Crystallographic and electrical study of the chromium substituted ferrous zinc copper ferrites

The structural and electrical properties of the oxidic spinel Zn_0·5Cu_0·5Fe _x Cr_2−x O₄ (x=0·8, 0·9, 1·0, 1·1) have been investigated through X-ray diffraction, electrical resistivity, and thermoelectric measurements. X-ray diffraction data showed formation of single spinel phase with cubic structure. D.C. resistivity measurements from room temperature to 850 K was carried out and activation energy for all the compositions evaluated. Thermoelectric measurements showedp-type semiconducting nature in all the samples.     

Transport properties of cold-worked aluminum at low temperatures

The electrical resistivity and thermoelectric power in annealed and cold-worked samples of Al and Al-Mg alloy have been measured between1.5 and8.5 K. The deviation from Matthiessen's rule is found to decrease with cold work, while the residual resistivity increases. The lattice imperfections also have strong effects on the thermoelectric power. A critical discussion focuses on the relation of and discrimination among these effects.     

Electrical resistivity and thermoelectric power of copper-germanium films

CuGe films over the whole composition range were prepared by the vapour quenching of the alloys onto glass substrates held at 300 K. The electrical resistivity, thermoelectric power and temperature dependence of the films were studied in the temperature range 100–500 K. The observed behaviour of the electrical resistivity and thermoelectric power is understandable on the basis of transmission electron microscopy and electron diffraction observations which indicate three structural regions. Up to 5 at.% Ge in copper the films are single phase with a structure similar to that of pure copper; in the range 5–80 at.% Ge in copper the films consist of a mixture of Cu₃Ge, copper and germanium; beyond 80 at.% the CuGe films are single-phase amorphous.     

Composition dependence of electrical properties of simultaneously evaporated Sb-Se thin films

Amorphous thin films of Sb-Se are prepared using the three-temperature method. The films are prepared with atomic compositions from 5–90 at.% Sb. The electrical resistivity, Hall voltage and thermoelectric power of annealed samples have been measured in the temperature range 25 to 250°C. On heat treatment the sharp fall of resistance of the annealed films is attributed to radical structural transformation from amorphous to crystalline. Electrical resistivity, Hall constant and thermoelectric power are found to vary with thickness and composition of the film. Paper presented at the 7th International Conference on Thin Films, New Delhi, December 7–11, 1987     

Property-processing relations in developing thermoelectric ceramics: Na<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript>2</Subscript>O<Subscript>4</Subscript>

Polycrystalline Na_1−x Co₂O₄ is a promising p-type oxide thermoelectric, and it was investigated in a property-processing study to enhance the thermoelectric properties for high temperature applications. The density of the ceramics was improved by a post-milling process, and consequently, we obtained better thermoelectric power factors (PF) due to an associated improvement in electrical conductivity. Through a milling process, and sintering at 1203 K, we obtained an enhanced thermoelectric power factor of ~4 μW/cm K² at 500 K for randomly orientated polycrystalline ceramics. The Seebeck coefficient variation with temperature demonstrates through modeling that the conduction mechanism changed from metallic to a semiconducting behavior between temperatures 300 to 400 K.     

Transport properties of trivalent substituted Li-ferrites

The electrical resistivity and thermoelectric power of Li_0.5Fe_2.5–x R _x O₄ (R = Al, La, Sm and Gd; x = 0.0 and 0.1) are studied. The distribution of the substituted ions over the different lattice sites is determined from IR spectra. The electrical resistivity is found to have a direct relation with the ionic radius of the substituted R ions. Meanwhile, the absolute value of thermoelectric power decreased with increasing ionic radius.     

Thermoelectric Power of Deoxygenated Bi1.6Pb0.4Sr2Ca2Cu3O10 + δ Sintered Superconducting Pellets

The thermal variation of the electrical resistivity and thermoelectric power of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_{10 +} pellets subjected to various degrees of deoxygenation is reported. The temperature dependence of the electrical resistivities of deoxygenated samples displays gradual transformation from metallic-like to semiconductor-like features in the normal state. All the samples however, show superconducting transition, but increasing deoxygenation depresses T _C0 from 102 to 45 K. Gross features of the temperature variation of thermoelectric power observed in properly oxygenated (Bi, Pb)-2223 cuprates are retained in all the deoxygenated samples. Our results on electrical resistivity and thermoelectric power in the normal state have been found to be consistent with a two-band model.     

Studies on the seebeck effect in semiconducting ZnO thin films

For ZnO thin films prepared by a pyrolytic technique, the thermoelectric power has been measured from room temperature up to 200 °C with reference to pure lead. The thickness and temperature dependence of its related parameters have been studied. The Fermi levels were determined using a nondegenerate semiconducting model. The carrier scattering index, activation energy and temperature coefficient of activation energy, have all been obtained at different ranges of thickness and temperature. All the samples were polycrystalline in structure and optically transparent.     

Deposition and annealing effect on lanthanum sulfide thin films by spray pyrolysis

Lanthanum sulfide thin films were prepared on glass substrates from aqueous medium using spray pyrolysis technique. The effect of preparative parameters such as substrate temperature and solution concentration on the films was studied. The lanthanum sulfide films were annealed in air at 300 °C for 2 h. The films were characterized by X-ray diffraction (XRD), optical microscopy, optical absorption, electrical resistivity and thermo-emf measurement techniques. The XRD studies revealed that the as deposited films are amorphous, while annealed films are polycrystalline. The optical band gap of the as deposited film is decreased from 2.5 to 2.2 eV after annealing due to improvement in crystallinity. The electrical resistivity is of the order of 10⁴-10⁵ Ω cm and showed semiconducting behaviour. Thermo-emf measurement revealed that the conductivity of lanthanum sulfide is p-type.     

Study of the dc resistivity and thermoelectric power in Mn-substituted Ni–Zn ferrites

The electrical resistivity and thermoelectric power as a function of temperature and Mn concentration for Ni_0.6-t Mn _t Zn_0.4Fe₂O₄ (t = 0, 0.1, 0.2, 0.3, 0.4 and 0.5) have been studied. It was observed that temperature variation of resistivity exhibits two breaks. Each break is associated with a change in activation energy. The activation energy in the paramagnetic region is found to be greater than that in the ferrimagnetic one. Moreover, it was found that the resistivity increases with increasing Mn content. The sign of thermoelectric power measurements revealed n-type conduction for all investigated samples. The results are explained according to the spin polaron model.     

Electrical properties of films grown on W and Mo substrates by titanium ion implantation in nitrogen atmosphere

Films consisting of alternating nitride and oxide layers differing in phase composition and structure are grown on polycrystalline tungsten and molybdenum substrates by ion implantation. The resistivity and thermoelectric power of the films are measured as functions of temperature, and the temperature coefficient of their resistance is determined. The phase composition and electrical properties of the films are shown to be governed by the nitrogen-ion dose delivered to the titanium target.Translated from Neorganicheskie Materialy, Vol. 41, No. 3, 2005, pp. 301–304.Original Russian Text Copyright © 2005 by Ignatenko, Badekin.This revised version was published online in April 2005 with a corrected cover date.This revised version was published online in April 2005 with a corrected cover date.     

DC resistivity and thermoelectric power in Ni-Cd ferrites

The electrical resistivity and Seebeck coefficient for Ni-Cd ferrites have been studied as a function of temperature. The lattice constant of the phases have been evaluated from X-ray powder data. The thermoelectric power measurements indicate that the samples aren-type semiconductors and the conduction mechanism is interpreted on the basis of localized model of polarons.     

Size and temperature dependence of thermoelectric power and electrical resistivity of vacuum-deposited antimony thin films

Thin antimony films of thicknesses in the range 30 to 200 nm have been vacuum deposited on glass substrates at room temperature. After annealing for about an hour at 500 K, the thermoelectric power and electrical resistivity were measured in vacuum as a function of temperature. The thermoelectric power and electrical conductivity data were combined and simultaneously analysed using the effective mean free path theory of size effect in thin films developed by Tellier and Pichard et al. In addition, their temperature dependence was also analysed. It was found that the thermoelectric power is positive and increases with increasing temperature and is inversely proportional to the thickness of the film. The electrical resistivity was found to be temperature dependent with the temperature coefficient of resistivity being positive, and inversely proportional to the thickness of the film. Analysis combining the data from the thermoelectric power and electrical conductivity measurements has led to the determination of mean free path, carrier concentration, effective mass, Fermi energy and the parameter The data were analysed for least squares fitting by local functions, such as the spline functions, which eliminates possible errors in conventional least squares fitting of data using non-local functions valid throughout the range.     

Comparison of structure and properties of alloys in amorphous,nanocrystalline and coarse-grained polycrystalline states

Some properties, including the microhardness, H _v, and electrical resistivity of a nanocrystalline, two coarse-grained polycrystalline and one amorphous alloys of Fe-Mo-Si-B of the same composition, were measured experimentally and compared. The structures of amorphous, nanocrystalline and coarse-grained Fe-Mo-Si-B alloys are also compared and discussed.     

Preparation and characterization of indium doped CdS0.2Se0.8 thin films by spray pyrolysis

The CdS_0.2Se_0.8 and indium doped CdS_0.2Se_0.8 thin films have been deposited onto the amorphous glass and fluorine doped tin oxide coated glass substrates by spray pyrolysis. The doping concentration of indium has been optimized by photoelectrochemical characterization technique. The structural, surface morphological, optical and electrical properties of CdS_0.2Se_0.8 and indium doped CdS_0.2Se_0.8 thin films have been studied. X-ray diffraction studies reveal that the films are polycrystalline in nature with hexagonal crystal structure. Scanning electron microscopy studies reveal that the grains are uniform with uneven spherically shaped, distributed over the entire substrate surface. The complete surface morphology has been changed after doping. In optical studies, the transition of the deposited films is found to be direct allowed with optical energy gaps decreasing from 1.91 to 1.67 eV with indium doping. Semiconducting behavior has been observed from resistivity measurements. The thermoelectric power measurements reveal that the films exhibit n-type conductivity.     

Transport Properties and Viscosity of Liquid CdTe Doped with In, Ge, and Sn

Data are presented on the high-temperature electrical conductivity, thermoelectric power (up to 1825 K), and viscosity (up to 1400 K) of undoped and doped (In, Ge, and Sn) CdTe melts. All of the materials were found to retain semiconducting properties upon melting, with a gradual increase in the contribution of metallic bonding, especially pronounced for the CdTe + 2 mol % Sn melt. The results are interpreted in terms of the double-structured melt model, which considers the coexistence of densely packed metallic regions and crystal-like CdTe clusters. The transition to metallic behavior of conductivity is accounted for by a gradual increase in the volume fraction of the densely packed, metallic phase. The doping effects on the conductivity and thermoelectric power of liquid CdTe are interpreted in terms of s–p hybridization.     

Thickness and temperature effects on thermoelectric power and electrical resistivity of (Bi0.25Sb0.75)2Te3 thin films

Thin films (Bi_0.25Sb_0.75)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 (Bi_0.25Sb_0.75)₂Te₃ films are semiconducting. Least square fit of electrical resistivity and thermoelectric power data with reciprocal thickness indicates that the results on (Bi_0.25Sb_0.75)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 (l_g), bulk resistivity (ρ_g), bulk thermoelectric power (S_g) and energy dependent mean free path relation power index (U_g) have been evaluated.     

Thermoelectric Power of Deoxygenated Bi1.6Pb0.4Sr2Ca2Cu3O10 + δ Sintered Superconducting Pellets

The thermal variation of the electrical resistivity and thermoelectric power of Bi_1.6Pb_0.4Sr₂Ca₂Cu₃O_{10 + δ} pellets subjected to various degrees of deoxygenation is reported. The temperature dependence of the electrical resistivities of deoxygenated samples displays gradual transformation from metallic-like to semiconductor-like features in the normal state. All the samples however, show superconducting transition, but increasing deoxygenation depresses T _C0 from 102 to 45 K. Gross features of the temperature variation of thermoelectric power observed in properly oxygenated (Bi, Pb)-2223 cuprates are retained in all the deoxygenated samples. Our results on electrical resistivity and thermoelectric power in the normal state have been found to be consistent with a two-band model.     

自燃法制备N型Bi掺杂LaNiO_3氧化物及其热电性能研究

以柠檬酸为螯合剂,各种硝酸盐为原料,采用简单的自燃法制备了金属Bi掺杂的N型钙钛矿结构的La1-xBixNiO3(x=0、0.025、0.05、0.075、0.1、0.15)热电材料前驱粉。前驱粉经煅烧、球磨、冷压、烧结等工艺获得块体材料。通过X射线衍射和扫描电镜观察等方法对样品的结构与形貌进行了分析表征。在573～1073K内测试了材料的电阻率和Seebeck系数,结果表明,该材料显示了较好的热电性能,掺杂Bi有助于显著降低材料的电阻率,优化材料的热电性能,其中试样La0.9Bi0.1NiO3组分材料在973K时的电阻率ρ=3.9606mΩ.cm,Seebeck系数S=-29.253μV/K,热电转换功率因子值p=2.16×10-5W/(m.K2)。     

The effect of Al-substitution on structure and electrical properties of Mn-Ni-Zn ferrites

X-ray diffraction, Infra-red spectroscopy and scanning electron microscopy have been used to investigate the Mn_0.5Ni_0.1Zn_0.4Al_xFe_{2 − x}O₄ system (0 ≤ x ≤ 0.15 in steps of 0.025). The analysis of IR spectra indicates the distribution of Al-ions between both A and B-sites. The electrical resistivity and thermoelectric power as a function of temperature and Al-content have been investigated. It is observed that the resistivity increases with increasing the Al-content. It is also found that the temperature variation of resistivity exhibits two breaks, each break is associated with a change in the activation energy. Measurement of the thermoelectric power reveals n-type conduction for all samples. The activation energies of all samples in the paramagnetic region are found to be greater than those in the ferrimagnetic region. The results are explained on the basis of the formation of spin polarons in the paramagnetic region.