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1.
The temperature‐dependent Raman spectra of ferroelectric Bi 4−xNd xTi 3O 12( x = 0, 0.5, 0.85) single crystals were recorded from 100 to 800 K. It was found that there is a critical Nd content x0 between 0.5 and 0.85. The Nd 3+ ions prefer to replace Bi 3+ ions in pseudo‐perovskite layers when x < x0, while they might begin to incorporate into (Bi 2O 2) 2+ layers when x ≥ x0. Nd substitution leads to a decrease in the ferroelectric–paraelectric transition temperature ( Tc). A monoclinic distortion of orthorhombic structure occurs in Bi 4Ti 3O 12 crystals at temperatures below 200 K. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
2.
A systematic study of the doping of the Mn-sites by cobalt in three series of manganites — La 0.76Ba 0.24(Mn 1−xCo x)O 3 single crystals, La 2/3Ba 1/3(Mn 1−xCo x)O 3 and La(Mn 1−xCo x)O 3 ceramics has been performed. It was found that La(Mn 1−xCo x)O 3 annealed at 800°C in the range 0.4 x0.9 is a mixture of ferromagnetic domains with ordered Mn and Co ions and ionically disordered spin-glass domains. In the quenched samples the fraction of spin-glass-type component increases strongly. The La 2/3Ba 1/3(Mn 1−xCo x)O 3 solid solutions exhibit also an evidence for phase separation in the range 0.5 x0.8. All the La(Mn 1−xCo x)O 3 samples show an insulating behavior, however, magnetoresistance reduces strongly when the cobalt content rises to x=0.5. The La 0.76Ba 0.24(Mn 1−xCo x)O 3 single crystals show first-order phase transition below their Curie points associated with a change of ground state of the Co 2+ ions. The magnetic phase diagrams are depicted. The results are discussed in terms of positive Mn 3+–O–Mn 4+, Mn 3+–O–Mn 3+, Mn 4+–O–Co 2+ and negative Mn 4+–O–Mn 4+, Co 2+–O–Co 2+, Co 2+–O–Mn 3+ superexchange interactions as well as Co 2+ and Mn 4+ ionic ordering. 相似文献
3.
We present a reliable method for growing single crystals of Y 1−xPr xBa 2Cu 3O 7−δ high- Tc superconductors in ZrO 2 crucibles. This method results in crystals with greatly improved superconducting properties compared to crystals grown with the previously reported methods which use Al 2O 3 crucibles. We describe techniques for crystal growth in both Al 2O 3 and ZrO 2 crucibles using an excess of BaCo 3 and CuO as the flux. The crystals were characterized by means of DC magnetic-susceptibility measurements, electrical-resistivity measurements, and electron microprobe analysis. The effects of Al contamination on the conditions for crystal growth and on the superconducting properties of the crystals are found to be quite significant. 相似文献
4.
Results of investigations into the physical properties of a number of new nonlinear crystals are presented. The parameters of frequency converters manufactured on their basis are compared, and second-harmonic generation of CO 2 lasers first excited by frequency conversion in LiInSe 2, AgGa 1– x
In xSe 2, Ag xGa xGe xS 2(1 + x), and Hg 1–x
Cd xGa 2S 4 crystals is investigated. The superiority of HgGa 2S 4, Hg 1–x
Cd xGa 2S 4, and AgGa 1–x
In xSe 2 over the well-known crystals has been demonstrated for frequency conversion both within the middle-IR range and from the visible range to the middle-IR range. Advantages of LiInSe 2 and AgGa 1–x
In xSe 2 crystals are demonstrated for the direct frequency conversion of femtosecond laser radiation to the middle-IR range compared to the cascade frequency conversion and direct frequency conversion in LiInS 2 crystals. 相似文献
5.
The luminescence and absorption properties of Ba(Y1−x
Er
x
)2F8 (x=0.001, 0.01, 0.05, 0.1, 0.2 and 0.3) and the Er3+-ion decay kinetics of luminescent transitions from three initial laser states, the4S3/2,4F.9/2 and4I11/2 manifolds, were measured. The crystal-field splitting schemes for allJ-manifolds which are involved in (J →J′)-luminescence transitions and stimulated emission parameters of Er3+ -ions in BaY2F8 were determined. A comparison of laser powers and efficiencies of BaY2F8 and Y3Al5O12, Lu3Al5O12 and LiYF4 single crystals doped with Er3+-ions shows the similar performance of these materials. 相似文献
6.
The electron spin resonance (ESR) spectra of undoped and manganese-doped BSCCO (2212) crystals (nominal composition Bi 2Sr 2CaCu 2–x
Mn xO y, where x=0.1) are compared.
Zh. Tekh. Fiz. 67, 137–138 (October 1997) 相似文献
7.
We have investigated the reflection spectra in polarized light at 80 and 295 K in an energy region of 1.0–4.8 eV for the single crystals of ternary and quaternary copperoxide systems with the participation of rareearth elements (La 2CuO 4–x
, LaCuO 4, Pr 2CuO 4–x
, GdBa 2Cu 3O 7–x
, and LaSrCaCuO). 相似文献
8.
Abstract The Raman spectra of Y B a2C u3O x, single crystals (x=6.25; 6.75; 7.0) were measured at pressures up to 22 GPa (35 GPa for x=6.25) at room temperature in nearly hydrostatic conditions. The frequency-volume curves for most of the Raman-active fundamental vibrations were derived from the present data making use of a previous high-pressure study of the equations of state of Y Ba 2 Cu 3 O x compounds. 相似文献
9.
X-ray structural, X-ray phase, and dilatometric analyses were used to explore specific features of the formation of solid
solutions in the (1 − x)SrTiO 3− xBiScO 3 system with x = 0.0, 0.1, 0.2, 0.3, 0.4, and 0.5. It was found that the synthesis of solid solutions from the initial Bi 2O 3, Sc 2O 3, TiO 2, and SrCO 3 components is accompanied by a considerable increase in the linear dimensions of the samples, depending on their composition.
Solid solutions with x > 0.1 are formed through intermediate phases (Sr 5Bi 6O 14 at x = 0.2; Sr 0.78Bi 2.22O 4 at x = 0.3; and Sr 2.25Bi 6.75O 12.38 at x = 0.4 and 0.5). It was shown that the samples with x = 0.2, 0.3, 0.4, and 0.5 have two phases: one with a cubic Pm3 m structure and one with a tetragonal I4/ mcm structure. 相似文献
10.
(CdO) 1?x–(InO 3/2) x thin films were deposited on glass substrates by the sol–gel method. The precursor solutions for the mixed oxide films were obtained from the mixture of the precursor solutions for CdO and In 2O 3 prepared separately. The investigated In atomic concentrations in the solution, x, were 0.0, 0.16, 0.33, 0.50, 0.67, 0.84, and 1. X-ray diffraction measurements showed that the films were mainly constituted of CdO, In 2O 3, and CdIn 2O 4. CdO and In 2O 3 were obtained for x=0 and 1, respectively. For x=0.67, which is the stoichiometric composition of the CdIn 2O 4 compound, only this oxide was formed. CdO and CdIn 2O 4 crystals were obtained in the Cd-rich region, whereas In 2O 3 and CdIn 2O 4 crystals were formed in the In-rich region. The PL spectra at 15 K for CdO showed the presence of two main emission bands at energies close to 2.2 and 3.0 eV. A blue-shift of these bands took place for increasing In concentration, which is related to the increase in the band gap energy of the mixed system in going from CdO, with a band gap energy of 2.46 eV, to CdIn 2O 4, with 3.2 eV, to In 2O 3, with 3.6 eV. 相似文献
11.
The glasses with the composition of 37.5Li 2O–(25 − x)Fe 2O 3– xNb 2O 5–37.5P 2O 5 (mol%) ( x = 5,10,15) are prepared, and it is found that the addition of Nb 2O 5 is effective for the glass formation in the lithium iron phosphate system. The glass–ceramics consisting of Nasicon-type Li 3Fe 2(PO 4) 3 crystals with an orthorhombic structure are developed through conventional crystallization in an electric furnace, showing electrical conductivities of 3 × 10 − 6 Scm − 1 at room temperature and the activation energies of 0.48 eV ( x = 5) and 0.51 eV ( x = 10) for Li + ion conduction in the temperature range of 30–200 °C. A continuous wave Nd:YAG laser (wavelength: 1064 nm) with powers of 0.14–0.30 W and a scanning speed of 10 μm/s is irradiated onto the surface of the glasses, and the formation of Li 3Fe 2(PO 4) 3 crystals is confirmed from XRD analyses and micro-Raman scattering spectra. The crystallization of the precursor glasses is considered as new route for the fabrication of Li 3Fe 2(PO 4) 3 crystals being candidates for use as electrolyte materials in lithium ion secondary batteries. 相似文献
12.
The dielectric nonlinearity of ferroelectric Li 2−x
Na xGe 4O 9 ( x≈0.23) crystals is measured in the neighborhood of the phase transition temperatures. The magnitude of the nonlinear coefficient
β is estimated from the shift in T
c and the reduction in ɛ
max under the influence of E
=, from the dielectric nonlinearity in the paraphase, and from the temperature dependence of P
s in crystalline Li 2−x
Na xGe 4O 9 ( x≈0.23). The resulting values of β are 1.87, 1.26, 2.17, and 1.17×10 −9 (CGSE cm 2) −2, respectively. The mechanism for the phase transition in crystalline Li 2−x
Na xGe 4O 9 ( x≈0.23) is discussed.
Fiz. Tverd. Tela (St. Petersburg) 41, 1070–1072 (June 1999) 相似文献
13.
An experimental study of nonreciprocal spatial-dispersion effects in para-(Cd 1−x
Mn xTe), ferro-(LiFe 5O 8), and antiferromagnetic (Cr 2O 3) crystals caused by an external magnetic field or magnetic order is reported.
Fiz. Tverd. Tela (St. Petersburg) 40, 946–948 (May 1998) 相似文献
14.
The ceramics and single crystals of the Bi 2Sr 2CaFe 2O x compound were synthesized. The X-ray diffraction data showed orthorhombic symmetry. The lattice parameters are equal to a=5.464 Å, b=5.453 Å, c=31.313 Å. The crystal structure is described by the primitive Bravais lattice with the possible space groups Pbmm. Pbm2 and Pb2 1m. The obtained X-ray patterns show the presence the incommensurate structural modulation with the following parameters: the modulation vector lies in the (100)-plane, the value of the wave-vector component q
b=0.22(3). The comparison of the obtained results with data for Fe-doped Bi 2Sr 2CaCu 2O x and Bi 2Sr 3Fe 2O x are presented. No magnetic peculiarities of the compound were found. Mssbauer measurements of the ceramic samples indicate the presence mainly of Fe 3+ oxidation state and Fe 4+ (about 20%). The decrease of the quadrupole-splitting values for 2212Fe in comparison with Fe-doped 2212Cu was revealed that may be connected with higher symmetry of the local environment of Fe atoms in 2212Fe. 相似文献
15.
Torque measurements have been performed at 4 and 77 K on single crystals of Mn 1?xFe 2+xO 4 (0< x<0.05) and MnFe 2?xTi xO 4 (0< x<0.1). The crystals were either quenched or slowly cooled causing a change of inversion by 0.1. It is found that the magnetic anisotropy due to the ferrous ions in the Ti-doped samples is 80 per cent larger than in the Mn 1?xFe 2+xO 4 crystals. In both crystal series the ferrous ion anisotropy in the slowly cooled crystals is 70 per cent higher than in the quenched crystals. The K1 of MnFe 2O 4 at 4 K is found to decrease from ?3.6 × 10 5 erg/cm 3 after show cooling, down to ?2.6 × 10 5 erg/cm 3 after quenching. 相似文献
16.
The luminescence and absorption properties of Ba(Y 1–x
Er
x
) 2F 8 ( x=0.001, 0.01, 0.05, 0.1, 0.2 and 0.3) and the Er 3+-ion decay kinetics of luminescent transitions from three initial laser states, the 4S 3/2, 4F. 9/2 and 4I 11/2 manifolds, were measured. The crystal-field splitting schemes for all J-manifolds which are involved in ( J J)-luminescence transitions and stimulated emission parameters of Er 3+ -ions in BaY 2F 8 were determined. A comparison of laser powers and efficiencies of BaY 2F 8 and Y 3Al 5O 12, Lu 3Al 5O 12 and LiYF 4 single crystals doped with Er 3+-ions shows the similar performance of these materials. 相似文献
17.
We have observed the anomalous magnetization of Bi 2Sr 2CaCu 2−xNi xO 8 ( x = 0 and 0.02) single crystals. Anisotropy decreases with iodine intercalation although it expands the space between CuO 2 layers. Iodine intercalation seems to suppress the magnetization anomaly for Ni = 1% crystals, but not for Ni = 1% substituted crystals. We have discussed these results in terms of the increase of anisotropy by Ni substitution and the dimensional crossover of flux lines. Effects of both oxygen concentration and substitution of a magnetic element for the Cu site on the anisotropy of Bi 2Sr 2CaCu 2O 8 crystals show the same tendency as the case of the YBa 2Cu 3O 7 superconductor. 相似文献
18.
利用一个空间零维大气等离子体模型对其中的氮氧化物在不同电离度情况下的变化规律进行了数值模拟,得到了放电后不同初始电子密度下的氮氧化物(包括NO,NO +,NO 2,NO 2+,N 2O,N 2O +,NO 3和N 2O 5)及影响其产消的主要反应物N和O 3的密度随时间的演化规律.结果表明,电子初始密度n e0=10 9 cm -3时,NO和NO 2的去除率较高,氮氧化物总密度较小,最适合消除氮氧化物污染.同时,还对N和O 3随电离度变化的行为进行了分析.
关键词:
大气等离子体
氮氧化物
电离度
数值模拟 相似文献
19.
Glasses of general formula xSb 2O 3 (1− x)B 2O 3 (0 x0.8) have been prepared by conventional melt- quenching. Mössbauer spectroscopy shows that a fraction of the Sb 3+ is converted to Sb 5+ and this fraction increases with x. High-field 11B MAS NMR gives well-resolved resonances from boron atoms which are 3- and 4-coordinated to oxygen. The fraction of 4-coordinated boron, N 4, goes through a maximum value of 0.12±0.01 at x=0.5. The position of the maximum in N 4 is consistent with the cation potential for Sb 3+, as observed for other systems. However, the low value of N 4 at this maximum is not so readily explained. The values are similar to those predicted if [BO 4] − were stabilised by [SbO 4] + but the trends with composition are different. 相似文献
20.
Solid solutions CaLa2-xEu
x
Ge3O10 (x = 0.0–0.6, Δx = 0.1) have been synthesized for the first time. The compounds are isostructural to CaLa2Ge3O10, they crystallize in the monoclinic system, space group P21/c, Z = 4. The low-temperature X-ray diffraction studies have revealed the strain anisotropy of germanate CaLa2Ge3O10 crystal lattice in the temperature range 80–298 K, and the linear thermal expansion coefficients have been calculated. The optical properties of the activated phases have been studied, and the influence of the dopant concentration and the excitation wavelength on the luminescence characteristics of the synthesized compounds has been established. 相似文献
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