Improved thermoelectric performances in textured Bi1.6Pb0.4Ba2Co2Oy/Ag composites

Bi_1.6Pb_0.4Ba₂Co₂O_y thermoelectric ceramics with small Ag additions (0, 1, 3, and 5 wt%) have been textured using the laser floating zone method. Microstructure has shown a slight decrease on the secondary phases content and a better grain alignment in Ag added samples. These microstructural features are reflected in the thermoelectric properties, which have shown a significant decrease of electrical resistivity, when the Ag content is raised. In spite of a corresponding decrease of Seebeck coefficient, all the Ag-containing samples possess higher Power Factor values than the Bi_1.6Pb_0.4Ba₂Co₂O_y ones. Moreover, the maximum Power Factor values (about 0.36 mW/K².m at 650 °C) have been measured in Bi_1.6Pb_0.4Ba₂Co₂O_y+3 wt% Ag samples, which are the best results reported in this family of materials.     

Sodium Doping Effects on Layered Cobaltate Bi2Sr2Co2Oy Thin Films

Highly c‐axis oriented Bi_2?xNa_xSr₂Co₂O_y (x = 0, 0.1, 0.2, 0.3) thin films were successfully deposited onto LaAlO₃ (0 0 1) single crystal substrates by the chemical solution deposition method. The Na‐doping effects on microstructures as well as transport and thermoelectric properties were investigated. The crystallite size normal to the thin film surface was decreased with Na doping, and the carrier concentration and mobility was enhanced and decreased, respectively. As for the transport properties, it is suggested that Na‐doping‐induced disorders play a more important role at low temperatures, while at the medium temperature the doping play a trivial role, at higher temperatures Na‐doping weakens the electron correlation. Combined with the transport properties and Seebeck coefficient results, it is suggested that the thermoelectric properties are mainly controlled by carrier concentration due to the hole doping in blocking layers. Power factor at 300 K was enhanced about 22% for the Bi_1.7Na_0.3Sr₂Co₂O_y thin film as compared with that of the undoped thin films, suggesting that Na doping at blocking layer in Bi₂Sr₂Co₂O_y was an effective route to enhance the thermoelectric power factor.     

Low thermal conductivity and thermoelectric properties of Si80Ge20 dispersed Bi2Sr2Co2Oy ceramics

Bi₂Sr₂Co₂O_y is a thermoelectric material with low thermal conductivity. The Bi₂Sr₂Co₂O_y/Si₈₀Ge₂₀ composite samples were prepared by solid phase sintering at high temperature to investigate the effects of Si₈₀Ge₂₀ alloys as the second phase on the microstructure and thermoelectric properties of the fabricated composites. An appropriate amount of the dispersed Si₈₀Ge₂₀ in the Bi₂Sr₂Co₂O_y matrix can reduce the resistivity of the composite successfully. In particular, the increase in phonon scattering caused by the second phase leads to a significant decrease in thermal conductivity, which improves the thermoelectric properties of the material significantly. At 923 K, the thermal conductivity of the Bi₂Sr₂Co₂O_y + 0.2 wt% Si₈₀Ge₂₀ sample achieves an ultralow value of 0.58 W/K·m. Its corresponding optimal dimensionless thermoelectric figure of merit value is 0.36, which is 56% higher than that of the pure Bi₂Sr₂Co₂O_y sample.     

Promising high temperature thermoelectric properties of dense Ba2Co9O14 ceramics

Layered cobalt oxides have shown high thermoelectric properties. The n = 1 member of the Ba_n+1Co_nO_3n+3(Co₈O₈) family, Ba₂Co₉O₁₄, a new layered cobalt oxides family with Co(II) and Co(III) in the CdI₂ layers, has been synthesized by solid state reaction and sintered as dense ceramics (relative density ∼ 93%) by Spark Plasma Sintering. It presents promising p-type thermoelectric properties at high temperature. The dimensionless figure of merit ZT is 0.032 at 660 K and 0.04 at 1000 K, which is about one quarter to one third of the ZT value of Ca₃Co₄O₉ ceramics.     

Microwave dielectric properties of LBBS glass added (Zn0.95Co0.05)2SiO4 for LTCC technology

The effects of Li₂O–B₂O₃–Bi₂O₃–SiO₂ (LBBS) glass on the sintering characteristics and microwave dielectric properties of (Zn_0.95Co_0.05)₂SiO₄ were investigated in this study. (Zn_0.95Co_0.05)₂SiO₄ powders were fabricated by traditional solid-state preparation, and LBBS glass was synthesised by quenching method. The LBBS glass can effectively reduce the sintering temperature of (Zn_0.95Co_0.05)₂SiO₄ from 1300 °C to 900 °C and thus promote the densification and uniformity of the specimens. XRD patterns indicated that no other secondary phases existed in our doping range (0–2 wt%). To obtain the highest sintering density and a uniform microstructure when the samples were sintered at 900 °C, the optimal doping content was set to be 1.5 wt%. The sample also demonstrated the following excellent microwave dielectric properties: ɛ_r=6.16, Qf=33,000 GHz and τ_f=−59 ppm/°C.     

Ag enhanced electrochemical performance for Na2Li2Ti6O14 anode in rechargeable lithium-ion batteries

Due to the characteristics of an electronic insulator, Na₂Li₂Ti₆O₁₄ always suffers from low electronic conductivity as anode material for lithium storage. Via Ag coating, Na₂Li₂Ti₆O₁₄@Ag is fabricated, which has higher electronic conductivity than bare Na₂Li₂Ti₆O₁₄. Enhancing the Ag coating content from 0.0 to 10.0 wt%, the surface of Na₂Li₂Ti₆O₁₄ is gradually deposited by Ag nanoparticles. At 6.0 wt%, a continuous Ag conductive layer is formed on Na₂Li₂Ti₆O₁₄. While, particle growth and aggregation take place when the Ag coating content reaches 10.0 wt%. As a result, Na₂Li₂Ti₆O₁₄@6.0 wt% Ag displays better cycle and rate properties than other samples. It can deliver a lithium storage capacity of 131.4 mAh g⁻¹ at 100 mA g⁻¹, 124.9 mAh g⁻¹ at 150 mA g⁻¹, 119.1 mAh g⁻¹ at 200 mA g⁻¹, 115.8 mAh g⁻¹ at 250 mA g⁻¹, 111.9 mAh g⁻¹ at 300 mA g⁻¹ and 109.4 mAh g⁻¹ at 350 mA g⁻¹, respectively.     

Intermediate-temperature conductivity of B-site doped Na0.5Bi0.5TiO3-based lead-free ferroelectric ceramics

Na_0.5Bi_0.5TiO₃ (NBT) based oxide-ion conductor ceramics have great potential applications in intermediate-temperature solid oxide fuel cells (SOFCs) and oxygen sensors. Na_0.5Bi_0.49Ti_1−xMg_xO_3−δ ceramics with x=0, 0.01, 0.02, 0.03, 0.05 and 0.08 were prepared by conventional solid-state reaction. XRD measurement and SEM analysis revealed the formation of pure perovskite structures without secondary phase. MgO doping greatly decreased the sintering temperature and inhibited grain growth. AC impedance spectroscopy measurement was adopted to measure the total conductivity, which was found to increase with MgO doping content ranging from 0 to 3 mol% and subsequently to decrease. High oxygen ionic conductivity σ_t=0.00629 S/cm was achieved for sample doped with 3 mol% MgO at 600 °C in air atmosphere.     

Enhanced transport critical current density of (Bi,Pb)-2223/Ag superconductor tapes added with nano-sized Bi2O3

Ag sheathed superconductor tapes with starting composition (Bi, Pb)-2223(Bi₂O₃)_0.01 were prepared. Bi₂O₃ with average size 150 nm was used in this work. The Bi₂O₃ amount was chosen based on our initial study on nano-sized Bi₂O₃ added pellets which showed an optimal superconducting property for 0.01 wt% addition. Non-added tapes were also prepared for comparison. The tapes were investigated by X-ray diffraction method, scanning electron microscopy and transport critical current density, J_c measurements (30 K to 77 K). The influence of different sintering times (50, 100, and 150 h) on J_c under applied magnetic field (0–0.75 T at 77 K) parallel and perpendicular to the surface of the tapes was also investigated. J_c of added tapes was found to increase significantly as compared with the non-added tapes. The Bi₂O₃ added tapes sintered for 150 h exhibited the highest J_c at 30 K of 57,900 A/cm² as compared with 19,400 A/cm² for the non-added tapes sintered for 100 h. The improvements in flux pinning and connectivity between grains due to nano Bi₂O₃ addition led to the enhancement of J_c.     

Piezoelectric and ferroelectric properties of lead-free [Bi1−y(Na1−x−yLix)]0.5BayTiO3 ceramics

Lead-free [Bi_1−y(Na_1−x−yLi_x)]_0.5Ba_yTiO₃ (BNLB-x/y) piezoelectric ceramics were prepared by sintering the constituent oxides, and their piezoelectric and ferroelectric properties studied. The results of X-ray diffraction (XRD) suggest that Li⁺ and Ba²⁺ diffuse into the Bi_0.5Na_0.5TiO₃ (BNT) lattices to form a solid solution with a single-phase perovskite structure. The ceramics can be well sintered at 1100–1150 °C. The introduction of Li⁺ and Ba²⁺ into Bi_0.5Na_0.5TiO₃ significantly decreases the coercive field, E_c but maintains the large remanent polarization, P_r of the materials. The ceramics exhibit relatively good piezoelectric properties and very strong ferroelectricity: piezoelectric constant, d₃₃ = 208 pC/N, planar electromechanical coupling factor, k_p = 37.0%, remanent polarization, P_r = 38.5 μC/cm², coercive field, E_c = 3.27 kV/mm. The depolarization temperature, T_d of BNLB-0.075/0.04 ceramics is about 190 °C.     

Catalytic removal of diesel soot particulates over K and Mg substituted La1 − xKxCo1 − yMgyO3 perovskite oxides

K and Mg substituted perovskite catalysts La_1 − xK_xCo_1 − yMg_yO₃ (x = 0–0.4, y = 0–0.2) for soot combustion were prepared by citric acid complexation and characterized by XRD, FT-IR, SEM, TEM, EDS, H₂-TPR, XPS and TG. Soot combustion was remarkably accelerated when K was introduced into LaCoO₃. Then Mg was doped into the K substituted LaCoO₃, soot combustion was further improved for the restrained growth of Co₃O₄ phase. K/Mg substitutions were responsible for enhancing activity of catalysts by improving reducibility as suggested by H₂-TPR studies. Among all the catalysts, La_0.6K_0.4Co_0.9Mg_0.1O₃ exhibited the highest activity.     

Preparation and performance of Na-doped La2Ce2O7 electrolytes for protonic ceramic fuel cells

The protonic material La₂Ce₂O₇ exhibits good tolerance to H₂O and CO₂ compared to BaCeO₃-based materials and has become increasingly popular for operation at low-to-intermediate temperatures in protonic ceramic fuel cells. In this work, doping La₂Ce₂O₇ with Na in a series with varying compositions is studied. All of the precursors are prepared by a common citrate-nitrate combustion method. X-ray diffraction images reveal that all of the La_2-xNa_xCe₂O_7-δ samples have a cubic structure. The La_2-xNa_xCe₂O_7-δ pellets are characterized by scanning electron microscopy and are observed to be dense without holes. The effects of Na-doping on the La₂Ce₂O₇ electrical conductivity are carefully investigated in air at 350–800 °C and 5%H₂-95% Ar environments at 350–700 °C. It is found that different levels of Na doping in La₂Ce₂O₇ are conducive to improving the electrical conductivity and sinterability. Among the pellets, La_1.85Na_0.15Ce₂O_7-δ exhibited the highest electrical conductivity in air and 5% H₂-95% Ar atmospheres. Anode-supported half cells with La_1.85Na_0.15Ce₂O_7-δ electrolyte are also fabricated via a dry-pressing process, and the corresponding single cell exhibited a desirable power performance of 501 mW cm⁻² at 700 °C. The results demonstrate that La_1.85Na_0.15Ce₂O_7-δ is a promising proton electrolyte with high conductivity and sufficient sinterability for use in protonic ceramic fuel cells operating at reduced temperatures.     

Low-temperature sintering and microwave dielectric properties of Nd(Co1/2Ti1/2)O3 ceramics using glass addition of oxides

The microstructures and microwave dielectric characteristics of complex perovskite Nd(Co_1/2Ti_1/2)O₃ ceramics with 60P₂O₅–15ZnO–5La₂O₃–5Al₂O₃–5Na₂O–5MgO–5Yb₂O₃ (PZLANMY) additions (1–4 wt%) prepared through the conventional solid-state route were investigated. It was found that Nd(Co_1/2Ti_1/2)O₃ ceramics can be sintered at 1210 °C owing to the sintering aid of PZLANMY-glass addition. At 1300 °C, Nd(Co_1/2Ti_1/2)O₃ ceramics with 1 wt% of PZLANMY-glass addition possess a dielectric constant (ε_r) of 27, a Q×f value of 64,000 GHz and a temperature coefficient of resonant frequency (τ_f) of ?29 ppm/°C. The PZLANMY-glass doped Nd(Co_1/2Ti_1/2)O₃ ceramics can find applications in microwave devices that require low sintering temperature.     

Effects of niobium doping site and concentration on the phase structure and oxygen permeability of Nb-substituted SrCoOx oxides

Niobium doping effect on phase structure, phase stability and electrical conductivity of SrCoO_x oxides and oxygen permeability of the corresponding membranes were systematically investigated. Niobium was successfully incorporated into A-site, B-site or simultaneously A and B double sites of SrCoO_x oxide and stabilized the perovskite structure with a cubic symmetry in air down to room temperature at a proper doping amount. However, the A-site doping could not stabilize the cubic structure under a more reducing atmosphere of nitrogen, as to SrCo_1?yNb_yO_3?δ, y ≥ 0.1 is necessary to sustain the cubic perovskite structure. Simultaneous doping of Nb at A and B sites is the most effective way to stabilize the perovskite structure under nitrogen atmosphere. Irrespective of doping site, the electrical conductivity decreased monotonously with Nb-doping amount. Both Nb_xSr_1?xCoO_3?δ and Nb_zSr_1?zCo_1?zNb_zO_3?δ envisaged a decrease in oxygen permeation flux with Nb-doping amount while SrCo_1?yNb_yO_3?δ reached the maximum flux at y = 0.1. Among all the membranes, SrCo_0.9Nb_0.1O_3?δ and Nb_0.05Sr_0.95Co_0.95Nb_0.05O_3?δ show the highest oxygen fluxes of 3.5 and 2.7 ml cm^?2 min^?1 at 900 °C under an air/helium gradient, respectively.     

Porous Ca3Co4O9 with enhanced thermoelectric properties derived from Sol–Gel synthesis

Highly porous Ca₃Co₄O₉ thermoelectric oxide ceramics for high-temperature application were fabricated by sol–gel synthesis and subsequent conventional sintering. Growth mechanism of misfit-layered Ca₃Co₄O₉ phase, from sol–gel synthesis educts and upcoming intermediates, was characterized by in-situ X-ray diffraction, scanning electron microscopy and transmission electron microscopy investigations. The Ca₃Co₄O₉ ceramic exhibits a relative density of 67.7%. Thermoelectric properties were measured from 373 K to 1073 K. At 1073 K a power factor of 2.46 μW cm⁻¹ K⁻², a very low heat conductivity of 0.63 W m⁻¹ K⁻¹ and entropy conductivity of 0.61 mW m⁻¹ K⁻² were achieved. The maintained figure of merit ZT of 0.4 from sol–gel synthesized Ca₃Co₄O₉ is the highest obtained from conventional, non-doped Ca₃Co₄O₉. The high porosity and consequently reduced thermal conductivity leads to a high ZT value.     

The relationship between the micro-mechanism and macroscopic dielectric properties in Ba1−xBixTi1−x−yZn0.75xW0.25x+yO3+y systems

A novel lead-free, high dielectric constant, ultra-wide temperature stable dielectric ceramic Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y (0.22≤x≤0.30, y=0.015) was synthesized by the traditional solid-state reaction method. The phase composition, electric and dielectric properties of the Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO₃ ceramics were investigated. The P-V-L dielectric theory was introduced. And, the chemical bond energy was calculated to track the changes in micro-structure. The relationships between chemical bond energy and the macroscopic dielectric properties(ε_r, dielectric stability and dielectric loss) in Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramics were discussed systematically. Owing to the inhomogeneous micro-structure and the diffusion in phase transition, Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramics showed a stable permittivity (~800±15%) over a ultra-wide temperature range (−30 to 375 °C). Moreover, dielectric loss was less than 0.02 and the insulation resistance was over 10¹² Ω cm. These features suggested that the Ba_1−xBi_xTi_1−x−yZn_0.75xW_0.25x+yO_3+y ceramic could be considered as a promising candidate material for energy storage applications in harsh environment.     

Synthesis of lithium LiNi1−yCoyO2 from lithium carbonate,nickel oxide and cobalt carbonate and their electrochemical properties

LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) were synthesized by solid state reaction method at 800 °C and 850 °C from Li₂CO₃, NiO and CoCO₃ as starting materials. The electrochemical properties of the synthesized LiNi_1?yCo_yO₂ were investigated. As the content of Co decreases, particle size decreases rapidly and particle size gets more homogeneous. When the particle size is compared at the same composition, the particles synthesized at 850 °C are larger than those synthesized at 800 °C. Among LiNi_1?yCo_yO₂ (y = 0.1, 0.3 and 0.5) synthesized at 850 °C, LiNi_0.7Co_0.3O₂ has the largest intercalated and deintercalated Li quantity Δx at the first charge–discharge cycle, followed in order by LiNi_0.9Co_0.1O₂ and LiNi_0.5Co_0.5O₂. LiNi_0.7Co_0.3O₂ synthesized at 850 °C has the largest first discharge capacity (142 mAh/g), followed in order by LiNi_0.9Co_0.1O₂ synthesized at 850 °C (113 mAh/g), and LiNi_0.5Co_0.5O₂ synthesized at 800 °C (109 mAh/g).     

Improvement of textured Bi1.6Pb0.4Sr2Co1.8Ox thermoelectric performances by metallic Ag additions

Bi_1.6Pb_0.4Sr₂Co_1.8O_x thermoelectric ceramics with small Ag additions (0, 1, and 3 wt%) have been successfully grown from the melt, using the laser floating zone method. Microstructure has shown a reduction in the amount of secondary phases and a better grain alignment with respect to the growth direction for an Ag content of 3 wt%. The microstructural evolution, as a function of Ag content, is confirmed with the electrical resistivity values, which show an important decrease for the 3 wt% Ag samples, leading to maximum power factor values of about 0.42 mW/K² m at 650 °C, which are among the best results obtained in this type of material.     

Synthesis of carbon coated Bi2O3 nanocomposite anode for sodium-ion batteries

Bi₂O₃ is a promising sodium storage material due to its high gravimetric specific capacity. However, Bi₂O₃ possesses lower electrochemical performance due to its poor electrical conductivity and structural integrity during Na⁺ insertion/extraction process. Here, we prepared a carbon coated Bi₂O₃ nanocomposite by a redox reaction and a carbon coating process. In this nanocomposite, the carbon layer can avoid the direct contact between Bi₂O₃ and electrolyte, which inhibits the repeated formation and decomposition of solid electrolyte interface film. Additionally, the carbon layer can enhance the electrical conductivity of Bi₂O₃ and suppress its aggregation due to its volume change during charge and discharge process. In addition, nano-sized Bi₂O₃ can reduce the transport distance of Na⁺ and electron. The nanocomposite shows excellent cycling performance and rate capability as anode for sodium-ion batteries. A high capacity of 421 mAh g⁻¹ can be maintained after 100 cycles at 1500 mA g⁻¹ and 392 mAh g⁻¹ can be shown at 3200 mAh g⁻¹.     

Improvement of thermoelectric performance of oxygen reduced Sr0.7Ba0.3Nb2O6-δ ceramics by Lanthanides doping

Thermoelectric properties of lantanide doped Sr_0.7Ba_0.3Nb₂O₆ ceramics were investigated in the temperature range from 323 K to 1073 K. A better electrical conductivity is obtained in the sample with larger ionic radius of doping element. Thus, the highest PF value is achieved in La-doped sample. The NbO₂ second phase is counterproductive to reduce the lattice thermal conductivity, so La-doped sample without impurity shows low thermal conductivity. Thus, La-doped sample shows an excellent thermoelectric performance ZT ∼ 0.35. The small average grain size and the nano-sized phases are observed in Gd and Dy doped samples, both of which contribute to scattering phonons, resulting in low thermal conductivities.     

Charge–discharge curves and discharge capacities of LiNi1−yCoyO2 synthesized from lithium carbonate and nickel and cobalt oxides

LiNi_1?yCo_yO₂ (y=0.1, 0.3, and 0.5) were synthesized by a solid-state reaction method at 800 °C and 850 °C using Li₂CO₃, NiO, and Co₃O₄ as the starting materials. The electrochemical properties of the synthesized LiNi_1?yCo_yO₂ were then investigated. For samples with the same composition, the particles synthesized at 850 °C were larger than those synthesized at 800 °C. The particles of all the samples synthesized at 850 °C were larger than those synthesized at 800 °C. LiNi_0.5Co_0.5O₂ synthesized at 850 °C had the largest first discharge capacity (159 mA h/g), followed in order by LiNi_0.7Co_0.3O₂ synthesized at 800 °C (158 mA h/g) and LiNi_0.9Co_0.1O₂ synthesized at 850 °C (151 mA h/g). LiNi_0.9Co_0.1O₂ synthesized at 850 °C had the best cycling performance with discharge capacities of 151 mA h/g at n=1 and 156 mA h/g at n=5.