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1.
Thin films of cubic BaTiO3 were processed hydrothermally at 40°–80°C by reacting thin layers of titanium organo metallic liquid precursors in aqueous solutions of either Ba(OH)2 or a mixture of NaOH and BaCl2. All films (thickness ∼1 μm) were polycrystalline with grain sizes ranging from nano- to micrometer dimensions. BaTiO3 formation was facilitated by increasing [OH-], [Ba2+], and the temperature. The film structure was related to the nucleation and growth behavior of the BaTiO3 particles. Films processed at relatively low [OH-], [Ba2+], and temperatures were coarse grain and opaque, but increasing [OH-], [Ba2+], and temperature caused the grain size to decrease, resulting in transparent films.  相似文献   

2.
Physical and dielectric properties of (1– x )PbZrO3· x BaTiO3 thin films prepared by a chemical coating process have been investigated as a function of BaTiO3 ( x ) content (0≤ x ≤0.2). Changing the molar ratio between propylene glycol and water prior to the deposition optimized the chemical precursors. (1– x )PbZrO3- x BaTiO3 thin films that contained a majority of perovskite phase, but also contained large amounts of other phases, were fabricated. These films could withstand fields of 250 kV/cm at 1 kHz. The microstructure of the thin films was found to depend on the BaTiO3 content. The phase transition from antiferroelectric to ferroelectric was gradually induced as the BaTiO3 content increased. A maximum dielectric constant of ∼809 was obtained at the composition of x = 0.1. A maximum dielectric constant of ∼809 was obtained at the composition of x = 0.1. A thin film at the low-field antiferroelectric-ferroelectric phase boundary with x = 0.05 exhibited the highest P sat and P r values. The maximum values of these were 45 and 31 μC/cm2, respectively.  相似文献   

3.
Fluorescence emissions at both 1.31 and 1.55 μm communication windows were observed from Pr3+/Er3+ codoped Ge-As-Ga-S glasses with a single wavelength pumping at 986 nm. The lifetime of the Er3+:4 I 11/2 level decreased as the Pr3+ concentration increased, and that of the Pr3+:1 G 4 level increased as the Er3+ concentration increased. Energy transfer from the Er3+:4 I 11/2 level to the Pr3+:1 G 4 level was responsible for emission of the 1.31 μm fluorescence from the Pr3+:1 G 4 level. Ge-As-Ga-S glasses that have been doped with Pr3+ and Er3+ cations are promising amplifier materials for both 1.31 and 1.55 μm communication windows.  相似文献   

4.
Compositional dependence of spontaneous emission probabilities between initial 4 F 3/2 and terminal 4 I J J = 9/2, 11/2, 13/2, 15/2) levels of Nd3+ were studied for about 90 samples of silicate, borate, and phosphate glasses using the Judd–Ofelt theory. The effect of the covalency of the Nd–O bond on the magnitude of intensity parameters was estimated from the variation of spectral profiles of the 4 I 9/24 G 5/2, 2 G 7/2 and 4 F 7/2, 4 S 3/2 transitions. Intensity parameters Ω4 and Ω6 and the spontaneous emission probabilities were strongly affected by the ionic packing ratio of the glass host. The results were discussed in terms of the site selectivity of Nd3+ ions in glasses.  相似文献   

5.
The photoluminescence of Mg-doped BaTiO3:Pr3+ (Pr3+: 0.1 mol%) ceramics was investigated by changing the doping concentration of Mg and the sintering temperature. The results indicated that the intensity of red emission due to the 1 D 23 H 4 transition of Pr3+ exhibited significant dependence on both the Mg doping content and the sintering temperature; the strongest red emission intensity was observed for 2.0 mol% Mg-doped ceramics sintered at 1050°C. An interpretation of the results obtained was made in terms of the changes in the crystal structure and microstructure of the ceramics.  相似文献   

6.
Crystals of β-Ca2SiO4 (space group P 121/ n 1) were examined by high-temperature powder X-ray diffractometry to determine the change in unit-cell dimensions with temperature up to 645°C. The temperature dependence of the principal expansion coefficients (αi) found from the matrix algebra analysis was as follows: α1= 20.492 × 10−6+ 16.490 × 10−9 ( T - 25)°C−1, α2= 7.494 × 10−6+ 5.168 × 10−9( T - 25)°C−1, α3=−0.842 × 10−6− 1.497 × 10−9( T - 25)°C−1. The expansion coefficient α1, nearly along [302] was approximately 3 times α2 along the b -axis. Very small contraction (α3) occurred nearly along [     01]. The volume changes upon martensitic transformations of β↔αL' were very small, and the strain accommodation would be almost complete. This is consistent with the thermoelasticity.  相似文献   

7.
Compositional dependence of spontaneous emission probabilities of Er3+ was studied for silicate, borate, and phosphate glasses using the Judd–Ofelt theory. Through all of the glass systems, spontaneous emission probabilities of the 4 I 13/24 I 15/294 I 9/24 I J, and 4 S 3/24 I J ( J = 9/2, 11/2,13/2,15/2) transitions increased with increased ionic packing ratio of the glass host, which varied markedly with the type of network modifier. The effect of Er–O covalency on the transition probabilities was discussed from the spectral profile of the 4 I 15/24 I 3/2transition in terms of nephelauxetic effect.  相似文献   

8.
Tm3+-Ho3+- and Tm3+-Ho3+-Eu3+-ion-codoped oxyfluoride transparent glass-ceramics containing PbF2 nanocrystals were prepared, and the near-infrared fluorescence properties of the Tm3+ ions were investigated for their potential use as a 1.4 μm amplifier. For all samples, the lifetime of the Tm3+:3 H 4 level increased with heat treatment because of the decrease of the phonon energy as PbF2 crystals were formed. Moreover, it was revealed that codoping with Ho3+ or Eu3+ was effective in suppressing the lifetime of the Tm3+:3 F 4 level by energy transfer to the Ho3+:5 I 7 or Eu3+:7 F 6 level. For the codoped samples, the heat treatments decreased the Tm3+:3 F 4 lifetime and increased the Tm3+:3 H 4 lifetime. This was attributed to the concentration of rare-earth ions in the fluoride crystallites. These properties improved the population inversion of the 1.4 μm transition.  相似文献   

9.
The third-order nonlinear optical susceptibilities χ(3) of M2O-B2O3 (M = Li, Na, K, Rb, Cs, and Ag) binary borate glasses have been measured by the third harmonic generation (THG) method. It is found that the enhancement of χ(3)by the structural change of BO3 units to BO4 units is small, while the enhancement of χ(3) due to the formation of non- bridging oxygen is rather significant. The effects of alkali cations on the χ(3) of alkali borate glasses are discussed in terms of the M-O bond character, focusing on the covalency of Li2O-B2O3 glasses. Comparison of the χ(3) values for Cs2O-B2O3 and Ag2O-B2O3 glasses which contain cations of comparable polarizability reveals that the χ(3) value is much greater for Ag2O-B2O3 glasses than for Cs2O-B2O3glasses, which is possibly due to the great contribution of Ag(4 dz2 + 5 s + 5 pz ) hybrid orbitals to the nonlinear optical response.  相似文献   

10.
The fracture energies and spalling resistance of high-Al2O3 refractories were studied. The fracture energies, γ WOF and γ NBT , were measured by the work-of-fracture and the notched-beam-test methods, respectively. Spalling resistance, as measured by the relative strength retained in a water quench, correlated well with the thermal-stress resistance parameter applicable to stable crack propagation under conditions of thermal shock, (γ WOF 2 E 0). Many of the refractories exhibited high ratios of γWOF to γNBT; such high ratios were shown analytically to maximize the parameter ( R 1111= E 0γWOF/S12) which describes the resistance to catastrophic spalling. The increase of crack length with increasing quenching temperature difference (Δ T ) was somewhat less than that predicted theoretically; the discrepancy was attributed to an increase of crack density with Δ T . In general, the results show that fracture energy is important in establishing the spalling resistance of high-Al2O3 refractories.  相似文献   

11.
Dysprosium-doped glasses were prepared in the system of gallium-based sulfide, tellurite, zirconium-baed and indium-based fluorides and their optical properties were studied. From the absorption cross sections of five f-f bands, three Judd-Ofelt parameters, ω t ( t = 2, 4, 6), of Dy3+ ion were determined. The compositional variaton of the ω2value showed the order sulfide > tellurite > fluorozirconate > fluoroindate, whereas the ω6 value showed the opposite tendency. Compositional variaton of the fluorescence intensity ratio of the (4F9/26H13/2)/(4F9/2)→6H15/2) is explained by the ratio of ω26 of doped Dy3+. The emission probabilities A and the branching ratio β from 6H9/2 and 6F11/2 levels, which are the doublet initial level of the 1.3 μm luminescence, were calculated for the glasses, and it was found that both values showed a tendency similar to that of ω2 against the glass composition. In the sulfide glass, A was 2.6 × 103S-1 and β was 93%, both the highest in all of the glasses investigated. By 1.06 μm pumping of a Nd: YAG laser, the sulfide glass showed strong 1.3 μm emission and the lifetime was 25 μs, resulting in a quantum efficiency of 7%. This value is higher than that of the Pr3+:1G4 level in ZBLAN glass with β= 60%.  相似文献   

12.
BaTiO3 coating films were prepared from Ba(CH3COO)2–Ti(OC3H7i)4–H2O–CH3COOH–C3H7iOH solutions containing poly(vinylpyrrolidone) (PVP) via single-step, nonrepetitive dip coating. The critical thickness—i.e., the maximum film thickness achieved without crack formation via nonrepetitive dip coating—was successfully increased by incorporation of PVP in the precursor solution. Relatively dense, crack-free BaTiO3 films >1 μm in thickness were achieved via single-step deposition using a solution containing PVP of average molecular weight of 630 000. Incorporation of an excess amount of PVP, however, led to a decrease in the critical thickness. Higher-molecular-weight PVP was more effective in increasing the critical thickness, whereas N-vinyl-2-pyrrolidone monomers did not affect the critical thickness. Stepwise heating of the gel films resulted in increased optical transmittance of the films, accompanied by film densification.  相似文献   

13.
Judd-Ofelt parameters Ω t with t = 2,4, 6 for the rare-earth ions Pr3+, Nd3+, Sm3+, Tb3+, Dy3+, Ho3+, Er3+, and Tm3+ in alkali and/or alkaline-earth silicate, borate, and phosphate glasses have been determined. The variations of Ω t with the number of 4 f electrons of the rare-earth ions are demonstrated, and factors affecting the Judd-Ofelt parameter Ω6are discussed. The intensity parameter Ω6 depends on the ionic packing ratio of the glass host by changing modifier type in silicate and borate glasses, and it is independent of that in a series of borate glasses as a function of modifier content and phosphate glasses. The peak wavenumbers of the transitions whose intensities are determined mainly by the Ω6<| U (6)|>2 term—where <| U (6)|> is one of the reduced matrix elements—shift systematically with the values of Ω6 for all the rare-earth ions.  相似文献   

14.
A thin plate of TeO2 glass of 5.0 × 4.0 × 0.25 mm3 size, which was large enough for various optical measurements, was obtained by a rapid quenching method. The linear refractive index was measured as a function of wavelength from 486.1 to 1000 nm. The refractive index at 486.1 nm was as high as 2.239. The optical energy band gap was estimated as 3.37 eV from the optical absorption spectrum. The third-order nonlinear optical susceptibility, χ(3), was determined by the third-harmonic generation (THG) method. The χ(3) value was as high as 1.4 × 10−12 esu, about 50 times as large as that of SiO2 glass. The results are discussed based on Lines' model in which an influence of cationic empty d -orbitals on the nonlinear properties was taken into account.  相似文献   

15.
Excitation of Tm3+ to 3 H 4 using the 791 nm pump source showed the frequency up-converted blue emission (∼480 nm) due to the Tm3+:1 G 43 H 6 transition in Tm3+/Nd3+ codoped CaO·Al2O3 glasses. Intensity and lifetime changes with rare-earth concentrations suggested the efficient energy transfer of Tm3+:3 H 4→ Nd3+:4 F 5/2 and Nd3+:4 F 3/2→ Tm3+:1 G 4. The latter transfer enabled Tm3+ to reach its 1 G 4 level, and the blue emission became possible through the 1 G 43 H 6 transition. Quantitative analysis with rate equations proved that these two transitions were the most efficient among all the possible energy transfer routes between Tm3+ and Nd3+. Calculated up-conversion efficiency of the Tm3+/Nd3+ combination in CaO·Al2O3 glass was 6.6 × 10−3, and it was ∼4 orders of magnitude larger than those reported for other oxide glasses.  相似文献   

16.
The thermal expansion of the hexagonal (6H) polytype of α-SiC was measured from 20° to 1000°C by the X-ray diffraction technique. The principal axial coefficients of thermal expansion were determined and can be expressed for that temperature range by second-order polynomials: α11= 3.27 × 10–6+ 3.25 × 10–9T – 1.36 × 10–12 T 2 (1/°C), and ş33= 3.18 × 10–6+ 2.48 × 10–9 T – 8.51 × 10–13 T 2 (1/°C). The σ11 is larger than α33 over the entire temperature range while the thermal expansion anisotropy, the δş value, increases continuously with increasing temperature from about 0.1 × 10–6/°C at room temperature to 0.4 × 10–6/°C at 1000°C. The thermal expansion and thermal expansion anisotropy are compared with previously published results for the (6H) polytype and are discussed relative to the structure.  相似文献   

17.
Photochemical hole burning (PHB) not only can be applied for data storage systems but also serves as a powerful method for studying the local structure around optical centers. The present work investigated the effects of aluminum, magnesium, and silicon ions on hole burning and the phonon sideband for borate glasses that exhibit PHB at room temperature. Hole burning was measured for the 5 D 0−7 F 0 transition of Sm2+ and the phonon sideband spectrum for the 5 D 0-7 F 0 transition of Eu3+. The hole width was closely related to local structural change, especially as it seemed to decrease with decreases in the number of nonbridging oxygens produced around the rare-earth ions. In the case of sodium aluminoborate glasses, the hole width decreased considerably with increasing alumina content. The ratio Γihh for 85B2O3·10Al2O3·5Na2O·1Sm2O3 glass, then, was 80 at room temperature, the largest value ever reported.  相似文献   

18.
Abstract. This paper deals with the third-order asymptotic theory for Gaussian autoregressive moving-average (ARMA) processes with unknown mean μ. We are interested in the estimation of ρ = ( α1…, αp, β1…, βq ), where α 1…, αρ and β 1…, βq are the coefficients of the autoregressive part and the moving-average part, respectively. First, we investigate the third-order asymptotic optimality of the bias adjusted maximum likelihood estimator (MLE) of ρ in the presence of the nuisance parameters μ and 2 (innovation variance). Next, for a Gaussian AR(1μ μ, 2), we propose a mean corrected estimator αc1c2 of the autoregressive coefficient. We make a comparison between the bias adjusted estimator αc1c2* and the bias adjusted MLE, in terms of their probabilities of concentration around the true value, or equivalently, in terms of their mean squared errors. Finally some numerical studies are provided in order to verify the third-order asymptotic theory.  相似文献   

19.
Either boehmite (γ-AlOOH) or gibbsite (γ-Al(OH)3) nanocrystalline thin films (h≈100 nm) can be precipitated from AlCl3 solution at fixed pH and temperature onto different substrates. It depends on the nature of the substrate (mica flakes, SiO2 flakes, or α-Al2O3 flakes), on their crystallographic properties (crystalline or amorphous), and on some experimental parameters (agitation rate, addition rate). According to the surface charge of the substrates, different alumina species are involved in the precipitation process. When negative charges are present on the substrate, the [Al3O(OH)3(OH2)9]4+ polycation is promoted, leading to the formation of the (Al4) tetramer ([Al4O(OH)10(OH2)5]o) and then to the precipitation of bohemite. When positive charges are present, a ligand bridge containing complex ([Al3O(OH)3(O2H3)3(OH2)9]+) is likely favored, giving rise to hexagonal ring structures or amorphous solids that lead to the formation of gibbsite. Besides the surface effects, crystalline substrates can act as a template during precipitation of aluminum species as shown for the formation of gibbsite on muscovite. Finally, calcination at 850°C of boehmite samples leads to porous γ-Al2O3 layers, while calcination of gibbsite leads to δ-Al2O3 layers.  相似文献   

20.
Tetragonal BaTiO3 thin films were prepared directly on Ti metal substrates in Ba(OH)2 solutions by a hydrothermal method at temperatures 400° to 800°C for 5 to 240 min. The film thickness estimated from weight gain of Ti plate was in the range from 0.5 to 2.5 μm, and it increased with increasing treatment temperature, treatment time, and Ba(OH)2 concentration. Rectangular crystals having {100} and {001} faces grew idiomorphically with approximate crystal size of 0.3 to 2.0 μm. The tetragonality of the BaTiO3 films became apparent when the average crystal size exceeded about 1 μm. Lattice parameters of the films were a = 3.994 Å, c = 4.035 Å, and c/a = 1.010. The films formed above 600°C had preferred orientation showing stronger XRD peaks of h 00 and 00 l than the other peaks.  相似文献   

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