Electronic transport properties of Ni-doped CoSb<Subscript>3</Subscript> prepared by encapsulated induction melting

Ni-doped CoSb₃ skutterudites were prepared by encapsulated induction melting and their thermoelectric and electronic transport properties were investigated. The negative signs of Seebeck and Hal coefficients for all Ni-doped specimens revealed that Ni atoms successfully acted as n-type dopants by substituting Co atoms. The carrier concentration increased as the Ni doping content increased, and the Ni dopants could generate excess electrons. However, the carrier mobility decreased as the doping content increased, which indicates that the electron mean free path was reduced by the impurity scattering. The Seebeck coefficient and the electrical resistivity decreased as the carrier concentration increased, as the increase in carrier concentration by doping overcame the decrease in the carrier mobility by impurity scattering. The Seebeck coefficient showed a negative value at all temperatures examined and increased as the temperature increased. The temperature dependence of electrical resistivity suggested that Co_1−xNi_xSb₃ is a highly degenerate semiconducting material. Thermal conductivity was considerably reduced by Ni doping, and the lattice contribution was dominant in the Ni-doped CoSb₃.     

Electronic transport properties of Te-doped CoSb<Subscript>3</Subscript> skutterudites prepared by hot pressing

Te-doped CoSb₃ (CoSb_3−yTe_y) skutterudites were prepared by hot pressing and their electronic transport properties examined. A single δ-phase was successfully obtained. The Seebeck and Hall coefficients confirmed that all the Te-doped CoSb₃ showed n-type conduction. The Te atoms successfully acted as electron donors by substitution of the Sb atoms. The carrier concentration increased an order of 10²⁰ cm⁻³ by Te doping, whereas the carrier mobility decreased as the doping content increased. The Seebeck coefficient and electrical resistivity decreased with an increase in the Te content. The doping considerably reduced the thermal conductivity due to electron-phonon scattering. The lattice contribution was dominant over the electronic contribution.     

Formation of high-density TiN/Ti<Subscript>5</Subscript>Si<Subscript>3</Subscript> ceramic composites using preceramic polymer

The formation, microstructure and properties of high-density TiN/Ti₅Si₃ ceramic composites created by the pyrolysis of preceramic polymer with filler were investigated. Methylpolysiloxane was mixed with TiH₂ as filler and ceramic composites prepared by pyrolysis at 1200°C to 1600°C under N₂, Ar and vacuum were studied. When a specimen with 70 vol.% TiH₂ was pyrolyzed up to 1600°C in a vacuum after a preheat treatment at 850°C in a N₂ atmosphere and subsequently heat-treated at 1600°C for 1 h under Ar at a pressure of 2 MPa, a ceramic composite with full density was obtained. The microstructure of the ceramic composite was composed of TiN and Ti₅Si₃ phases. Under specific pyrolysis conditions, a ceramic composite with a density of 99.2 TD%, a Vickers hardness of 18 GPa, a fracture toughness of 3.5 MPam^1/2, a flexural strength of 270 MPa and a electrical conductivity of 6200 ohm⁻¹·cm⁻¹ was obtained.     

Microstructure and Physical Properties of Tb<Subscript>2</Subscript>TiO<Subscript>5</Subscript> Neutron Absorber Synthesized by Ball Milling and Sintering

Tb₂TiO₅ neutron absorber was synthesized by ball milling and sintering. Microstructure character of ball-milled Tb₄O₇-17.605%TiO₂ (mass fraction, %) powders and sintered bulks was analyzed using XRD, SEM and TEM. The microhardness, coefficient of thermal expansion and thermal conductivity of sintered bulks were measured. The experiment results showed that the nanocrystalline solid solution was obtained during ball milling. After 96 h of ball milling, TiO₂ was completely solved in Tb₄O₇ and the crystal size of Tb₄O₇ was up to 37 nm. The bulk materials prepared by cold isostatic pressing were sintered at 1300 °C. Tb₂TiO₅ bulks with an orthorhombic structure were obtained. The microhardness of sintered bulks, as well as the thermal conductivity, increased firstly with increasing ball milling time and then decreased. The coefficient of thermal expansion decreased initially and then increased with increasing ball milling time. For the sintered bulk with powder milled for 48 h, the highest values of both microhardness and thermal conductivity were observed, whereas the lowest coefficient of thermal expansion was exhibited. In addition, with increasing testing temperature, the thermal conductivity of sintered bulks initially fell and then rebounded while an opposite trend was found in the coefficient of thermal expansion.     

Effects of Sc doping on electrical conductivity of BaZrO<Subscript>3</Subscript> protonic conductors

BaZr1-xScxO3-0.5x (x=0.07,0.10,0.13,0.16) powders were prepared by solid-state reaction method,and ZnO was used as sintering aid.Samples with different amount of ZnO additive were sintered at 1450 ℃ for 6 h in air.Single cubic perovskite phase proton conductors were obtained.Conductivity was measured by electrochemical workstation.It was shown that Sc doping could increase conductivity through enhancing the carrier concentration in the material,but excessive Sc content might decrease the carrier concentration because of its charge compensation.ZnO had an influence on carrier concentration and mobility and affected the electrical conductivity.2 mol％ ZnO and 13 mol％ ScO1.5 doped sample showed the highest DC conductivity of 3.6 × 10-3 S·cm-1 tested at 800 ℃ in wet hydrogen atmosphere.     

Cr doping effect in B-site of La<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript> on its phase stability and performance as an SOFC anode

La_0.75Sr_0.25Cr _y Mn_1−y O₃ (LSCM) (y = 0.0–0.6) composite oxides were synthesized by a complexing process of combining ethylene diamine tetraacetic acid (EDTA) and citrate. X-ray diffraction (XRD), temperature-programmed reduction, electrical conductivity, I–V polarization, and impedance spectroscopy were conducted to investigate the Cr doping effect of La_0.75Sr_0.25MnO₃ on its phase stability and electrochemical performance as a solid-oxide fuel cell (SOFC) anode. The chemical and structural stabilities of the oxides increased steadily with increasing Cr doping concentration, while the electrical conductivity decreased on the contrary. At y ≥ 0.4, the basic perovskite structure under the anode operating condition was sustained. a cell with 0.5-mm-thick scandia-stabilized zirconia electrolyte and La_0.75Sr_0.25Cr _y Mn_1−y O₃ anode delivered a power density of ∼15 mW·cm⁻² at 850°C.     

Microstructure and Thermomechanical Properties of Atmospheric Plasma-Sprayed Yb<Subscript>2</Subscript>O<Subscript>3</Subscript> Coating

In this study, a Yb₂O₃ coating was fabricated by the atmospheric plasma spray technique. The phase composition, microstructure, and thermal stability of the coating were examined. The thermal conductivity and thermal expansion behavior were also investigated. Some of the mechanical properties (elastic modulus, hardness, fracture toughness, and flexural strength) were characterized. The results reveal that the Yb₂O₃ coating is predominantly composed of the cubic Yb₂O₃ phase, and it has a dense lamellar microstructure containing defects. No mass change and exothermic phenomena are observed in the thermogravimetry and differential thermal analysis curves. The high-temperature x-ray diffraction results indicate that no phase transformation occurs from room temperature to 1500 °C, revealing the good phase stability of the Yb₂O₃ coating. The coefficient of thermal expansion of the Yb₂O₃ coating is (7.50-8.67)?×?10^?6 K^?1 in the range of 200-1400 °C. The thermal conductivity is about 1.5 W m^?1 K^?1 at 1200 °C. The Yb₂O₃ coating has excellent mechanical properties and good damage tolerant. The unique combination of these properties implies that the Yb₂O₃ coating might be a promising candidate for T/EBCs applications.     

Thermal and structural role of additives in P<Subscript>2</Subscript>O<Subscript>5</Subscript>-ZnO-Sb<Subscript>2</Subscript>O<Subscript>3</Subscript> glass for low expansion sealing materials

A glass based on the P₂O₅-ZnO-Sb₂O₃ ternary system was modified with various additives, such as RO (R=Ca, Ba and Mn), B₂O₃ and V₂O₅, for low temperature and low expansion sealing materials. The glass transition temperature (T_g) and coefficient of thermal expansion (CTE) were monitored and reduced with additive compositions of RO. Additional incorporation of B₂O₃ at the expense of RO also showed a similar result. Significant improvement was observed when the glass was modified with V₂O_5. A glass showing T_g<350 °C along with CTE<65×10⁻⁷/°C was found, suggesting a high potential for low temperature sealing materials especially for display applications. The role of the quaternary element within the glass is discussed, along with the structural effect using Raman spectroscopy.     

Thermoelectric properties of the 0.05 wt.% SbI3-Doped n-Type Bi2(Te0. 95Se0. 05)3 alloy fabricated by the hot pressing method

Thermoelectric properties of the 0.05 wt.% SbI₃-doped n-type Bi₂(Te_o.95Se_o.o5)₃ alloy, fabricated by hot pressing at temperatures ranging from 350°C to 550°C, were characterized. The electron concentration of the alloy decreased as the hot pressing temperature increased due to the annealing-out of the excess Te vacancies. When hot pressed at 350°C, a figure-of-merit of 0.75x10^-3/K was obtained due to the low Seebeck coefficient of -145 μV/K and relatively high electrical resistivity of 2.05 mΩ-cm. Upon increasing the hot pressing temperature, however, the figure-of-merit was improved mainly due to the increase of the Seebeck coefficient. A maximum figure-of-merit of 2.1x10^-3/K was obtained by hot pressing at 550°C.     

Solvothermal synthesis and thermoelectric properties of skutterudite compound Fe（0.25）Ni（0.25）Co（0.5）Sb3

Nanostructured skutterudite-related compound Fe_0.25Ni_0.25Co_0.5Sb₃ was synthesized by a solvothermal method using FeCl₃, NiCl₂, CoCl₂, and SbCl₃ as the precursors and NaBH₄ as the reductant. The solvothermally synthesized powders consisted of fine granules with an average particle size of tens of nanometers. The bulk material was prepared by hot pressing the powders. Transport property measurements indicated a heavily doped semiconductor behavior with n-type conduction. The thermal conductivity is about 1.83 W·m⁻¹·K⁻¹ at room temperature and decreases to 1.57 W·m⁻¹·K⁻¹ at 673 K. The low thermal conductivity is attributed to small grain size and high porosity. A maximum dimensionless figure of merit of 0.15 is obtained at 673 K.     

Thermoelectric Properties of Cu-doped Bi<Subscript>2−x</Subscript>Sb<Subscript>x</Subscript>Te<Subscript>3</Subscript> Prepared by Encapsulated Melting and Hot Pressing

P-type Bi_2?xSb_xTe₃:Cu_m (x = 1.5–1.7 and m = 0.002–0.003) solid solutions were synthesized using encapsulated melting and were consolidated using hot pressing. The effects of Sb substitution and Cu doping on the charge transport and thermoelectric properties were examined. The lattice constants decreased with increasing Sb and Cu contents. As the amount of Sb substitution and Cu doping was increased, the electrical conductivity increased, and the Seebeck coefficient decreased owing to the increase in the carrier concentration. All specimens exhibited degenerate semiconductor characteristics and positive Hall and Seebeck coefficients, indicating p-type conduction. The increased Sb substitution caused a shift in the onset temperature of the intrinsic transition and bipolar conduction to higher temperatures. The electronic thermal conductivity increased with increasing Sb and Cu contents owing to the increase in the carrier concentration, while the lattice thermal conductivity slightly decreased due to alloy scattering. A maximum figure of merit, ZT_max = 1.25, was achieved at 373 K for Bi_0.4Sb_1.6Te₃:Cu_0.003.     

Control of microwave dielectric properties in 0.42ZnNb<Subscript>2</Subscript>O<Subscript>6</Subscript>−0.58TiO<Subscript>2</Subscript> ceramics by the quantitative analysis of phase transition

Phase constitutions of ZnNb₂O₆−TiO₂ mixture ceramics were significantly changed according to the sintering temperature. Phase transition procedures and their effect on the microwave dielectric properties of 0.42ZnNb₂O₆−0.58TiO₂ were investigated using X-ray powder diffraction and a network analyzer. The fractions of the phases composing the mixture were calculated by measuring integral intensities of each reflection. The structural transitions in 0.42ZnNb₂O₆−0.58TiO₂ were interpreted as the association of two distinct steps: the columbite and rutile to ixiolite transition present at lower temperatures (900–950°C) and the ixiolite to rutile transition at higher temperatures (1150–1300°C). These transitions caused considerable variation of microwave dielectric properties. Importantly, τ_f was modified to around 0 ppm/°C in two sintering conditions (at 925°C for 2 hr and at 1300°C for 2 hr), by the control of phase constitution.     

Recovery of V<Subscript>2</Subscript>O<Subscript>5</Subscript> from Bayer liquor by ion exchange

A new technology was developed to recover V2O5 from Bayer spent liquor by ion exchange.The experimental results show that in the conditions of 105°C and 0.20-0.25 mass ratios between CaO in lime and Al2O3 in spent liquor, the precipitation rate of vanadium in Bayer liquor is more than 85%.The vanadium-bearing precipitation is leached by NaHCO3 solution.The leaching rate of vanadium can reach 85% in the conditions of 95°C, 40 g·L-1 of NaHCO3 concentration, and ventilating of CO2.The 201 × 7 type of resin has...     

Effect of compaction method on the structure and properties of bulk Cu + Cr<Subscript>3</Subscript>C<Subscript>2</Subscript> composites

Cu + Cr₃C₂ composites have been produced using the mechanical alloying of the elemental components, followed by severe plastic deformation by torsion, magnetic-pulse pressing, and electric-pulse plasma sintering. The composites are studied using X-ray diffraction and light and electron microscopy, as well as measurements of the hardness, density, and electric conductivity. Magnetic-pulse pressing at a temperature of 500°C makes it possible to produce volume nanocomposites with a homogeneous distribution of dispersed carbides over the copper matrix, which has a density of 96%, a Vickers microhardness of 4.6 GPa, a Rockwell hardness of 69 HRA, and an electric conductivity of 19% IACS units. Using electric-pulse plasma sintering at a temperature of 700°C, composites with the nanostructured copper matrix, which contains carbide inclusions and consists of domains surrounded by a layer of nearly pure copper, have been produced. These composites have a density of 88%, a Vickers microhardness of 4.0 GPa, a Rockwell hardness of 58 HRA, and electric conductivity of 26% IACS units.     

Synthesis and thermal expansion of 4J36/ZrW<Subscript>2</Subscript>O<Subscript>8</Subscript> composites

Gas atomized 4J36 alloy powder was milled for 72 h then mixed with ZrW₂O₈ powder and sintered at 600°C for 4 h under argon atmosphere. 4J36/ZrW₂O₈ composites containing 10 vol.%, 20 vol.%, 30 vol.%, and 40 vol.% ZrW₂O₈ were fabricated, the relative density of which ranged from 70% to 80%. Thermal expansion coefficients of the composites decreased as the amount of ZrW₂O₈ increased, in agreement with the rule of the mixture. The coefficient of thermal expansion of the 4J36/40 vol.%ZrW₂O₈ composite in 25–100°C is 0.55 × 10⁻⁶/°C.     

Effects of cryogenic treatment on the thermal physical properties of Cu<Subscript>76.12</Subscript>Al<Subscript>23.88</Subscript> alloy

The thermal diffusion coefficient,heat capacity,thermal conductivity,and thermal expansion coefficient of Cu76.12Al23.88 alloy before and after cryogenic treatment in the heating temperature range of 25°C to 600°C were measured by thermal constant tester and thermal expansion instrument.The effects of cryogenic treatment on the thermal physical properties of Cu76.12Al23.88 alloy were investigated by comparing the variation of the thermal parameters before and after cryogenic treatment.The results show that the variation trend of the thermal diffusion coefficient,heat capacity,thermal conductivity,and thermal expansion coefficient of Cu76.12Al23.88 alloy after cryogenic treatment was the same as before.The cryogenic treatment can increase the thermal diffusion coefficient,thermal conductivity,and thermal expansion coefficient of Cu76.12Al23.88 alloy and decrease its heat capacity.The maximum difference in the thermal diffusion coefficient between the before and after cryogenic treatment appeared at 400°C.Similarly,thermal conductivity was observed at 200°C.     

Thermoelectric properties of In<Subscript>z</Subscript>Co<Subscript>4</Subscript>Sb<Subscript>12</Subscript> skutterudites

In this study, indium-filled CoSb₃ skutterudite is synthesized via encapsulated induction melting and subsequent annealing at 823 K for six days, and the crystal structure, lattice constant, filler position, phase homogeneity and stability were investigated. All of the In-filled CoSb₃ samples were n-type conducting samples. The temperature dependence of the electrical resistivity showed In_zCo₄Sb₁₂ is a highly degenerate semiconducting material. The thermal conductivity was reduced considerably by In filling. The highest thermoelectric figure of merit value was achieved when the In filling fraction is 0.25. It was found that the ZT of the In-filled CoSb₃ (In_zCo₄Sb₁₂) was higher than that of the In-substituted CoSb₃ (Co_3.75In_0.25Sb₁₂ and Co₄Sb_11.75In_0.25). This is mainly due to the lower thermal conductivity and higher Seebeck coefficient.     

Transport properties on Sn-filled and Te-doped CoSb<Subscript>3</Subscript> skutterudites

Sn-filled and Te-doped CoSb₃ skutterudites (Sn_xCo₈Sb_23.25Te_0.75) were synthesized by the encapsulated induction melting process. Single δ-phase was successfully obtained by subsequent heat treatment at 823 K for 6 days. Structural characterizations were carried out through X-ray diffraction studies. Transport properties such as the Seebeck coefficient, electrical resistivity, thermal conductivity, carrier concentration and mobility were measured and analyzed. The unfilled Co₈Sb_23.25Te_0.75 sample showed n-type conductivity from 300 K to 700K. However, the Sn-filled Sn_xCo₈Sb_23.25Te_0.75 showed n-type conductivity for z=0.25 and 0.5, and p-type conductivity for z=1.0 and 1.5 from 300 K to 700 K. Thermal conductivity was reduced by the impurity-phonon scattering. The dimensionless figure of merit (ZT) was remarkably improved over that of untreated CoSb₃. However, the ZT value decreased when filling with z≥1.0 because the conductivity type was changed from n-type to p-type, thereby allowing bipolar conduction. The details are discussed in terms of the two-band model and the bipolar thermoelectric effect.     

Effects of defects generated in ALD TiO<Subscript>2</Subscript> films on electrical properties and interfacial reaction in TiO<Subscript>2</Subscript>/SiO<Subscript>2</Subscript>/Si system upon annealing in vacuum

Thin TiO₂ layers grown at 130°C on SiO₂-coated Si substrates by atomic layer deposition (ALD) using TTIP and H₂O as precursors were annealed, and the effects of the annealing temperature on the resulting electrical properties of TiO₂ and the interface properties between a Pt electrode and TiO₂ were examined using transmission line model (TLM) structures. The as-deposited TiO₂ thin film had an amorphous structure with OH groups and a high resistivity of 6×10³Ω-cm. Vacuum annealing at 700 °C transformed the amorphous film into an anatase structure and reduced its resistivity to 0.04Ω-cm. In addition, the vacuum-annealing of the TiO₂/SiO₂ structure at 700°C produced free silicon at the TiO₂-SiO₂ interface as a result of the reaction between the Ti interstitials and SiO₂. The SiO₂ formed on the TiO₂ surface caused a Schottky contact, which was characterized by the TLM method. The use of the TLM method enabled the accurate measurement of the resistivity of the vacuum-annealed TiO₂ films and the characterization of the Schottky contacts of the metal electrode to the TiO₂.     

Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-TiC Composite Prepared by Spark Plasma Sintering Process: Evaluation of Mechanical and Tribological Properties

Al₂O₃-10TiC composites were synthesized by spark plasma sintering (SPS) process. Microstructural and mechanical properties of the composite reveal homogeneous distribution of the fine TiC particles in the matrix. The samples were produced with different sintering temperature, and it shows that the hardness and density gradually increases with increasing sintering temperature. Abrasion wear test result reveals that the composite sintered at 1500 °C shows high abrasion resistance (wt. loss ~ 0.016 g) and the lowest abrasion resistance was observed for the composite sample sintered at 1100 °C (wt. loss ~ 1.459 g). The profilometry surface roughness study shows that sample sintered at 1100 °C shows maximum roughness (R_a = 6.53 µm) compared to the sample sintered at 1500 °C (R_a = 0.66 µm) corroborating the abrasion wear test results.