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1.
We have investigated the structural and electrical characteristics of the Ag/n-TiO2/p-Si/Al heterostructure. Thin films of pure TiO2 were deposited on p-type silicon (100) by optimized pulsed laser ablation with a KrF-excimer laser in an oxygen-controlled environment. X-ray diffraction analysis showed the formation of crystalline TiO2 film having a tetragonal texture with a strong (210) plane as the preferred direction. High purity aluminium and silver metals were deposited to obtain ohmic contacts on p-Si and n-TiO2, respectively. The current–voltage (IV) characteristics of the fabricated heterostructure were studied by using thermionic emission diffusion mechanism over the temperature range of 80–300 K. Parameters such as barrier height and ideality factor were derived from the measured IV data of the heterostructure. The detailed analysis of IV measurements revealed good rectifying behavior in the inhomogeneous Ag/n-TiO2/p-Si(100)/Al heterostructure. The variations of barrier height and ideality factor with temperature and the non-linearity of the activation energy plot confirmed that barrier heights at the interface follow Gaussian distributions. The value of Richardson’s constant was found to be 6.73 × 105 Am?2 K?2, which is of the order of the theoretical value 3.2 × 105 Am?2 K?2. The capacitance–voltage (CV) measurements of the heterostructure were investigated as a function of temperature. The frequency dependence (Mott–Schottky plot) of the CV characteristics was also studied. These measurements indicate the occurrence of a built-in barrier and impurity concentration in TiO2 film. The optical studies were also performed using a UV–Vis spectrophotometer. The optical band gap energy of TiO2 films was found to be 3.60 eV.  相似文献   

2.
Glass with compositions xK2O-(30 ? x)Li2O-10WO3-60B2O3 for 0 ≤ x ≤ 30 mol.% have been prepared using the normal melt quenching technique. The optical reflection and absorption spectra were recorded at room temperature in the wavelength range 300–800 nm. From the absorption edge studies, the values of the optical band gap (E opt) and Urbach energy (ΔE) have been evaluated. The values of E opt and ΔE vary non-linearly with composition parameter, showing the mixed alkali effect. The dispersion of the refractive index is discussed in terms of the single oscillator Wemple Di-Domenico model.  相似文献   

3.
A BiCu2PO6 microwave dielectric ceramic was prepared using a solid-state reaction method. As the sintering temperature increased from 800°C to 880°C, the bulk density of BiCu2PO6 ceramic increased from 6.299 g/cm3 to 6.366 g/cm3; the optimal temperature was 860°C. The best microwave dielectric properties [permittivity (? r ) = ~16, a quality factor (Q × f) = ~39,110 GHz and a temperature coefficient of resonant frequency (τ f ) = ~?59 ppm/°C] were obtained in the ceramic sintered at 860°C for 2 h. Then, TiO2 with a positive τ f (~+400 ppm/°C) was added to compensate the τ f value. The composite material was found to have a near-zero τ f (+2.7 ppm/°C) and desirable microwave properties (? r  = 19.9, Q × f = 24,885 GHz) when synthesized at a sintering temperature of 880°C. This system could potentially be used for low-temperature co-fired ceramics technology applications.  相似文献   

4.
We report single-crystal growth of the superconducting pyrochlore Cd2Re2O7 using a vapor transport technique. Several parameters of the growth conditions, including hot-zone temperature and starting stoichiometry, were varied in order to control the formation of ReO2 inclusions, as confirmed by the electron microscopy, resistivity, and magnetic susceptibility measurements. The Rietveld refinement of x-ray (neutron) powder diffraction was found to be consistent with a cubic structure Fd3m with lattice constant a = 10.2250 (10.2358) Å and reduced coordinate of O1 = 0.3184 (0.3177) at 293 K (250 K). We also studied the oxygen stoichiometry by means of redox reactions, electron microprobe analysis (EMPA), and x-ray/neutron diffractions. Particularly, the neutron powder diffraction on the 114Cd-enriched specimens yielded an oxygen deficiency δ = 0.14 ± 0.03 solely at the O2 site, which was consistent with the EMPA results. The EMPA indicated that the oxygen deficiency is homogeneous in the bulk and in a range of 0.01 ± 0.18–0.23 ± 0.19.  相似文献   

5.
Nd/Nb-co-substituted Bi3.15Nd0.85Ti3?x Nb x O12 (BNTN x , x = 0.01, 0.03, 0.05 and 0.07) thin films were grown on Pt/Ti/SiO2/Si (100) substrates by chemical solution deposition. The effects of Nb content on the micro-structural, dielectric, ferroelectric, leakage current and capacitive properties of the BNTN x thin films were investigated. A low-concentration substitution with Nb ions in BNTN x can greatly enhance its remanent polarization (2P r) and reduce the coercive field (2E c) compared with those of Bi4Ti3O12 (BIT) thin film. The highest 2P r (71.4 μC/cm2) was observed in the BNTN0.03 thin film when the 2E c was 202 kV/cm. Leakage currents of all the films were on the order of 10?6 to 10?5 A/cm2, and the BNTN0.03 thin film has a minimum leakage current (2.1 × 10?6 A/cm2) under the high electric field (267 kV/cm). Besides, the CV curve of the BNTN0.03 thin film is the most symmetrical, and the maximum tunability (21.0%) was also observed in this film. The BNTN0.03 thin film shows the largest dielectric constant and the lowest dielectric loss and its maximum Curie temperature is 410 ± 5°C.  相似文献   

6.
The magnetic susceptibility of Czochralski-grown single crystals of Bi2Te3-Sb2Te3 alloys containing 0, 10, 25, 40, 50, 60, 65, 70, 80, 90, 99.5, or 100 mol % Sb2Te3 has been investigated. The magnetic susceptibility of these crystals was determined at the temperature T = 291 K and the magnetic field H oriented parallel (χ) and perpendicularly (χ) to the trigonal crystallographic axis C 3. A complicated concentration dependence of the anisotropy of magnetic susceptibility χ has been revealed. The crystals with the free carrier concentration p ≈ 5 × 1019 cm?3 do not exhibit anisotropy of magnetic susceptibility. The transition to the isotropic magnetic state occurs for the compositions characterized by a significantly increased (from 200 to 300 meV) optical bandgap.  相似文献   

7.
The doping level dependence of thermoelectric properties of delafossite CuAlO2 has been investigated in the constant scattering time (τ) approximation, starting from the first principles of electronic structure. In particular, the lattice parameters and the energy band structure were calculated using the total energy plane-wave pseudopotential method. It was found that the lattice parameters of CuAlO2 are a = 2.802 Å and c = 16.704 Å, and the internal parameter is u = 0.1097. CuAlO2 has an indirect band gap of 2.17 eV and a direct gap of 3.31 eV. The calculated energy band structures were then used to calculate the electrical transport coefficients of CuAlO2. By considering the effects of doping level and temperature, it was found that the Seebeck coefficient S(T) increases with increasing acceptor doping (A d) level. The values of S(T) in our experiments correspond to an A d level at 0.262 eV, which is identified as the Fermi level of CuAlO2. Based on our experimental Seebeck coefficient and the electrical conductivity, the constant relaxation time is estimated to be 1 × 10?16 s. The power factor is large for a low A d level and increases with temperature. It is suggested that delafossite CuAlO2 can be considered as a promising thermoelectric oxide material at high doping and high temperature.  相似文献   

8.
TlCrS2 and TlCrSe2 crystals were synthesized by solid-state reaction. X-ray diffraction analysis showed that TlCrS2 and TlCrSe2 compounds crystallize in the hexagonal crystal system with lattice parameters a = 3.538 Å, c = 21.962 Å, c/a ≈ 6.207, z = 3; a = 3.6999 Å, c = 22.6901 Å, c/a ≈ 6.133, z = 3; and X-ray densities ρ x = 6.705 and 6.209 g/cm3, respectively. Magnetic and electric studies in a temperature range of 77–400 K showed that TlCrS2 and TlCrSe2 are semiconductor ferromagnets. Rather large deviations of the experimental effective magnetic moment of TlCrS2 (3.26 μB) and TlCrSe2 (3.05 μB) from the theoretical one (3.85 μB) are attributed to two-dimensional magnetic ordering in the paramagnetic region of strongly layered ferromagnets TlCrS2 and TlCrSe2. The effect of the magnetic phase’s transition on the charge transport in TlCrS2 and TlCrSe2 is detected.  相似文献   

9.
We have investigated the critical behavior in amorphous Fe85Sn5Zr10 alloy ribbon prepared using a single-roller melt-spinning method. This alloy shows a second-order magnetic transition from paramagnetic to ferromagnetic (FM) state at the Curie temperature T C (~306 K). To obtain more information on the features of the magnetic transition, a detailed critical exponent study was carried out using isothermal magnetization M (H, T) data in the vicinity of the T C. Modified Arrott plot, Kouvel–Fisher plot, Widom’s scaling relation and critical isotherm analysis techniques were used to investigate the critical behavior of this alloy system around its phase transition point. The values of critical exponents determined using the above methods are self-consistent. The estimated critical exponents are fairly close to the theoretical prediction of the three-dimensional (3D) Heisenberg model, implying that short-range FM interactions dominate the critical behavior in amorphous Fe85Sn5Zr10 alloy ribbon.  相似文献   

10.
Kinetics of variations in the components of total impedance for single-crystal Pb0.75Sn0.25Te:In samples is investigated upon switching on and switching off of the illumination source at temperature 4.2 K and frequency 106 Hz. The calculation carried out in the context of representation of equivalent circuits showed that the parameters of a parallel R p C p chain, which approximates the sample behavior, correlate strictly. In the region of low resistances R p , the values of C p increase abruptly following the law C p R p ?2 . It is of no importance what method of decreasing the resistance is used—heating of the sample or its illumination at low temperature. The obtained results were analyzed taking into account the contribution of the impurity subsystem to conductivity and the possible manifestation of Maxwell-Wagner-type effects.  相似文献   

11.
Sintered Bi0.5(Na0.8K0.2)0.5TiO3 + x wt.% ZnO nanoparticle (BNKT–xZnOn) ceramics have been fabricated by conventional annealing with the aid of ultrasound waves for preliminary milling. Because of the presence of the liquid Bi2O3–ZnO phase at the eutectic point of 738°C, the sintering temperature decreased from 1150°C to 1000°C, and the morphology phase boundary of BNKT–xZnOn ceramics can be clarified by two separated peaks at (002)T and (200)T of 2θ in the x-ray diffraction (XRD) patterns. The improvement of ferroelectric properties has been obtained for BNZT–0.2 wt.% ZnOn ceramics by the increase of remanent polarization up to 20.4 μC/cm2 and a decrease of electric coercive field down to 14.2 kV/cm. The piezoelectric parameters of the ceramic included a piezoelectric charge constant of d 31 = 78 pC/N; electromechanical coupling factors k p = 0.31 and k t = 0.34, larger than the values of 42 pC/N, 0.12 and 0.13, respectively, were obtained for the BNKT ceramics.  相似文献   

12.
The results of studying the electrical properties and isochronous annealing of p-ZnSnAs2 irradiated with H+ ions (energy E = 5 MeV, dose D = 2 × 1016 cm?2) are reported. The limiting electrical characteristics of irradiated material (the Hall coefficient R H (D)lim ≈ ?4 × 103 cm3 C?1, conductivity σ (D)lim ≈ 2.9 × 10?2 Ω?1 cm?1, and the Fermi level position F lim ≈ 0.58 eV above the valence-band top at 300 K) are determined. The energy position of the “neutral” point for the ZnSnAs2 compound is calculated.  相似文献   

13.
In single crystals of copper-doped and undoped Bi2Te2.85Se0.15 solid solutions with an electron concentration close to 1 × 1019 cm?3, the temperature dependences are investigated for the Hall (R 123, R 321) and Seebeck (S 11) kinetic coefficients, the electrical-conductivity (σ 11), Nernst-Ettingshausen (Q 123), and thermalconductivity (k 11) coefficients in the temperature range of 77–400 K. The absence of noticeable anomalies in the temperature dependences of the kinetic coefficients makes it possible to use the one-band model when analyzing the experimental results. Within the framework of the one-band model, the effective mass of density of states (m d ≈ 0.8m 0), the energy gap (εg ≈ 0.2 eV), and the effective scattering parameter (r eff ≈ 0.2) are estimated. The obtained value of the parameter r eff is indicative of the mixed electron-scattering mechanism with the dominant scattering by acoustic phonons. Data on the thermal conductivity and the lattice resistivity obtained by subtracting the electron contribution according to the Wiedemann-Franz law are presented.  相似文献   

14.
Transition-metal trichalcogenides MX3 (M = Ti, Zr, Nb, Ta; X = S, Se) are well-known inorganic quasi-one-dimensional conductors. Among them, we have investigated the thermoelectric properties of titanium trisulfide TiS3 microribbon. The electrical resistivity ρ, thermal conductivity κ, and thermoelectric power S were measured using 3ω method. The weight mean values were found to be ρ = 5 mω m and κ = 10 W K?1 m?1 along the one-dimensional direction (b-axis) of the TiS3 microribbon. Combined with the thermoelectric power S = ?530 μV K?1, the figure of merit was calculated as ZT = 0.0023. This efficiency is the same as that of randomly oriented bulk TiS3. We also estimated the anisotropy of σ and κ using the present results and those for randomly oriented bulk material. The obtained weak anisotropy for TiS3 is attributable to strong coupling between triangular columns consisting of TiS3 units. These experimental results are consistent with theoretical results obtained using density functional theory (DFT) calculations.  相似文献   

15.
Li2Mg2TiO5, a rock-salt structured ceramic fabricated by a solid-state sintering technique, was characterized at the microwave frequency band. As a result, a microwave dielectric permittivity (εr) of 13.4, a quality factor of 95,000 GHz (at 11.3 GHz), and a temperature coefficient of resonance frequency (τf) of ? 32.5 ppm/°C have been obtained at 1320°C. Li2Mg2TiO5 ceramics have low permittivity, a broad processing temperature region, and a low loss, making them potential applications in millimeter-wave devices. Furthermore, B2O3 addition efficiently lowered the sintering temperature of Li2Mg2TiO5 to 900°C, which opens up their possible applications in low-temperature co-fired ceramics (LTCC) technology.  相似文献   

16.
Electrical and thermoelectric properties of a lightly doped n-Bi2Te2.7Se0.3 solid solution have been studied in the temperature range 77–300 K. The results are compared with data for the compound PbTe0.9Se0.1 with a similar magnitude of the Seebeck coefficient S at 84 K. Along with lower thermal conductivity, Bi2Te2.7Se0.3 has a higher electrical conductivity σ and a much weaker temperature dependence. As a result, the power coefficient S 2σ in optimal samples begins to decrease only when the density of minority carriers becomes significant. In this case, |S| considerably exceeds the standard value of 200 μV/K. The reduction of the electron density reduces the thermoelectric figure of merit Z at its maximum and slightly lowers the temperature of the maximum; therefore, the expected effect on the average value of Z in the range 77–300 K is absent. Similar behavior is observed in Bi2Te2.88Se0.12, although the effect is less pronounced. The experimental results are discussed taking into account possible changes in the dominant scattering mechanisms, carrier density, and electron energy spectrum. __________ Translated from Fizika i Tekhnika Poluprovodnikov, Vol. 38, No. 7, 2004, pp. 811–815. Original Russian Text Copyright ? 2004 by Konstantinov, Prokof’eva, Ravich, Fedorov, Kompaniets.  相似文献   

17.
We have investigated the Structural, mechanical and thermodynamic properties of Cu2CoXS4 (X = Si, Ge, Sn) by using the density functional theory method. In this paper, we used GGA-PBE functional to find the equilibrium structural parameters and to calculate the elastic properties. The Mulliken population analysis indicates the bonds between S atoms and other three atoms in Cu2CoXS4 (X = Si, Ge, Sn) exhibit the feature of covalent bond. Furthermore, the calculated elastic constants prove the mechanical stability of Cu2CoXS4 (X = Si, Ge, Sn) in I\(\bar 4\)2m structure. The results are given for B/G and A U reveal Cu2CoXS4 (X = Si, Ge, Sn) can behave as a ductile and elastic material. Finally, the heat capacity, thermal expansion, entropy and Debye temperature are also reported at the different pressures (0~50 GPa) and temperatures (0~1000 K).  相似文献   

18.
Cu0.003Bi0.4Sb1.6Te3 alloys were prepared by using encapsulated melting and hot extrusion (HE). The hot-extruded specimens had the relative average density of 98%. The (00l) planes were preferentially oriented parallel to the extrusion direction, but the specimens showed low crystallographic anisotropy with low orientation factors. The specimens were hot-extruded at 698 K, and they showed excellent mechanical properties with a Vickers hardness of 76 Hv and a bending strength of 59 MPa. However, as the HE temperature increased, the mechanical properties degraded due to grain growth. The hot-extruded specimens showed positive Seebeck coefficients, indicating that the specimens have p-type conduction. These specimens exhibited negative temperature dependences of electrical conductivity, and thus behaved as degenerate semiconductors. The Seebeck coefficient reached the maximum value at 373 K and then decreased with increasing temperature due to intrinsic conduction. Cu-doped specimens exhibited high power factors due to relatively higher electrical conductivities and Seebeck coefficients than those of undoped specimens. A thermal conductivity of 1.00 Wm?1 K?1 was obtained at 373 K for Cu0.003Bi0.4Sb1.6Te3 hot-extruded at 723 K. A maximum dimensionless figure of merit, ZT max = 1.05, and an average dimensionless figure of merit, ZT ave = 0.98, were achieved at 373 K.  相似文献   

19.
Temperature dependences of the Hall coefficient R, electrical conductivity σ, and thermopower α0 are investigated in the range of 4–300 K. The specific features observed in temperature dependences R(T), σ(T), and α0(T) are interpreted in the context of a model with two types of charge carriers.  相似文献   

20.
In this work, Te-doped and S-filled S x Co4Sb11.2Te0.8 (x = 0.1, 0.15, 0.2, 0.25, 0.3, 0.4) skutterudite compounds have been prepared using solid state reaction and spark plasma sintering. Thermoelectric measurements of the consolidated samples were examined in a temperature range of 300–850 K, and the influences of S-addition on the thermoelectric properties of S x Co4Sb11.2Te0.8 skutterudites are systematically investigated. The results indicate that the addition of sulfur and tellurium is effective in reducing lattice thermal conductivity due to the point-defect scattering caused by tellurium substitutions and the cluster vibration brought by S-filling. The solubility of tellurium in skutterudites is enhanced with sulfur addition via charge compensation. The thermal conductivity decreases with increasing sulfur content. The highest figure of merit, ZT = 1.5, was obtained at 850 K for S0.3Co4Sb11.2Te0.8 sample, because of the low lattice thermal conductivity.  相似文献   

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