On the Thermoelectric Properties of Zintl Compounds Mg3Bi2−x Pn x (Pn = P and Sb)

A series of Zintl compounds Mg₃Bi_2-x Pn _x (Pn = P and Sb) have been synthesized by the solid-state reaction method. While Sb can be substituted to a level as high as x = 1.0, P can be substituted only up to x = 0.5. The thermoelectric potential of these compounds has been evaluated by measuring resistivity (ρ), Seebeck (α) and Hall coefficients, and thermal conductivity between 80 K and 850 K. The measured resistivity and Seebeck coefficient values are consistent with those expected for small-bandgap semiconductors. Hall measurements suggest that the carriers are p type with concentration (p) increasing from ~10¹⁹ cm^?3 to ~10²⁰ cm^?3 as the Bi content is increased. The Hall mobility decreases with increasing temperature (T) and reaches a more or less similar value (~45 cm²/V s) for all substituted compositions at room temperature. Due to mass defect scattering, the lattice thermal conductivity (κ _L) is decreased to a minimum of ~1.2 W/m K in Mg₃BiSb. The power factor (α ²/ρ) is found to be rather low and falls in the range 0.38 mW/m K² to 0.66 mW/m K². As expected, at a high temperature of 825 K, the total thermal conductivity (κ) of Mg₃BiSb reaches an impressive value of ~1.0 W/m K. The highest dimensionless figure of merit (ZT) is realized for Mg₃BiSb and is ~0.4 at 825 K.     

Thermoelectric Properties of (Bi1−x Sb x )2S3 with Orthorhombic Structure

Thermoelectric properties of the substitution system (Bi_1?x Sb _x )₂S₃ have been investigated, where binary Bi₂S₃ and Sb₂S₃ are narrow-gap semiconductors. It is confirmed that metallic conduction, originating from mobile electrons due to production of sulfur vacancies, is observed in Bi₂S₃ over a wide temperature range below room temperature. In Sb₂S₃, mobile carriers are not created and insulating behavior is observed because of the considerably wide bandgap. Change of the carrier number by substitution of antimony contributes strongly to the thermoelectric properties (resistivity and Seebeck coefficient). As a result, the nondimensional figure of merit, ZT, decreases monotonically with increasing antimony content. The maximum value of ZT is obtained in Bi₂S₃ as ZT ≈ 0.1 at room temperature. It is pointed out that control of the carrier number, which is achieved by production of sulfur vacancies, is important to achieve high thermoelectric performance in the (Bi_1?x Sb _x )₂S₃ system. It is possible that the thermoelectric efficiency could be improved by control of the carrier concentration in the bismuth-rich region, including pure binary Bi₂S₃.     

In Situ Preparation and Thermoelectric Properties of B4C1−x –TiB2 Composites

B₄C_1?x –TiB₂ composites were prepared by in situ reactive spark plasma sintering of B₄C with addition of nano-TiO₂ powder. The effect of TiO₂ addition on the sinterability of boron carbide was studied. The composition and the microstructure of the dense composites are characterized by means of x-ray diffraction (XRD), scanning electron microscopy (SEM), and energy-dispersive x-ray spectroscopy (EDX). The studies show that the composites contain boron carbide and TiB₂ phases with a homogeneous structure. In addition, the correlation between the composition and the thermoelectric properties was investigated. The electrical conductivity of the composite increased with increasing addition of TiO₂, and the Seebeck coefficient decreased with TiO₂ addition. The percolation threshold ø _c for TiB₂ in the B₄C_1?x –TiB₂ system was found to be in the range of 0.139 to 0.189. The thermal conductivity was reduced in the whole measuring temperature range from 50°C to 800°C below ø _c. Accordingly, a significant enhancement in the dimensionless figure of merit ZT of the composites was achieved compared with that of boron carbide without TiO₂ addition, with ZT achieving its maximum value at 10 wt.% TiO₂.     

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.     

Effect of Addition of Ag, In or Pb on the Structure and Thermoelectric Performance of β-Zn4Sb3

Zn₄Sb₃ bulk alloys with addition of Ag, Pb or In were prepared by high- frequency induction melting and post-annealing. X-ray powder diffraction analysis showed that the lattice of the compound was distorted by the additions. Differential scanning calorimetry analysis revealed that the phase transition from ?? to ?? or ?? to ???? was suppressed by the addition of In or Ag. A high carrier concentration and high thermal conductivity were found in the sample with Ag or In additions. However, lower electric resistivity, nearly the same Seebeck coefficient, and low thermal conductivity, as compared with the undoped sample, were found in the sample with Pb addition, leading to good thermoelectric performance. The highest ZT value of 1.12 at 605?K was achieved for the Pb_0.02Zn₄Sb₃ sample in this work, which is about 30% larger than that for the undoped ??-Zn₄Sb₃.     

Synthesis and Thermoelectric Properties of an Sn1 – xPbxSb4Te8 Solid Solution Doped with Bismuth

Semiconductors - The thermoelectric properties of a solid solution of Sn1 – xPbxSb4Te8 and Sn1 – xPbxSb4 – yBiyTe8...     

Thermoelectric Properties of Light-Element-Containing Zintl Compounds CaZn2−x Cu x P2 and CaMnZn1−x Cu x P2 (x = 0.0–0.2)

Light-element-containing CaAl₂Si₂-type Zintl phases CaZn_2?x Cu _x P₂ and CaMnZn_1?x Cu _x P₂ (x = 0.0–0.2) have been synthesized by solid-state reaction. Electrical resistivity (ρ), Seebeck coefficient (α), and thermal conductivity (κ) were measured over a wide temperature (T) range (80–1000 K) to evaluate the thermoelectric potential of these materials. Below 300 K, the power factor (PF; α ²/ρ) is very small. Above 600 K, however, PF increases rapidly for all compositions because of a rapid increase of α and a simultaneous decrease of ρ. The measured large α is consistent with the wider band gap expected for these compositions. Compared with the pure compounds, larger PF values are observed for the Cu-substituted compounds; the largest observed PF is ～0.5 mW/m K². The thermal conductivity is found to be rather low, despite the presence of light elements, and is in the range 1.0–1.5 W/m K at 1000 K. Because of the combination of low κ and moderate PF values, the dimensionless figure of merit ZT = α ² T/ρκ reaches a maximum of 0.4 for CaZn_1.9Cu_0.1P₂.     

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.     

Thermoelectric Properties of Ca3−x Dy x Co4O9+δ with x = 0.00, 0.02, 0.05, and 0.10

Polycrystalline samples of Ca_3?x Dy _x Co₄O_9+δ (x = 0.00, 0.02, 0.05, and 0.10) have been prepared by conventional solid-state synthesis. The x-ray diffraction (XRD) results revealed that all the samples are single phase. The thermoelectric properties were measured at 25 K to 300 K. The thermopower of all the samples was positive, indicating that the predominant carriers are holes over the entire temperature range. The electrical resistivity of all the samples exhibited the nonmetal-to-metal transition at below 75 K. The electrical resistivity decreased and the thermopower increased with increasing Dy³⁺ content. Among all the samples, Ca_2.9Dy_0.10Co₄O_9+δ had the highest dimensionless figure of merit of 0.044 at 300 K.     

Ellipsometric Studies of the Optical Properties of Bi2Se3 and Bi2Se3〈Cu〉 Single Crystals

Semiconductors - By spectroscopic ellipsometry, the imaginary and real parts of the dielectric functions of Bi2Se3 and Bi2Se3〈Cu〉 single crystals are obtained in the photon-energy...     

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.     

Ferroelectric,Ferromagnetic, and Magnetoelectric Properties of Multiferroic Ni0.5Zn0.5Fe2O4–BaTiO3 Composite Ceramics

Lead-free multiferroic composite ceramics xNi_0.5Zn_0.5Fe₂O₄–(1 ? x)BaTiO₃ (x = 0.2, 0.5, 0.8) with a 0–3-type connection structure have been prepared by a traditional ceramic process. The cubic spinel Ni_0.5Zn_0.5Fe₂O₄ phase and the tetragonal perovskite BaTiO₃ phase were confirmed by x-ray diffraction. The effect of Ni_0.5Zn_0.5Fe₂O₄ ferrite content on ferroelectric and ferromagnetic behavior, and the magnetoelectric coupling effect of the composite ceramics is discussed. With increasing Ni_0.5Zn_0.5Fe₂O₄ ferrite content, the saturation magnetization of the composite ceramic increased and the saturation polarization decreased. The magnetoelectric coupling response voltage was observed to decrease rapidly for samples with x = 0.2, then 0.5, then 0.8. The highest magnetoelectric coupling response voltage, measured for 0.2Ni_0.5Zn_0.5Fe₂O₄–0.8BaTiO₃, was 150 μV, which corresponds to a maximum magnetoelectric coupling voltage coefficient of 109 μV/cm Oe. When x = 0.5, the maximum magnetoelectric response voltage is only 8 μV, and when x = 0.8, no magnetoelectric response voltage is detected because of very large leakage current of the 0.8Ni_0.5Zn_0.5Fe₂O₄–0.2BaTiO₃ composite ceramic.     

Fabrication of Highly (0?0?l)-Textured Sb2Te3 Film and Corresponding Thermoelectric Device with Enhanced Performance

An approach for fabrication of highly (0?0?l)-textured Sb₂Te₃ thin film with layered structure by the magnetron sputtering method is reported. The composition, microstructure, and thermoelectric properties of the thin films have been characterized and measured by x-ray diffraction, scanning electron microscopy with energy-dispersive x-ray spectroscopy, and a thermoelectric (TE) measurement system, respectively. The results show that well-oriented (0?0?l) Sb₂Te₃ thin film with layered structure is beneficial for improvement of thermoelectric properties, being a promising choice for planar TE devices. The power generation and cooling performance of a layered p-Sb₂Te₃ film device are superior to those of the ordinary thin-film device. For a typical parallel device with 38 layered Sb₂Te₃ film elements, the output voltage, maximum power, and corresponding power density are up to 10.3?mV, 11.1?μW, and 73?mW/cm², respectively, for a temperature difference of 76?K. The device can produce a 6.1?K maximum temperature difference at current of 45?mA. The results prove that enhanced microdevice performance can be realized by integrating (0?0?l)-oriented Sb₂Te₃ thin films with a layered architecture.     

Character of Interaction in the SnSb2Te4–SnBi2Te4 System and the Thermoelectric Properties of (SnSb2Te4)1 – x(SnBi2Te4)x Solid Solutions

Semiconductors - For the first time, the character of the interaction of components along the cut of SnSb2Te4–SnBi2Te4 is studied by various physicochemical methods in a wide temperature...     

Effects of Cu on the interfacial reactions between Sn–8Zn–3Bi–xCu solders and Cu substrate

The microstructure, thermal property, and interfacial reaction with Cu substrate of Sn–8Zn–3Bi–xCu (x = 0, 0.5, 1) lead-free solders were investigated in this work. Cu–Zn intermetallics formed in the solder matrix and the melting temperature increases slightly with Cu addition. After soldering at 250 °C for 90 s, a flat Cu₅Zn₈ layer and a scallop CuZn₅ layer formed at the interfaces of all samples. The CuZn₅ intermetallic compound (IMC) transformed to Cu₅Zn₈ IMC with longer reaction time due to the diffusion of Cu atoms from Cu substrate. The interfacial IMC layer grew thicker with the reaction time following a parabolic law which suggested the interfacial reactions were diffusion controlled. The calculation results show that the activation energy of IMC growth for Cu-containing solders is larger than that of Sn–8Zn–3Bi solder, which demonstrated that a small amount of Cu addition to the solder can effectively suppressed the growth of the interfacial IMC.     

Combustion Synthesis and Optical Properties of Eu3+-Doped BaGd2ZnO5 f–f Transition Nanophosphor for White LED

An Eu³⁺-doped BaGd_2(1?x)ZnO₅ nanophosphor has been synthesized by means of a single-step, urea-assisted, solution-combustion process. The structural, morphological, and optical properties of the nanophosphor were studied by x-ray diffraction (XRD), scanning electron microscopy, transmission electron microscopy, and photoluminescence spectroscopy. The XRD results showed that the pure orthorhombic BaGd₂ZnO₅ structure with space group Pbnm was obtained at 900°C. The intense red luminescence at 628 nm on near-UV (396 nm) excitation is because of the hypersensitive ⁵D₀ → ⁷F₂ transition of luminescent activator Eu³⁺ ions, located at a site with no inversion symmetry in the BaGd₂ZnO₅ crystal lattice. The optimum doping concentration and decay time of Eu³⁺-doped BaGd_2(1?x)ZnO₅ nanophosphor were also determined. The emission could be effectively tuned from blue to the white and red regions by varying the concentration of europium ions. Decay curve analysis revealed that cross-relaxation is primarily responsible for the concentration quenching. High luminescent intensity, low-cost, easy synthesis, uniform shape, and controlled color tunability suggest use of BaGd₂ZnO₅:Eu³⁺ as an efficient red-emitting nanophosphor for near-UV-based LED solid-state lighting applications.     

IMC Growth at the Interface of Sn–2.0Ag–2.5Zn Solder Joints with Cu,Ni, and Ni–W Substrates

Growth of intermetallic compounds (IMC) at the interface of Sn–2.0Ag–2.5Zn solder joints with Cu, Ni, and Ni–W substrates have been investigated. For the Cu substrate, a Cu₅Zn₈ IMC layer with Ag₃Sn particles on top was observed at the interface; this acted as a barrier layer preventing further growth of Cu–Sn IMC. For the Ni substrate, a thin Ni₃Sn₄ film was observed between the solder and the Ni layer; the thickness of the film increased slowly and steadily with aging. For the Ni–W substrate, a thin Ni₃Sn₄ film was observed between the solder and Ni–W layer. During the aging process a thin layer of the Ni–W substrate was transformed into a bright layer, and the thickness of bright layer increased with aging.     

In Situ Synthesis of the Peapod-Like Cu–SnO2@Copper Foam as Anode with Excellent Cycle Stability and High Area Specific Capacity

The theoretical specific capacity of tin oxide (SnO₂) anode material is more than twice that of graphite material (782 vs 372 mAh g^–1), whereas its potential usage is limited fatally by its huge volume expansion during lithiation. An effective solution is to encapsulate tin oxide into hollow structure such as yolk-shell based on the principle of confinement. However, in light of the restricted space of active substance, this kind of hollow electrode always has the low capacity, severely limiting its commercial value. Herein, a peapod-like Cu-SnO₂@copper foam (CF) as high area specific capacity anode based on the Kirkendall effect, in which the “pod and peas” in the peapod-like structure are composed of SnO₂ and Cu nanoparticles, respectively, is tactfully designed and constructed. Compared to other SnO_x-based electrodes with different hollow structure designs in published reports, the unique peapod-like Cu-SnO₂@CF anode delivers a remarkably high first reversible capacity of 5.80 mAh cm^-2 as well as excellent cycle stability with 66.7% capacity retention and ≈100% coulombic efficiency after 200 cycles at a current density of 1 mA cm^–2, indicative of its quite promising application toward high-performance lithium-ion batteries.     

Semiconducting Transport in Pb10−XCux(PO4)6O Sintered from Pb2SO5 and Cu3P

The recent claim on the discovery of ambient-pressure room-temperature superconductivity in Cu-doped lead-apatite has attracted sensational attention. The intriguing compound has been fabricated by sintering lanarkite (Pb₂SO₅) and copper(І) phosphide (Cu₃P). To verify this exciting claim, Pb₂SO₅, Cu₃P, and finally the modified lead-apatite Pb_10−xCu_x(PO₄)₆O have been successfully synthesized. Detailed electrical transport and magnetic properties of these compounds are systematically analyzed. It turns out that Pb₂SO₅ is a highly insulating diamagnet and Cu₃P is a paramagnetic metal. The obtained nominal Pb_10−xCu_x(PO₄)₆O compound sintered from Pb₂SO₅ and Cu₃P exhibits semiconductor-like transport behavior with a large room-temperature resistivity of ≈1.94 × 10⁴ Ω·cm, although the major phase of the compound shows consistent X-ray diffraction spectrum with the previously reported structure data. In addition, when a Pb_10−xCu_x(PO₄)₆O pellet pressed from uniformly ground powder is located on top of a commercial Nd₂Fe₁₄B magnet at room temperature, no repulsion can be felt and no magnetic levitation is observed either. The large difference in electrical and magnetic properties between the compounds and the previously reported compounds might be induced by distinct fine crystallographic structures, diverse multi-phase distributions, and different concentrations of impurity phases such as Cu₂S, all of which deserve further study.