that of the spinel phase. The structure of XRD-pure Li4Mn5O12 comprises nano-domains with a Li2MnO3-like and a Li4/3−x
Mn5/3+x
O4 composition rather than a single spinel phase with Li in tetrahedral and Li1/3Mn5/3 in octahedral spinel sites. The annealing of Li4Mn5O12 at temperature higher than 600 °C leads to its decomposition into monoclinic Li2MnO3 and spinel Li4/3−x
Mn5/3+x
O4. 相似文献
8.
The thermoelectric power and d.c electrical conductivity of x V2O5⋅40CaO⋅(60−x)P2O5 (10 ≤ x ≤ 30) glasses were measured. The Seebeck coefficient (Q) varied from +88 μ V K−1 to −93 μV K−1 as a function of V2O5 mol%. Glasses with 10 and 15 mol% V2O5 exhibited p-type conduction and glasses with 25 and 30 mol% V2O5 exhibited n-type conduction. The majority charge carrier reversal occurred at x = 20 mol% V2O5. The variation of Q was interpreted in terms of the variation in vanadium ion ratio (V5 +/V4 +). d.c electrical conduction in x V2O5⋅40CaO⋅(60−x)P2O5 (10 ≤ x ≤ 30) glasses was studied in the temperature range of 150 to 480 K. All the glass compositions exhibited a cross over from
small polaron hopping (SPH) to variable range hopping (VRH) conduction mechanism. Mott parameter analysis of the low temperature
data gave values for the density of states at Fermi level N (EF) between 1.7 × 1026 and 3.9 × 1026 m−3 eV−1 at 230 K and hopping distance for VRH (RVRH) between 3.8 × 10−9m to 3.4 × 10−9 m. The disorder energy was found to vary between 0.02 and 0.03 eV. N (EF) and RVRH exhibit an interesting composition dependence. 相似文献
9.
The substituted nonstoichiometric perovskite Pr1−x
Ca
x
MnO3−y
compounds have been synthesized by a standard combustion technique, which show uniphase solid solutions. The all samples
of the Pr1−x
Ca
x
MnO3−y
system show an orthorhombic crystal system and the cell volumes are decreased with increasing the larger amounts of substituted
atoms or the increasing x values. The mixed valence of Mn ions is identified by the XAS (XANES/EXAFS) spectroscopy and the amounts of Mn4+ ions are determined by an iodometric titration method. Nonstoichiometric chemical formulas of the Pr1−x
Ca
x
Mn1−τ3+Mnτ4+O3−y
compounds have been obviously formulated. Magnetic properties are investigated by SQUID and thus the Pr1−x
Ca
x
MnO3−y
(x = 0.4, 0.6, and 0.8) compounds show the transition from antiferromagnetic state to paramagnetic state. The Pr1−x
Ca
x
MnO3−y
(x = 0.0, 0.2, and 1.0) compounds show the transition from ferromagnetic state to paramagnetic state. The facts that Mn4+ contents play important roles in the magnetic ordering have been found out. The transport properties have been studied by
the DC electrical conductivity measurement under magnetic fields of 0 G and 3 kG. Maximum and minimum MR ratios are 1016%
of the Pr0.6Ca0.4MnO2.846, and −77.5% of the PrMnO3.021 compound, respectively. 相似文献
10.
B. K. Sarkar A. S. Verma R. C. Gupta K. Singh 《International Journal of Thermophysics》2010,31(3):620-629
Using photoacoustic spectroscopy, the composition-dependent absorption coefficient (α), thermal diffusivity (σ), and optical bandgap (E
g) of Zn1−x
Mn
x
Te diluted magnetic semiconductor have been measured. For higher Mn compositions, the absorption spectrum of the Zn–Mn–Te
system consists of three regions, viz., the high absorption region, the exponential region, and the weak absorption tail.
The bandgap follows a nonlinear variation with composition, showing a downward bowing with a minimum around x = 0.31 as a consequence of the electro-negativity difference between the substituted atoms. The composition-dependent band-edge
effective mass of the carriers does not show the bowing behavior indicating that the momentum matrix is not the same for all
the Zn1−x
Mn
x
Te alloys due to different lattice constants. The absorption spectra show that the transition is allowed and direct. 相似文献
11.
This paper describes the synthesis and spectroscopic studies of the glass system, 20Na2O-(20-x) ZnO-xZnF2-60B2O3(x = 0, 5, 10, 15, 20), prepared by melt quenching method. The analyses of DSC and XRD did not show the crystallinity of the
glass sample. 11B MAS-NMR shows the presence of sharp peak around −14 ppm. From the IR studies, the broadening of the peak around 1200–1400
and 800–1100 cm−1 shows the presence of mixed linkages like B-O-B, B-O-Zn in the network. 相似文献
12.
Yogesh Sharma N. Sharma G. V. Subba Rao B. V. R. Chowdari 《Bulletin of Materials Science》2009,32(3):295-304
Cadmium ferrite, CdFe2O4, is synthesized by urea combustion method followed by calcination at 900°C and characterized by X-ray diffraction (XRD),
scanning electron microscopy (SEM), high-resolution transmission electron microscopy (HR-TEM) and selected area electron diffraction
(SAED) techniques. The Li-storage and cycling behaviour are examined by galvanostatic cycling, cyclic voltammetry (CV) and
impedance spectroscopy in the voltage range, 0·005–3·0 V vs Li at room temperature. CdFe2O4 shows a first cycle reversible capacity of 870 (± 10) mAhg−1 at 0·07C-rate, but the capacity degrades at 4 mAhg−1 per cycle and retains only 680 (± 10) mAhg−1 after 50 cycles. Heat-treated electrode of CdFe2O4 (300°C; 12 h, Ar) shows a significantly improved cycling performance under the above cycling conditions and a stable capacity
of 810 (± 10) mAhg−1 corresponding to 8·7 moles of Li per mole of CdFe2O4 (vs theoretical, 9·0 moles of Li) is maintained up to 60 cycles, with a coulombic efficiency, 96–98%. Rate capability of
heat-treated CdFe2O4 is also good: reversible capacities of 650 (± 10) and 450 (± 10) mAhg−1 at 0·5 C and 1·4 C (1 C = 840 mAg−1) are observed, respectively. The reasons for the improved cycling performance are discussed. From the CV data in 2–15 cycles,
the average discharge potential is measured to be ∼0·9 V, whereas the charge potential is ∼2·1 V. Based on the galvanostatic
and CV data, ex situ-XRD, -TEM and -SAED studies, a reaction mechanism is proposed. The impedance parameters as a function of voltage during the
1st cycle have been evaluated and interpreted.
Dedicated to Prof. C N R Rao on his 75th birthday, and his contributions to science for the past 56 years 相似文献
13.
Series of glass based on the (80 − x)TeO2–20ZnO–(x)Er2O3 system (0.5 mol% ≤ x ≤ 2.5 mol%) has successfully been made by melt quenching technique. The optical properties of glass have been investigated
by means of IR and Raman spectroscopy. It is observed that as the Er2O3 content is being increased, the sharp IR absorption peaks are consistently shifted from 650 to 672 cm−1 while the Raman shift intensity around 640–670 cm−1 is decreases but increases around 720–740 cm−1. It is found out that both phenomenons are related to the structural changes between the stretching vibration mode of TeO4 tbp and TeO3 tp, and bending vibration mode of Te–O bonds in the glass linkages. 相似文献
14.
K. M. Reddy A. Punnoose 《Journal of Materials Science: Materials in Electronics》2007,18(11):1137-1142
We report the development of ferromagnetism in ∼30 nm sized well-characterized Ti1−x
Co
x
O2 powders with x = 0.00015–0.006 and its absence for x > 0.006. In addition, these studies show the effect of Co doping on the structural stability and anatase to rutile phase
transformation. X-ray diffraction data of samples synthesized by a wet chemical method and annealed at 450 °C indicate a limited
solubility of ∼1.2% for Co in the anatase TiO2 matrix, and with further increase, the CoTiO3 phase is formed along with increased presence of rutile TiO2. The bandgap (∼3.23 eV) of the anatase TiO2 remained almost unchanged for x < 0.006, but decreased rapidly for x ≥ 0.006 approaching 2.8 eV for x = 0.03. The magnetic data from Ti1−x
Co
x
O2 samples with x = 0.006 showed a coercivity H
c ∼ 150 Oe and a weak magnetic moment of 0.2 μB/ion at 300 K. The ferromagnetism of Ti0.994Co0.006O2 with open hysteresis loops continue up to a high superparamagnetic blocking temperature T
B ∼ 675 K, above which a superparamagnetic behavior was observed. Systematic changes in the structural, magnetic and optical
properties suggest that Co doping is an excellent method to tailor the physical properties of TiO2 nanoparticles. 相似文献
15.
We have performed partial HSO4− substitution in CsH2PO4 and studied the associated structural changes and the proton conductivity of the resultant (CsH2PO4)1 − x
(CsHSO4)
x
solid solutions in the range x = 0.01–0.3. The results indicate that, at room temperature, the solid solutions are disordered. In the range x = 0.01–0.1, they are isostructural with the low-temperature phase of CsH2PO4 (sp. gr. P21/m), and their unit-cell parameters increase with x, whereas in the range x = 0.15–0.3 the solid solutions are isostructural with the high-temperature, cubic phase of CsH2PO4 (Pm3m), and their unit-cell parameter decreases. The conductivity of the (CsH2PO4)1 − x
(CsHSO4)
x
solid solutions with x ≤ 0.3 depends significantly on their composition and increases at low temperatures by up to four orders of magnitude, approaching
that of the superionic phase of CsH2PO4 in the range x = 0.15–0.3 because of the hydrogen bond weakening and increased proton mobility. The conductivity of the superionic phase
decreases with increasing x by no more than a factor of 1.5–2, and the superionic phase transition, which occurs at 231°C in CsH2PO4, shifts to lower temperatures and disappears for x ≥ 0.15. The activation energy for low-temperature conduction decreases with increasing x: from 0.9 eV in CsH2PO4 to 0.48 eV at x = 0.1. 相似文献
16.
A. V. Semeno A. A. Pronin N. E. Sluchanko N. A. Samarin A. V. Kuznetsov S. V. Demishev 《Journal of Superconductivity and Novel Magnetism》2007,20(2):109-112
Electron spin resonance of a single crystal of CuGeO3 doped with 2% of Co has been studied at f = 99 GHz in temperature range 1.8–50 K. Contributions to ESR absorption from Cu2+ chains and from Co2+ ions were derived. It is found that functions obtained for ESR integrated intensities: Curie-Weiss for Cu2+ (χCu ∼ C
Cu/(T + Θ), with Θ = 92 K) and Curie for Co2+ (χCo ∼ C
Co/T) are well consistent with temperature dependence of static magnetic susceptibility. Strong dependence of ESR absorption on
polarization of oscillating magnetic field was discovered for Co2+ contribution. Polarization effect was studied for magnetic field applied along a, b and c directions. Values of g-factors of resonance lines are presented. 相似文献
17.
A. A. Patil P. P. Hankare A. B. Gaikawad K. M. Garadkar 《Journal of Materials Science: Materials in Electronics》2012,23(4):909-912
Preparation of layered type semiconductor Mo0.5W0.5S2
− thin films has been successfully done by using chemical bath deposition method. Objective of the studies are related to structural,
optical, morphological and electrical properties of the thin films. The preparation method is based on the reaction between
tartarate complex of Mo and W with thiourea in an aqueous alkaline medium at 363 K. X-Ray diffraction reveals a polycrystalline
film composed of both MoS2 and WS2 phases. The optical study shows that the band gap of the film is 1.6 eV. Electrical conductivity is high which is in the
order of 10−3–10−2 (Ώ cm)−1. 相似文献
18.
V. P. Dotsenko I. V. Berezovskaya N. P. Efryushina A. S. Voloshinovskii G. B. Stryganyuk 《Journal of Materials Science》2010,45(6):1469-1472
The luminescence properties of Sm3+ ions in YAl3B4O12 were studied upon synchrotron excitation in the 3.8–11 eV region. In addition to the 4f → 4f excitation bands, the excitation spectra of the Sm3+ emission contain broad bands at 6.1 and ~7.0 eV. These bands are attributed to charge transfer transition in Sm3+–O2− complexes and 4f → 5d transition of Sm3+ ions, respectively. The optical absorption edge of YAl3B4O12 was determined at 7.3 eV. A comparison with the results of electronic structure calculations on YAl3B4O12 is also made. 相似文献
19.
A new glass system SnO–MgO–P2O5 with low viscosity has been developed by a melt-quenching method. Formation, thermal properties, and chemical durability
of these glasses have been investigated. For a constant P2O5 concentration, the glass formation ability is enhanced with the increasing Sn/(Sn + Mg) ratio. The glasses exhibit low glass
transition temperature (T
g = 270–400 °C), low dilatometric softening temperature (T
DS = 290–420 °C), and high thermal expansion coefficient (CTE = 110–160 × 10−7 K−1). With the increasing Sn/(Sn + Mg) ratio, T
g and T
DS decrease, and CTE increases. When Sn/(Sn + Mg) ratio is varied, the relationship between chemical durability and thermal properties of the
present glasses is not consistent with what expected in general cases. It is noted that the glasses with 32–32.5 mol% P2O5 exhibit excellent chemical durability and tunable T
g, T
DS, and CTE (by varying Sn/(Sn + Mg) ratio). 相似文献
20.
Gd3+ was chosen as a substitute for Bi3+ in BiNbO4 ceramics, and the substitution effects on the sintering performance and microwave dielectric properties were studied in this
paper. The high temperature triclinic phase was observed only in the Bi0.98Gd0.02NbO4 ceramics when sintered at 920 °C. Both bulk densities and dielectric constant (εr) increased with the sintering temperature, while decreased with the Gd content. The quality factor (Q) exhibited a correlation to the Gd content and the microstructures of Bi1−x
Gd
x
NbO4 ceramics. At the sintering temperature of 900 °C, Bi0.992Gd0.008NbO4 ceramics exhibited microwave dielectric properties of εr ∼ 43.87, Q × f ∼ 16,852 GHz (at 4.3 GHz), and its temperature coefficient of resonant frequency (τf) was found to be near-to-zero. 相似文献