Thermoelectric Power Measurements Research Articles

An investigation on SILAR deposited Cu$_{x}$S thin films

A copper sulfide thin film was deposited on glass substrate by successive ionic layer adsorption and reaction method at room temperature, using cupric sulfate and sodium sulfide aqueous solutions as precursors. The structural, surface morphological, optical, and electrical properties of the as-deposited film were investigated via X-ray diffraction, scanning electron microscopy, energy dispersive X-ray analysis, optical absorption, and d.c. 2-point probe methods. The film was found to be amorphous, dense, and uniform. Average atomic percentage of Cu:S in the as-deposited film was calculated as 63:37. The band gap energy of copper sulfide thin film was found to be 2.14 eV and the resistivity was 10^{-2} Omega cm at room temperature. The effect of annealing on crystal structure was also studied and reported. X-ray diffraction patterns revealed that annealing the film at various temperatures slightly improved the crystallinity. By using thermoelectric power measurement, p-type electrical conductivity was determined for as-deposited and annealed samples.

Synthesis and Characterization of Nanocrystalline (CdS) 0.6Te0.4 Thin Films Deposited by Closed Space Sublimation Technique

The ternary alloy of (CdS)0.6Te0.4 thin films were deposited onto rotating amorphous glass substrates by using closed space sublimation, at a base pressure of 10 -5 torr. The crystalline, morphological, optical and transport properties of the deposited films were studied by using X-Ray Diffraction (XRD), Scanning Electron Microscopy (SEM), UV-VIS-NIR Spectrophotometer, Four Probe method and Thermo Electric Power (TEP) measurement. The XRD exhibits the deposited thin film has polycrystalline nature having monoclinic phase. The dislocation density (δ), strain (e) and the number of crystallites per unit area (N) have been found to be 2.047 x 10 14 lines / cm 2 , 0.9926 and 9.264 x 10 17 respectively. The SEM reveals the homogeneity of the deposited samples. Optical study performed to estimate optical band gap using absorbance spectra and found to be in the range of 1.6 - 2.1 eV. The four probe method estimates the Electrical Resistivity = 0.2045 Ω-cm and Activation Energy = 0.01822 eV. The Fermi energy = 0.2628 eV and Scattering Coefficient = 2.3188 evaluated by using TEP.

Transport Properties of AgInSe<sub>2</sub> Crystals

AgInSe2 crystals were grown by Bridgman technique. The crystals were identified structurally by X-ray diffraction technique. Measurements of electrical conductivity and Hall effect were performed in the temperature range (138 K - 434 K) and (220 K - 488 K) for thermoelectric power measurements. From these measurements, many physical parameters were determined. The energy gap was calculated to be 1.24 eV. The conductivity type was found to be n-type. Crystallite size (D) of the obtained AgInSe2 crystals was calculated to be 70 nm. The lattice parameters for the prepared crystals were a = 6.0938 ? and c = 11.7775 ?.

Low temperature TEP measurement setup for thin plates and films

A setup to measure thermoelectric power (TEP) of thin plates and films is designed, developed and tested to work in 77K-300K range. Sample is pressure mounted flat on two Cu blocks having independent resistive heaters of appropriate power and platinum resistance thermometers (PRTs), which results in several advantages. For instance, the arrangement allows for very large range of PID controlled stable temperature gradients 0.5 to 100 K between the blocks, and the distance between the blocks can be adjusted according to the sample size. The measurements can be performed in both vacuum and inert gas atmosphere. The dimensions of the sample-holder-unit have been optimized to fit commercial Liquid Nitrogen/Helium dewars with neck sizes >56 mm. The setup also allows resistivity ρ(T) measurements and with suitable temperature sensors can be easily adapted to lower temperatures down to 4.2K. To check the performance, variety of measurements were carried out on different samples of Al, Cu, Mo, MgB2, YBa2Cu3O7 superconductor and Bi2Te3 in thin plate and film forms.

Concentration of electrons at grain boundaries in TiO2 (rutile): Impact on charge transport and reactivity

This work determined the local concentration of electrons in the grain boundary layer of TiO2 (rutile) at elevated temperatures (1223–1323K) in the gas phase of controlled oxygen activity (10−11Pa<p(O2)<10−5Pa). The determination is based on the measurements of thermoelectric power for both single crystal and polycrystalline specimen of pure TiO2. It is shown that the concentration of electrons in the grain boundary layer of polycrystalline TiO2 is larger than that in the bulk phase by a factor ranging between 4 at 1323K, and 13 at 1273K. The present finding is crucial in understanding the reactivity of polycrystalline TiO2 and its performance in solar energy conversion by TiO2.

Charge and mass transport properties of La2Ni0.95Al0.05O4.025+δ

In this work, mass and charge transport properties of acceptor doped lanthanum nickelate, La2Ni0.95Al0.05O4.025+δ (LNAO), were analyzed. The thermal expansion, electrical conductivity and thermoelectric power of LNAO were measured as a function of temperature in 25–1000°C range and oxygen partial pressure (pO2) in −14⩽log(pO2/atm)⩽−1 range. The average thermal expansion coefficient was 13.77×10−6K−1. The electrical conductivity was analyzed in relation to the thermoelectric power to elucidate the positive deviation of the activity coefficient of hole on the basis of the delocalized electron model. The thermoelectric power measurement shows a p-type to n-type transition. The chemical diffusion coefficient (D̃chem) and surface exchange coefficient (ksurf.) were calculated by 4-probe DC conductivity measurement and ksurf. was slightly higher than (D̃chem). The best-estimated hole-mobility values showed very weak temperature dependence. The results were compared with the literature results on La2NiO4+δ.

Low Temperature Chemical Synthesis of p-Type SnS Thin Films Suitable for Photovoltaic Structures

SnS thin film has been deposited on glass substrate at room temperature using low cost, environmental friendly chemical bath deposition (CBD) technique. The structural parameters of the deposited film have been investigated through X- ray diffraction measurements. The deposited SnS film found almost crystalline with preferred orientations along (111) planes revealing an orthorhombic phase of herzenbergite SnS structure. The lattice parameters and dislocation density were determined. The average grain size estimated to be ~ 25 nm. The surface morphology of the film examined using scanning electron microscopy (SEM) show uniform granular and any crack or pinhole free deposition of the film. The chemical compositions of the film examined using energy dispersive analysis of x-rays (EDAX) confirmed stoichiometric deposition. The analysis of the optical absorption spectra of the deposited film in the wavelength range of 200-1200 nm indicate that direct allowed transitions are dominant in the film. The direct band gap of the film determined to be ~ 1.92 eV which is higher than those reported earlier for bulk or single crystal SnS, exhibiting quantum size effect at the observed grain size in the film. This value of band gap is promising for possible use of the deposited film as absorption layer in photovoltaic structures like solar cells. The thermoelectric power measurements indicate p-type electrical conductivity of the deposited films. A systematic study on room temperature chemical deposition and characterization of SnS thin films suitable for absorber layer in photovoltaic structures has been reported.

Austenite Formation in a Cold-Rolled Semi-austenitic Stainless Steel

The progress of the martensite (α′) to austenite (γ) phase transformation has been thoroughly investigated at different temperatures during the continuous heating of a cold-rolled precipitation hardening metastable stainless steel at a heating rate of 0.1 K/s. Heat-treated samples have been characterized using different experimental complementary techniques: high-resolution dilatometry, magnetization, and thermoelectric power (TEP) measurements, micro-hardness-Vickers testing, optical/scanning electron microscopy, and tensile testing. The two-step transformation behavior observed is thought to be related to the presence of a pronounced chemical banding in the initial microstructure. This banding has been characterized using electron probe microanalysis. Unexpectedly, dilatometry measurements seem unable to locate the end of the transformation accurately, as this technique does not detect the second step of this transformation (last 20 pct of it). It is shown that once the starting (A S) and finishing (A F) transformation temperatures have been estimated by magnetization measurements, the evolution of the volume fractions of austenite and martensite can be evaluated by TEP or micro-hardness measurement quite reliably as compared to magnetization measurements. The mechanical response of the material after being heated to temperatures close to A S, A F, and (A F − A S)/2 is also discussed.

The effects of high energy probe sonication on the thermoelectric power of large diameter multiwalled carbon nanotubes synthesized by chemical vapor deposition

The thermoelectric properties of large diameter multiwalled carbon nanotubes synthesized by chemical vapor deposition have been measured after successively longer periods of high energy probe sonication. Electrical conductivity decreases with increased sonication time due to shortening of the nanotubes. The initial Seebeck coefficient before sonication is −2.5μV/K, but increases to 12μV/K for sonication periods longer than 12h. This effect is attributed to the introduction of defects and shortening of the nanotubes during sonication which exposes previously shielded carbon from internal walls to oxygen doping from exposure to atmosphere which results in increased p-type doping and a positive thermoelectric power. Temperature dependent measurements indicate that this oxygen doping of the exposed nanotube ends has a thermally activated charge transfer energy since low temperature thermoelectric power measurements of the sonicated samples approach that of the raw n-type nanotubes.

Opto-structural and electrical properties of chemically grown Ga doped MoBi2Se5 thin films

An arrested precipitation route was developed to obtain gallium doped MoBi2Se5 thin films on substrate support. High purity organometallic complexes of Mo–triethanolamine (Mo–TEA), Bi–triethanolamine (Bi–TEA), Ga–triethanolamine (Ga–TEA) allow to react with sodium selenosulphite (Na2SeSO3) in the presence of sodium dithionite (Na2S2O4) as a reducing agent in an aqueous alkaline reaction bath. As deposited thin films were characterized by X-ray diffraction, which reveals that material is nanocrystalline with mixed phases of rhombohedral (Bi2Se3)-hexagonal (MoSe2)-hexagonal (GaSe) structures. Scanning electron micrographs show the grain of granular morphology decreases with increase in Ga concentration. Energy dispersive x-ray analysis shows presence of Mo, Bi, Ga and Se elements in stoichiometric ratio confirms the chemical formula MoBiGaSe5. Optical absorbance of the films show direct allowed transition in visible region having band gap energy in the range of 1.30–1.47 eV. Thermoelectric power and electrical conductivity measurements have been carried out for thin film samples in the temperature range 300–500 K and results revealed that n-type semiconducting behavior. It is interesting to note that Ga doping in MoBi2Se5 changes n to p type conductivity.

A Contribution of Thermoelectric Properties of the Quaternary Chalcogenide Compound Tl_2GaInSe_4 Crystal

Thermoelectric transport measurements were made on single crystal samples of Tl2GaInSe4. The crystal was prepared by a special design based on the Bridgman technique. Measurements of thermoelectric power were carried out in a special high vacuum-tight calorimeter when the direction of temperature gradient is perpendicular to the cleavage plane. The measurements covered a temperature range extending from 300 to 725 K. The results indicate P -type conductivity for our investigated samples. At room temperature the value of thermoelectric power was 735 μV/deg. The electron to hole mobility ratio was found to be 1.35. The e ective mass of holes at room temperature was evaluated as 4.635×10−29 kg, while for electron was equal to 8.468×10−31 kg. The relaxation time of majority and minority carriers was estimated as τp = 2.968×10−10 s and τn = 7.326×10−12 s, respectively. Also, the di usion coe cient of holes and electrons at room temperature was calculated and found to be 265.132 cm/s and 358.139 cm/s, respectively. The di usion length of holes and electrons are found to be Lp = 2.805× 10−4 cm and Ln = 5.122 × 10−5 cm. In addition to these pronounced parameters, the e ciency of thermoelectric element ( gure of merit) was evaluated which leads to better applications in many elds.

Effect of nanoscale precipitation on strengthening of ferritic ODS Fe–Cr–Al alloy

The kinetics of Fe rich α and Cr rich α′ phase separation during aging of Fe–Cr–Al oxide dispersion strengthened alloys have been analysed with a combination of atom probe tomography and thermoelectric power measurements. The slight lattice parameter decrease measured by X-ray diffraction after thermal aging was associated with a lattice misfit between the emerging α and α′ domains. The elastic strain associated with this misfit and the different elastic moduli for the α and α′ phases would produce an increase in internal stresses that would retard the motion of dislocations and thus would be the main cause for the strengthening.

Catalytic properties of nanosized zinc aluminates prepared by green process using Opuntia dilenii haw plant extract

Various nanosized zinc aluminate (ZnAl2O4) samples were prepared by a conventional and a microwave method both with and without using Opuntia dilenii haw plant extract, and were characterized by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), high resolution scanning electron microscopy (HRSEM), energy dispersion scanning (EDX), temperature dependent conductance measurements, thermoelectric power measurements, ultraviolet-visible (UV-Vis) diffuse reflectance spectroscopy, and photoluminescence spectroscopy. The formation of a pure ZnAl2O4 phase was confirmed by XRD and FT-IR. A change in morphology from nanosized plates to nanosized sheets with, respectively, the conventional and microwave heating methods was clearly shown by HRSEM. UV-Vis diffusion reflectance spectroscopy measured the band gaps of ZnAl2O4 nanosized plates and nanosized sheets as 3.5 and 3.9 eV, respectively. The synthesized ZnAl2O4 was single crystalline and has three photoluminescence emissions at 482, 528, and 540 nm. ZnAl2O4 nanosized sheets prepared by the microwave method showed higher catalytic activity for the oxidation of benzyl alcohol (85% conversion) than ZnAl2O4 nanosized plates prepared by the conventional method (60% conversion).

Resolving Individual Solute Levels of AA6061 through Multiple Sub-Ambient Temperatures Thermoelectric Power Measurements

This work concentrates on assessment of the TEP change of AA6061 during isothermal aging at 177 °C and the following interrupted aging at 65 °C. The results show that the TEP is sensitive to follow the microstructural changes undergone during all aging stages. Multiple sub-ambient temperature dependences TEP of binary Al-X alloys as well as the AA6061 subjected to the above mentioned heat treatments were undertaken. The solute level of individual element of the alloy, particularly those contributing to the clustering/precipitation, can be extracted and evaluated.

Effects of cryogenic and stress relief treatments on temper carbide precipitation in AISI D2 tool steel

The effects of cryogenic and stress relief treatments on temper carbide precipitation in the cold work tool steel AISI D2 were studied. For the cryogenic treatment the temperature was −196°C and the holding time was 2, 24 or 30 h. The stress relief heat treatment was carried at 130°C/90 min, when applied. All specimens were compared to a standard thermal cycle. Specimens were studied using metallographic characterisation, X-ray diffraction and thermoelectric power measurements. The metallographic characterisation used SEM (scanning electron microscopy) and SEM-FEG (SEM with field emission gun), besides OM (optical microscopy). No variation in the secondary carbides (micrometre sized) precipitation was found. The temper secondary carbides (nanosized) were found to be more finely dispersed in the matrix of the specimens with cryogenic treatment and without stress relief. The refinement of the temper secondary carbides was attributed to a possible in situ carbide precipitation during tempering.

Resolving Individual Solute Levels of AA6061 through Multiple Sub-Ambient Temperatures Thermoelectric Power Measurements

Resolving Individual Solute Levels of AA6061 through Multiple Sub-Ambient Temperatures Thermoelectric Power Measurements

Anisotropic transport and magnetic properties and magnetic-field tuned states of CeZn11single crystals

We present detailed temperature and field dependent data obtained from magnetization, resistivity, heat capacity, Hall resistivity and thermoelectric power measurements performed on single crystals of CeZn11. The compounds orders antiferromagnetically at $\sim$ 2 K. The zero-field resistivity and TEP data show features characteristic of a Ce-based intermetallic with crystal electric field splitting and possible correlated, Kondo lattice effects. We constructed the T-H phase diagram for the magnetic field applied along the easy, [110], direction which shows that the magnetic field required to suppress T_N below 0.4 K is in the range of 45-47.5 kOe. A linear behavior of the rho(T) data, H||[110], was observed only for H=45 kOe for 0.46 K<T<1.96 K followed by the Landau-Fermi-liquid regime for a limited range of fields, 47.5 kOe< H<60 kOe. From the analysis of our data, it appears that CeZn11 is a weakly to moderately correlated local moment compound with rather small Kondo temperature. The thermoelectric and transport properties of CeZn11 are mostly governed by the CEF effects. Given the very high quality of our single crystals, quantum oscillations are found for both CeZn11 and its non-magnetic analogue, LaZn11.

Crystal structure and physical properties of LaPd2Ge and a novel compound LaPdGe3

The crystal structures of LaPd2Ge and LaPdGe3 have been refined by X-ray diffraction on powdered polycrystalline samples. These ternaries crystallize in YPd2Si (Pnma) and BaNiSn3 (I4mm) structure types, respectively. As revealed by electrical resistivity, thermoelectric power and specific heat measurements, the former compound is superconducting below 0.6K, which is not the case for the latter one (at least down to 0.3K). Moreover, LaPdGe3 was found to be a typical metal in comparison to LaPd2Ge which is rather a semimetal.

Pure and Sr(II)-Added Copper Aluminate Nanocomposites: Structural, Electrical and Alcohol Sensing Studies

The effect of ethylenediamine addition in the sol-gel method for the preparation of pure and Sr(II)-added nano copper aluminate (CuAl2O4) composites for the enhancement in their structural, electrical, and alcohol sensing properties were investigated. The effect of addition of Sr(II) to pure CuAl2O4 in both the methods were also discussed. X-ray diffraction, scanning electron microscopy, nitrogen adsorption/desorption isotherms, temperature dependant conductance measurements and thermoelectric power measurements were used to characterize the composites prepared. Among the composites, 0.8 molar ratio strontium added copper aluminate composite prepared by modified sol-gel method showed the highest sensitivity towards alcohols. The stability, response and recovery of MS-CuSA5 were also discussed. The response and recovery characteristics showed that the order of sensing alcohols by the composites was butanol > isopropanol > ethanol > methanol, which could be explained on the basis of oxidation of alcohols.

Structural, Transport, and Magnetic Properties of (Ru0.9Nb0.1)Sr2(Gd0.67R0.67Ce0.66)Cu2O z (R = Nd, Gd, and Tb)

Samples with nominal compositions of (Ru0.9Nb0.1)Sr2(Gd0.67R0.67Ce0.66)Cu2Oz (R = Nd, Gd, Tb) were prepared, and the influence of doped rare-earth element on the structural, magnetic and superconducting properties of these samples has been investigated. Resistivity and room-temperature thermoelectric power measurements showed that the superconductivity is mainly affected by the change in the hole concentration induced by doping of the rare-earth element. All of these samples exhibited weak ferromagnetic behavior at temperatures below approximately 90 K with the branching of zero-field-cooled (ZFC) and field-cooled (FC) magnetization. In the ZFC magnetization measurements, diamagnetic transition was observed at temperatures below approximately 15 K for the R=Gd and Nd samples. Magnetization measurements also revealed that the partial substitution of Tb for Gd results in a significant enhancement of weak-ferromagnetic component of the FC magnetization, as well as an increase in the magnetic ordering temperature up to 20 K. A quite opposite behavior was observed in the FC magnetization for the case of the R=Nd sample. The experimental results are discussed in conjunction with the local structural changes in the Ru sublattice, which are induced by doping of the rare-earth element, based on the results of Rietveld refinement of the X-ray diffraction data.