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1.
We have calculated the anisotropic frequency dependent dielectric function for the 1T and 2H phases of TaS2 and TaSe2 using the linear muffin tin orbital method within the atomic sphere approximation. We find significant anisotropy in the
frequency dependent dielectric function for the 1T and 2H phases at low energies (less than 4 eV). Unfortunately there are
no experimental data to compare with. The averaged dielectric function agrees with the available experimental data except
that the calculated peak heights are underestimated and shifted to higher energies by 1–2eV. 相似文献
2.
The compounds CuxNb3Se4 (0≤x≤0,45) and HxNb3Se4 (0≤x≤2·10−3) were prepared by electrochemical titration from Nb3Se4. The samples were characterized by X-ray analysis and q-probe conductivity measurements as a function of temperature. The
Cu-compound is isostructural with Nb3Se4 for 0≤x≤0.2 and shows new phases for 0,2≤x≤0,45. The H-compound shows an impurity controlled conductivity in the temperature
range from 20 to 200 °C and an intrinsic type conductivity in the temperature range from 330 to 450 °C. The activation engines
are 0 and 0.15 eV, respectively. Rapid proton conduction in HxNb3Se4 makes it difficult to control the composition as demonstrated by exposure of the samples to different atmospheres. An increasing
H-concentration decreases drastically the conductivity by several orders of magnitude. 相似文献
3.
4.
The photoelectromagnetic effect of InP is studied in quantizing magnetic fields at 4·2 K in an energy range 1·4–1·5 eV for linearly polarized light. Depending on the sample surface condition two types of spectral oscillations may appear, those associated with interband transitions between Landau levels or the LO phonon type usually seen in photoconductivity. An analysis of the spectral oscillations gives: E0 = 1·423±0·001 eV; Δ0 = 0·102±0·006 eV; hωL = 0·036 eV. 相似文献
5.
Temperature and frequency dependence of dielectric constant (ε′) and dielectric loss (ε″) are studied in glassy Se70Te30 and Se70Te28Zn2. The measurements have been made in the frequency range (8-500 kHz) and in the temperature range 300 to 350 K. An analysis of the dielectric loss data shows that the Guintini's theory of dielectric dispersion based on two-electron hopping over a potential barrier is applicable in the present case.No dielectric loss peak is observed in glassy Se70Te30. However, such loss peaks exist in the glassy Se70Te28Zn2 in the above frequency and temperature range. The Cole-Cole diagrams have been used to determine some parameters such as the distribution parameter (α), the macroscopic relaxation time (τ0), the molecular relaxation time (τ) and the Gibb's free energy for relaxation (ΔF). 相似文献
6.
The dc electric field dependence of the low frequency dielectric constant was investigated in the linear chain compound orthorhombic TaS3. While the dielectric constant is barely effected by an applied dc field below the threshold field of the nonlinear conduction, in the current carrying state a large enhancement is observed. Inductive response at the narrow band noise frequency was also detected. 相似文献
7.
The dipole moment of D2O has been determined from Stark effect measurements for the 313–220 and 441–532 microwave transitions as 1·857 ± 0·006 and 1·869 ± 0·005D respectively. A rotational dependence of dipole moment has also been established for HDO through μa in the 220–221 and 532–533 transitions; μa was determined as 0·662 ± 0·001 and 0·644 ± 0·001D respectively. The total dipole moment for HDO has been determined from the 321–414 transition to be 1·85 ± 0·01D and to lie within 0·1° of the bisector of the HOD angle. High resolution Stark spectroscopy has been performed on the 624–615 transition of D2O with improved precision using the 337 μm emission line of the HCN laser. This experiment has confirmed the dipole results from the microwave work and the frequency of the 624–615 transition in D2O has been determined as 890 395 ± 3 MHz. The slight increase of dipole moment with deuteration is consistent with the dipole moment for H2O determined from the dielectric constant. This increase is discussed for the vibrational ground state (as for ammonia) in terms of anharmonicity in the bending vibration. The change of μ with rotational transition is interpreted in terms of large changes in molecular geometry for certain rotational states due to centrifugal distortion. 相似文献
8.
The optical properties of thick sputtered films (~30μ) of amorphous Ge, grown with different substrate temperatures (0ˇ-T sˇ-350°C), were obtained between 0·05 and 4·5 eV by a combination of reflectance, transmittance and ellipsometric measurements. The refractive index at 0·15 eV decreases monotonically with increasing T s, or equivalently, with increasing density, and is 4·13±0·05 eV in the highest density films. The absorption edge is approximately exponential (102?α?104 cm?1) but shifts monotonically to higher energy and increases in slope with increasing T s. Similarly, the peak in ε2 grows by about 10% and shifts by about 0·15 eV to higher energies, reaching a maximum of about 23 at 2·90±0·05 eV in the high density films. The peak in the transition strength ω2ε2 occurs at 4·2±0·2 eV in all films, but increases in magnitude with increasing T s. The sum rules for n eff(ω) and ε0,eff(ω) are evaluated for ▄ω?5 eV and vary monotonically with T s. These trends are neither compatible with Galeener's void resonance theory nor with changes in the oxygen content of the films, determined by the examination of absorption peaks at 0·053 eV and 0·09 eV. An explanation, suggested here and expanded in I, is based on the observed changes in the structure of the network and voids. 相似文献
9.
Fu-Ling Tang Zheng-Xin Zhu Hong-Tao Xue Wen-Jiang Lu Yu-Dong Feng Zhi-Min Wang Yi Wang 《Physica B: Condensed Matter》2012,407(24):4814-4818
Two kinds of exchange–correlation functional GGA–PBE and HSE06 were used in the first principle method to calculate the complex dielectric function of CuInSe2 and CuAlSe2. Compared with experimental data, GGA–PBE functional cannot properly predict dielectric function, while calculated results by HSE06 quantitatively agree with experimental data. With HSE06 functional, optical properties of CuIn1−xAlxSe2 (x=0, 0.25, 0.5, 0.75 and 1) were calculated. As x increases from 0 to 1, within the solar spectrum, the real and the imaginary parts of the dielectric functions reduce, the static dielectric constant decreases from 7 to 5, the absorption coefficient and refractive indices decrease, while the optical band gap increases from 1.07 to 2.61 eV. 相似文献
10.
采用固相烧结法合成了单相巨介电常数氧化物CaCu3Ti4O12(CCTO).用阻抗分析仪分析了10—420 K温度范围内的介电频谱和阻抗谱特性,并结合ZVIEW软件进行了模拟.结果表明:温度高于室温时,频谱出现两个明显的弛豫台阶,低频弛豫介电常数随温度升高而显著增大,表现出热离子极化特点;温度低于室温时,频谱表现出类德拜弛豫,且高、低平台介电常数值基本不随温度变化,表现出界面极化特点和较好的温度稳定性.频谱中依次出现的介电弛豫对应于阻抗谱中
关键词:
3Ti4O12')" href="#">CaCu3Ti4O12
介电频谱
阻抗谱
Cole-Cole半圆弧 相似文献
11.
The frequency and temperature dependence of real and imaginary parts of the dielectric constant (ε′,?ε″), the phase shift (?) and the ac-conductivity (σ) of polycrystalline complexes (β-CD)2·BaI7·11H2O and (β-CD)2·CdI7·15H2O (β-CD?=?β-cyclodextrin) has been investigated over the frequency and temperature ranges 0–100?kHz and 140–420?K in combination with their Raman spectra, DSC traces and XRD patterns. The ε′(T), ε″(T) and ?(T) values at frequency 300?Hz in the range T<330?K show two sigmoids, two bell-shaped curves and two minima respectively revealing the existence of two kinds of water molecule, the tightly bound and the easily movable. Both complexes show the transition of normal hydrogen bonds to flip-flop type at 201?K. In the β-Ba complex most of the eleven water molecules remain tightly bound and only a small number of them are easily movable. On the contrary, in the β-Cd case the tightly bound water molecules are transformed gradually to easily movable. Their DSC traces show endothermic peaks with onset temperatures 118°C, 128°C for β-Ba and 106°C, 123°C, 131°C for β-Cd. The peaks 118°C, 106°C, 123°C are related to the easily movable and the tightly bound water molecules, while the peaks at 128°C, 131°C are caused by the sublimation of iodine. The activation energy of Ba2+ ions is 0.52?eV when all the water molecules exist in the sample and 0.99?eV when the easily movable water molecules have been removed. In the case of β-Cd the corresponding activation energies are 0.57?eV and 0.33?eV. The Raman peaks at 179?cm?1, 170?cm?1 and 165–166?cm?1 are due to the charge transfer interactions in the polyiodide chains. 相似文献
12.
Homogeneous Bi2Se3 crystals with various germanium content were prepared by means of modified Bridgman technique. Reflectivity measurements in the region of plasma resonance frequency of the free carriers revealed a shift of the reflectivity minimum towards shorter wavelengths for samples with higher germanium content. Combining the reflectivity data and the results of the Hall constant measurement we determined the free-carrier concentration for individual Ge-doped Bi2Se3 samples. It is shown that the germanium atoms give rise to donor levels. The ionization energy of these levels was estimated at less than 0·026 eV. The donor levels are most probably connected with the existence of singly ionized germanium atoms in interstitial positions. 相似文献
13.
Two-photon conductivity in GaAs and CdS0·5Se0·5 were investigated with modelocked Nd:glass laser pulse excitation, with a view to determine their suitability for picosecond pulsewidth measurement. The contrast ratio using GaAs as twophoton conductor was 1.8 and it increased to 2.4 when CdS0·5Se0·5 was used. The improved contrast ratio in the case of CdS0·5Se0·5 was partly due to the improved resolution of the crystal (2 ps) and partly due to the extended square-law region. 相似文献
14.
Sb2Te3?x Se x (x=0·00?1·25) single crystals were prepared from 5N purity elements using a modified Bridgman method. Measurements of the reflectivity spectra in the plasma resonance frequency range, Hall constantR H(B∥c) and electrical conductivityσ ⊥C were carried out on these samples at room temperature. With increasing selenium content a shift of the reflectivity minimum towards longer wavelengths was observed as well as an increase of the Hall constant and a decrease of the electrical conductivity — the incorporation of Se atoms into the Sb2Te3 crystal lattice results obviously in a decrease in the concentration of free carriers. This effect is accounted for by a change in the polarity of bonds in the Sb2Te3 crystal lattice, due to the formation of Se Te x substitutional defects. 相似文献
15.
The optical properties of the Bridgman method grown Ga4Se3S crystals have been investigated by means of room temperature, transmittance and reflectance spectral analysis. The optical data have revealed an indirect allowed transition band gap of 2.08 eV. The room temperature refractive index, which was calculated from the reflectance and transmittance data, allowed the identification of the dispersion and oscillator energies, static dielectric constant and static refractive index as 21.08 and 3.85 eV, 6.48 and 2.55, respectively. 相似文献
16.
Abstract This paper presents the results of the investigation of dielectric dispersion and ultrasonic velocity in the ferroelectric (CH3)2NH2Al(SO4)2 · 6H2O crystal. The crystal shows a critical slowing down process of polarization with an extremely long relaxation time of the dipole system (τ = 1.6 · 10?7s at the phase transition point). The dielectric response over the frequency range up to 56 GHz in the paraelectric phase can be well described in terms of a monodispersive Debye-type formula. The activation energy of dipoles in the paraelectric phase is 0.11 eV = 8.5 kTc . The results show that the proper ferroelectric phase transition is nearly critical and of the order-disorder type. 相似文献
17.
Synthesis, crystal structure, and dielectric properties of [C6H4(NH3)2]2ClBiCl6.H2O are reported. The compound crystallizes in the monoclinic system with space group P21/n. The unit cell dimensions are a = 9.836(5), b = 19.582(5), c = 13.082(5) ?, β = 104.731(5)° with Z = 4. The atomic arrangement can be described by an alternation of organic and inorganic layers. The anionic layer is built
up of octahedral of [BiCl6]3- arranged in sandwich between the organic layers. The crystal packing is governed by means of the ionic N–H···Cl hydrogen
bonds, forming a three-dimensional network. The dielectric properties have been investigated at temperature range from 297
to 410 K at various frequencies (10 Hz–100 kHz). Dielectric studies were performed to confirm results obtained with thermal
analysis. The evolution of dielectric constant as a function of temperature and frequency of single crystal has been investigated
in order to determine some related parameters. 相似文献
18.
M. Parto D. Deger K. Ulutas Ş. Yakut 《Applied Physics A: Materials Science & Processing》2013,112(4):911-918
A comparison of structure and dielectric properties of TlSbS2 thin films, deposited in different thicknesses (400–4100 Å) by thermal evaporation of TlSbS2 crystals that were grown by the Stockbarger–Bridgman technique and the bulk material properties of TlSbS2 are presented. Dielectric constant ε 1 and dielectric loss ε 2 have been calculated by measuring capacitance and dielectric loss factor in the frequency range 20 Hz–10 KHz and in the temperature range 273–433 K. It is observed that at 1 kHz frequency and 293 K temperature the dielectric constant of TlSbS2 thin films is ε 1=1.8–6 and the dielectric loss of TlSbS2 thin films is ε 2=0.5–3 depending on film thickness. In the given intervals, both of dielectric constant and dielectric loss decrease with frequency, but increase with temperature. The maximum barrier height W m is calculated from the dielectric measurements. The values of W m for TlSbS2 films and bulk are obtained as 0.56 eV and 0.62 eV at room temperature, respectively. The obtained values agree with those proposed by the theory of hopping over the potential barrier. The temperature variation of ac conductivity can be reasonably interpreted in terms of the correlated barrier hopping model since it obeys the ω s law with a temperature dependent s (s<1) and going down as the temperature is increased. The temperature coefficient of capacitance (TCC) and permittivity (TCP) are evaluated for both thin films and bulk material of TlSbS2. 相似文献
19.
We analyze the Dyson equation/Ward identity system for the axial gauge n · A = 0 gluon propagator Δμν(q)whenn · q = 0. The solution behaves like (q?4 + (q2)ν?1) for small q2, and we are able to calculate the power ν analytically. It turns out to be 0.1737. This analytic calculation verifies our earlier numerical solutions to these equations. For static problems, n · q = 0 is the temporal gauge, and in this gauge the gluon propagator is directly related to the color dielectric constant. We can thus calculate the dielectric constant in the infrared limit. 相似文献
20.
《Solid State Ionics》1986,20(2):159-165
Cd2P2Se6 - Ag4P2Se6 system was investigated and Cd2−xAg2xP2Se6 mixed crystals have been found for 0<x<0.3. Their conductivity has been found to have ionic character. Silver ion conductivity values are reported. From diffuse reflectance data, the bandgaps for Cd2P2Se6 and Ag4P2Se6 have been estimated as equal to 2.4 eV and 1.8 eV, respectively. 相似文献