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1.
《Materials Chemistry and Physics》1998,57(1):57-66
Thin films (Bi0.25Sb0.75)2Te3 alloy of thickness in the range 400–2200 Å have been deposited on clean glass substrates by the flash evaporation technique in a vacuum of 1 × 10−5 Torr. Investigation by X-ray diffraction (XRD) and transmission electron microscopy (TEM) showed that all the films were polycrystalline and the grain size increased with increasing film thickness. Annealing treatment leads to grain growth. Electrical resistivity and thermoelectric power measurements were carried out for different thicknesses of the films in the temperature range 300–450 K. The dependences of resistivity and thermoelectric power on the temperature show that (Bi0.25Sb0.75)2Te3 films are semiconducting. Least square fit of electrical resistivity and thermoelectric power data with reciprocal thickness indicates that the results on (Bi0.25Sb0.75)2Te3 alloy films agree with the prediction of size effect theories. The effective mean free path model of size effect with perfect diffuse scattering is used for the analysis of the data. From the fit, the important physical parameters i.e., mean free path (lg), bulk resistivity (ρg), bulk thermoelectric power (Sg) and energy dependent mean free path relation power index (Ug) have been evaluated. 相似文献
2.
Bismuth–antimony–tellurium-based nanopowders were fabricated by a chemical process in which dissolved Bi, Te and Sb salts were directly reduced in each element via surfactant-assistant polyol reducing agents. XRD patterns of the synthesized nanopowders showed that the formed phases correspond mainly to (Bi0.5Sb0.5)2Te3 and Bi0.5Sb1.5Te3, respectively. The phases revealed that the three different elements were stably alloyed as ternary composition in one powder via the simple chemical route. The nanopowders were consolidated into bismuth telluride-based bulk materials that exhibited electrical resistivity above 5.6 × 10?5 Ωm, 150 μ V/K of the Seebeck coefficient and 0.7 W/mK of thermal conductivity at room temperature. These results showed that p-type thermoelectric nanopowders obtained from a simplified chemical process could be used in making thermoelectric materials towards high performances. 相似文献
3.
L. Deng H.A. Ma T.C. Su F.R. Yu Y.J. Tian Y.P. Jiang N. Dong S.Z. Zheng X. Jia 《Materials Letters》2009,63(24-25):2139-2141
Skutterudite compounds Co4Sb12 ? xTex with bcc crystal structure were prepared by high pressure and high temperature (HTHP) method. The study explored chemical doping with Te at the Sb site in an attempt to optimize the thermoelectric figure of merit ZT in the system Co4Sb12 ? xTex. The electrical resistivities, Seebeck coefficients and thermal conductivities of the samples were measured in the temperature range of 300–710 K. We found that the presence of Te substantially decreased the electrical resistivity without any detrimental effect on the Seebeck coefficients, which improved the power factor. Among all the samples, Co4Sb11.5Te0.5 shows the highest power factor of 35.3 µw/(cmK2) at 710 K, and the maximum ZT value reaches 0.67 at 710 K. 相似文献
4.
《Materials Characterization》2007,58(5):479-484
We reported the Ag adding effects on the crystallization behavior in Ge2Sb2Te5 film. Agx(Ge2Sb2Te5)1 − x films (where x = 0–0.2) were deposited on SiO2 wafer and glass substrate by RF magnetron co-sputtering and annealed by RTA (rapid thermal annealing) at various temperature to crystallize. The effects of Ag adding on the structural, thermal and electrical properties were measured by X-ray diffraction, X-ray reflectivity, AFM, SEM, DSC and 4-point probe analysis. It was found that the crystallization temperature increased by Ag adding in Ge2Sb2Te5 films. However, the surface of Agx(Ge2Sb2Te5)1 − x films got rough when annealing temperature and Ag contents increased. According to the Kissinger method, the activation energy for crystallization increased as the Ag content increased. It is thought that Ag atoms in Ge2Sb2Te5 act as an amorphous stabilizer and they make it hard to switch from amorphous to crystalline phase. From this study, we would show the Ag0.06(Ge2Sb2Te5)0.94 film is suitable for phase change memory material because of its higher crystallization temperature and structural stability. 相似文献
5.
《Materials Letters》2005,59(8-9):966-970
The electronic transport properties of the flash-evaporated n-type Bi2Te2.4Se0.6 thin films have been investigated. The thickness dependence of Seebeck coefficient and electrical resistivity has been analyzed by the effective mean free path model. It was found that both the Seebeck coefficient and the electrical resistivity have a linear relation with the reciprocal of film thickness. The data analyzed by the effective mean free path model have been combined to evaluate important material parameters such as mean free path, its energy dependence, and Fermi energy. Annealing effects on the electronic transport properties have been also examined in conjunction with the antistructure defects. It was found that the annealing treatment is necessary for Bi2Te2.4Se0.6 thin films to reduce the antistructure defects and to improve their thermoelectric properties. 相似文献
6.
Jae-Hong Lim MiYeong Park Dong-Chan Lim Nosang V. Myung Jung-Ho Lee Young-Keun Jeong Kyu Hwan Lee 《Materials Research Bulletin》2012,47(10):2748-2751
SbxTey films were potentiostatically electrodeposited from acidic nitric baths at room temperature by controlling the applied potential. Near-stoichiometric Sb2Te3 thin films were obtained at applied potentials between ?0.15 and ?0.30 V vs. saturated calomel electrode (SCE). Post-annealing in a reducing environment resulted in an improvement in the crystal structure without the evaporation of the Te element. This result was indicated by a significant reduction in the electrical resistance and decrease in the FWHM of the main diffraction peaks. The power factor (σS2) increased from 44.2 to 372.1 μW/m K2 after annealing at 473 K. 相似文献
7.
Fengrong Yu Bo Xu Jianjun Zhang Dongli Yu Julong He Zhongyuan Liu Yongjun Tian 《Materials Research Bulletin》2012,47(6):1432-1437
Using Bi2Te3 nanopowders prepared from ball milling of elemental Bi and Te, nanocrystalline Bi2Te3 bulks were fabricated with high pressure sintering technique under variable pressures. The structural and thermoelectric properties were characterized, revealing a strong correlation with the sintering pressure. The nanocrystalline Bi2Te3 bulk fabricated under 2 GPa exhibits good thermoelectric properties with ZT over 0.8 from 300 to 460 K and a peak ZT of 1.03 occurring at 403 K, which can be attributed to the small thermal conductivity from enhanced phonon scattering by grain boundaries and defects, as well as to the good electrical property comparable to that of the zone melting material. 相似文献
8.
Physical properties of Bi2 (Te,Se)3 and Bi2Se1.2Te1.8 prepared using solid-state microwave synthesis
Bi2(Te, Se)3 and Bi2Se1.2Te1.8 bulk products were synthesised using standard solid-state microwave synthesis. The Bi2(Te, Se)3 and Bi2Se1.2Te1.8 were then deposited thermally onto glass substrates at a pressure of 10? 6 Torr. The structure of the samples was analysed using X-ray diffraction (XRD), and the powders and thin films were observed to be polycrystalline and rhombohedral in structure. The surface morphology of the samples was determined using scanning electron microscopy (SEM). From the measurements of optical properties, the energy gap values for the Bi2Te3, Bi2Se3, and Bi2Se1.2Te1.8 thin films were 0.43, 0.73, and 0.65 eV, respectively. 相似文献
9.
《Materials Chemistry and Physics》2005,89(2-3):402-405
Spray pyrolysis method is used to deposit lanthanum telluride (La2Te3) thin films on glass substrates. The films are deposited by pyrolysis of sprayed solutions of LaCl3 and Te metal dissolved in concentrated HCl and HNO3 along with hydrazine hydrate as a reducing agent. X-ray diffraction analyses show that the films are polycrystalline with La2Te3 phase. The films have a direct optical band gap of 2.2 eV. The films are p-type semiconductors with an electrical resistivity of the order of 104 Ω cm at ambient temperature (27 °C). 相似文献
10.
Bi2S3 thin films were grown by successive ionic layer adsorption and reaction method (SILAR) onto the glass substrates at room temperature. The as prepared thin film were annealed at 250 °C in air for 30 min. These films were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), atomic force microscopy (AFM) and electrical measurement systems. The X-ray diffraction patterns reveal that Bi2S3 thin film have orthorhombic crystal structure. SEM images showed uniform deposition of the material over the entire glass substrate. The optical energy band gap observed to be decreased from 1.69 to 1.62 eV for as deposited and annealed films respectively. The I–V measurement under dark and illumination condition (100 W) show annealed Bi2S3 thin film gives good photoresponse as compared to as deposited thin film and Bi2S3 thin film exhibits photoconductivity phenomena suggesting its useful in sensors device. The thermo-emf measurements of Bi2S3 thin films revealed n-type electrical conductivity. 相似文献
11.
Er2O3 (0–0.8 wt.%)-doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state reaction method. The effects of Er2O3 on the microstructure and electrical properties were investigated. X-ray diffraction (XRD) data shows that Er2O3 in an amount of 0.2–0.8 wt.% can diffuse into the lattice of the BNKT18 ceramics and form the pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain sizes of BNKT18 ceramics decrease with the increase of Er2O3 content; in addition, the modified ceramics have the clear grain boundary and a uniformly distributed grain size. At room temperature, the electrical properties of the BNKT18 ceramics have been improved with the addition of Er2O3, and the BNKT18 ceramics doped with 0.6 wt.% Er2O3 have the highest piezoelectric constant (d33 = 138 pC/N), the highest planar coupling factor (kp = 0.2382), the highest remnant polarization (Pr = 25.2 μC/cm2), the higher relative dielectric constant (εr = 936) and lower dissipation factor (tanδ = 0.047) at a frequency of 10 kHz. Moreover, the Tm and Td of the samples increase with the addition of Er2O3. 相似文献
12.
《Materials Research Bulletin》2006,41(8):1558-1564
Uniform, adherent and reproducible bismuth oxide thin films have been deposited on glass substrates from aqueous Bi(NO3)3 solution, using the solution spray technique. Their structural, surface morphological, optical, and electrical properties were investigated by XRD, AFM, optical absorption, electrical resistivity and thermo-emf measurements. The structural analysis from XRD pattern showed the formation of mixed phases of monoclinic Bi2O3 (predominant), tetragonal β-Bi2O3 and nonstiochiometric Bi2O2.33. The surface morphological studies on atomic force micrographs revealed round grain morphology of bismuth oxide crystallites. The optical studies showed a direct band gap of 2.90 eV for as-prepared bismuth oxide films. The electrical resistivity measurements of bismuth oxide films indicated a semiconducting behavior with the room temperature electrical resistivity of the order of 107 Ω cm. From thermo-emf measurements, the electrical conductivity was found to be of n-type. 相似文献
13.
Amorphous Se82 ? xTe18Sbx thin films with different compositions (x = 0, 3, 6 and 9 at.%) were deposited onto glass substrates by thermal evaporation. The transmission spectra, T(λ), of the films at normal incidence were obtained in the spectral region from 400 to 2500 nm. Based on the use of the maxima and minima of the interference fringes, a straightforward analysis proposed by Swanepoel has been applied to derive the optical constants and the film thickness. The dispersion of the refractive index is discussed in terms of the single-oscillator Wemple and DiDomenico model. Tauc relation for the allowed non-direct transition describes the optical transition in the studied films. With increasing antimony content the refractive index increases while the optical band gap decreases. The optical band gap decreases from 1.62 to 1.26 eV with increasing antimony content from 0 to 9 at.%. The chemical-bond approach has been applied successfully to interpret the decrease of the optical gap with increasing antimony content. 相似文献
14.
L. Deng X.P. Jia T.C. Su S.Z. Zheng X. Guo K. Jie H.A. Ma 《Materials Letters》2011,65(19-20):2927-2929
InxCo4Sb12 (0.1 ≤ x ≤ 0.5) skutterudite compounds with bcc crystal structure have been prepared by high-pressure and high-temperature (HPHT) method. Through this method, the processing time can be reduced from a few days to half an hour. The constituent phases of all resultant samples were determined by X-ray diffraction. The Seebeck coefficient, electrical resistivity, power factor and thermal conductivity of InxCo4Sb12 (0.1 ≤ x ≤ 0.5) were all measured in the temperature range of 302–665 K. Among all the samples, In0.5Co4Sb12 showed the highest power factor of 31.3 μWcm? 1 K? 2 at 616 K and the lowest thermal conductivity of 2.193 Wm? 1 K? 1 at 568 K. As a result, the maximum dimensionless figure of merit (ZT) value of In0.5Co4Sb12 reached 0.88 at 665 K, which can be attributed to its low thermal conductivity and high power factor. 相似文献
15.
《Optical Materials》2007,29(12):1405-1411
Highly transparent and conducting indium oxide thin films are prepared on glass substrates from precursor solution of indium chloride. These films are characterized by X-ray diffraction, scanning electron microscopy and optical transmission. The preferential orientation of these films is found to be sensitive to deposition parameters. A comparative study has been made on the dependence on the thickness of the film on substrate temperatures with aqueous solution and 1:1 C2H5OH and H2O as precursors. Films deposited at optimum conditions have 167 nm thickness and exhibited a resistivity of 2.94 × 10−4 Ω m along with transmittance better than 82% at 550 nm. The analytical expressions enabling the derivation of the optical constants of these films from their transmission spectrum only have successfully been applied. Finally, the refractive index dispersion is discussed in terms of the single-oscillator Wemple and Didomenico model. 相似文献
16.
Chuen-Shii Chou Chun-Yu Wu Ru-Yuan Yang Cheng-Yang Ho 《Advanced Powder Technology》2012,23(3):358-365
This study investigates effects of the zinc oxide (ZnO) addition and the sintering temperature on the microstructure and the electrical properties (such as dielectric constant and loss tangent) of the lead-free piezoelectric ceramic of bismuth sodium titanate (Na0.5Bi0.5TiO3), NBT, which was prepared using the mixed oxide method. Three kinds of starting powders (such as Bi2O3, Na2CO3 and TiO2) were mixed and calcined. This calcined NBT powder and a certain weight percentage of ZnO were mixed and compressed into a green compact of NBT–ZnO. Then, this green compact of NBT–ZnO was sintered to be a disk doped with ZnO, and its characteristics were measured. In this study, the calcining temperature was 800 °C, the sintering temperatures ranged from 1000 to 1150 °C, and the weight percentages of ZnO doping included 0.0, 0.5, 1.0, and 2.0 wt%. At a fixed wt% ZnO, the grain size increases with increase in the sintering temperature. The largest relative density of the NBT disk obtained in this study is 98.3% at the calcining temperature of 800 °C, the sintering temperature of 1050 °C, and 0.5 wt% ZnO addition. Its corresponding dielectric constant and loss tangent are 216.55 and 0.133, respectively. 相似文献
17.
《Materials Letters》2007,61(11-12):2460-2463
Ga-doped zinc oxide (ZnO:Ga) transparent conductive films with highly (002)-preferred orientation were deposited on glass substrates by DC reactive magnetron sputtering method in Ar + O2 ambience with different Ar/O2 ratios. The structural, electrical, and optical properties were investigated by X-ray diffraction, Hall measurement, and optical transmission spectroscopy. The resistivity and optical transmittance of the ZnO:Ga thin films are of the order of 10− 4 Ω cm and over 85%, respectively. The lowest electrical resistivity of the film is found to be about 3.58 × 10− 4 Ω cm. The influences of Ar/O2 gas ratios on the resistivity, Hall mobility, and carrier concentration were analyzed. 相似文献
18.
Gd2O3 (0–0.8 wt.%)-doped 0.82Bi0.5Na0.5TiO3–0.18Bi0.5K0.5TiO3 (BNKT18) lead-free piezoelectric ceramics were synthesized by a conventional solid-state process. The effects of Gd2O3 on the microstructure, the dielectric, ferroelectric and piezoelectric properties were investigated. X-ray diffraction (XRD) data shows that Gd2O3 in an amount of 0.2–0.8 wt.% can diffuse into the lattice of BNKT18 ceramics and form a pure perovskite phase. Scanning electron microscope (SEM) images indicate that the grain size of BNKT18 ceramics decreases with the increase of Gd2O3 content; in addition, all the modified ceramics have a clear grain boundary and a uniformly distributed grain size. At room temperature, the ferroelectric and piezoelectric properties of the BNKT18 ceramics have been improved with the addition of Gd2O3, and the BNKT18 ceramics doped with 0.4 wt.% Gd2O3 have the highest piezoelectric constant (d33 = 137 pC/N), highest relative dielectric constant (εr = 1023) and lower dissipation factor (tan δ = 0.044) at a frequency of 10 kHz. The BNKT18 ceramics doped with 0.2 wt.% Gd2O3 have the highest planar coupling factor (kp = 0.2463). 相似文献
19.
100-nm thick films of Al1 ? xCux alloys were prepared on glass substrates by thermal diffusion technique. The Cu atomic concentration was varied from 10% to 90%. Alloys were prepared at different temperatures into a vacuum oven with Argon atmosphere. Two thermal processes were used: i) heating the film at 400 °C in a single step, and ii) heating the films in sequential steps at 100, 200, 300 and 400 °C. Morphology, electrical resistivity, and crystalline orientation of the alloys were studied. The electrical resistivity and surface roughness of the alloys were found to depend strongly on the atomic composition and the diffusion temperature. However, we did not find differences between samples prepared under the two thermal processes. Alloys prepared with x = 0.6 and x = 0.1–0.3 as Cu at concentration exhibited values on electrical resistivity and surface roughness lower than pure Al. Different phases of the Al1 ? xCux films were observed as a function of Cu concentration showing a good agreement with the AlCu phase diagram. 相似文献
20.
《Materials Chemistry and Physics》2004,83(2-3):245-249
The band gap energy of bismuth(III) selenide in thin-film form was determined using the optical and thermal methods. The optical band gap energy of 0.35 eV was calculated on the basis of the recorded optical spectra in the near-infrared region, within the framework of a parabolic approximation for the dispersion relation, using the equations which arise from Fermi’s golden rule for electronic transitions from valence to conduction band. From the temperature dependence of the dark electrical resistance of the bismuth(III) selenide thin films in the region of intrinsic and extrinsic conduction, a thermal band gap energy of 0.37 eV and an ionization energy of the donor impurity level of 0.13 eV were calculated. The thermal, as well as the optical band gap energy are in excellent agreement with a literature value for bulk bismuth(III) selenide. On the basis of these data, several conclusions on the film microstructure (nanocrystalline versus glassy) are derived and also an estimation of the higher bound to the Bohr’s excitonic radius for bulk Bi2Se3 is given. 相似文献