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1.
S. Ouhenia D. Chateigner M.A. Belkhir E. Guilmeau C. Krauss 《Journal of Crystal Growth》2008,310(11):2832-2841
Calcium carbonate precipitates are prepared from a solution of CaCl2 and K2CO3 in the presence of polyacrilic acid. The effect of polyacrilic acid incorporation in the [25–80 °C] temperature range on crystal morphologies and CaCO3 precipitated polymorph concentrations are investigated using scanning electron microscopy and X-ray diffraction quantitative microstructural and phase analysis. Large changes in morphology and phase proportions are observed in the presence of polyacrylic acid, which strongly depend on the solution temperature. While crystallization of vaterite is favoured in the presence of polyacrilic acid up to 50 °C, it is largely destabilized at higher temperatures. Our process also enables the elaboration of particles in the range 10–20 nm. 相似文献
2.
《Journal of Non》2003,330(1-3):128-141
The electrical and dielectric properties for three series of MoO3–Fe2O3–P2O5 and one series of SrO–Fe2O3–P2O5 glasses were measured by impedance spectroscopy in the frequency range from 0.01 Hz to 3 MHz and over the temperature range from 303 to 473 K. It was shown in Part I that the MoO3 is incorporated into phosphate network and the structure/properties are strongly influenced by the overall O/P ratio. The Fe2O3 content and Fe(II)/Fetot ratio in these glasses have significant effects on the electrical conductivity and dielectric permittivity. With decreasing Fe2O3 content in MoO3–Fe2O3–P2O5 glasses with O/P at 3.5 the dc conductivity, σdc(ω) decreases for two orders of magnitude, which indicates that the conductivity for these glasses depends on Fe2O3 and is independent of the MoO3 content. Also, the dielectric properties such as ′(ω), ″(ω) and σac(ω) and their variation with frequency and temperature indicates a decrease in relaxation intensity with increase in the concentration of MoO3. On the other hand, the dc conductivity for MoO3–Fe2O3–P2O5 glasses with O/P > 3.5 increases with the substitution of MoO3 which has been explained by an increase in the number of non-bridging oxygens and formation of Fe–O–P bonds that are responsible for formation of small polarons. The increase in the dielectric permittivity, ′(ω) with increasing MoO3 content is attributed to the increase in the deformation of glass network with increasing bonding defects. For SrO–Fe2O3–P2O5 glasses the conductivity and dielectric permittivity remained constant with increasing SrO. 相似文献
3.
Heat exchanges in a sealed ampoule in the LTVG (low temperature vapour growth) furnace have been modelled in order to compute temperature fields and control the growth of HgI2 crystals from vapour phase at low temperatures. We use a coupled conductive-radiative model to determine the shapes of the source and the crystal at different equilibrium states (i.e. without growth rate). The model involves conductivity anisotropy in the crystal and radiative exchanges between grey and diffuse surfaces (source and crystal interfaces, Pyrex walls), which are considered as opaque. Internal buoyancy effect is not taken into account as the pressure inside the ampoule is very small. The source temperature is fixed. For different undercoolings, i.e. for different cold finger temperatures, the “equilibrium” isotherm between the source/gas and crystal/gas interface has been numerically obtained. This “equilibrium” isotherm, which is associated with the stop of the growing process, gives a crystal shape. This shape is compared with experimental results given by the ETH-Zürich group. The model would permit a better understanding and control of the future HgI2 crystal growth experiment. The computations are performed using a finite element package (FIDAP). 相似文献
4.
Tellurium oxide glasses were prepared by the hammer and anvil technique. The glass systems are (0.85TeO2 + 0.15Z), where Z = K2O, TiO2, V2O5, MnO, Fe2O3, CoO, NiO or CuO. A second group is a ternary system 0.85TeO2+(0.15 − x)TiO2 + xFe2O3) with x=0.0, 0.05, 0.1, 0.15 mol. X-ray diffraction, infrared spectroscopy and differential thermal analysis measurements were carried out. The present study showed the different glass-forming groups, the glass transition and crystallization temperatures as well as the crystallization processes. 相似文献
5.
Vitreous BeF2 was prepared by two techniques; (1) remelting of a technical grade material, and (2) vacuum distillation/fluoridation. Infrared spectroscopy studies have established that the first material contains about 0.5 wt.% hydroxyl, predicted to be coherently incorporated into the vitreous network as edge-linked [Be(OH)4]2− units. The distilled BeF2 is water-free. The dc electrical conductivity of the remelted BeF2 was measured as σ = (7.9 × 103/T) exp(−24500 cal/mol/RT) ω−1 cm−1 and for the distilled BeF2 as σ = (3.0 × 105/T) exp(−36700 cal/mol/RT ω−1 cm−1 at temperatures to 280°C. Ionic transport studies utilizing a dc electrolysis polarization technique with N2−F2 and H2−HF gas electrodes have demonstrated that the fluorine ion is the transport species. A general model for fluorine transport is proposed based upon a modified anti-Frenkel defect model. The difference in the fluorine transport process for the undistilled grade of BeF2 is seen as a consequence of the anti-Frenkel defect pair interaction with the [Be(OH)4[2− groupings. 相似文献
6.
TiN films were grown on SUS304 substrates heated by an induction furnace in a vertical cold wall reactor. Scanning electron microscopy, transmission electron microscopy and X-ray diffraction were used to characterize the microstructures of films obtained at different deposition conditions (temperature, gas flow rate and gas composition). Film structures obtained in the present vertical reactor had the following features compared with those in the tubular reactor: (1) Abnormally grown “star-shaped” crystals were observed on the surfaces of films deposited in the following ranges of total gas flow rate (QT), temperature (T) and partial pressures (P): 9.0×10−6 ≤ QT ≤ 1.6×10−5 m3 s−1, 1223 ≤ T ≤ 1273 K, 0.92 ≤ PTiCl4 ≤ 6.18 kPa, PH2 = PN2. The matrix grains were responsible for (211) preferred orientation. (2) Surface morphologies did not vary so much with PTiCl4. On the other hand, a drastic change was brought about by adding HCl to the source gas, i.e., plate-shaped crystals dominated and the large “star-shaped” crystals were no longer present. (3) The apparent activation energy for deposition reaction was 230 kJ/mol (1173 ≤ T ≤ 1273 K) and 76.5 kJ/mol (1273 ≤ T ≤ 1373 K) at PTiCl4 = 2.43 kPa and PH2 = PN2 = 49.45 kPa. 相似文献
7.
Shanzhong Wang Shengwu Xie Qianjun Pang Hang Zheng Yuxing Xia Rongbin Ji Yan Wu Li He Zuoming Zhu Guohua Li Zhaoping Wang 《Journal of Crystal Growth》2000,220(4):548-553
We report on a detailed investigation on the temperature-dependent behavior of photoluminescence from molecular beam epitaxy (MBE)-grown chlorine-doped ZnSe epilayers. The overwhelming neutral donor bound exciton (Cl0X) emission at 2.797 eV near the band edge with a full-width at half-maximum (FWHM) of 13 meV reveals the high crystalline quality of the samples used. In our experiments, the quick quenching of the Cl0X line above 200 K is mainly due to the presence of a nonradiative center with a thermal activation energy of 90 meV. The same activation energy and similar quenching tendency of the Cl0X line and the I3 line at 2.713 eV indicate that they originate from the same physical mechanism. We demonstrate for the first time that the dominant decrease of the integrated intensity of the I3 line is due to the thermal excitation of the “I3 center”-bound excitons to its free exciton states, leaving the “I3 centers” as efficient nonradiative centers. The optical performance of ZnSe materials is expected to be greatly improved if the density of the “I3 center” can be controlled. The decrease in the luminescence intensity at moderately low temperature (30–200 K) of the Cl0X line is due to the thermal activation of neutral-donor-bound excitons (Cl0X) to free excitons. 相似文献
8.
Ritu Srivastava S. Chandra 《Progress in Crystal Growth and Characterization of Materials》2002,44(3):2847-139
Highly porous silica alcogel, with pores entrapped with liquid electrolyte solutions of KH2PO4, has been successfully prepared by hydrolysis and polycondensation of tetraethylorthosilicate (TEOS) giving interesting “solid-liquid electrolyte composites”. The entrapped liquid electrolyte solution gives high liquid-like ionic conductivity (10−5 S·cm−1). Further, on storage the entrapped solution slowly reaches the surface pore-heads where it evaporates resulting in the growth of long crystalline whiskers. Higher relative humidity (>60%) slows down the evaporation and has been found to be favorable for whisker growth. 相似文献
9.
Teruo Sakaino Sang-Soo Lee Masanori Iwamoto Haruhiko Ogata Yoshihiko Yamato 《Journal of Non》1986,80(1-3):693-697
An improved apparatus capable of quantatively measuring the inhomogeneity of glasses within several minutes was developed as a prototype for practical use. Inhomogeneities were measured for several kinds of glass articles on the market, such as plate, bottle and optical glasses etc. and a “relative homogeneity” has been proposed for the purpose of deciding a ranking of glasses measured in comparison to the powdered single crystal of CaF2 as a standard material of uniformity. 相似文献
10.
Mahender Singh K. L. Bhatia N. Kishore Partap Singh R. S. Kundu 《Journal of Non》1995,180(2-3):251-259
AC conductivity and dielectric relaxation measurements of the bulk amorphous compositions in the pseudo-binary system (As2S3)1-x(PbS)x (x = 0, 0.1, 0.4 and 0.5) in the frequency range 500 Hz-10 kHz and in the temperature span 180–450 K are reported. The temperature dependence of the ac conductivity, σac(ω), has a broad structure at all frequencies in compositions with x = 0.1, 0.4 and 0.5 whose peak position is not thermally activated. A similar structure was also observed in the data on the dielectric constant, ε1, which peaked at a frequency of 1 kHz in the composition with x = 0.5. Analysis of the results using the correlated barrier hopping model revealed that the electronic conduction takes place by single polaron and bipolaron hopping processes at high and low temperatures, respectively, in compositions containing Pb. The microstructure and phase-separation in the glasses containing Pb influence the electrical transport and dielectric dispersion. This study has revealed the possible presence of a phase transformation at around 300 K at a frequency of 1 kHz in the dielectric dispersion behaviour of composition with x = 0.5. 相似文献
11.
In vitro degradation studies of calcium phosphate glass ceramics prepared by controlled crystallization 总被引:5,自引:0,他引:5
Calcium phosphate glass ceramics with incorporation of small additions of two nucleating agents, MgO and K2O were prepared in the metaphosphate and pyrophosphate region, using an appropriate two-step heat treatment of controlled crystallization defined by differential thermal analysis results. Identification and quantification of crystalline phases precipitated from the calcium phosphate glass were performed using X-ray diffraction and Rietveld analysis. The β-Ca2P2O7 (β-DCP), KCa(PO3)3, β-Ca(PO3)2 and Ca4P6O19 phases were detected in the glass ceramics. In order to evaluate the degradation of the glass ceramics prepared, degradation studies were carried out during 42 days in Tris-HCl solution at 37 °C, pH 7.4, using granules in the range of 355–415 μm. The materials presented a weight loss ranging up to 12%. The ions leached during the immersion mainly originated from the KCa(PO3)3 phase, probably due to the presence of K+ ion in the calcium metaphosphate, and the residual glassy phase. The structural changes at the surface of materials during degradation have been analyzed by Fourier transform infrared spectroscopy and X-ray diffraction. Results showed that significant surface changes occurred with immersion time, with the decrease of KCa(PO3)3, β-Ca2P2O7 and β-Ca(PO3)2 phases occurring at different periods of immersion. This study has demonstrated an easy way to prepared calcium phosphate materials with specific calcium phosphate phases and crystallization, and therefore specific degradation rates. 相似文献
12.
By selecting carefully controlled conditions for the thermal treatment of sodium borate glasses coated with PbO films, it is possible to prevent Pb2+ ions from penetrating deeply into the glass. For low alkali glasses, an interdiffusion layer can be formed, which sub-surface cation profiling (by ion beam induced radiation) shows is a solid solution of Na2O and B2O3 in PbO which acts as solvent. Experiments with 18.0 mol-% Na2O glass show that it is possible to transform such an interdiffusion layer into a second type in which Na2O and B2O3 together act as solvent and the concentration of PbO solute varies through the layer. For both types of layer the Na2O : B2O3 ratio is different from that of the glass substrate, and for the production of the second type of layer it is shown that an important factor connected with penetration of PbO into the glass surface is a “sweating” process in which thermal treatment of the glass, even in the absence of PbO, results in migration of Na+ ions so that the glass surface has a Na2O content higher than that of the bulk glass. Changes in the UV spectra of the Pb2+ ion are correlated with the formation of the interdiffusion layers, and results show that types of layer have optical basicities significantly greater than that of the glass substrate, through either the high PbO or high Na2O content. 相似文献
13.
The diffusion coefficient of sodium, 22Na, and silver, 110Ag, and electrical conductivity for sodium borate glasses (4–24 mol% Na2O) has been measured from 100°C to slightly below the glass transition temperature, Tg. Unlike silicate glasses where the self-diffusion coefficient is much larger than the impurity diffusion coefficient, DNa and DAg had close to the same magnitude in the sodium borate glasses. In some glasses, DAg was slightly larger than DNa. Na2O-Ag2O-B2O3 glasses show a relatively small mixed alkali effect, despite the significant mass difference between Ag(≈108) and Na(≈23). It is concluded that the mixed alkali effect is more dependent upon the difference in ionic radii rather than differences in mass. 相似文献
14.
Glasses of composition 65 mol% LiNbO3:: 35 mol% SiO2 have been shown to be Li+ ion conductors with a conductivity at 200°C > 1 × 10−5 (η cm)−1 and an activation energy of 0.54 eV. The addition of approximately 0.1 mol% Fe2O3 leads to an enhancement of conductivity to ≈10−3 (η cm)−1 at 200°C and an activation energy of 0.67 eV. The effect of Fe is shown to be in the control of microstructure in the glass, with Fe2O3 concentrations < 1 mol% acting as a grain growth inhibitors and larger concentrations acting as a nucleating agents. A model for this process based on the expected stoichiometry of the melt and the effect of Fe2+ and Fe3+ in charge compensation is in excellent agreement with experimental data from electron spin resonance. 相似文献
15.
The internal friction of xNa2O·(0.5−x)V2O5·O.5P2O5(x = 0.025–0.3) glasses was studied using the low-frequency torsion pendulum technique. The temperature spectrum of internal friction reveals three maxima. Maximum 1, the so-called “electron” maximum, is the same as observed in binary vanadium-phosphate glasses. The origin of maximum 2 can be attributed to ion migration. Maximum 3 appears for glasses containing more than 10 mol.% Na2O and is probably connected with sodium-proton interactions. 相似文献
16.
Interconnecting cage-like porous structures of several halide compounds were prepared by the selective leaching of one eutectic phase method. The binary eutectic precursors were prepared by directional solidification using the Bridgman crystal growth technique. Porous NaMgF3 (40% pore volume), CaF2 (57% pore volume) and BaF2 (43% pore volume) crystals were obtained after water leaching the NaF component of the directionally solidified NaF/NaMgF3, NaF/CaF2 and NaF/BaF2 eutectics with the appropriate entangled microstructure. The growth conditions for eutectic-coupled growth and the morphology of the eutectics have been determined. In the coupled growth regime, the size of the eutectic phases “λ” is fairly uniform and varies with the eutectic growth rate “v” as λ2v=constant, which allows us to control the pore size within the 0.5–10 μm range. The simplicity and versatility of the eutectic growth also allows us to fabricate highly aligned porous structures at relatively high production rates. 相似文献
17.
E.M. Larson A.J.G. Ellison F.W. Lytle A. Navrotsky R.B. Greegor J. Wong 《Journal of Non》1991,130(3):260-272
The La L1 and L3 XANES and L3 EXAFS have been investigated for the series of glasses 10K2O---50SiO2---x La2O3 (x = 1, 5, 10) and (10 − x)K2O---40SiO2−(x/3)La2O3 (x = 7.5, 5, 2.5) and model compounds La2O3, LaAlO3, LaPO4, La2NiO4, La2CuO4 and La(OH)3. An edge resonance at 25 eV above the L1 edge in the glass spectra is concentration-dependent, decreasing in intensity with increasing lanthanum concentration. The 2s → nd forbidden transition increases with La2O3 concentration, indicating a reduction in the ‘average’ site symmetry of the first coordination shell of La. Mapping X(k) space, which is a new and promising technique, was employed to extract bond distance, coordination number and thermal parameters from the EXAFS. By this method, one calculates the complete X(k) space a function of all physically reasonable values of the adjusted parameters in all possible combinations. The advantage in this method is the assurance of a global minimum. Bond lengths were comparable to those obtained by Fourier transforming the phase corrected EXAFS. The values are 2.42 Å (± 0.03 Å) for La---O. The coordination numbers (N ≤ 7 ± 1.5) were derived by mapping and comparison to the published structures for other La compounds. X(k) mapping is compared with least-squares fitting the data, and the correlation between the Debye-Waller factor and coordination number is also discussed. 相似文献
18.
Optical third-harmonic generation from some high-index glasses was investigated. The highest χ(3) was obtained from As2S3 glass 2.2 × 10−12 esu/ This value was 100 times higher than that of pure SiO2 glass and comparable with that of the polymer with monomer-doping, which are known as organic materials with quite high χ(3). From the relationship between χ(3) and composition, sulfide glasses were found to have higher χ(3) than oxide or semiconductor-doped oxide glasses with similar refractive indices. 相似文献
19.
Single wavelength reflectance anisotropy (RA) has been used to monitor the growth of InP onto (001) InP substrates in real time under atmospheric pressure atomic layer epitaxy “(ALE)-like” conditions in which the In and P precursors were introduced sequentially into the reactor. The RA data indicates that at temperatures below 325°C the initial interaction of TMI with surface P-dimers results in a change in anisotropy and that the resulting surface is unreactive towards phosphine or additional TMI possibly as a result of a residual species of the type In(CH3)x where x = 1–3 acting as a site blocker or preventing In dimer formation. At higher temperatures, the RA data indicates that for InP growth on (001) InP using phosphine and trimethylindium (TMI) the onset of growth occurs between 300–325°C. This observation is implied directly from the appearance of the recovery portion of the RA transient which indicates that the second half of the ALE-like cycle restores the surface to the starting P-stabilised conditions. This low temperature for the onset of growth as compared to conventional InP MOCVD is attributed to the operation of a surface catalysed reaction of both phosphine and TMI. 相似文献
20.
For vertical Bridgman growth of the nonlinear optical material GaSe in an ampoule sufficiently long that flow and dopant transport are not significantly influenced by the upper free surface, we show computationally that steady rotation about the ampoule axis strongly affects the flow and radial solid-phase dopant segregation. Radial segregation depends strongly on both growth rate U and rotation rate Ω over the ranges 0.25 μms−1U3.0 μms−1 and 0Ω270 rpm. For each growth rate considered, the overall radial segregation passes through two local maxima as Ω increases, before ultimately decreasing at large Ω. Rotation has only modest effects on interface deflection. Radial segregation computed using a model with isotropic conductivity (one-third the trace of the conductivity tensor) predicts much less radial segregation than the “correct” model using the anisotropic conductivity, with the segregation decreasing monotonically with Ω. Consideration of a model in which centrifugal acceleration is deliberately omitted shows that, as Ω increases, diminution and ultimately disappearance of the “secondary” vortex lying immediately above the interface is due to centrifugal buoyancy, while axial distension of the larger “primary” vortex above is due to Coriolis effects. These results, which are qualitatively different from those accounting for centrifugal buoyancy, suggest that several earlier computational and analytical predictions of rotating vertical Bridgman growth are either limited to rotation rates sufficiently low that centrifugal buoyancy is unimportant, or are artifacts associated with its neglect. The overall radial segregation depends approximately linearly on the product of
and the growth rate U for the conditions considered, where
is the segregation coefficient. 相似文献