Transport and Thermoelectric Properties of the Ca1?xSrxRu1?yMnyO3 System

The magnetic, transport, and thermoelectric properties of Ca_1−x Sr _x Ru_1−y Mn _y O₃ have been investigated. Ferromagnetism with relatively high T _C (>200 K) was introduced by Mn doping. In particular, ferromagnetism appeared in the Ca_0.5Sr_0.5Ru_1−y Mn _y O₃ system at y > 0.2. The maximum T _C (=270 K) was recorded for a specimen of Ca_0.5Sr_0.5Ru_0.4Mn_0.6O₃. The ferromagnetism seems to be due to the mixed-valence states of Mn³⁺, Mn⁴⁺, Ru⁴⁺, and Ru⁵⁺ ions. The metallic character of Ru-rich specimens was suppressed by Mn substitution, and the system was transformed into a semiconductor at relatively low Mn content near y = 0.1. Specimens with higher Mn content (y > 0.8) had large thermoelectric power (50 μV K⁻¹ to 130 μV K⁻¹ at 280 K) accompanied by relatively low resistivity (0.03 Ω cm to 1 Ω cm). The Ca_0.5Sr_0.5Ru_1−y Mn _y O₃ system seems to have good potential as a thermoelectric material for use above 300 K.     

Structure and High-Temperature Thermoelectric Properties of the n-Type Layered Oxide Ca2?xBix?δMnO4?γ

We have investigated the effects of Bi doping on the crystal structure and high-temperature thermoelectric properties of the n-type layered oxide Ca₂MnO_4−γ . The electrical conductivity σ and the absolute value of the Seebeck coefficient S were, respectively, found to increase and decrease with Bi doping. The thermal conductivity κ of doped Ca₂MnO_4−γ is relatively low, 0.5 W/m K to 1.8 W/m K (27°C to 827°C). Consequently, the ZT value, ZT = σS ² T/κ, increases with Bi doping. The maximum ZT is 0.023 for Ca_1.6Bi_0.18MnO_4−γ at 877°C, which is ten times higher than that of the end member, Ca₂MnO_4−γ . The increase of ZT mainly results from the considerable increase of σ, which can be explained in terms of structural change. The␣Mn-O(1) and the Mn-O(2) distances in the c-direction and ab-plane, respectively, increase with increasing Bi concentration, indicating that the valence state of Mn ions decreases with the increase of electron carriers in the CaMnO₃ layers. In addition, the Mn-O(2)-Mn bond angle increases linearly with Bi doping, leading to an improvement of the electron carrier mobility.     

The Influence of Sintering Temperature on the Microstructure and Thermoelectric Properties of n-Type Bi2Te3?xSex Nanomaterials

Pure Bi₂Te₃ and Bi₂Se₃ nanopowders were hydrothermally synthesized, and n-type Bi₂Te_3−x Se _x bulk samples were prepared by hot pressing a mixture of Bi₂Te₃ and Bi₂Se₃ nanopowders at 623 K, 648 K or 673 K and 80 MPa in vacuum. The phase composition of the powders and bulk samples were characterized by x-ray diffraction. The morphology of the powders was examined by transmission electron microscopy. The microstructure and composition of the bulk samples were characterized by field-emission scanning electron microscopy and energy-dispersive x-ray spectroscopy, respectively. The density of the samples increased with sintering temperature. The samples were somewhat oxidized, and the amount of oxide (Bi₂TeO₅) present increased with sintering temperature. The samples consisted of sheet-like grains with a thickness less than 100 nm. Seebeck coefficient, electrical conductivity, and thermal conductivity of the samples were measured from room temperature up to 573 K. Throughout the temperature range investigated, the sample sintered at 623 K had a higher power factor than the samples sintered at 648 K or 673 K.     

Effect of Substrate on the Structure and Thermoelectric Properties of n-Type Bi2Te3?ySey Thin Films Prepared by Electrodeposition

n-Type Bi₂Te_3−y Se _y thin films were prepared by potentiodynamic electrodeposition onto Au, Bi, and Bi₂Te_3−y Se _y substrates at room temperature. The electrochemical behaviors of Bi³⁺, HTeO₂ ⁺, and H₂SeO₃ on different substrates were investigated by cyclic voltammetry. The morphology, composition, and structure of the films were studied by using environmental scanning electron microscopy (ESEM), energy-dispersive spectroscopy (EDS), and x-ray diffraction (XRD), respectively. The thermoelectric properties of n-type Bi₂Te_3−y Se _y films were determined by measuring the Seebeck coefficient (α) and electrical resistivity (ρ). The results showed that the composition and morphology of the films were sensitive to the substrate material. X-ray diffraction (XRD) analysis indicated that the preferred orientation of annealed films was affected by the substrate and that the film prepared on the Bi₂Te_3−y Se _y substrate exhibited the strongest (015) orientation, with rhombohedral structure. It was proved that the properties of the annealed films could be affected by the substrate and that the film with the highest power factor (P = α ²/ρ) was obtained on the Bi₂Te_3−y Se _y substrate.     

Synthesis and Thermoelectric Properties of InzCo4?xFexSb12 Skutterudites

The thermoelectric properties of In-filled and Fe-doped CoSb₃ (In _z Co_4−x -Fe _x Sb₁₂) skutterudites prepared by encapsulated induction melting were examined. A single δ-phase was obtained successfully by subsequent annealing at 823 K for 120 h. The Hall and Seebeck coefficients of the In _z Co_4−x Fe _x Sb₁₂ samples had positive signs, indicating p-type conduction. The electrical conductivity was increased by Fe doping, and the thermal conductivity was decreased by In filling due to phonon scattering. The thermoelectric properties were improved by In filling and Fe doping, and were closely related to the optimum carrier concentration and phonon scattering.     

Properties and structure of (As2Se3)1 ? z (SnSe2) z ? x (Tl2Se) x and (As2Se3)1 ? z (SnSe) z ? x (Tl2Se) x glasses

Tin is stabilized in the bivalent and tetravalent states in the structure of (As₂Se₃)_{1 − z} (SnSe₂) _{z − x} (Tl₂Se) _x and (As₂Se₃)_{1 − z} (SnSe) _{z − x} (Tl₂Se) _x glasses. The presence of bivalent tin in the structural network of a glass does not give rise to extrinsic conductivity. Dependences of density, microhardness, and the glass-transition temperature on the composition of the glasses are interpreted using a model according to which the structure of the glasses is composed of structural units that correspond to As₂Se₃, AsSe, TlAsSe₂, Tl₂Se, SnSe, and SnSe₂ compounds. Original Russian Text ? G.A. Bordovsky, A.V. Marchenko, E I. Terukov, P.P. Seregin, T.V. Likhodeeva, 2008, published in Fizika i Tekhnika Poluprovodnikov, 2008, Vol. 42, No. 11, pp. 1353–1356.     

Synthesis and Measurement of the Thermoelectric Properties of Multiphase Composites: ZnSb Matrix with Zn4Sb3, Zn3P2, and Cu5Zn8

We synthesized a series of samples with composition around 52 at.% zinc (Zn), 44 at.% antimony (Sb), 4 at.% phosphorus (P), and up to 3 at.% copper (Cu) by melting the elements and subsequent annealing. This resulted in dense and almost crack-free samples. X-ray powder diffraction (XRD) and scanning electron microscopy (SEM) revealed composites with a majority phase of ZnSb containing varying amounts of Zn₃P₂ and Cu₅Zn₈, in addition to Zn₄Sb₃ in some of the samples. We measured the Seebeck coefficient, electrical conductivity, and thermal conductivity as a function of temperature. The thermoelectric performance tended to improve with increasing Cu content. At Cu content of 2 at.%, a reduced resistivity allows for the highest dimensionless figure of merit, with a maximum zT value of 0.18 at around 573 K.     

Fe3+-substitution effect on the thermal variation of J–E characteristics and DC resistivity of quadruple perovskite CaCu3Ti4O12

The electrical properties of cubic perovskite series, CaCu_3–xTi_4–xFe_2xO₁₂ with x = 0.0, 0.1, 0.3, 0.5, and 0.7, have been studied by employing current density as a function of electric field characteristics registered at different temperatures and thermal variations of direct current electrical resistivity measurements. All of the compositions exhibit strong non-ohmic behavior. The concentration dependence of breakdown field, the temperature at which switching action takes place, and maximum value of current density (J_max) has been explained on account of structural, microstructural, and positron lifetime parameters. The highest ever reported value of J_max = 327 mA/cm² has been observed for pristine composition. The values of the nonlinear coefficient advise the suitability of ceramics for low-voltage varistor applications. The Arrhenius plots show typical semiconducting nature. The activation energy values indicate that electric conduction proceeds through electrons with deformation in the system.     

Effects of Synthesis and Spark Plasma Sintering Conditions on the Thermoelectric Properties of Ca3Co4O9+δ

Ca₃Co₄O_9+δ samples were synthesized by solid-state (SS) and sol–gel (SG) reactions, followed by spark plasma sintering under different processing conditions. The synthesis process was optimized and the resulting materials characterized with respect to their microstructure, bulk density, and thermoelectric transport properties. High power factors of about 400 μW/m·K² and 465 μW/m·K² (at 800°C) were measured for SS and SG samples, respectively. The improved thermoelectric performance of the SG sample is believed to originate from the smaller particle sizes and better grain alignment. The SG method is suggested to be a beneficial means of obtaining high-performance thermoelectric materials of Ca₃Co₄O_9+δ type.     

Improved Thermoelectric Properties of (GeTe)90(AgySb2?yTe3?y)10 by Tuning the Ag-to-Sb Ratio

(GeTe)₉₀(Ag _y Sb_2−y Te_3−y )₁₀ (y = 0.6, 0.7, 0.8, 1.0) compounds were prepared by combining melting and hot pressing, and the thermoelectric properties were studied over the temperature range of 300 K to 770 K. Powder x-ray diffraction results revealed that all the samples were the rhombohedral phase with space group R3m. The electrical conductivity of samples decreased with temperature, while the Seebeck coefficient increased. The thermal conductivity of all the samples was very low, especially for those with the lower y values. High ZT values above 1.6 were obtained for the samples with y = 0.6, 0.7, and 0.8.     

Effects of Reaction Temperature on Thermoelectric Properties of p-Type Nanostructured Bi2−x Sb x Te3 Prepared Using Hydrothermal Method and Evacuated-and-Encapsulated Sintering

We report fabrication of nanostructured Bi_2?x Sb _x Te₃ using hydrothermal method followed by cold-pressing and evacuated-and-encapsulated sintering techniques. To obtain lower resistivity, the reaction temperature in the hydrothermal synthesis is investigated, and the effects on the ZT values of Bi_2?x Sb _x Te₃ are reported. Both the x = 1.52 and 1.55 samples hydrothermally synthesized at 160°C show lower resistivity than the x = 1.55 sample hydrothermally synthesized at 140°C. However, the power factor is lower for the samples synthesized at 160°C due to the accompanying smaller thermopower. All three samples exhibit remarkably low thermal conductivity of around 0.41 W m^?1 K^?1 at room temperature. The peak ZT value occurs at 270 K for all three samples, being ZT = 1.75, 1.29, and 1.17 for x = 1.55 (synthesized at 140°C), 1.55 (synthesized at 160°C), and 1.52 (synthesized at 160°C), respectively.     

Thermoelectric Properties of Ag-Doped n-Type (Bi2?xAgxTe3)0.96?(Bi2Se3)0.04 Pseudobinary Alloys

n-Type thermoelectric powders of (Bi_2−x Ag _x Te₃)_0.96−(Bi₂Se₃)_0.04 (0 ≤ x ≤ 0.05) have been synthesized by mechanical alloying and then consolidated by spark plasma sintering. The analysis results show that the grain size of pure Bi, Te, Ag, and Se powders is decreased to about 1 μm to 0.5 μm after they are mechanically alloyed for 2 h. The power factor of bulk material increases with increasing Ag-doping content, while the trend for the lattice thermal conductivity is the opposite. Bulk (Bi_0.99Ag_0.04)₂(Te_0.96Se_0.04)₃ after milling for 12 h exhibits a higher power factor, lower thermal conductivity, and thus a higher ZT of 0.74 at 373 K.     

Effect of the Phase Composition and Local Crystal Structure on the Transport Properties of the ZrO2–Y2O3 and ZrO2–Gd2O3 Solid Solutions

Russian Microelectronics - The results of investigating the crystal structure, ionic conductivity, and local structure of the (ZrO2)1 –x(Gd2O3)x and (ZrO2)1 –x(Y2O3)x (x = 0.04, 0.08,...     

Effect of Chromium Doping on the Thermoelectric Properties of Bi2Te3: Cr x Bi2Te3 and Cr x Bi2−x Te3

The thermoelectric (TE) properties of Bi₂Te₃ compounds intercalated and substituted with Cr, namely Cr _x Bi₂Te₃ and Cr _x Bi_2?x Te₃, respectively, have been investigated to study the influence of chromium on the TE properties of Bi₂Te₃. The Seebeck coefficients were found to be positive for all the samples in the temperature range between 300 K and 550 K. Although no effective enhancement of the Seebeck coefficient was observed, doping with Cr by means of either substitution or intercalation clearly not only improved the electrical conductivity but also lowered the thermal conductivity of Bi₂Te₃. As a result of the improvement, the figure of merit ZT is increased up to 0.8 and 0.65 at 300 K for 1% intercalated and 1% substituted Bi₂Te₃, respectively.     

Enhanced Thermoelectric Properties Obtained by Compositional Optimization in p-Type BixSb2?xTe3 Fabricated by Mechanical Alloying and Spark Plasma Sintering

Bi _x Sb_2−x Te₃ bulk alloys are known as the best p-type thermoelectric materials near room temperature. In this work, single-phase Bi _x Sb_2−x Te₃ (x = 0.2, 0.25, 0.3, 0.34, 0.38, 0.42, 0.46, and 0.5) alloys were prepared by spark plasma sintering (SPS) using mechanical alloying (MA)-derived powders. A small amount (0.1 vol.%) of SiC nanoparticles was added to improve the mechanical properties and to reduce the thermal conductivity of the alloys. The electrical resistivity decreases significantly with increasing ratio of Sb to Bi in spite of the weaker decreasing trend in Seebeck coefficient, whereby the power factor at 323 K reaches 3.14 × 10⁻³ W/mK² for a sample with x = 0.3, obviously higher than that at x = 0.5 (2.27 × 10⁻³ W/mK²), a composition commonly used for ingots. Higher thermal conductivities at low temperatures are obtained at the compositions with lower x values, but they tend to decrease with temperature. As a result, higher ZT values are obtained for Bi_0.3Sb_1.7Te₃, with a maximum ZT value of 1.23 at 423 K, about twice the ZT value (about 0.6) of Bi_0.5Sb_1.5Te₃ at the same temperature.     

Electrical and Thermal Properties of the Ca3?xGdxCo4O9+δ System

The effects of Gd substitution on the thermoelectric (TE) properties of Ca₃Co₄O_9+δ have been systematically investigated from 25 K to 335 K. Partial substitution of Gd in Ca₃Co₄O_9+δ results in an increase of thermopower and resistivity, and a decrease of thermal conductivity. A maximum dimensionless figure of merit (ZT) of 0.028 was achieved at 335 K for Ca_2.4Gd_0.6Co₄O_9+δ , which is about one order of magnitude larger than that for Ca₃Co₄O_9+δ . The investigation demonstrates that the TE performance of the Ca₃Co₄O_9+δ system can be improved through Gd doping.     

Current-voltage characteristic and the spectrum width of electrons tunneling through W-WO2-(Au 147? )-Al2O3-Al and Nd-Nd2O3-(Au 55? )-Nd2O3-Nd nanosandwiches. Part II: Construction and analysis of 1D models for 3D nanosandwiches

This is the second part of the series of two articles devoted to the analysis of electron tunneling through magic nanoclusters of Au₅₅ and Au₁₄₇. Models of 1D projections of W-WO₂-(Au₁₄₇⁻)-Al₂O₃-Al and Nd-Nd₂O₃-(Au₅₅⁻)-Nd₂O₃-Nd 3D tunnel nanostructures are constructed with the use of the highest occupied molecular orbital (HOMO) levels E_HOMO^- E_{HOMO^ - } of the anions of the nanoclusters of Au₅₅ and Au₁₄₇, and the potentials of Au, W, Al, and Nd atoms calculated in the first part of this study. The levels of the bottom of the potential wells of 1D structures are chosen so that they include resonance energy levels coinciding with the anion level E_HOMO^- E_{HOMO^ - } for an appropriate 3D structure (Au₁₄₇⁻ or Au₅₅⁻). With regard to the potentials in the structures of a nanocapacitor and the image forces, the current-voltage characteristic (CVC) and the width of the resonance peak in the spectrum of tunneling electrons are calculated as a function of the potential difference across the external electrodes of metal-metal nanodiodes. A scheme of a hypothetical high-frequency nanoscale metal transistor is proposed that is based on a cluster of Au₁₄₇ that does not produce hot electrons.     

First principles study of the electronic structure and photovoltaic properties of β-CuGaO2 with MBJ + U approach

Based on the density functional theory, the energy band and electronic structure of β-CuGaO₂ are calculated by the modified Becke-Johnson plus an on-site Coulomb U (MBJ + U) approach in this paper. The calculated results show that the band gap value of β-CuGaO₂ obtained by the MBJ + U approach is close to the experimental value. The calculated results of electronic structure indicate that the main properties of the material are determined by the bond between Cu-3d and O-2p energy levels near the valence band of β-CuGaO₂, while a weak anti-bond combination is formed mainly by the O-2p energy level and Ga-4s energy level near the bottom of the conduction band of β-CuGaO₂. The β-CuGaO₂ thin film is predicted to hold excellent photovoltaic performance by analysis of the spectroscopic limited maximum efficiency (SLME) method. At the same time, the calculated maximum photoelectric conversion efficiency of the ideal CuGaO₂ solar cell is 32.4%. Relevant conclusions can expand β-CuGaO₂ photovoltaic applications.     

Synthesis,Structure and Electrical Properties of(SnO2)x(In2O3)1?x(x=0.5–1) Nanocomposites

The experimental results of synthesizing thin films (<1 μm thick) of (SnO₂) _x (In₂O₃)_{1 − x} (x = 0.5–1 wt) nanocomposites fabricated by high-frequency magnetron sputtering of metal-oxide targets in a controlled Ar + O₂ atmosphere are presented. The films, deposited on hot substrates (400°C), are studied by the X-ray diffraction analysis, atomic-force microscopy, and optical and electrical methods. The effect of the synthesis conditions and film composition on the size of crystalline grains, band gap, and the concentration and mobility of free charge carriers was determined. It is shown that films of the composition (SnO₂) _x (In₂O₃)_{1 − x} with x = 0.9 are the most promising for applications in gas sensorics.