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1.
The tridecameric aluminum polymer [AlO4Al12(OH)24(H2O)12]7+ was prepared by forced hydrolysis of Al3+ up to an OH/Al molar ratio of 2.2. Upon addition of sulfate the tridecamer crystallised as the monoclinic basic aluminum sulfate Na0.1[AlO4Al12(OH)24(H2O)12](SO4)3.55. These crystals have been studied using Raman microscopy at 300 and 77 K and compared to Na2SO4·xH2O and Al2(SO4)3·xH2O. The Raman spectrum of basic aluminum sulfate is dominated by two broad bands, which are assigned to the 2 and 4SO4 2– triplets at 446, 459 and 496 cm–1 and 572, 614 and 630 cm–1. The 1 is observed as a single band at 990 cm–1, partly overlapped by the 3 triplet at 979, 1009 and 1053 cm–1 of the sulfate group in the Al13 sulfate structure. Furthermore the band at 726 cm–1 is assigned to an Al–O mode of the polymerised Al–O–Al bonds in the Al13 Keggin structure. For the first time the OH-stretching region of the basic aluminum sulfate has been reported. The 77 K spectrum shows the presence of 3 crystal water bands at 3035, 3138 and 3256 cm–1 accompanied by 3 Al–H2O bands at 3354, 3418 and 3498 cm–1 and 4 Al-OH bands at 3533, 3584, 3671 and 3697 cm–1.  相似文献   

2.
The phase diagram of the TlInSe2–TlSmSe2 system was mapped out using differential thermal analysis, microstructural examination, and x-ray diffraction data. The system was found to contain a partial solid-solution series (0–9 mol % TlSmSe2 at room temperature) and a quaternary compound of composition Tl2InSmSe4, which melts congruently at 1250 K. The electrical conductivity and Hall coefficient of TlInSe2–TlSmSe2 alloys were measured as a function of temperature. With increasing Sm content, the lattice parameters of the solid solution increase linearly, while its band gap decreases.  相似文献   

3.
The infrared spectra of amorphous thin films consisting of GeO2 co-evaporated with CeO2 are presented and interpreted in relation to the spectrum of the pure amorphous GeO2 film. The lower frequency side of the broad absorption band within this spectrum peaking at 730 cm–1 is believed to be due to defect centres similar to the O 1 and O 3 + centres found in a-SiO2. Absorption at higher frequencies within this band is due to the O stretch vibrations of the Ge-O-Ge linkage. After considering the vibrations of the O 1 and O 3 + centres in detail, it is shown that the band at 495 cm–1 cannot be due to either of these centres and must therefore by caused by some other reactive defect centres. The variation of the position of the 730 cm–1 peak within the series of spectra is noted and probable explanations are offered. The optical absorption edge of a-GeO2 thin film is compared with that of a-SiO and a possible explanation of the basic differences is proposed.  相似文献   

4.
A low cost chemical bath deposition (CBD) technique has been used for the preparation of Cu2–xSe thin films on glass substrates. Structural, electrical and optical properties of these films were investigated. X-ray diffraction (XRD) study of the Cu2–xSe films annealed at 523 K suggests a cubic structure with a lattice constant of 5.697 Å. Chemical composition was investigated by X-ray photoelectron spectroscopy (XPS). It reveals that absorbed oxygen in the film decreases remarkably on annealing above 423 K. The Cu/Se ratio was observed to be the same in as-deposited and annealed films. Both as-deposited and annealed films show very low resistivity in the range of (0.04–0.15) × 10–5 -m. Transmittance and Reflectance were found in the range of 5–50% and 2–20% respectively. Optical absorption of the films results from free carrier absorption in the near infrared region with absorption coefficient of 108 m–1. The band gap for direct transition, Eg.dir varies in the range of 2.0–2.3 eV and that for indirect transition Eg.indir is in the range of 1.25–1.5 eV.  相似文献   

5.
Electron spin resonance (ESR) spectra of Gd3+ ions doped in K2SO4-ZnSO4 glasses have been studied on an X-band ESR spectrometer at different temperatures (–120 to 150 C). The ESR spectrum at room temperature exhibits three prominent features with effectiveg-values of 5.6, 2.83 and 2.02. The spectra are similar to the U spectra familiar in many oxide and fluoride glasses, indicating very low and disordered site symmetries with a broad distribution of crystal fields. Remarkable changes have been observed in the spectrum with changes in the temperature, concentration and glass composition. The broadening of theg 2.02 line with increasing Gd3+ ion content indicates that the dipole-dipole interaction between the resonant centres increases with increase in Gd3+ ion content. A weak band at 36350cm–1 is observed in the optical absorption spectrum of 0.5mol% Gd3+ in K2SO4-ZnSO4 glass which has been assigned to the transition8S7/26P7/2.  相似文献   

6.
Infrared and structural properties of Y1–x Nd x Ba2Cu3O7– (0 x 1) were investigated using infrared absorption spectroscopy and X-ray powder diffraction. The unit cell parameters of the samples were defined using X-ray diffraction data. The resistance measurements showed that the samples revealed superconductivity in the temperature range of 80–100 K. It was observed that by the substitution of Nd to Y in YBa2Cu3O7 – IR band at 573 cm–1 that is assigned as Cu–O axial antisymmetric stretching mode shifts to 533 cm–1 while the band at 620 cm–1 that is due to Cu–O symmetric stretching mode in YBa2Cu3O7– shifts to 588 cm–1.  相似文献   

7.
Thin films of WO3/CeO2 deposited by vacuum co-evaporation (10–6 torr) on to Corning 7059 glass slides at room temperature have been shown to be amorphous in structure. The optical absorption spectra of amorphous WO3/CeO2 thin films have been measured at room temperature. The optical absorption edge of WO3/CeO2 and WO3 thin films above 105 cm–1 follows the Davis and Mott equation for the non-direct optical transitions. The optical absorption coefficient, , below this obeys the Urbach exponential relation. The value of the optical band gap of amorphous WO3 thin films is in good agreement with that found by Deb. The shift of the optical gap to lower energies and that of the Urbach energies to higher energies as the content of CeO2 is increased, indicate that both parameters are strongly dependent on the concentration of Ce4+ present in the structure. Thus, the increase of Ce4+ is thought to lead to strong potential fluctuations which cause an increase in the density of localized states in the gap.  相似文献   

8.
Single crystals of -Al2O3 were implanted with iron ions at room temperature to fluences ranging from 4×1016 Fe cm–2 to 1×1017 Fe cm–2. The microstructure and composition in the implanted region were examined using analytical electron microscopy techniques. Special emphasis was placed on monitoring the microstructural changes which take place during post-implantation annealing. Clusters of metallic -Fe were identified in the specimen after implantation to a dose of 1×1017 Fe cm–2. Analytical electron microscopy of implanted specimens annealed in oxygen revealed the redistribution of the implanted iron and the formation of surface precipitates of -Fe2O3, subsurface precipitates of various forms of spinel, and, in some cases, subsurface precipitates of iron, depending on the annealing temperature. Examination of implanted specimens annealed under reducing conditions revealed the presence of precipitates of -Fe.  相似文献   

9.
A new topotactic sintering method using Fe2O3 (obtained from FeO · OH) and BaCO3 is developed for preparing cheaper grain oriented barium hexaferrite. Fe2O3 and BaCO3 (precipitate grade) are wet mixed in a ball mill in stoichiometric proportion. The mixed slurry is then dried at 110° C for about 12h. The dried powder mixture containing moisture as a binder is uniaxially compacted at 5×106–10×106 kg m–2 pressure. The green compacts are air sintered in the temperature range 1100–1300° C for 1 H. The best results of the sintered ferrite show maximum energy product (BH) max in the range 7–10 kTAm–1. The bulk of commercial requirements for toy magnets etc. may be met by this method of production which eliminates steps like calcination and cost intensive wet magnetic compaction.  相似文献   

10.
Rare-earth molybdates of the type R2(MoO4)3 with R=La, Ce, Pr, Nd, Sm and Eu were prepared and characterized, and the electrical conductivity, and Seebeck coefficient, S in the temperature range 450–1200 K were measured. These molybdates are concluded to be insulating solids with a band gap which increases slowly going down the series from 2.30 eV for La molybdate to 3.20 eV for Eu molybdate. The plots of log and S versus T –1 show, in general, three linear regions with two break temperatures T 1 and T 2 occurring due to a change in the conduction mechanism. At higher temperatures the intrinsic conduction in these solids occurs via a band mechanism. The O2– 2p and Mo6+ 4d orbitals form the valence and conduction bands, respectively. These bands are the main support of conduction in La, Sm and Eu molybdates; however, for Ce, Pr and Nd molybdates 4f n levels fall within the band gap and become very effective in electrical conduction. The main charge-carrying entities seem to be electrons in Ce, Pr and Nd molybdates and holes in La, Sm and Eu molybdates. On the basis of mobility calculations of charge carriers it is concluded that the charge carriers in these bands become polarons which are, in fact, the charge carrying entities. At lower temperatures electrical conduction is mainly extrinsic. Cerium molybdate shows a semiconductor-semimetal transition around 940 K.  相似文献   

11.
Equations which describe incongruent nucleation and subsequent crystal growth have been derived. A ZrF4-BaF2-LaF3-AlF3-NaF glass was used to test the validity of these equations. Nucleation rate measurements were fitted to theory and some growth rate measurements were found in reasonable agreement with theoretical predictions. Both nucleation theory and crystal growth theory were used for computer simulations of the crystallization behaviour during heat treatments. Some heat treatments were performed in a differential scanning calorimeter to verify the theories. The experimental results were in good agreement with the numerical data. Using these theoretical results it is possible to estimate fibre scattering losses due to crystallization. Depending on drawing temperature, estimated losses can vary from 0.014 (310 °C) to 25 (320 °C) or more dB km–1.Nomenclature a s the chemical activity of component A in solution referred to the activity of the component in crystalline form - c c A the concentration of A in the crystalline form (mol m–3) - c r A the concentration of A in the liquid at the interface (mol m–3) - c 1 A the concentration of A far from the interface in the bulk (mol m–3) - c e A the equilibrium concentration of A (mol m–3) - D the diffusion coefficient (m2s–1) - G the free energy difference between the liquid and the crystal, equal to the molar Gibbs' free enthalpy of component A in solution minus the molar Gibbs' enthalpy of the crystalline form of A (J mol–1). - -G free energy difference between crystal A and pure liquid A (J mol–1) - G a activation energy for growth (J mol–1) - G r free energy difference between the liquid (of composition c r A ) at the interface and the pure liquid A - G 1 free energy difference between the liquid (of compositionc 1 A ) far from the interface and the pure liquid A - H f heat of fusion of the pure component A (J mol–1) - I the nucleation frequency (1 m–3 s–1) - k Boltzmann constant (J K–1) - K a constant of the order 1032–1033 Pa m–3 K–1 - r the radius of the spherical crystal - R gas constant (J mol–1 K–1) - t time (s) - T temperature (K) - T T 1 - T the undercooling of the melt of compositionx A (T 1 is the liquidus of the melt and depends onx A). - T 1 liquidus temperature (K) - T m melting temperature of pure component A (K) - T p temperature at the top of the DSC peak (K) - u crystal growth rate (ms–1) - V m molar volume of the crystallizing phase (mol m–3) - x A molar fraction of the precipitating component A in the melt (for an example: see Appendix) - viscosity (Pa s) - jump distance of the order of molecular dimensions (m) - 0 frequency of vibration (s–1) - surface tension of the crystal-liquid interface (J m–2) - the thickness of the diffusion layer  相似文献   

12.
Carbon nitride (CN x ) films were prepared on silicon (100) wafers and ITO conductive glasses by cathode electrodeposition, using dicyandiamide (C2H4N4) in acetone as precursors. The composition ratios (N/C) were approximated to or larger than 1 from XPS. The optical properties and electrical resistivities of the films were investigated. Intense PL with two bands in the range 2.5–3.5 eV was observed on the CN x films. The band gaps (E opt) deduced from measurements of the optical absorption coefficients in the UV-VIS spectra were found to be in the range of 1.1–1.6 eV. From the PL and UV-VIS spectra, the nitrogen content has a large effect on the PL band gap and E opt. The electrical resistivities of the films on Si wafers are in the 109–1010 · cm range.  相似文献   

13.
The dependence of oxygen modes intensity on pump power and temperature in YBa2Cu3O7–x single crystals with different oxygen contents (0<x<1) has been measured. When YBa2Cu3O6.5 crystals are heated, the peak intensity of the 500-cm–1 band (apex oxygen) decreases, that of the 590-cm–1 band (defect mode) increases, and the peak intensity of the 330-cm–1 band (plain oxygen) remains unchanged. The resonant dependence of the apex oxygen, and the intensity of the defect modes have also been measured. In order to explain the experimental results we suppose that the apex oxygen ion is in a double-well potential.  相似文献   

14.
The tridecameric aluminum polymer [AlO4Al12(OH)24(H2O)12]7+ was prepared by forced hydrolysis of Al3+ up to an OH/Al molar ratio of 2.2. Upon addition of sulfate the tridecamer crystallised as the monoclinic basic aluminum sulfate Na0.1[AlO4Al12(OH)12(H2O)12](SO4)3.55. These crystals have been studied using FT-Raman microscopy and compared to the basic aluminum nitrate, Na2SO4·xH2O and Al2(SO4)3·xH2O. The Raman spectrum of basic aluminum sulfate is dominated by two broad bands which are assigned to the 1 and 3 bands at 981 and 1051 cm– 1 of the sulfate group in the Al13 sulfate structure. Furthermore the band at 724 cm– 1 is assigned to an Al–O mode of the polymerised Al–O–Al bonds in the Al13 Keggin structure. The sharp band at 1066 cm– 1 and the minor band at 1384 cm– 1 are interpreted to be due to a small amount of nitrate impurity on a different position in the structure than the nitrate present in the Al13 nitrate crystal structure, based on the shift in band position of both the 1 symmetric stretching and 3 asymmetric stretching modes.  相似文献   

15.
In this study, Cr x Ti1–2x Nb x O2 (0 x 0.5) rutile solid solutions have been synthesized from gels built from hydrolysis-condensation of Cr (III) acetylacetonate, NbCl5 and Ti (IV) isopropoxide mixture (polymeric gel). Characterization of these solid solutions was carried out by X-ray diffraction, ultraviolet-visible and infrared spectroscopy, differential thermal and thermogravimetric analysis and CIELAB (Commission Internationale del'Eclairage L*a*b*) parameter measurements. The results obtained by the polymeric gel method were compared with those obtained by traditional ceramic synthesis. This comparison reveals some differences with regard to synthesis temperatures and reaction mechanisms. The formation of Cr x Ti1–2x Nb x O2 (0 x 0.5) rutile solid solutions by the ceramic method requires temperatures of about 1200°C and soaking times of several days. These solid solutions are synthesized at 1000°C in 24 h by the polymeric gel method. In ceramic synthesis, the CrNbO4 compound with rutile structure appears as an intermediate compound in the formation of rutile solid solutions. In polymeric gel synthesis, however, the CrNbO4 rutile compound was not detected in the samples.  相似文献   

16.
The immobilization of strontium over titania was carried out by the method of coprecipitation. From a preliminary study, an appreciable uptake (52.8%) of90Sr was observed over preformed titania material. A weighable amount of strontium was coprecipitated with Ti(IV) hydroxide and a maximum of 34 wt% Sr was found to be adsorbed. The leachability of the mixed materials prepared by the addition of 250 and 400 mg Sr2+, calcined at 1000 °C, by soxhlet apparatus refluxing at 97 °C and repeated seven times at intervals of 24 h, was found to be of the order of 10–9 and 10–5 g cm–2 d–1, respectively. X-ray powder diffraction analysis revealed that strontium was immobilized in the crystalline matrix of rutile, which suffered some structural changes with the formation of new phases, SrTiO3+Sr2TiO4 and SrTiO3, respectively.  相似文献   

17.
The iron behaviour in phosphate/water/polyethylene glycol (PEG) was studied in-situ and ex-situ by spectrometry Raman, ESCA spectroscopy, X-ray diffraction, Auger spectroscopy were used as surface analysis methods. It changes with phosphate concentration. At low phosphate concentration (5 × 10–4 M-10–3 M-5 × 10–3 M), iron is corroded. The thin corrosion layer is a mixture of iron oxides (-Fe2O3, Fe3O4) and iron phosphate(Fe3(PO4)2, 8H2O). At high phosphate concentration (10–2 M-5 × 10–2 M), the iron is protected. The protection could be due to an heterogenous layer containing PEG 400 and phosphates.  相似文献   

18.
Electron paramagnetic resonance (EPR) and optical absorption spectra of Cu2+ ions in 80Na2B4O7-(20 – x)NaF – xCuO (NFNB) glass system with 0 x 6 mol% have been studied. EPR spectra of all the glass samples exhibit resonance signals characteristic of Cu2+ ions. The values of spin-Hamiltonian parameters indicate that the Cu2+ ions in sodium fluoride-sodium borate (NFNB) glasses were present in octahedral sites with tetragonal distortion. The number of spins (N) participating in resonance was calculated as a function of temperature for NFNB glass sample containing 1 mol% of Cu2+ ions and the activation energy was calculated. From the EPR data, the paramagnetic susceptibility () was calculated at various temperatures and the Curie constant was calculated from the 1/ – T graph. The optical absorption spectra of these samples show a broad absorption band centered at 13280 cm–1 which is assigned to the 2 B 1g 2 B 2g transition of Cu2+ ions in distorted octahedral sites. The optical band gap energy (E opt) and Urbach energy (E) are calculated from their ultraviolet edges. It is observed that as the copper ion concentration increases, E opt decreases while E increases. This has been explained as due to the creation of additional localized states by CuO, which overlap and extend in the mobility gap of the matrix. By correlating the EPR and optical data, the molecular orbital coefficients have been evaluated.  相似文献   

19.
Point contact measurements in oriented La2–xSrxCuO4 samples were performed using metal tips. The current-voltage curves measured along the CuO plane direction (ab) are characteristic of the Andreev reflection phenomenon. The superconducting energy gap in theab plane is determined, ab = 6± 1 meV, with a possibility for the existence of a lower subgap in the plane. A lower limit for the Fermi velocity in the CuO planes is also set by the measurements;V F6×107 cm/sec, which is significantly higher than the average velocity obtained by band calculations. The results are discussed in the context of different models for superconductivity in the layered oxides. In particular, we raise the possibility of an anisotropic gap parameter which may indicate a nonstandards-wave pairing in La2–xSrxCuO4. A comparison with previous results obtained on YBa2Cu2O7– is made.  相似文献   

20.
Growth-induced linear defects are shown to strongly affect the microwave surface resistance, Rs, of highly biaxially oriented high temperature superconductor (HTS) YBa2Cu3O7– (YBCO) films. Measured Rs(77 K) turned out to be 4–5 times higher than in single crystals. The films were deposited by modified pulse-laser technique, Jc(77 K) = (3-6) × 106 A/cm2, onto LaAlO3 substrates. Rs(T) was measured at 134 GHz and 20–100 K. TEM/HREM study of YBCO films deposited at Ts = 750°C–780°C revealed a reduction of edge dislocation density with Ts increase (from 2 · 1011 to 1010 lines/cm2). YBCO films deposited at Ts = 780°C exhibited the smallest Rs(77 K, 134 GHz) < 120 m and the lowest density of dislocations detected by HREM and X-ray analysis. A nature of the dislocation effect is discussed within a model of local anisotropic elastic deformation in a vicinity of dislocation cores, where Tc variation and an enhancement of normal quasiparticle density are significant.  相似文献   

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