Seeback Coefficient Research Articles

Nano structure Ti-doped skutterudite CoSb3 thin films through layer inter-diffusion for enhanced thermoelectric properties

Ti-doped CoSb3 thin films were prepared through layer inter-diffusion method and the prepared thin films have unique architecture, containing nano-size grains. According to the Raman analysis, the films have weaker atomic vibration after Ti doping. This nano-structure and the weak atomic vibration can scatter a wide-range spectrum of phonons, resulting the significantly decrease of thermal conductivity. In addition, this material design also leads to a very important improvement of the absolute Seeback coefficient value, which increases from about 50 μVK−1 to over 100 μVK-1. As the result, the maximum ZT value is 0.86 at 523 K for a Ti doped sample, which is six times higher than the un-doped sample and is comparable to the best value for the CoSb3 based thin films. A flexible CoSb3 based thin film thermoelectric generator was also fabricated and shows that the response time of all the touch events is below 1 s.

Electronic structure and transport coefficients of the thermoelectric materials Bi2Te3 from first-principles calculations

The electronic structures of bulk Bi2Te3 crystals were investigated by the first-principles calculations. The transport coefficients including Seeback coefficient and power factor were then calculated by the Boltzmann theory, and further evaluated as a function of chemical potential assuming a rigid band picture. The results suggest that p-type doping in the Bi2Te3 compound may be more favorable than n-type doping. From this analysis results, doping effects on a material will exhibit high ZT. Furthermore, we can also find the right doping concentration to produce more efficient materials, and present the “advantage filling element map” in detail.

High-Efficiency Electrochemical System for Harvesting Low-Grade Heat Energy

Tremendous thermal energy exists in low-grade heat sources (<100 °C), so high-efficiency and low-cost thermal energy harvesting system is highly demanded to utilize them. Current technologies, such as thermoelectric device, still have a low efficiency to satisfy commercial application. As an alternative choice, thermogalvanic cell, the electrochemical counterpart of thermoelectric device has benefit of higher electrochemical Seebeck coefficient low thermal conductivity, and material abundance. However, its efficiency is incomparable to thermoelectric system due to the low ionic conductivity. Another approach to utilize the high electrochemical Seeback coefficient is the thermally regenerative electrochemical cycle (TREC) aimed for harvesting high temperature thermal energy (>500 °C) half a century ago. In this approach, the electrochemical cell is discharged at T1 and recharged at a different temperature T2. The electrochemical Seeback effect induces lower charging voltage at T2 than the discharging voltage at T1, and thus net electricity is generated as the difference between the discharged and charged energy. This thermal-cycle-like design could lead high efficiency by decoupling electrical conduction and thermal conduction. However, large polarization of electrode materials of TREC has suppressed low temperature thermal energy (<100 °C). Here we demonstrate a new effective TREC to utilize low-grade heat by employing proper materials. The demonstrated system achieved very high efficiency at low temperature range. We believe that the demonstrated system is anticipated to be a good alternative choice of low cost and high efficiency thermal energy harvesting system from various low heat sources such as heat engine system, solar thermal, geothermal, and body heat.

Synthesis of fibrous reticulate nanocrystalline n-type MoBi2(Se1−xTex)5 thin films: Thermocooling applications

In the present investigation n-type MoBi2(Se1−xTex)5 nanocrystalline thin films with various compositions of Se and Te were successfully deposited on ultrasonically cleaned glass substrates using recently developed Arrested Precipitation Technique (APT). The effect of composition on optical, morphological, structural, electrical and thermocooling properties of MoBi2(Se1−xTex)5 were investigated using UV–vis–NIR Spectroscopy, scanning electron microscopy, energy dispersive spectroscopy, X-ray diffractometer, thermoelectric power and thermocooling measurements. Thermoelectric properties including electrical conductivity (σ), Seeback coefficient (S) and figure of merit (ZT) were measured at 300K. Our aim is to investigate thermocooling behavior in respect of variation in composition of Se and Te in MoBi2(Se1−xTex)5 thin films along with optostructural and optoelectric properties.

The Characterization of CdS Thin Film Prepared by CBD Method

CdS thin film was deposited onto glass substrates by the chemical bath deposition. The deposition temperature was maintained at 75 °C. The crystal structure, surface morphology, optical and electrical properties have investigated employing X-ray diffraction (XRD), scanning electron microscopy (SEM), spectrophotometer and seeback coefficient measurement, respectively. The XRD reveals CdS thin film grown at 75 °C has the mixed hexagonal and cubic structure. The optical band gap energy is 2.4 eV. The seeback coefficient is 197.3μV/k at room temperature. The electric resistivity of CdS thin film is in the order of 10000Ω•cm.

Preparation and Thermoelectric Properties of SiC Matrix Composites Prepared under a Low Sintering Temperature

SiC powders with nickel powders and sintering aids were prepared by pressureless sintering at 1500oC under a N2 atmosphere. XRD, TEM, SEM techniques were used to characterize the phases and microstructure of the specimens. The thermoelectric properties of SiC matrix composites were investigated by measuring the Seebeck coefficient and the electrical conductivity. The main phase of all samples was -SiC, the Ni2Si can be observed with adding nickel powders. The largest electric conductivity was close to 3.5 m-1-1 at about 973K. The highest Seeback coefficient was up to 1800 V/K at 1073K. The transition from n-type to p-type was occurred.

Determination of the optimal concentration of ions Zn2+ in the flex-free system Mn-Zn through the study of electrical and magnetic susceptibility characteristics

In order to study the practicability delimitating the optimal electrical properties have been studied for soft ferrite system Mn|.xZnxFe204, which prepared by solid state method in the temperature range 300 to 550 K by substituting Mn2+ ions instead of Zr,2+ ions. The resulting of this study shows that the electrical conductivity for these systems were optimal value (10"6 £T! cm. The calculation of activation energy gave of 0.25 eV and 0.33 eV, The positive sign of thermoelectric power (seeback coefficient) for these systems means that the majority carriers were holes, Also the optimal magnetic susceptibility properties resulted in values -132xlO"5 , -662x1 0'5. From the electrical properties (electrical conductivity and thermoelectric power ) and magnetic susceptibility, the optimal results when concentration ions for these systems is Fe2O4 , which means equaled 0.4 to Zn2+ ions and 0.6 الخلاصة

Effect of pressure and quenching on superconductive La2CuO4+ delta (0< delta

Samples of ${\mathrm{La}}_{2}$${\mathrm{CuO}}_{4+\mathrm{\ensuremath{\delta}}}$ in the range 00.1 were prepared by electrochemical insertion of oxygen in KOH; the oxygen content was determined by iodometric titration. The temperature variations of resistance R and Seeback coefficient \ensuremath{\alpha} were used to monitor as a function of the compositional parameter \ensuremath{\delta} not only the evolution of the superconductive transition temperature ${\mathit{T}}_{\mathit{c}}$, but also the diffusion-controlled spinodal phase segregation occurring in the temperature range 200T\ensuremath{\le}300 K. The data also show that the \ensuremath{\delta} interstitial oxygen atoms ${\mathrm{O}}_{\mathit{i}}$ per formula unit enter as ${\mathrm{O}}_{\mathit{i}}^{2\mathrm{\ensuremath{-}}}$ ions at least in the range 0\ensuremath{\le}0.070. Comparison of the transport properties of samples slow-cooled from room temperature to 77 K reveals an ${\mathrm{O}}_{\mathit{i}}$-atom segregation over the range 0\ensuremath{\le}0.066; this segregation disappears for \ensuremath{\delta}&gt;${\mathrm{\ensuremath{\delta}}}_{\mathit{o}}$ where the ${\mathrm{O}}_{\mathit{i}}$ atoms become ordered, and 0.066${\mathrm{\ensuremath{\delta}}}_{\mathit{o}}$0.070 was determined. Analysis of neutron-diffraction data from available literature gives a spinodal decomposition temperature ${\mathit{T}}_{\mathit{s}}$ vs \ensuremath{\delta} that falls to 200 K at ${\mathrm{\ensuremath{\delta}}}_{\mathit{s}}$(max)\ensuremath{\approxeq}0.05; the diffusion-controlled spinodal phase segregation occurs within the phase field of the ${\mathrm{O}}_{\mathit{i}}$-disordered orthorhombic structure.The oxygen-rich phase having ${\mathrm{\ensuremath{\delta}}}_{\mathit{s}}$(max)\ensuremath{\approxeq}0.05 is superconductive with a zero-resistance temperature ${\mathit{T}}_{0}$=26 K that is lower than the ${\mathit{T}}_{0}$=32 K observed for \ensuremath{\delta}&gt;${\mathrm{\ensuremath{\delta}}}_{\mathit{o}}$; ${\mathit{T}}_{0}$ falls to a minimum near \ensuremath{\delta}=0.0625 within the compositional range ${\mathrm{\ensuremath{\delta}}}_{\mathit{s}}$(max)${\mathrm{\ensuremath{\delta}}}_{\mathit{o}}$, which suggests the presence of a competitive nonsuperconductive line phase near p=1/8 holes per Cu atom as is found in the ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Ba}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$ system near x=1/8. A nonsuperconductive transition at ${\mathit{T}}_{\mathit{d}}$=47\ifmmode\pm\else\textpm\fi{}1 K was found in slow-cooled samples over the range 0${\mathrm{\ensuremath{\delta}}}_{\mathit{o}}$; it is suppressed by both high pressure and the quenching procedure. We associate it with the competitive nonsuperconductive phase stabilized near p=1/8. In the ordered-${\mathrm{O}}_{\mathit{i}}$ phase found for \ensuremath{\delta}&gt;${\mathrm{\ensuremath{\delta}}}_{\mathit{o}}$, a ``tail'' in the R-vs-T curve extends into the superconductive temperature range where \ensuremath{\alpha}=0; it is attributed to a liquid-vortex state rather than a second superconductive phase. The pressure dependences of ${\mathit{T}}_{\mathit{c}}$ and the ${\mathrm{O}}_{\mathit{i}}$-atom mobility were used to distinguish the superconductive phases found for \ensuremath{\delta}${\mathrm{\ensuremath{\delta}}}_{\mathit{o}}$ and \ensuremath{\delta}&gt;${\mathrm{\ensuremath{\delta}}}_{\mathit{o}}$. The appearance of a nonsuperconductive line phase in the interval ${\mathrm{\ensuremath{\delta}}}_{\mathit{s}}$(max)${\mathrm{\ensuremath{\delta}}}_{0}$ permits reconciliation of the data, including indirect evidence for charge fluctuations stabilized below a ${\mathit{T}}_{\mathrm{\ensuremath{\rho}}}$150 K in this interval. The indirect evidence for charge fluctuations is the same as that discussed by us elsewhere in the framework of a model developed for the system ${\mathrm{La}}_{2\mathrm{\ensuremath{-}}\mathit{x}}$${\mathrm{Sr}}_{\mathit{x}}$${\mathrm{CuO}}_{4}$.

Thermopower of thin iron films

Thin iron films were prepared by evaporation in a high vacuum system (pressure in the 10 −5 MPa range). The thermopower was measured in situ near room temperature as a function of film thickness. Iron films with rather high resistivity values showed a strong thickness effect of the Seeback coefficient, S, with the difference between S (bulk) and S (film) reaching values of up to (19±3) μV/K for a sample 5 nm thick. The difference between S (bulk) and S (film) decreased with increasing d values. However, a sample with a resistance value of 50 μΩ cm at d = 5 n had an S value which differed by less than 3 μV/K from S (bulk).

Long-term drift in mineral-insulated Nicrosil-sheathed type K thermocouples

The drift in signal for Nicrosil-sheathed type K thermocouple probes has been measured over 1000 h at temperatures up to 1300 °C. It is shown that thermoelectric hysteresis is the dominant process for temperatures below 800 °C, giving drifts of up to 1.5 °C. At higher temperatures the drift is influenced by irreversible changes in Seeback coefficient and is below 3 °C when A1 and Mn are present in the negative thermoelement and Nicrosil is used as the sheathing alloy. This represents a ten-fold improvement in stability over conventional type K probes. Since hysteresis in type N alloys extends over twice the temperature range of that in type K, some comparisons have been made between the two types at 500 and 1000 °C. The drift is larger in the type N probes, being + 5 °C at 1000 °C.

Electrical conductivity and nonstoichiometry of the perovskite-type compound La 0.80Sr 0.20CuO y

Electrical conductivity, nonstoichiometry (oxygen deficiency) and Seeback coefficient of the perovskite-type compound La 0.80Sr 0.20CuO y were measured at 1073, 1173 and 1273K as a function of oxygen partial pressure (10 5 to 10 1 Pa). The compound has nonstoichiometry from y=2.50 to 2.47. The majority of carriers are holes as confirmed by the sign of the Seebeck coefficient. The equilibrium constant for carrier formation K i and the hole mobility μ h were determined by using the relation between electrical conductivity and nonstoichiometry. The enthalpy of carrier formation was estimated to be 182 kJ mol −1. The hole mobility was calculated to be 0.18 cm 2V −1s −1 at 1073 K, 0.63 cm 2V −1s −1 at 1173 K and 0.38 cm 2V −1s −1 at 1273 K.

Nature of principal scattering mechanism in well-annealed antimony thin films—analysis from thermoelectric data

Antimony thin films of different thicknesses have been vacuum-deposited onto cleaned glass substrates held at room temperature, and their thermoelectric power and electrical resistivity have been evaluated as functions of temperature and thickness. The Jain-Verma theory of the size effect on the thermoelectric power of thin films has been applied to the experimental data to understand the nature of the scattering mechanism in antimony thin films. The carrier mean free path I g and the Seeback coefficient S g of the bulk (with thin film microstructure) have been evaluated at room temperature from the resistivity-thickness and thermoelectric power-thickness plots, respectively, as 1200 Å and 30.1 μVK −1. Using these values S f / S g , the thermoelectric power of the films (in the units of S g , as given by the Jain-Verma theory has been plotted as a function of thickness t/ I g (in units of I g ) for different values of the scattering parameter b to generate a family of curves. By finding out on what curve or curves the experimental thermoelectric power values lie, the scattering parameter has been evaluated to be −0.2, so that the relaxation time τ varies as τ= a E −0.2 in antimony thin films. It is inferred from this that the major scattering process in our antimony thin films is lattice scattering even though other scattering processes also occur to a lesser extent in the films in the temperature range studied.

Transport properties of MoSe x Te2−x (0 ≤x ≤ 2) single crystals

The layer type MoSe x Te2−x (0 ≤x ≤ 2) have been grown in single crystalline form by chemical vapour transport technique using bromine as the transporting agent. The electrical resistivity and Hall mobility perpendicular to thec-axis of the crystals were measured at room temperature. The variation of the Seeback coefficient with temperature was also investigated.

Experimental studies of electrical conduction mechanism of H 2-reduced BaTiO 3

ESR, resistivity and Seeback coefficient measurements have been performed on both ceramics and single crystals of reduced semiconducting BaTiO 3. From the results that the observed temperature dependence of the Seeback coefficient can be explained by the temperature dependence of carrier concentration estimated from the electric resistivity making use of the data of electron mobility, it is concluded that the electric conduction in reduced BaTiO 3 is due to the band conduction rather than to the hopping process. From the measurement of the temperature dependence of the ESR intensity of the F-center, the number of electrons trapped at the F-centers decreases exponentially with temperature, while the number of conduction electrons increases. This temperature dependence can not be simply explained as that of the unionized donors in semiconductor. Therefore, the ESR signal considered as that of the F-center may not be due to simple donors, even though some of the conduction electrons may be originated in them.

II. Experimental Hall effect data for amorphous semiconductors

Abstract This paper presents the main features of the experimental data on Hall effect measurements in amorphous semiconductors reported so far. More specially, it analyses data on chalcogenide glasses, tetrahedral CdGe x As2 glasses and amorphous germanium, silicon and arsenic. Kolomiets and his group at the Ioffe Institute of Leningrad were the first to study systematically the properties of amorphous semiconductors. Kolomiets and Nazarova (1960) published the first experimental work on the Hall effect in chalcogenide glasses, having examined vitreous materials of the Tl2SeAs2(SeTe)3 system II. Two features of great interest emerged from this work. The first is the magnitude of the Hall mobility, which was found to be a few times 10−l cm2 V−1 s−1 throughout; the second is the sign anomaly of the Hall coefficient, i.e. n-type Hall coefficient but p-type Seeback coefficient. Eighteen years later these features still represent the principal differences between Hall effect results on amorphous, as compared ...