Waste heat recovery from car's exhaust gases provides an opportunity to significantly improve the overall car engine efficiency. One approach for recovering energy from the exhaust gases is to generate electrical power through thermoelectric conversion. A thermoelectric device, using a commercially available thermoelectric generator module was made, in order to measure the gained power and efficiency at different places of the exhaust pipe of a small size car (Toyota Starlet, 1300cc), for various engine loads. With the use of a modeling approach, we evaluated the thermal contact resistances and their influence on the final device efficiency.
The electrical conductivity σ and the thermal conductivity λ were investigated at varying temperature (40 < T < 120°C) for two sulphate compounds, anhydrous mercury(II) sulphate HgSO_{4} and cerous(III) sulphate Ce_{2}(SO_{4})_{3}·H_{2}O. It seems likely that each of the two sulphate salts undergoes structural phase transition around 90°C. The differential thermal analysis thermogram was carried out as an aid for confirming of the observed phase transitions. The mechanism of the heat transfer is mainly due to phonons. Interpretation of the obtained data was given on the basis of the reorientational motion of the SO_{4}‾ ‾ ions.
We measured thermopower, thermal conductivity and electrical resitivity for Ca₂Sn sample across 4-350 K temperature range. Contrary to expectations from recent DFT based calculations the thermopower is not particularly large, reaching 7 μV at 350 K. The thermoelectric figure of merit renders this material in unmodified form practically unusable for thermoelectric aplications.
In the presence of hybridization of the f states with the conduction electrons Ce-based compounds can show large peaks in the temperature dependence of the Seebeck coefficient, which makes them interesting materials for applications. The Seebeck coefficient and electrical resistivity of the bulk, arc-melted, single phase samples of Ce(Ni_{1-x}Cu_{x})₂Si₂ and CeNi₂(Si_{1-y}Ge_{y})₂ alloys were measured over the temperature range of 2 K to 300 K. All the samples exhibited a positive Seebeck coefficient, which reaches up to ım50μV/K at 150 K and it can be shifted up to 300 K by appropriate doping. The thermoelectric power factor, PF = S²/ρ, reached a maximum of 1.4×10¯³ Wm¯¹K¯² at 290 K and 1.1×10¯³ Wm¯¹K¯² at 110 K for x=0.25 and y=0.75, respectively. For selected representatives of the studied series thermoelectric properties have been measured up to 1000 K.
We report a detailed study of the resistivity (ρ(T)) and thermoelectric power (S(T)) of the alloy U_{0.05}Y_{0.95}Al_2, which crystallises in the cubic MgCu_2-type structure. The resistivity is found to follow ρ(T) ∝ ln T between 15 and 40 K and a quasi-linear temperature dependence -T^{1.16} for T <10 K. At a magnetic field of 9 T a Kondo-type maximum occurs in the resistivity data at 7 K, below which the Fermi liquid behaviour (ρ(T) ∝ T^2) is recovered. S(T)/T shows a T^{0.5} power law for T <12 K. The low-temperature unconventional features observed in U_{0.05}Y_{0.95}Al_2 are presumably due to the presence of the two-channel Kondo effect.
We report on a new series of filled skutterudites derived from CoSb_3 with double filling of the cage (by In, Sn) in order to lower the thermal conductivity. As expected for Co-rich side samples, the Seebeck coefficient indicates n-type, with surprisingly high values at 300 K.
High precision measurements of the Seebeck coefficient S(T) were carried out on the single crystals of RB_{12} (R = Ho, Er, Tm, Lu) at temperatures 2-300 K. It was shown that the effects of phonon drag result from vibrations of rare earth ions (ħω_E≈10-33 meV) in the rigid framework structure of the B_{12} clusters and determine the main contribution to thermopower at intermediate temperatures (30-300 K). The correlated behavior of transport parameters favors the appreciable enhancement of spin fluctuations in the sequence of magnetic compounds (HoB_{12}-TmB_{12}) when approaching to the valence instability state in YbB_{12}. The giant increase in S(T) detected in the vicinity of the Néel temperature T_N for HoB_{12}, ErB_{12}, and TmB_{12} seems to result from the density of states renormalization caused by antiferromagnetic ordering.
The temperature dependence of the electrical conductivity σ , the Hall coefficient R and the thermopower coefficient α in the solid solutions TlIn_{1-x}Yb_xTe₂ (0 ≤ x ≤0.10) have been investigated in the temperature range of 80-1000 K. The effective masses of electrons and holes have been determined on the basis of the kinetic parameters. It was established that starting from x = 0.05 the solid solutions of TlIn_{1-x}Yb_xTe₂ belong to narrow-gap semiconductors having high values of the interaction matrix element. It is shown that the samples of TlIn_{1-x}Yb_xTe₂ in the region of 0.10 ≥ x ≥ 0.05 are promising materials for the energy converters operating at high temperatures.
The change of thermopower is investigated in Fe-based glassy alloys during structural relaxation and amorphous-crystalline transformation. It was found, that thermopower shifts to negative direction until solely the relaxation proceeds. This negative shift is composition independent. The net shape of thermopower curves is composed from the thermopower of the individual constituent crystalline phases after the crystallization process.
In this paper, the thermopower (U) and hardness (HV) of FINEMET type glasses are studied during structural relaxation and beyond the crystallization onset. In this multicomponent alloy (Fe_{73.5-x}Si_{13.5}B_{9}Nb_{x}Cu_{1}) both property changes are more complex than that in binary Fe-B glasses. The phenomenon of relaxation and the crystallization onset can be successfully distinguished in both property changes. Simultaneously with the hardness increase, a slope increase in the thermopower versus temperature dependences was observed if crystallization started. The character of both property changes does alter drastically at the beginning of amorphous-nanocrystalline transformation. Similar trends were measured on samples undergoing traditional isothermal and pulse heat treatments.
Transport and magnetic properties of polycrystalline Tm_{0.03}Yb_{0.97}B₁₂ samples were investigated at temperatures 1.8-300 K in magnetic fields up to 9 T. The activated behavior of resistivity, the Hall coefficient and thermopower is described in terms of a narrow gap ε_g ≈ 16.6 meV, which controls the charge transport in Tm_{0.03}Yb_{0.97}B₁₂ at T>40 K. The maximum of magnetic susceptibility found at 50 K is shown to be induced by a spin gap Δ ≈ 4.7 meV being close to the half of the spin fluctuation energy in YbB₁₂. Large diffusive thermopower S=AT, A=-29.1 μV/K² and the Pauli susceptibility χ₀ ≈ 7.2×10¯³ emu/mol found below 20 K seem to be associated with the many-body resonance, which corresponds to states with an enhanced effective mass m* ≈ 250m₀ (m₀ - free electron mass). The effective parameters of magnetic centers and the analysis of anomalies favor the nonequivalent states of substitute Tm ions.
Thermoelectric power and surface magnetic characterization of Ni evaporated layers will be presented, with the comparison with the bulk Ni material. The bulk electrical and magnetic properties are developed gradually, approaching the bulk properties, as the layer thickness increases. Below the thickness of 180 nm, the evaporated layers are amorphous. The epitaxial stresses can appear in both, the anomaly observed in the thermopower and the surface coercivity measurements.
We present results of extensive measurements of magnetic susceptibility, electrical resistance, specific heat and thermoelectric power of two series of solid solutions GdNi_{x}Ga_{4-x} and GdCu_{x}Ga_{4-x}, for ranges of doping x from 0.6 to 1 and from 1 to 1.5, respectively. All studied phases display the Curie-Weiss behaviour of magnetic susceptibility and antiferromagnetic ordering at temperatures below 23 K. Substitution of gallium with transition metal atoms has strong influence on Néel temperatures of all studied phases, shifting them by few K, depending on x. Metamagnetic-like anomalies are observed for some compositions. Behaviour of the electrical resistivity reveals metallic nature of all samples. Their magnetic ordering is reflected in low-temperature anomalies of the resistivity and the heat capacity.
High quality single crystals of some representatives of half-Heusler family were grown from Bi-flux. For single crystals characterization, X-ray diffraction and scanning electron microscopy techniques were used. The low-temperature physical properties of the synthesized crystals were determined by means of magnetization, magnetic susceptibility, electrical resistivity and heat capacity measurements. For each compound but LuPtBi, the electrical resistivity varies in a semimetallic manner at high temperatures, and exhibits a metallic character at low temperatures. LuPtBi is metallic in the whole temperature range studied. The bismuthides HoPdBi, LuPdBi, LuPtBi and YPtBi were found superconducting below the critical temperature T_{c} = 0.7, 1.8, 0.9, and 0.96 K, respectively. For the compounds GdPdBi, DyPdBi and HoPdBi, an antiferromagnetic ordering was found to set in below T_{N} = 12.8, 3.7, and 1.9 K, respectively. HoPdBi is thus an intriguing material in which both cooperative phenomena coexist.
The heat diffusivity D, the electrical resistivity ρ and the thermoelectric power S of tetragonal Mn_{2-x}Cr_{x}Sb single crystals with 0.02 < x < 0.12 have been measured in the temperature range of 90 K < T < 350 K and along different crystal axes. The heat conductivity κ and σ = 1/ρ are anisotropic along the crystal axes a, c with a ratio of 2:1. κ(T) , ρ(T) and S(T) show anomalies at the spin reorientation temperature T_{Rm} of the matrix (M) Mn_{2-x}Cr_{x}Sb, but also at that of the coherent ferromagnetic precipitate (P) Mn_{1.037}Cr_{0.11}Sb, T_{R}_{p} which is assigned to variations in the spin dependent scattering at the M /P interfaces via changes in the relative orientation of the magnetization vectors of matrix and precipitate (spin valve effect).
Magnetic susceptibility, electrical resistivity, and thermopower of the series of the R_3Cu_3Sb_4 compounds (R=La-Sm) were measured over the temperature ranges 1.9-300 K (susceptibility and resistivity) and 80-370 K (thermopower). Below 25 K, resistivity of these compounds grows exponentially with decreasing temperature. For some compounds, R = Ce, Sm, a maximum on temperature dependence of resistivity is observed. Ce_3Cu_3Sb_4 compound undergoes a magnetic transition at 12 K.
The new type of the working media for thermomagnetic devices is proposed: the intermetallic compounds which have large magnetocrystalline anisotropy and exhibit the spontaneous phase transition from the antiferromagnetic (AF) to ferromagnetic (F) state when the temperature increases above the critical value T_{t}. Moreover, the anisotropy in AF state in the fields below the critical AF-F transition field must be much lower than in the F state. In the present paper the Gd_{0.6}Sm_{0.4}Mn_{2}Ge_{2} compound belonging to the tetragonal RMn_{2}Ge_{2} system is investigated. This compound has the critical temperature T_{t} = 280 K. The thermomagnetic cycle can be realized on the AF-F-AF transition near T_{t2}. The interval of the working temperatures can be shifted with the change of the Gd and Sm concentration.
The paper presents experimental study of the spin Seebeck effect based on the widely used ferromagnetic Co₇₉Si₁₀X layer, partially covered with Pt layer. The total thickness of tested sample is about 20 μm, which makes it the first confirmed presence of the spin Seebeck effect in bulk material. Experiment was carried out under magnetic flux density 300 mT, room temperature and for constant temperature difference across the sample ranging from 1 K to 21 K. The measured value of induced voltage drop achieved 0.5 μV per 1 K.
High-quality single crystal of Ce_{2}RhSi_{3} was studied by means of thermoelectric power measurements carried out down to 2 K in external magnetic fields up to 13 T. The results obtained above 50 K were interpreted in terms of a modified two-band model that takes into account temperature variation of the width of 4f-derived narrow band located near the Fermi level. At lower temperatures the thermopower exhibits more complex temperature dependences that likely involve interplays of magnetic exchange, Kondo and crystal-field interactions.
An overview of the achieved Inverse Spin Hall Effect voltage (V_{ISHE}) is presented to find upper limit of this V_{ISHE}. Comprehensive review confirms that the most significant spin systems are based on YIG substrate. The Pt ISHE interfaces are the most popular, however, the best result was reported for the Ir₂₀Mn₈₀ ISHE interface. Moreover, in this paper the transvers spin Seebeck effect (SSE) is measured in bulk sample of Ni_{76.1}Fe_{15.9}Cu_{4.3}Mo_{3.6} with Pt interface. The max. measured value of V_{ISHE} for NiFeCuMo alloy with Pt is 0.493 μV with ΔT= 21.5 K.
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