共查询到20条相似文献,搜索用时 31 毫秒
1.
Hallconstant, conductivity and Hall mobility of ZnO crystals were measured as function of temperature (4 °K < T < 370 °K) and orientation. Value and anisotropy of mobility can be explained (50 °K < T < 370 °K) by polar optical scattering, deformation potential sc., piezoelectric sc. and sc. by ionized impurities. The anisotropy of mobility is caused only by piezoelectric sc. Maximum values of μH are reached for μH ⊥ c, with 2400 cm2/V sec at 40 °K and for μH ¦ c with 1350cm2/Vsec at 60 °. Below 50 °K Hallconstant, conductivity and Hall mobility are influenced by impurity band conduction processes. The crystals have impurity concentration in the 1016 cm?3 range, but they show different donor activation energies depending on growth conditions: Type I: 38,4 meV (50 °K < T < 100 °K) and Type II: 20,3 meV (50 °K < T < 100 °K) and 6 meV (25 °K < T < 50 °K). 相似文献
2.
Experimental and theoretical investigations have been performed to determine the thermal conductivity of hydrogen in the temperature range between 2000 and 7000 °K. For this purpose the radial temperature distributions for various currents and theE-I-characteristic of a low current wall-stabilized hydrogen arc have been measured. In the dark region of the arc outside the bright core the temperature and the thermal conductivity between 2000 and 4500 °K were found by means of the schlieren technique. The electron temperature in the core of the arc results from spectroscopic measurements. The gas temperature has been calculated with a formula, derived from the kinetic theory of gases. Assuming a constant collision integralQ eH 11 the radial distribution of electric conductivity has been calculated according to Langevin's formula. The valueQ eH 11 =30·10?16 cm2 results by comparing the integrated conductance with the measured one. Since now the radial distribution of power input and the temperatures are known, the thermal conductivity between 4500 and 7000 °K can be determined as well. The total course of the heat conductivity shows a strong peak at the temperature of 3740 °K characteristic for the dissociation process. 相似文献
3.
F.J. Di Salvo B.G. Bagley J.M. Voorhoeve J.V. Waszczak 《Journal of Physics and Chemistry of Solids》1973,34(8):1357-1362
A new polymorph of the layered compound tantalum disulfide, 4Hb-TaS2, has been prepared in single crystal form. Measurements of magnetic susceptibility, electrical resistivity, and differential heat capacity show two first order transitions at 20 and 315°K. The 315°K transition involves only a small volume and enthalpy change, as in the previously observed transitions of another polymorph, 1T-TaS2. The resistivity measurements show metallic like conductivity, as in 2H-TaS2, when the current is parallel to the layers, but semiconducting like conductivity, as in 1T-TaS2, when perpendicular to the layers. The properties of 4Hb-TaS2 are moderately well described as a ‘mix’ of those of 1T-TaS2 and 2H-TaS2. 相似文献
4.
The thermal diffusivities of UC1 ? xNx of several compositions were measured from 100 to 1000 °K by a laser flash method. The thermal conductivity was separated into electronic and phonon components by assuming the constant Lorenz number. The phonon conductivity showed an anomalous behaviour against composition at low temperatures. The total thermal conductivity of UC1 ? xNx showed a minimum above 300 °K at an intermediate composition which moved to higher carbon content with increasing temperature. This behaviour was explained by the temperature dependence of the lattice and electronic components. 相似文献
5.
K.W. Plumlee B.M. Hoffman M.T. Ratajack C.R. Kannewurf 《Solid State Communications》1974,15(10):1651-1654
We report electrical and magnetic studies of [NEt4]2[CuII(mnt)2]. This crystal is composed of chains of theplanar [CuII(mnt)2]?2 anions (space group and z = 1) which exhibit only weak magnetic interactions. The material behaves as a semiconductor; from 300–400°K the conductivity increases by six orders of magnitude and the resistivity values above 300°K are comparable to those of some of the better known wide band-gap inorganic semiconductors. In contrast with the behavior of other linear chain systems, at room temperature the conductivity along the chain (σ∥) is less than that perpendicular to the chain (σ⊥). As the temperature is increase, the anisotropy ratio, σ∥/σ⊥, becomes greater than unity and increases to 1.6 × 102 at 400°K. 相似文献
6.
M. Kh. Balapanov R. Kh. Ishembetov K. A. Kuterbekov M. M. Kubenova R. F. Almukhametov R. A. Yakshibaev 《Ionics》2018,24(5):1349-1356
The electronic and ionic conductivity, the electronic and ionic Seebeck coefficients, and the thermal conductivity of Na x Cu2 ? x S (x = 0.05, 0.1, 0.15, 0.2) compounds were measured in the temperature range of 20–450 °С. The total cationic conductivity of Na0.2Cu1.8S is about 2 S/cm at 400 °С (the activation energy ≈ 0.21 eV). Over the studied compounds, the composition Na0.2Cu1.8S has the highest electronic conductivity (500–800 S/cm) in the temperature range from 20 to 300 °С, and the highest electronic Seebeck coefficient (about 0.2 mV/K) in the same temperature range is observed for Na0.15Cu1.85S composition; the electronic Seebeck coefficient increases abruptly above 300 °С for all compounds. The thermal conductivity of superionic Na0.2Cu1.8S is low, which causes high values of the dimensionless thermoelectric figure of merit ZT from 0.4 to 1 at temperatures from 150 to 340 °С. 相似文献
7.
《Solid State Ionics》1986,21(2):97-115
The relations between the orientational disorder of SiO4(PO4) tetrahedra and fast sodium diffusion in superionic NASICON have been studied by conductivity (complex impedance method), DSC, X-ray powder difraction and vibrational spectroscopy (IR and Raman). Sol-gel routes allow to obtain pure glassy NASICON (Na1+xZr2SixP3-xO12x≅2) in the 500−700°C temperature range. Tetragonal zirconia nucleates above 700°C and disappears at about 900°C when the isolated tetrahedra framework is formed: a high orientational static disorder of tetrahedra exists and the symmetry is rhombohedral at all studied temperatures (20−600 K). Thermal treatment above 1100°C induces a drastic decrease of the static orientational disorder and nucleation of monoclinic zirconia. The resulting compound exhibits a monoclinic symmetry at R.T. and three phase transitions, two diffuse at about 60 K and 520 K and the 423 K monoclinic-rhombohedral transition associated with the superionic conducting state. An increase in dynamic disorder (broad Rayleigh wing up to 500 cm-1 is simultaneously observed. The lower the static disorder at low temperature, the higher the dynamic orientational disorder and the phase transitions, and the lower the activation energy of conductivity at high temperature. 相似文献
8.
U. Plantikow 《Zeitschrift für Physik A Hadrons and Nuclei》1970,237(5):388-402
In a cascade arc chamber a stationary nitrogen plasma was produced at a pressure of 1 atm. In this plasma the integral material function, the E-I-characteristic, could be measured very exactly. From this characteristic the transport coefficients of nitrogen — the electrical conductivity σ and the heat flux potentialS — were evaluated in dependence on the arc radiusr with the arc currentI as parameter. With these and by the help of the temperature distributions measured by Schade the transport coefficients dependent on temperatureT only were obtained. The thermal conductivity κ was found by differentiation of theS(T)-curve. The evaluation was only performed up to 13,000 °K because the radiation has been neglected in the calculation what is no longer allowed above 13,000 °K. At low currents the influence of the high field strength causes non-LTE increasing with rising field strength. This effect of non-LTE could be regarded qualitatively and quantitatively. As result the thermal and electrical conductivity ofN 2 from 5,000 °K to 13,000 °K were obtained. The consistence with former measurements and with theoretical calculations is very satisfying. 相似文献
9.
The electrical conductivity properties of Dion-Jacobson type layered perovskites A′Ca2Nb3O10 (A′=K, Rb, Cs) was investigated under different gas atmospheres. An increase in the electrical conductivity by about 2–5
orders in magnitude in both ammonia and hydrogen atmospheres is observed compared to air. Among the members of the series,
the compound with the smallest size of the alkali ion, i.e. KCa2Nb3O10, exhibits the highest conductivity. In air and hydrogen, a single activation energy value in the range 0.25 – 0.80 eV is
observed, while in ammonia a sharp increase in the electrical conductivity is found at about 500 °C. The activation energy
at low-temperatures (300–500 °C) is attributed to ionic motion and at higher temperatures (500–700 °C) to both defect formation
and ionic motion. The unusual electrical conductivity behavior in ammonia is explained on the basis of the model developed
for alkali halides. EMF measurements reveal that the layered perovskites are ionic (proton) conductors. The electrical conductivity
changes as a function of the ammonia gas concentration; accordingly, layered perovskites appear to be useful solid electrolytes
in galvanic cells for practical applications, e.g. for gas sensors.
Paper presented at the 7th Euroconference on Ionics, Calcatoggio, Corsica, France, Oct. 1–7, 2000. 相似文献
10.
Anomalous behavior has been observed in the ionic conductivity of (Na,K) mixed crystals of the alkali gallates and aluminate of the β-Al2O3 type fast ion conductors. The conductivity goes through a minimum at some intermediate composition as a consequence of a maximum in the activation energy, and is most pronounced in the (Na,K)-β-gallate, followed by (Na,K)-β-Al2O3 and (Na,K)-β“-gallate. The effect is similar to the well-known “mixed alkali effect” in glasses. A second anomaly consisting of a pronounced increase in conductivity over about a 70° temperature range, without any permanent change in activation energy, was observed for some compositions of (Na,K)-β“-gallate. 相似文献
11.
Sergei G. Buga Nadejda R. Serebryanaya Gennadii A. Dubitskiy Elena E. Semenova Viktor V. Aksenenkov Vladimir D. Blank 《高压研究》2013,33(1):86-90
We have obtained the metastable phase of the thermoelectric alloy Bi0.4Sb1.6Te3 with electron type conductivity for the first time using the method of quenching under pressure after treatment at P=4.0 GPa and T=400–850 °C. We have consequently performed comparative studies with the similar phase of Sb2Te3. The polycrystalline X-ray diffraction patterns of these phases are similar to the known monoclinic structure α-As2Te3 (C2/m) with less monoclinic distortion, β ≈ 92°. We have measured the electrical resistivity and the Hall coefficient in the temperature range of T=77?450 K and we have evaluated the Hall mobility and density of charge carriers. The negative Hall coefficient indicates the dominant electron type of carriers at temperatures up to 380 K in the metastable phase of Sb2Te3 and up to 440 K in the metastable state of Bi0.4Sb1.6Te3. Above these temperatures, the p-type conductivity proper to the initial phases dominates. 相似文献
12.
The conductivity mechanism in pure and doped, β-rhombohedral, polycrystalline boron between 1.5 °K and 900 °K is clarified by measurements of electrical conductivity, photoconductivity, electron paramagnetic resonance and thermoelectric effect. The semiconductor behaviour of boron between 1.5 and 900 °K is similar to that of doped and compensated germanium and silicon at helium temperatures concerning the temperature-independent number of carriers and the thermally activated conduction process at low and high carrier concentrations. The paramagnetic centres are nearly localized electrons at 1.5 °K and nearly free electrons at 900 °K with a continuous transition between these two extreme kinds of behaviour. Mobilities of charge carriers in carbon doped boron over a range from 1016 cm?3 to 1020 cm?3 and 77 °K to 900 °K were measured for the first time and were found to obey an exponential law. 相似文献
13.
B. Pongs T. Wokrina S. Matejcek C. Buschhaus E. Dormann 《The European Physical Journal B - Condensed Matter and Complex Systems》2002,28(3):289-297
The quasi-one dimensional pyrene (PY) organic conductor (PY)7(PY)4(AsF6)4
. 4CH2Cl2shows parallel as well as 60° rotated PY radical cations in its stacks, but crystallizes in two different modifications I and II. One of the seven intra-stack
pyrene molecules is susceptible to a reorientation by 60°, that is stable already at room temperature for modification II, but occurs at a hysteretic first order transition between
170 K and 240 K for modification I. Crystal structure, microwave conductivity and static magnetic susceptibility are typical
for a quasi-one dimensional organic conductor with Peierls transition at TP = 73 K (mod. I) or TP = 105 K (mod. II). The pyrene radical packing is analysed by continuous wave and pulsed electron spin resonance measurements,
using 9.45 GHz as well as 425 MHz as measuring frequency. Anisotropy of the conduction electron diffusion constant exceeds
1000 in the metallic phase.
Received 22 March 2002 Published online 31 July 2002 相似文献
14.
Prasad Varanasi Babu R.P. Bangaru 《Journal of Quantitative Spectroscopy & Radiative Transfer》1975,15(3):267-273
Line intensities at 150°K and 295°K, self-broadened half-widths at 171°K, 200°K, 250°K and 295°K, and hydrogen-broadened half-widths at 171°K, 200°K and 295°K have been measured in the ν1+v3 band of C2H2 at 1·525 μm. The absolute intensity of the band has been determined independently by employing the Wilson-Wells-Penner-Weber technique. Our best estimate for the absolute intensity of the band is Sv=7·82 ± 0·07 cm?2 atm?1 at 295°K. Line intensities calculated using this value of Sv are in good agreement with the measured intensities at the two extreme temperatures of 150°K and 295°K considered in the present study, thereby not suggesting any significant intensity anomalies. Line positions have been measured for the first time for this band for R(29)?P(25). 相似文献
15.
LiSn2P3O12 with sodium (Na) super ionic conductor (NASICON)-type rhombohedral structure was successfully obtained at low sintering temperature, 600 °C via citric acid-assisted sol-gel method. However, when the sintering temperature increased to 650 °C, triclinic structure coexisted with the rhombohedral structure as confirmed by X-ray diffraction analysis. Conductivity–temperature dependence of all samples were studied using impedance spectroscopy in the temperature range 30 to 500 °C, and bulk, grain boundary and total conductivity increased as the temperature increased. The highest bulk conductivity found was 3.64?×?10?5 S/cm at 500 °C for LiSn2P3O12 sample sintered at 650 °C, and the lowest bulk activation energy at low temperature was 0.008 eV, showing that sintering temperature affect the conductivity value. The voltage stability window for LiSn2P3O12 sample sintered at 600 °C at ambient temperature was up to 4.4 V. These results indicated the suitability of the LiSn2P3O12 to be exploiting further for potential applications as solid electrolytes in electrochemical devices. 相似文献
16.
L. Pintilie I. Pintilie D. Petre T. Botila M. Alexe 《Applied Physics A: Materials Science & Processing》1999,69(1):105-109
Thermally stimulated current (TSC) measurements performed in the 100 K–400 K temperature range on Bi4Ti3O12 (BiT) thin films annealed at 550 °C and 700 °C had revealed two trapping levels having activation energies of 0.55 eV and
0.6 eV. The total trap concentration was estimated at 1015 cm−3 for the samples annealed at 550 °C and 3×1015 cm−3 for a 700 °C annealing and the trap capture cross-section was estimated about 10−18 cm2. From the temperature dependence of the dark current in the temperature range 20 °C–120 °C the conduction mechanism activation
energy was found to be about 0.956–0.978 eV. The electrical conductivity depends not only on the sample annealing temperature
but also whether the measurement is performed in vacuum or air. The results on the dark conductivity are discussed considering
the influence of oxygen atoms and oxygen vacancies.
Received: 28 January 1998 / Accepted: 8 January 1999 / Published online: 5 May 1999 相似文献
17.
D. Walton 《Solid State Communications》1974,14(4):335-339
A phonon scattering mechanism based on the structure of amorphous solids is proposed. Employing two adjustable parameters this mechanism accounts for the thermal conductivity of vitreous SiO2 and GeO2 at temperatures below 100°K. 相似文献
18.
The d.c. electrical conductivity of pure, doped and quenched samples of LiNH4SO4 is measured between liquid nitrogen temperature and 290°C. A-type conductivity anomalies are observed at 10°C and at 186.5°C along the ferroelectric axis. The mechanisms of electrical conduction in the various phases and at the transition points are discussed. 相似文献
19.
Abhai Mansingh R.P Tandon J.K Vaid 《Journal of Physics and Chemistry of Solids》1975,36(11):1267-1271
An asymmetric distribution of relaxation times has been inferred from an increase in the Cole-Cole distribution parameter α with increasing values of ωτ in 62% v2O5–38% P2O2 glass. The conventional Debye type relaxation loss peaks in the frequency range 102–105 Hz are observed in this sample above 85°K. The extrapolated values of dielectric constant and relaxation time below 100°K seem unexpectedly large while the high temperature extrapolated values of ?' are close to ?∞ as expected. Probably the conventional dielectric loss peaks are observed only above a critical temperature at which the carriers gain sufficient energy to be excited to the conduction band edge. Below this temperature hopping of carriers within kT of the Fermi level may dominate and conventional Debye type dielectric loss peaks may lose their significance as envisaged in the models of frequency dependent ac conductivity. 相似文献
20.
N. F. Kartenko T. S. Orlova L. S. Parfen’eva B. I. Smirnov I. A. Smirnov 《Physics of the Solid State》2014,56(11):2348-2352
Natural composites (biocarbons) obtained by carbonization of beech wood at different carbonization temperatures T carb in the range of 800–2400°C have been studied using X-ray diffraction. The composites consist of an amorphous matrix and nanocrystallites of graphite and graphene. The volume fractions of the amorphous and nanocrystalline phases as functions of T carb have been determined. Temperature dependences of the phonon thermal conductivity κ(T) of the biocarbons with different temperatures T carb (1000 and 2400°C) have been analyzed in the range of 5–300 K. It has been shown that the behavior of κ(T) of the biocarbon with T carb = 1000°C is controlled by the amorphous phase in the range of 5–50 K and by the nanocrystalline phase in the range of 100–300 K. The character of κ(T) of the biocarbon with T carb = 2400°C is determined by the heat transfer (scattering) in the nanocrystalline phase over the entire temperature range of 5–300 K. 相似文献