共查询到20条相似文献,搜索用时 125 毫秒
1.
Duan’s simple model is extended to analyze the mixing of the 4f
N − 15d configuration with the 4f
N
states. The explicit static coupling and traditional dynamic coupling are considered, and the parameters are fitted according
to the absorption spectrum in LiYF4: Nd3+. The parameter values obtained are as follows: T
32 = −28i × 10−7, T
52 = −1151i × 10−7, A
322 = 192i × 10−12 cm, A
524 = i × 10−12 cm, A
726 = 54i × 10−12 cm, and A
766 = −680i × 10−12 cm. Compared to the experimental measurements, the present model yields better results than those obtained from the Judd-Ofelt
theory.
The text was submitted by the authors in English. 相似文献
2.
Wenwei Ge Hong Liu Xiangyong Zhao Xiaobing Li Xiaoming Pan Di Lin Haiqing Xu Xiangping Jiang Haosu Luo 《Applied Physics A: Materials Science & Processing》2009,95(3):761-767
In this paper, a single crystal of 0.96Na0.5Bi0.5TiO3-0.04BaTiO3 with dimensions of Φ 30×10 mm was grown by the top-seeded-solution growth method. X-ray powder diffraction results show that the as-grown crystal
possesses the rhombohedral perovskite-type structure. The dielectric, piezoelectric and electrical conductivity properties
were systematically investigated with 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples. The room-temperature dielectric constants
for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal samples are found to be 650, 740 and 400 at 1 kHz. The (T
m, ε
m) values of the dielectric temperature spectra are almost independent of the crystal orientations; they are (306°C, 3718),
(305°C, 3613) and (307°C, 3600) at 1 kHz for the 〈001〉, 〈110〉 and 〈111〉 oriented crystal. The optimum poling conditions were
obtained by investigating the piezoelectric constants d
33 as a function of poling temperature and poling electric field. For the 〈001〉 and 〈110〉 crystal samples, the maximum d
33 values of 146 and 117 pC/N are obtained when a poling electric field of 3.5 kV/mm and a poling temperature of 80°C were applied
during the poling process. The as-grown 0.96Na0.5Bi0.5TiO3-0.04BaTiO3 crystal possesses a relatively large dc electrical conductivity, especially at higher temperature, having a value of 1.98×10−11 Ω−1⋅m−1 and 3.95×10−9 Ω−1⋅m−1 at 25°C and 150°C for the 〈001〉 oriented crystal sample. 相似文献
3.
A. A. Petukhov B. E. Zhurtanov S. S. Molchanov N. D. Stoyanov Yu. P. Yakovlev 《Technical Physics》2011,56(4):520-525
The electroluminescent characteristics of an InGaAsSb/GaAlAsSb heterostructure LED emitting at 1.85 μm are studied in the
temperature range 20–200°C. It is shown that the emission power exponentially drops as P ≅ 0.4exp(2.05 × 103/T) with a rise in temperature primarily because of an increase in the Auger recombination rate. It is found that band-to-band
radiative recombination goes in parallel with recombination through acceptor levels, the latter causing the emission spectrum
to broaden. With a rise in temperature, the activation energy of the acceptor levels decreases by the law ΔE≅ 32.9 − 0.075T and the maximum of the LED’s emission spectrum shifts toward the long-wavelength range (hν
max = 0.693 − 4.497 × 10−4
T). Based on the dependence E
g
= hν
max − 0.5kT and experimental data, an expression is derived for the temperature variation of the bandgap in the In0.055Ga0.945AsSb active area, E
g
≅ 0.817 − 4.951 × 10−4
T, in the range 290 K < T < 495 K. The resistance of the heterostructure decreases exponentially with rising temperature as R
0 ≅ 5.52 × 10−2exp(0.672/2kT), while cutoff voltage U
cut characterizing the barrier height of a p−n junction decreases linearly with increasing temperature (U
cut = −1.59T + 534). It is found that the current through the heterostructure is due to the generation-recombination mechanism throughout
the temperature interval. 相似文献
4.
The incorporation of Sn into LPE GaAs was studied as a function of the atomic fractionx
Sn
l
of Sn in the liquid (1.6×10−4≤x
Sn
l
≤0.54), the growth temperatureT
K
and the cooling rate α. The diffusion coefficient of As in Ga for moderate Sn-doping was deduced from the growth velocities
to beD
As (760° C)=(3.3±1.0)×10−5 cm2/s. The epitaxial layers were analyzed after van der Pauw with special emphasis on the sources of experimental error. With
the aid of current mobility theories the concentrations of the ionized donors and acceptors were derived. From their dependence
onx
Sn
l
, on α and onT
K
combined with the Schottky-barrier model of Sn incorporation it can be concluded that the melt and the growing crystal surface
were in thermal equilibrium. The diffusion coefficient of Sn in GaAs is about 8×10−14 cm2/s at 760° C. The distribution coefficient for Sn increases from 4.4×10−5 to 12.3×10−5 in the temperature range from 690 to 800° C. The total Sn incorporationx
Sn
s
was measured using the atomic absorption spectroscopy for the first time down tox
Sn
s
=1017/cm3. From these data it can be concluded that up tox
Sn
l
=0.54 the dopant Sn is incorporated as donor and as acceptor only and that within the experimental scatter there is no indication
of incorporation as a neutral species. 相似文献
5.
The lattice parameters of CdF2 andβ-PbF2 have been determined over the temperature range 300–670 K. The coefficient of expansion at room temperature is 21·3 × 10−6 K−1 and 25·4 × 10−6 K−1 for CdF2 and PbF2 respectively and it increases linearly with temperature over the range of temperature covered. The Grüneisen parameter decreases
with temperature in both the crystals. 相似文献
6.
E. I. Lakhno E. I. Burmakin I. V. Korzun G. Sh. Shekhtman 《Physics of the Solid State》2012,54(3):504-507
The rubidium monoferrite RbFeO2-based solid solutions with the composition Rb2 − 2x
Fe2 − x
P
x
O4 have been synthesized, and their crystal structure and the temperature and concentration dependences of the total and electron
conductivities have been studied. The introduction of P5+ ions has been found to sharply decrease the electron conductivity that prevails in pure rubidium monoferrite and, at the
same time, to increase the ionic conductivity. The latter becomes dominant as the phosphorus concentration increases. The
maximum rubidium-cation conductivity of the materials under study is ∼3 × 10−2 S/cm at 300°C and ∼3 × 10−1 S/cm at 700°C. The results have been compared with the previously obtained data for similar solid solutions based on rubidium
monogallate and monoaluminate. 相似文献
7.
A. V. Besnosov S. Yu. Savinov O. O. Novozhilova M. A. Antonenkov 《Physics of Atomic Nuclei》2011,74(14):1930-1936
Presented are the results of experimental research of temperature and velocity fields for lead and lead-bismuth coolant flows
in channels having circular and annular cross sections under varying oxygen content in the coolant and varying characteristics
of insulating coatings. Tests are performed under the following operating conditions: (1) lead-bismuth eutectic—temperature
T = 400−520°C, thermodynamic oxygen activity a = 10−5–100, average flow velocity of the coolant w = 0.12−1.84 m/s, value of magnetic induction B = 0−0.85 T, Reynolds number Re = (0.24–3.5) × 105, Hartmann number Ha = 0−500, and Peclet number Pe = 320−4600; (2) lead coolant-T = 400−550°C, a = 10−5−100, w = 0.1−1.5 m/s, Re = (2.36−2.99) × 105, and Pe = 500−7000. 相似文献
8.
A. Axmann M. Schulz C. R. Fritzsche 《Applied Physics A: Materials Science & Processing》1977,12(2):173-178
The ions of Sb, As, and P have been implanted into germanium at energies ranging from 200 keV to 700 keV. Annealing was performed
at 400°C, 550°C, and 650°C. The doping profile was determined by differentialCV-measurements. Strong outdiffusion (80%) and diffusion into the bulk material was observed after annealing. The remaining
doping concentration and the diffusion constants were determined by a computer fit at 650°C. We foundD
Sb=1.8×10−13 cm2/s,D
As=9×10−14 cm2/s andD
P=4×10−14 cm2/s. Lower values of the diffusion constant were determined when the samples were covered with a SiO2 layer. 相似文献
9.
The electrical and galvanomagnetic properties of high-porosity biocarbon preforms prepared from white pine wood by pyrolysis
at carbonization temperatures T
carb = 1000 and 2400°C have been studied. Measurements have been made of the behavior with temperature of the electrical resistivity,
as well as of magnetoresistance and the Hall coefficient in the 1.8–300-K temperature interval and magnetic fields of up to
28 kOe. It has been shown that samples of both types (with T
carb = 1000 and 2400°C) are characterized by high carrier (hole) concentrations of 6.3 × 1020 and 3.6 × 1020 cm−3, respectively. While these figures approach the metallic concentration, the electrical resistivity of the biocarbon materials
studied, unlike that of normal metals, grows with decreasing temperature. Increasing T
carb brings about a decrease in electrical resistivity by a factor 1.5–2 within the 1.8–300-K temperature range. The magnetoresistance
also follows a qualitatively different pattern at low (1.8–4.2 K) temperatures: it is negative for T
carb = 2400°C and positive for T
carb = 1000°C. An analysis of experimental data has revealed that the specific features in the conductivity and magnetoresistance
of these samples are described by quantum corrections associated inherently with structural characteristics of the biocarbon
samples studied, more specifically with the difference between the fractions of the quasi-amorphous and nanocrystalline phases,
as well as with the fine structure of the latter phase forming at the two different T
carb. 相似文献
10.
The distinctive features of the low-frequency internal friction Q
−1(T) of (Cu-Sn)-Nb composites at high temperatures (up to 400°C) are investigated for strains in the range 10−5–10−4. Considerable hysteresis of Q
−1(T) in the heating-cooling cycle is recorded, including the presence of a minimum at ∼175°C when the sample is heated to 400°C
and two peaks P
2 (at 280°C) and P
1 (at ∼100°C) when the sample is cooled from 400°C. The activation energy of the anomalous internal friction background (up
to 175°C), the oxygen diffusion parameters, and the oxygen concentration in the niobium fibers (all of which govern the peak
P
2) are calculated, and the value and temperature dependence of the yield point of the bronze matrix (which govern the peak
P
1) are estimated.
Zh. Tekh. Fiz. 68, 114–117 (November 1998) 相似文献
11.
In the present study, a kind of solid polymer electrolyte (SPE) based on poly(vinylidene difluoride-co-hexafluoropropylene)/poly(methyl methacrylate) blends was prepared by a casting method to solve the safety problem of lithium
secondary batteries. Owing to being plasticized with a room temperature ionic liquid, N-butyl-N′-methyl-imidiazolium hexafluorophosphate, the obtained SPE shows a thermal decomposition temperature over 300°C and an ionic
conductivity close to 10−3 S cm−1. The SPE-3 sample, in which the weight of two polymers is equivalent, possesses an ionic conductivity of 0.45 × 10−3 S cm−1 at 25°C and presents an electrochemical window of 4.43 V. The ionic conductivity of the SPE-3 is as high as 1.73 × 10−3 S cm−1 at 75°C approaching to that of liquid electrolyte. The electrochemical performances of the Li/LiFePO4 cells confirmed its feasibility in lithium secondary batteries. 相似文献
12.
Chen Li-chuan A. Rabenau W. Weppner 《Applied Physics A: Materials Science & Processing》1978,17(3):233-237
The ionic and electronic conductivities of Ag2Tl6I10 single crystals have been studied as a function of crystallographic orientation and temperature from 20 to 135°C. EMF as
well as AC and DC techniques have been employed. The highly anisotropic material is predominantly an Ag+-ion conductor parallel toc-direction, with the Ag+ ions moving through linear channels that are not interconnected. The conductivity σ‖c
=1.6×10−7Ω−1cm−1 at 25°C, with an activation enthalpy for σ‖c
of 0.38 eV. The conduction perpendicular toc-direction has been found to be predominantly electronic with a value of σ⊥c
=3×10−9Ω−1cm−1 at 25°C and an activation enthalpy for σ⊥c
of 0.64 eV. This is the first observation of one-dimensional Ag+ conduction and this type of orientation-dependent change from ionic to electronic conduction.
On leave from Institute of Physics, Academia Sinica, Peking, China. 相似文献
13.
The temperature characteristics of a Y-cut Z-propagation LiNbO3 crystal light modulator, with manufacturing errors, in the absence and presence of an electric field have been investigated
by analyses and experiments. According to our analyses, when the Z-axis of the LiNbO3 crystal is at an angle of 0.22° with respect to the normal of the input surface of the crystal, we found the theoretical
fluctuation of the normalized output-light intensity with temperature to be less than 7:75 × 10−6/°C. This magnitude is less than 1% of the theoretical intensity fluctuation of a conventional temperature-compensation LiNbO3 light modulator. The measured temperature characteristics of a prototype of this modulator were 2 × 10−4/°C in the absence of an electric field (OFF state) and 2:8 × 10−4/°C in the presence of an external field (ON state). During a running test of longer than 8 hours at room temperature, the
intensity fluctuation of this prototype was 0.01% in the OFF state, and 0.07% in the ON state. 相似文献
14.
M.?Cristina?Gon?alves Verónica?de?Zea Bermudez M.?M.?Silva M.?J.?Smith Enrique?Morales Rute?A.?Sá Ferreira Luís?D.?Carlos 《Ionics》2010,16(3):193-201
Variable chain length di-urethane cross-linked poly(oxyethylene) (POE)/siloxane hybrid networks were prepared by application
of a sol-gel strategy. These materials, designated as di-urethanesils (represented as d-Ut(Y′), where Y′ indicates the average
molecular weight of the polymer segment), were doped with lithium triflate (LiCF3SO3). The two host hybrid matrices used, d-Ut(300) and d-Ut(600), incorporate POE chains with approximately 6 and 13 (OCH2CH2) repeat units, respectively. All the samples studied, with compositions ∞ > n ≥ 1 (where n is the molar ratio of (OCH2CH2) repeat units per Li+), are entirely amorphous. The di-urethanesils are thermally stable up to at least 200 °C. At room temperature the conductivity
maxima of the d-Ut(300)- and d-Ut(600)-based di-urethanesil families are located at n = 1 (approximately 2.0 × 10−6 and 7.4 × 10−5 Scm−1, respectively). At about 100 °C, both these samples also exhibit the highest conductivity of the two electrolyte systems
(approximately 1.6 × 10−4 and 1.0 × 10−3 Scm−1, respectively). The d-Ut(600)-based xerogel with n = 1 displays excellent redox stability. 相似文献
15.
Gold electrodes with known contact geometries were studied using impedance spectroscopy. From these data it was possible to
determine the specific polarisation conductivity per unit length of three-phase boundary (TPB). The values were found to be
(3÷22)×10−4 S·cm−1 dependent on the electrode history in pure oxygen at 977 °C and 2×10−6 S·cm−1 at 977 °C in “pure” hydrogen (PO2=10−20 atm at 1001 °C). The results are compared with previous data obtained for platinum electrodes. 相似文献
16.
A. V. Pashchenko V. P. Pashchenko A. G. Sil’cheva V. K. Prokopenko A. A. Shemyakov Yu. F. Revenko V. P. Komarov S. V. Gorban’ 《Physics of the Solid State》2011,53(2):309-315
The structure and properties of lanthanum strontium manganite perovskites La0.6Sr0.2Mn1.2 − y
Cr
y
O3 ± δ (y = 0–0.3) sintered at 1430°C have been studied by X-ray, resistive, and magnetic (χac and 55Mn NMR) methods. The parameter of the rhombohedrally distorted (R
$
\bar 3
$
\bar 3
c) perovskite structure decreases with increasing y. The real perovskite structure contains point (anion and cation vacancies) and cluster-type nanostructure defects. The analysis
of asymmetrically broadened 55Mn NMR spectra has confirmed the high-frequency electron-hole exchange Mn3+ ↔ Mn4+ and local inhomogeneity of their surrounding by other ions and point and cluster-type defects. An increase in the Cr content
leads to an increase in the resistivity and the magnetoresistive effect and a decrease in the metal-semiconductor and ferromagnetic-paramagnetic
phase transition temperatures (T
ms
and T
c
) due to the distortion of the exchange interactions Mn3+ ↔ Mn4+ by chromium ions, vacancies, and clusters. Introduction of Cr decreases the ferromagnetic component and increases the activation
energy. The magnetoresistive effect near T
ms
and T
c
is caused by scattering of charge carriers from intercrystallite nanostructure inhomogeneities of the lattice, and the low-temperature
effect is associated with the tunneling on mesostructural intercrystallite boundaries. 相似文献
17.
We have studied the magnetic aftereffects in the Ni
x
Fe3−x−ΔO4 system, for 0≦x≦1 and 10−5≦Δ≦2×10−1, between 80 and 500 K. The samples were obtained by sintering at 1400°C in an appropriate gas atmosphere. The measurements
are based on the deviation from equilibrium that is produced in a Maxwell-Wien bridge when the self-induction of a coil with
ferrite core varies because of the phenomenon of magnetic aftereffects. The numerical analysis of the results shows the presence
of relaxation processes at 300 K (III), 330 K (IIa), and above 500 K (I). The Processes III and IIa are related to the concentration
of nickel,x, and of vacancy, Δ. It is seen that the IIa peak can be attributed to a process of diffusion of Ni ions in the spinel lattice
by means of vacancies on octahedral sites. 相似文献
18.
The luminescence kinetics of the Cd II ion at a wavelength of 441.6 nm has been studied experi-mentally in a high-pressure
He-Cd mixture in the presence of Ar, Ne, Xe, and CCl4 impurities. Cadmium ions were excited through the bombardment of a cadmium foil heated up to 240°C by a pulsed electron beam
with an electron energy of 150 keV, a pulse duration of 3 ns, and a current of 500 A. The constants of collisional quenching
of the Cd II 5s
2
2
D
5/2 level by Ar, Ne, and Xe atoms and CCl4 molecules and the integral luminescence quenching constants of this level in the helium medium by these impurity gases have
been determined. The constants of collisional quenching appeared to be 8.1 × 10−12 (Ar), 1.2 × 10−12 (Xe), 1.5 × 10−13 (Ne), and 1.8 × 10−10 cm3/s (CCl4, for λ = 325 nm), while the integral constants were found to be, respectively, 4.1 × 10−11, 3.4 × 10−11, 9.5 × 10−12, 1.4 × 10−9 cm3/s for Ar, Ne, Xe, and CCl4 at a buffer gas pressure of 1 atm.
Original Russian Text ? A.I. Miskevich, Liu Tao, 2009, published in Optika i Spektroskopiya, 2009, Vol. 107, No. 1, pp. 45–49. 相似文献
19.
A Tm, Mg co-doped LiTaO3 crystal has been grown by Czochralski method. Room temperature polarized absorption spectra and fluorescence spectrum of
the Tm, Mg:LiTaO3 crystal were measured and analyzed. The maximum absorption cross-section is 6.0791 × 10−20 cm2 at around 790 nm with full width at half maximum of 5 nm. The emission cross-section of 3
F
4 manifold was 2.2 × 10−20 cm2. The spectroscopic parameters of Tm3+ ion were calculated by applying the Judd-Ofelt approach, and the intensity parameters Ω2, Ω4, and Ω6 were obtained to be 7.71 × 10−20, 1.09 × 10−20, and 1.16 × 10−20 cm2, respectively. The branching ratios and radiative lifetimes were also presented and the radiative lifetime of Tm3+
3
F
4 → 3
H
6 transition is 968.3 μs. The results were also analyzed and compared with other Tm3+ doped hosts. 相似文献
20.
G. A. Oganesyan I. I. Novak 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2009,3(6):962-965
The electrical properties of thermal donors formed in the bulk and near-surface regions in silicon samples with (3–9) × 1017 cm−3 oxygen concentrations under elastic tensile stress σ of about 1 GPa have been studied. The original method allowing us to
control an introduced elastic tensile stress during the thermal donor’s formation at T = 450°C by a double-crystal X-ray diffractometer has been used. The formation of thermal donors in silicon with a high oxygen
concentration of 9.3 × 1017 cm−3 under tensile stress has been found to be less effective than in silicon with a low oxygen concentration of (3–5) × 1017 cm−3. Single-charged donors are formed in silicon with a low oxygen concentration under tensile stress while double-charged donors
are formed in silicon with a high oxygen concentration. 相似文献