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1.
The electrical conductivity and Seebeck coefficient for nickel ferrite and nickel ferrite with 5% silica has been studied as a function of temperature. The lattice constant and the existence of a single phase are established from X-ray studies. Both the ferrites exhibit a transition near the Curie temperature with a change in slope of the conductivity (log σT) versus temperature (103/T) curves. It is found that the activation energy in the paramagnetic region is higher than that in the ferrimagnetic region for both the ferrites. 相似文献
2.
TiS1.7 crystals have been grown by vapour transport technique employing a two-zone furnace with the temperatures of reaction and growth zone maintained at 1073 K and 973 K, respectively. We have measured the variation of electrical conductivity (s̀) with temperature (T) of TiS1.7 single crystals. It has been found that the conductivity increases at temperatures T > 433 K, which provides convincing evidence that the TiS1.7 crystal is a semiconductor. Another electronic characteristic of TiS1.7 crystals observed in the present investigation is the occurrence of voltage controlled negative resistance (VCNR) at a field of 32.1 V cm-1 to 35.7 V cm-1. All the polytypes of TiS1.7 were found to exhibit VCNR nearly at the same field which indicates that the VCNR is polytype independent property. The occurrence of VCNR has been explained on the intervally transfer of electrons in the conduction band. 相似文献
3.
The fluorine-ion conductivity of single crystals with a tysonite (LaF3) structure with heterovalent isomorphic substitutions of highly polarizable Cd2+ cations with a 18-electron shell for rare earth ions Ce3+ have been studied for the first time. Ce0.995Cd0.005F2.995 single crystals have been grown from melt by the Bridgman technique in a fluorinating atmosphere. The fluorine-ion conductivity of single crystal is measured by impedance spectroscopy in the temperature range from 153 to 1073 K, where it increases by a factor of 109, approaching the value σdc = 5 × 10–2 S/cm at 1073 K. At T0 = 450 ± 20 K, the dependence σdc(T) is split into two portions with the ion-transport activation enthalpy ΔHσ = 0.39 ± 0.01 eV (T < T0) and ΔHσ = 0.23 ± 0.02 eV (T > T0). It is found that at T = 293 K the conductivity σdc = 3 × 10–5 S/cm of Ce0.995Cd0.005F2.995 crystal is higher by a factor of 10 than the conductivity of the tysonite matrix CeF3 and close to the σdc value for Ce0.995Sr0.005F2.995 crystal. This finding indicates a significant effect of the substitutions of Cd2+ ions for Ce3+ on the σdc value and the advantage of Cd2+ ions over Ca2+ and Ba2+ from the viewpoint of increasing σdc. 相似文献
4.
L. E. Soshnikov V. M. Trukhan T. V. Golyakevich H. L. Soshnikova 《Crystallography Reports》2005,50(1):S37-S45
Elastic and dielectric properties of CdP2, ZnP2, and ZnAs2 single crystals are investigated at frequencies of 102, 103, 104, 106, and 107 Hz in the [00l], [h00], and [hk0] directions in the temperature range 78–400 K. The elastic constants, the Gruneisen parameters, and the force constants of the crystals are calculated from the measured ultrasonic velocities. The elastic constants Cij decrease with an increase in temperature and anomalously change in narrow (ΔT = 10–20 K) temperature ranges. The permittivity sharply increases from ε ≈ 7–14 at 78–150 K to ε ≈ 102–103 in the temperature range 175–225 K without any signs of a structural phase transition. The behavior of the temperature-frequency dependences of the complex permittivity ε*(f, T) is typical of relaxation processes. The dielectric relaxation in AIIB 2 V is considered on the basis of the model of isolated defects. The conuctivity σ of the single crystals under study is a sum of the frequency-dependent (hopping) conductivity σh and the conductivity σs that is typical of semiconductors. The hopping conductivity increases with an increase in frequency according to the law σ h ~fα, where α < 1 at low temperatures and α > 1 at high temperatures. 相似文献
5.
M. A. Gaffar A. M. Abousehly A. Abu El‐Fadl M. M. Mostafa 《Crystal Research and Technology》2006,41(11):1120-1130
The dielectric constant (ϵ), dielectric loss (tanδ) and ac conductivity (σac) of virgin and thermally cycled undoped and Ni2+‐doped K2ZnCl4 (KZC) crystals in the ferroelectric‐commensurate (FC), incommensurate (IC) and normal phases (N) have been studied. Anomalous behaviour at the two‐phase transition points was observed while measuring ϵ along the polar a‐axis for the undoped sample. With increasing Ni2+concentration a systematic shift of the phase transition temperature towards lower values and a continuous inhibition of the peak height were detected. ϵ changed linearly with lnf up to f =105 Hz. tanδ along the a‐axis declared the phase transitions by peak changes. After Ni2+‐doping this behaviour was preserved at the FC‐IC phase transition point while the IC‐N phase transition was manifested by a change in the slope of the straight line representing the tanδ‐T dependence. The ac conductivity changed lineally with frequency according to a relation of the form σac = σo f β where 0>β>1.9. σac increased monotonically with increasing temperature and doping concentration in the low‐temperature phases tending to merge in one straight‐line with high activation energy that might be due to superionic dc conduction in the high temperature N‐phase. Doping with Ni2+ pinned stripples, decreased the soliton‐soliton interaction, weakened discommensuration effects, shortened the IC‐phase and strongly affected the ‘chaotic' behaviour at the TC‐IC. (© 2006 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
6.
O. Karabulut M. Parlak K. Yilmaz R. Turan B. G. Akinoglu 《Crystal Research and Technology》2003,38(12):1071-1076
GaSe single crystals grown by Bridgman method have been doped by ion implantation technique. The samples were bombarded in the direction parallel to c‐axis by Si ion beam of about 100 keV to doses of 1 × 1016 ions/cm2 at room temperature. The effects of Si implantation with annealing at 500 and 600 °C on the electrical properties have been studied by measuring the temperature dependent conductivity and photoconductivity under different illumination intensities in the temperature range of 100–320 K. It is observed that Si implantation increases the room temperature conductivity 10−7 to 10−3 (Ω‐cm)−1 depending on the post annealing temperature. The analysis of temperature dependent conductivity shows that at high temperature region above 200 K, the transport mechanism is dominated by thermal excitation in the doped and undoped GaSe samples. At lower temperatures, the conduction of carriers is dominated by variable range hopping mechanism in the implanted samples. Annealing of the samples at and above 600 °C weakens the temperature dependence of the conductivity and photoconductivity. This indicates that annealing of the implanted samples activates Si‐atoms and increases structural deformations and stacking faults. The same behavior was observed from photoconductivity measurements. Hence, photocurrent‐illumination intensity dependence in the implanted samples obeys the power low Ipc ∝ Φn with n between 1 and 2 which is an indication of continuous distribution of localized states in the band gap. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
7.
H. Neumann B. Schumann D. Peters A. Tempel G. Kühn 《Crystal Research and Technology》1979,14(4):379-388
CuInS2 thin films with thicknesses in the range of 500 Å were deposited onto semi-insulating (111) A-oriented GaAs substrates by flash evaporation in the substrate temperature range Tsub = 570 … 870 K. Epitaxial growth begins at Tsub = 645 K. The films had always the chalcopyrite structure. Indications to a transition from the chalcopyrite phase to the sphalerite phase were observed at Tsub = 870 K. Films grown at Tsub ≦ 800 K showed n-type conductivity whereas at growth temperatures Tsub ≧ 850 K the films were always p-type conducting. A donor level and an acceptor level with ionization energies of 0.24 eV and 0.22 eV, respectively, were found from an analysis of the electrical measurements. 相似文献
8.
The electrical conductivity σ(ω) and the dielectric constant ?(ω) of heat-treated polyacrylonitrile (PAN) samples obtained by pyrolysis at temperatures up to 550°C, were measured in the frequency range from 500 Hz to 250 MHz at room temperature. For samples treated at temperatures below 300°C and for frequencies up to 200 MHz, the conductivity obeys a ωs law (s = 1) while ? does not change significantly. For heat-treatment temperatures above 300°C, the behaviour of σ(ω) is greatly modified. In fact, ?(ω) greatly increases at low frequencies for increasing heat-treatment temperatures, and is strongly dependent frequency. Our results can be explained with the help of two randomly distributed phases in the medium and by introducing percolation theory. 相似文献
9.
D. Ravinder 《Crystal Research and Technology》1991,26(4):457-464
The electrical conductivity (σ) of lithium ferrite sintered at 950, 1000, 1050 and 1100 °C was investigated in the temperature range of 300 to 1000 K. Three distinct regions have been observed in log (σT) vs 103/T curves for four samples of lithium ferrite sintered at different temperatures. The conduction in the first region is due to impurities. In the second and third region is due to ordered and disordered state of the material. The transition from the first region to the second region is due to lowering of symmetry. The transition from second to third region is due to magnetic transition, i.e. ferrimagnetic to paramagnetic state. The transition temperatures are nearly equal to the Curie temperatures of the materials. The porosity and activation energy were calculated. It was found that the electrical conductivity is progressively increasing with increase of sintering temperature while the porosity and activation energy decrease continuously. The Seebeck coefficient (Q), carrier concentration (n) and mobility (μ) of charge carriers have been discussed as a function of sintering temperature and temperature. 相似文献
10.
Epitaxial layers of CuIn0.7Ga0.3Se2 could be prepared by flash evaporation onto (111)A-oriented GaAs substrates in the substrate temperature range Tsub = 745 … 870 K. At Tsub = 745 … 820 K the films had the chalcopyrite structure, at Tsub = 820 … 845 K an additional pseudohexagonal phase was found. Indications to the presence of a sphalerite phase were found at high substrate temperatures. Films grown at Tsub ≦ 750 K were always n-type conducting and showed a largely pronounced impurity band conduction effect. At Tsub ≧ 860 K the films were always p-type conducting and two acceptor states with ionization energies of some 10−3 eV and of 125 … 140 meV were found. 相似文献
11.
Yu. V. Shaldin S. Matyjasik N. E. Novikova M. Tseitlin E. Mozhaev M. Roth 《Crystallography Reports》2010,55(6):1012-1018
The temperature dependences of the pyroelectric coefficients of KTiOAsO4 and RbTiOAsO4 single crystals grown by flux crystallization have been investigated in the temperature range of 4.2–300 K. With an increase
in temperature, superionic conductivity first arises in KTiOAsO4 (at T > 200 K) and then (at T > 270 K) in RbTiOAsO4. This conductivity is much higher in the samples polarized at T = 4.2 K. An exponential change in the crystal resistivity along the polar direction is simultaneously observed. The results
of measurements in the range of 4.2–200 K indicate larger values of pyroelectric coefficients when compared with potassium
and rubidium titanyl-phosphate crystals. A correlation between the pyroelectric coefficients and a change in the lattice constants
at isomorphic substitutions of K atoms for Rb and P atoms for As has been revealed within the symmetry approach. 相似文献
12.
Dielectric characteristics of neodymium heptamolybdate crystals grown by gel encapsulation technique
Sushma Bhat S. K. Khosa Dr. P. N. Kotru R. P. Tandon 《Crystal Research and Technology》1995,30(2):267-273
Results obtained from the dielectric studies of neodymium heptamolybdate crystals grown in the system Nd(NO3)3 –MoO3 –NH4OH– HNO3 —Na2SiO3 by gel encapsulation technique are presented. The variation of dielectric constant (ε′), dielectric loss (tanδ) and conductivity (σ) with frequency at different temperatures is studied. The dielectric constant of the material increases sharply, attains a peak value and then decreases rapidly, as material's temperature rises from room temperature to higher degrees. The temperature at which the peak value is attained is the transition temperature of the material. Dielectric loss (tan δ) follows almost a similar behaviour. The conductivity (σ) is also found to be temperature-and frequency-dependent. This sharp rise in ε′ is attributed to the contribution from space charge polarization. Theoretically obtained data using the expression ε′ = a0 + a1 T2 and —In σ = a + b(T — T0)2 for T < T0) fits very well with the experimentally obtained data indicating that space charge polarization increases as some power of temperature larger than one. 相似文献
13.
M. F. Mostafa A. A. Youssef Th. Sh. El Dean A. M Mostafa I. S. Ahmed Farag 《Crystal Research and Technology》2008,43(5):547-560
The crystal structure of bis‐(methyltriphenylphosphonium) tetrabromocobaltate (II), [(C19H18P)2 CoBr4] is determined: Mr = 933.203, monoclinic, P21, a = 9. 6977 (3) Å, b = 12.5547 (4)Å, c = 16.4503 (6)Å, β = 105.603 (2)°, V = 1929.04 (11)Å3, Z = 2, Dx = 1.607 Mg m‐3, T = 298 K. Differential thermal analysis at high temperatures shows three endothermic peaks characterizing four phases, with onset temperatures at T1= 313±2 K, T2 = 320±4 K and T3= 360±1 K. The structural instability detected via the temperature dependence of permittivity at T1 is ascribed to order‐disorder transition associated with cation dipole reorientation. Permittivity and ac conductivity studies as a function of temperature (295 K‐375 K) and frequency (0.11 kHz < f <100 kHz) are presented. The results indicate the importance of the cation size and shape on the phase transitions in the system. Bulk conductivity behavior is thermally activated. The associated activation energies are in the range 2.9 to 1.0 eV depending on the temperature regime. Two contributions to the ac conductivity, one dominating at low temperatures and high frequencies which are characterized by superlinear frequency exponent and the second dominates at high temperatures characterized by a sublinear frequency exponent. The behavior is interpreted in terms of the jump relaxation model. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim) 相似文献
14.
W. Bollmann 《Crystal Research and Technology》1978,13(8):1001-1007
The electrical conductivity σ of CaMoO4 crystals was investigated between room temperature and 850°C. The mobility vv and the diffusion coefficient Dv of the O− ion vacancies have been derived from σ: vvT = 3300 exp (−1.52 eV/kT) cm2 K/Vs, Dv = (0.1…1) × exp (−1.52 eV/kT) cm2/s. An absorption occuring in crystals which are reduced or X-irradiated at low temperatures is dichroitic and caused by Mo5+ ions. For measurement in c direction the oscillator strength of the 680 nm absorption band is found to be about 0.1. 相似文献
15.
B. Schumann A. Tempel G. Kühn H. Neumann D. Peters W. Hrig 《Crystal Research and Technology》1979,14(6):665-669
CuGaTe2 thin films with thicknesses in the range from 0.1 to 0.2 μm were deposited onto semi-insulating (111) A-oriented GaAs substrates by flash evaporation under controlled growth conditions. Epitaxial growth begins at a substrate temperature of Tsub = 695 K. In the range Tsub = 695 … 820 K the films have the chalcopyrite structure, at Tsub = 820 to 840 K a second phase was observed besides the chalcopyrite phase. At Tsub > 840 K the films become polycrystalline. All epitaxial films were p-type conducting and showed an increase of the hole concentration with rising substrate temperature. The measured mobilities indicate to the presence of a high concentration of neutral impurities or defects. 相似文献
16.
V. I. Dotsenko V. V. Pustovalov V. A. Sirenko V. S. Fomenko 《Crystal Research and Technology》1984,19(8):1031-1038
The effect of the superconducting transition on the flow stress in single and polycrystals of Pb-In and Pb-Sn alloys has been studied in the temperature range 1.8 K to Te. Unlike earlier efforts, these experiments involved investigation of the magnetic flux trapping. Two types of temperature dependences of the magnetic flux trapping, B0(T), were revealed. In Pb-1.9 at.% In and Pb-6 at.% Sn alloys (subjected to various thermal treatment), B0 monotonically rises with lowering temperature. In Pb-1.8, 3 at.% Sn single crystals the flux trapping arises at high strains (> 50%) and low temperatures (<2.5 K). In this case B0 magnitude depends on the strain rate. The difference in the B0(T) behaviour is associated with dissimilar flux pinnig by pinning centres. The date on B0(T) obtained give an insight into the two types of the Δσ(T) dependences; taking into account of the flux trapping allowed the Δσ values to be corrected, so that as a result, a single ΔσSN(T) curve was obtained for all the alloys and structures studied. 相似文献
17.
The paper deals with conductivity, thermoelectric power and field effect measurements on amorphous Ge specimens prepared by the decomposition of germane gas in a rf glow discharge. Substrate temperatures Td of 300, 400 and 500 K were used during deposition. The sign of the thermoelectric power S is negative throughout the temperature range investigated (200–500 K). Above 300 K, the conductivity activation energy in specimens prepared at Td = 500 K lies between 0.40 and 0.43 eV; it is equal to the gradient of the S versus 1/T curves, suggesting transport in the extended electron states. Below room temperature there is an increasing contribution in all specimens from electron hopping transport in localized states lying about 0.25 eV below ?C. Both conductivity and thermoelectric power results can be interpreted satisfactorily in terms of these two current paths. Hopping at the Fermi level has not been observed. The preliminary field effect measurements indicate that, as in amorphous Si, ?f lies near a density of state minimum. The density of states at ?f is appreciably higher than that in similarly prepared Si specimens. 相似文献
18.
N. P. Skvortsova 《Crystal Research and Technology》1996,31(3):373-384
Experimental results on the superlocalization of plastic deformation at high strains and high temperatures in LiF single crystals are described. The physical conditions of transition to a localized plastic flow in the temperature range of 603 K to 1073 K T (0.53–0.94Tmp) using constant strain rate compression tests under strain rates from 10−3s−1 to 10−2s−1 are found. The results indicate that the deformation mechanism involves dislocation climb, controlled by diffusion. The connection of high temperature flow instability with an excessive concentration of point defects (strain vacancies) in zone of shear has been confirmed. 相似文献
19.
Polythiophene (PTP) and poly (vinyl acetate) (PVAc) composite films were prepared by chemical oxidative polymerization method with FeCl3 as an oxidant, in methanol at room temperature. Their dc conductivities as a function of temperature (313–358 K) were measured. An attempt has been made to investigate the effect of temperature and concentration of ferric chloride oxidant on the conductivity of polythiophene–poly(vinyl acetate) composite films. For fixed wt% of PVAc, the dc electrical conductivity of the film initially increases with the molar concentration of FeCl3 and then decreases with the further increase in the concentration of FeCl3. The temperature dependence of conductivity showed Arrhenius behavior. The conductivity isotherms show VTF behavior which is typical for ion conducting polymers. The Nyquist plot of Z′ vs. Z″ were plotted for frequency range 100 Hz–200 kHz and temperature range of 313–358 K. These plots consist of semicircles for higher temperatures. This suggests Debye type relaxation mechanism. The equivalent circuit consists of parallel combination of bulk resistance RB and bulk capacitance CB. The bulk resistance RB of the samples decreased with increase in temperature. 相似文献
20.
The electrical properties of CuInSe2 epitaxial layers on (111)A-, (110)-, and (100)-oriented GaAs substrates are investigated. At substrate temperatures Tsub ≧ 820 K the p-type conductivity observed is governed by an acceptor state with an ionization energy of about 110 meV independent of the substrate orientation. At Tsub ≦ 770 K three different acceptor states are found in dependence on the substrate orientation: 390 meV for (111)A-, 110 meV for (110)-, and a very shallow acceptor for (100)-oriented substrates. A possible correlation between these acceptor states and intrinsic defects is proposed. 相似文献