Development of mixed conducting dense nickel/Ca-doped lanthanum zirconate cermet for gas separation application

La_1.95Ca_0.05Zr₂O_7-δ (LCZ) and Ni–LCZ cermet have been prepared by combustion synthesis and conventional solid state mixing methods respectively. Both the materials are sintered in air and controlled atmosphere (5% H₂ in Ar). The density obtained for the material sintered at 1400 °C in controlled atmosphere is found to be more than 99.5%. This sintering temperature (1400 °C) is considered to be much lower compared to the conventional sintering temperature. The corresponding total conductivity for such Ni–LCZ cermet materials is ～400 S/cm measured at 750 °C having 40 vol% of Ni and 60 vol% LCZ.     

Synthesis of La0.85Sr0.15Ga0.85Mg0.15O2.85 materials for SOFC applications by acrylamide polymerization

The La_0.85Sr_0.15Ga_0.85Mg_0.15O_2.85 (LSGM) powders are synthesized using a novel method based on acrylamide polymerization technique. The phase evolution was determined by using XRD analysis. The sintering property was studied by using dilatability analysis. The electrical conductivity was also measured. XRD pattern indicates that the perovskite phase is formed at 1000 °C, and the impurity phase, LaSrGa₃O₇ still exists in the sintered sample. The shrinkage curve shows that the fast sintering temperature is 1432 °C. The sinterability was investigated as a function of sintering time and temperature. The results show that the densification rate of the sample was fast at first 5 h. The electrical conductivity was 0.093 S/cm at 800 °C. And a transitional temperature in the Arrhenius plot is 700 °C.     

Sintering temperature-induced electrical properties of (Ba0.90Ca0.10)(Ti0.85Zr0.15)O3 lead-free ceramics

Effects of the sintering temperature on the microstructure and electrical properties of (Ba_0.90Ca_0.10)(Ti_0.85Zr_0.15)O₃ (BCTZ) lead-free piezoelectric ceramics have been studied, where these ceramics were prepared by the conventional oxide-mixed method at varied sintering temperatures from 1300 °C to 1500 °C. These BCTZ ceramics exhibits a phase transition from a rhombohedral phase to the coexistence of rhombohedral and tetragonal phases with an increase of sintering temperature. With an increase of sintering temperature, their relative density and average grain size gradually increase, and electrical properties are improved greatly. These BCTZ ceramics sintered at ～1440 °C have optimum electrical properties: d₃₃ ～ 442 pC/N and k_p ～ 48.9%, making it a promising material for lead-free piezoelectric ceramics.     

Influence of the synthesis method on the porosity,microstructure and electrical properties of La0.7Sr0.3MnO3 cathode materials

Lanthanum strontium manganite (La_1 ? xSr_xMnO₃, LSM) has been studied as a promising material for application as a cathode in solid oxide fuel cells. In the present work La_0.7Sr_0.3MnO₃ nanopowders were synthesized by three different methods (combustion, citrate and solid-state) and characterized by thermal analysis, X-ray diffraction, physical adsorption of N₂ and scanning electron microscopy. All powders exhibited single LSM phase formation with crystallite sizes in the range of 12–20 nm. Nanopowders were sintered at 1100 °C to produce porous pellets. The porosity, particle size and microstructure of LSM sintered bodies are strongly dependent on the preparation methodology. The samples synthesized by combustion and citrate methods presented smaller particle sizes and higher porosity after sintering than that derived from solid-state synthesis. However, the electrical conductivity, measured by two-probe technique, was very similar for all three samples.     

Synthesis and characterization of nanocrystalline ferroelectric Sr0.8Bi2.2Ta2O9 by conventional and microwave sintering: A comparative study

In recent years mechanical activation technique has been utilized to synthesize the nanocrystalline form of compounds resulting in enhancement in the properties. Also, microwave sintering is being preferred over conventional sintering due to rapid processing and uniform temperature distribution throughout the specimen. In the present work, nanocrystalline non-stoichiometric strontium bismuth tantalate (SBT) of the composition Sr_0.8Bi_2.2Ta₂O₉ ferroelectric ceramics were synthesized by microwave sintering process (with sintering temperatures of 1000 °C and 1100 °C) and conventional solid state reaction process (with sintering temperature of 1100 °C) with an objective of comparing the properties of the synthesized specimens by the two processes. X-ray diffraction analysis shows the formation of single phase layered perovskite structure formation by both the processes. Scanning electron microscopy reveals the formation of a finer granular microstructure in the specimen synthesized by microwave sintering compared to that in the specimen prepared by conventional sintering. The specimen prepared by microwave sintering process exhibits improved electrical properties with higher dielectric constant, higher piezoelectric and pyroelectric coefficients and lower dielectric loss.     

Electrical conductivity and stability of A-site deficient (La,Sc) co-doped SrTiO3 mixed ionic-electronic conductor

Mixed ionic–electronic conductors with high ionic conductivity play an important role in modern solid-state ionic devices. The ionic conductivity of SrTiO₃-based materials can be significantly improved by creating deficiency on the A-site and acceptor-doping on the B-site. We report in this paper a remarkable enhancement of ionic conductivity, sinterability and thermal stability of (La, Sc) co-doped SrTiO₃ by creating deficiency on the A-site. The ionic conductivity of (La_0.3Sr_0.7)_0.95Sc_0.10Ti_0.90O_3–δ varies from 0.005 S/cm at 500 °C to 0.01 S/cm at 700 °C and to 0.018 S/cm at 950 °C in 5%H₂/Ar. These values are nearly eight times higher than that of La_0.3Sr_0.7TiO_3–δ at T ≥ 700 °C. The A-site deficiency in (La, Sc) co-doped SrTiO₃ also improves the thermal and electrical stabilities in various atmospheres. A possible charge compensation mechanism among defects in the (La_0.3Sr_0.7)_0.95Sc_0.10Ti_0.90O_3–δ is also discussed.     

Microstructures and electrical properties of calcium substituted LaFeO3 as SOFC cathode

Mixed ionic and electronic conductors of La_1−xCa_xFeO_3−δ (LCF, x =0.0–0.5) have been investigated using X-ray diffraction (XRD), scanning electron microscopy (SEM), dilatometry, and four-probe electrical conductivity measurements. Ca substitution on La site reduces the LaFeO₃ sinterability and the cell volume of this orthorhombic crystal. Dense samples for property studies can be sintered at 1320 °C. Nevertheless, the sintering temperature is near the decomposition temperature of LCF for those solid solutions of x ≥ 0.3. The LCF decomposition is evident when a La-poor secondary phase, not detected in XRD, was revealed in SEM micrographs of 1270 °C thermally etched samples of x ≥ 0.3. Dilatometric studies demonstrate linear increments in thermal expansion with increasing temperature in samples of x ≤ 0.2, while show strange bendings in thermal expansion curves of x = 0.4 and 0.5. The bending in thermal expansion indicates influences of the secondary phase. The TEC value of compositions of x ≤ 0.2 is between 10.8 and 11.7 × 10⁻⁶ °C⁻¹. The LCF electrical conductivity increases with the Ca content and its temperature dependence can be described by the small polaron hopping mechanism. The composition around x = 0.15 promises to be a superior cathode for SOFC since it thermally matches with 8 mol% YSZ and 10 mol% Dy, Er substituted LAMOX electrolytes and possesses electrical conductivity near 90 S cm⁻¹ at 800 °C.     

Powder synthesis and properties of LiTaO3 ceramics

The LiTaO₃ powders with sub micrometer grade grain size have been synthesized successfully using a molten salt method. Lithium tantalate began to form at 400 °C reaction temperature and transformed to pure phase without residual reactants when it was processed at 500 °C for 4 h in static air. The undoped LiTaO₃ ceramics with a Curie temperature about 663 °C were obtained by pressureless sintering at 1300 °C for 3 h. The relative dielectric constant (ɛ_r) increases from 50 to 375 at temperature ranging from 30 to 663 °C and then decreases quickly as the temperature increases above 663 °C. The ceramics shows a relative dielectric constant of 49.4, a dielectric loss factor (tan δ) of 0.007, a coercive field (Ec) of 28.66 kV/cm and a remnant polarization (Pr) of 32.48 μC/cm² at room temperature.     

Synthesis of lanthanum zirconium oxide nanomaterials through composite-hydroxide-mediated approach

A novel thermal barrier coating material, lanthanum zirconium oxide (La₂Zr₂O₇) has been synthesized through the composite-hydroxide-mediated method at low temperature. The phase structures, morphology, thermal stability and thermal conductivity of the as-synthesized La₂Zr₂O₇ were investigated systematically. The X-ray diffraction (XRD) patterns revealed a single phase with cubic pyrochlore structure for La₂Zr₂O₇ after treated at 1300 °C for 100 h. The transmission electron microscope (TEM) and scanning electron microscope (SEM) analyses showed that the sample was made up of sphere-like nanoparticles with the size between 50 and 100 nm. Furthermore, the thermal analysis result demonstrated the La₂Zr₂O₇ sample had high thermal stability even at 1300 °C. As the temperature increased to 1200 °C, the thermal conductivity value could be as low as 1.75 W m^?1 K^?1. Due to the high-temperature stability and lower thermal conductivity, the La₂Zr₂O₇ material is expected to be a promising candidate for the use of thermal barrier coatings.     

Preparation and characterization of the bismuth sodium titanate (Na0.5Bi0.5TiO3) ceramic doped with ZnO

This study investigates effects of the zinc oxide (ZnO) addition and the sintering temperature on the microstructure and the electrical properties (such as dielectric constant and loss tangent) of the lead-free piezoelectric ceramic of bismuth sodium titanate (Na_0.5Bi_0.5TiO₃), NBT, which was prepared using the mixed oxide method. Three kinds of starting powders (such as Bi₂O₃, Na₂CO₃ and TiO₂) were mixed and calcined. This calcined NBT powder and a certain weight percentage of ZnO were mixed and compressed into a green compact of NBT–ZnO. Then, this green compact of NBT–ZnO was sintered to be a disk doped with ZnO, and its characteristics were measured. In this study, the calcining temperature was 800 °C, the sintering temperatures ranged from 1000 to 1150 °C, and the weight percentages of ZnO doping included 0.0, 0.5, 1.0, and 2.0 wt%. At a fixed wt% ZnO, the grain size increases with increase in the sintering temperature. The largest relative density of the NBT disk obtained in this study is 98.3% at the calcining temperature of 800 °C, the sintering temperature of 1050 °C, and 0.5 wt% ZnO addition. Its corresponding dielectric constant and loss tangent are 216.55 and 0.133, respectively.     

A study on the phase transformation of the nanosized hydroxyapatite synthesized by hydrolysis using in situ high temperature X-ray diffraction

The biodegradable hydroxyapatite (HA) was synthesized by hydrolysis and characterized using high temperature X-ray diffraction (HT-XRD), differential thermal analysis and thermogravimetry (DTA/TG), and scanning electron microscopy (SEM). The in situ phase transformation of the HA synthesized from CaHPO₄·2H₂O (DCPD) and CaCO₃ with a Ca / P = 1.5 in 2.5 M NaOH_(aq) at 75 °C for 1 h was investigated by HT-XRD between 25 and 1500 °C. The HA was crystallized at 600 °C and maintained as the major phase until 1400 °C. The HA steadily transformed to the α-tricalcium phosphate (α-TCP) which became the major phosphate phase at 1500 °C. At 700 °C, the minor CaO phase appeared and vanished at 1300 °C. The Na⁺ impurity from the hydrolysis process was responsible for the formation of the NaCaPO₄ phase, which appeared above 800 °C and disappeared at 1200 °C.     

Hydrothermal-induced growth of Ca10V6O25 crystals with various morphologies in a strong basic medium at different temperatures

The Ca₁₀V₆O₂₅ crystals with various morphologies were synthesized by a facile hydrothermal method in a strong basic medium. The effects of the pH of synthesizing solution, hydrothermal reaction temperature and time on the morphology and crystallinity of Ca₁₀V₆O₂₅ powders were investigated. The as-synthesized powders were characterized by X-ray diffraction, scanning electron microscopy, transmission electron microscopy, UV–vis spectrophotometer and vibrating sample magnetometer. The experimental results demonstrate that phase-pure Ca₁₀V₆O₂₅ powders could be hydrothermally obtained at temperatures ranging from 120 °C to 180 °C for 12–48 h with the pH ≥ 12.5 of synthesizing solution. The morphology of Ca₁₀V₆O₂₅ powders was strongly dependent on the synthesis parameters, such as pH, temperature and time. The Ca₁₀V₆O₂₅ microspheres were obtained at 180 °C for 48 h with the pH = 12.5 of synthesizing solution. The UV–vis diffuse reflectance spectra have shown that the Ca₁₀V₆O₂₅ powders efficiently absorb UV light with an absorption edge at about 380 nm. All the samples noticeably exhibit a superparamagnetic behavior with a nearly zero magnetic remanence (remanent magnetization). The hydrothermally synthesized Ca₁₀V₆O₂₅ powders may be employed as a potential candidate in novel electronic and biomedical applications.     

Optical,electrical properties,characterization and synthesis of Ca2Co2O5 by sucrose assisted sol gel combustion method

Sol–gel combustion method has been used as an efficient and simple method to synthesize pure Ca₂Co₂O₅ (CCO-225) ceramic powder using sucrose which play a dual role as the gelling agent and combustion fuel. The advantage of this method is simple low cost and environmental friendly. The synthesized sample is sintered at various temperatures the products were characterized by powder X-ray diffraction (XRD), Thermogravimetric and differential thermal analysis (TGA-DTA), Fourier transformer infrared spectroscopy (FTIR), Scanning electron microscope (SEM) and UV–Visible diffuse reflectance spectroscopy (DRS). X-ray diffraction pattern of sintered sample at 800 °C confirmed the formation of single phase Ca₂Co₂O₅ and also it is proved in thermal analysis. SEM image indicates the obtained samples are diffused platelet like morphology and its grain size will be in the range of 150–300 nm. CCO-225 ceramic material has a wide range of optical and electronic applications due to its wide band gap energy of 3.50 eV. The dielectric constant, dielectric loss and AC conductivity were analyzed at different temperatures and frequencies of the applied field. The AC conductivity studies carried out in the frequency range of 50 Hz to 5 MHz at various temperatures from 30 °C to 400 °C. The result reveals that the space charge polarization leads for conduction mechanism.     

Synthesis and magnetocaloric properties of La0.85K0.15MnO3 nanoparticles

In this paper, La_0.85K_0.15MnO₃ nanoparticles were successfully synthesized at relatively low calcinated temperature from a polyaminocarboxylate complex precursor with diethylenetriaminepentaacetic acid (H₅DTPA) as ligand, and the magnetocaloric properties were investigated. The phase transformation, chemical composition, and microstructure of La_0.85K_0.15MnO₃ nanoparticles were characterized by X-ray diffraction (XRD), thermogravimetric (TG), differential scanning calorimetry (DSC), transmission electron microscopy (TEM) and electron diffraction (ED). The results revealed that La_0.85K_0.15MnO₃ nanoparticles calcined at temperatures within the range of 600–1000 °C are of pure single-phase rhombohedral structure and the grain sizes were precisely controlled by varing the calcined temperature. The relationship between magnetocaloric properties and the calcined temperature of La_1?xK_xMnO₃ nanoparticles was also investigated systematically. From the magnetic measurements as function of temperature and magnetic applied field, we have discovered that the Curie temperature T_C is 274.5 K and is independent of the calcined temperature. From the measurements and calculation of isothermal magnetization at different temperatures, the maximum magneticentropy changes close to T_C (274 K) of the samples calcined at 600 °C, 800 °C and 1000 °C are 2.02, 3.06 and 3.56/kg K at H = 2T, respectively. Also La_0.85K_0.15MnO₃ nanoparticle displays a second-order phase transition. These results suggest that this material is a candidate for use as an active for magnetic refrigerent around the room temperature.     

Effect of V2O5 additive to 0.4SrTiO3–0.6La(Mg0.5Ti0.5)O3 ceramics on sintering behavior and microwave dielectric properties

The effect of V₂O₅ addition on the microwave dielectric properties and the microstructures of 0.4SrTiO₃–0.6La(Mg_0.5Ti_0.5)O₃ ceramics sintered for 5 h at different sintering temperature were investigated systematically. It was found that the sintering temperature was effectively lowered about 200 °C by increasing V₂O₅ addition content. The grain sizes, bulk density as well as microwave dielectric properties were greatly dependent on sintering temperature and V₂O₅ content. The 4ST–6LMT ceramics with 0.25% V₂O₅ sintered at 1400 °C for 5 h in air exhibited optimum microwave dielectric properties of ɛ_r = 50.7, Q × f = 15049.6 GHz, T_f = −1.7 ppm/°C.     

Influence of yttrium dopant on the synthesis of ultrafine AlN powders by CRN route from a sol–gel low temperature combustion precursor

Y-doped ultrafine AlN powders were synthesized by a carbothermal reduction nitridation (CRN) route from precursors of Al₂O₃, C and Y₂O₃ prepared by a sol–gel low temperature combustion technology. The Y dopant reacted with alumina and thus forming yttrium aluminate of AlYO₃, Al₃Y₅O₁₂ and Al₂Y₄O₉, which formed a liquid at about 1400 °C and promoted the transformation of Al₂O₃ to AlN and the growth of AlN particles. Compared with the conventional solid CRN process, Y dopant reduced the synthesis temperature by 150 °C, and Al₂O₃ transformed to AlN completely at 1450 °C. The content of Y dopant had little effect on the synthesis temperature of AlN whereas it influenced the phase of Y compounds in the products. As the Y/Al molar ratio was in the range of 0.007648–0.022944, the particle sizes of Y-doped AlN powders synthesized at 1450 °C were 150–300 nm.     

Temperature stable microwave dielectric ceramic 0.3Li2TiO3–0.7Li(Zn0.5Ti1.5)O4 with ultra-low dielectric loss

In the present work, the 0.3Li₂TiO₃–0.7Li(Zn_0.5Ti_1.5)O₄ ceramic was prepared via the conventional solid state reaction route, and the phase composition, microstructure, and sintering behavior were investigated. The ceramic sample sintered at 1100 °C for 2 h demonstrated high microwave dielectric performance with a relative permittivity of 23.5, a high quality factor (Qf) ~ 88,360 GHz (at 7.4 GHz), and near zero temperature coefficient of resonant frequency about ? 0.8 ppm/°C. These results indicate that the 0.3Li₂TiO₃–0.7Li(Zn_0.5Ti_1.5)O₄ ceramic might be a good candidate for dielectric resonators, filters and other microwave electronic device applications.     

Comparison of electrochemical performances of LiFePO4/C composite materials by two preparation routes

This study reports on the preparation of LiFePO₄/C composite materials prepared by the hydrothermal and sol–gel processes for comparison. The synthesis condition on the hydrothermal process was performed at 170 °C for 19 h. The polystyrene (PS) polymer was used as a carbon source; the PS was added at a range of 0–5 wt.%. The temperature of the post-thermal process was set at 750–850 °C. The citric acid (denoted as CA) was used as the reducing agent and the carbon source in the sol–gel process. The temperatures of the sintering process were set at a range of 650–850 °C. The optimal sintering temperature was at 850 °C for 12 h in the hydrothermal process; the optimal carbon residue content was approximately 3.20 wt.%. It was revealed that the highest discharge capacity of LiFePO₄/C composites by the hydrothermal process at 0.1 C is 163 mAh g^?1. The optimal sintering temperature was found to be at 750 °C for the sol–gel process. The highest carbon content was approximately 11.94 wt.% as the molar ratio of CA is 1.0. The highest discharge capacity of LiFePO₄/C composites by the sol–gel process at 0.1 C was approximately 130.35 mAh g^?1.     

Effect of characteristics of (Sm,Ce)O2 powder on the fabrication and performance of anode-supported solid oxide fuel cells

Effect of characteristics of Sm_0.2Ce_0.8O_1.9 (SDC) powder as a function of calcination temperature on the fabrication of dense and flat anode-supported SDC thin electrolyte cells has been studied. The results show that the calcination temperature has a significant effect on the particle size, degree of agglomeration, and sintering profiles of the SDC powder. The characteristics of SDC powders have a significant effect on the structure integrity and flatness of the SDC electrolyte film/anode substrate bilayer cells. The SDC electrolyte layer delaminates from the anode substrate for the SDC powder calcined at 600 °C and the bilayer cell concaves towards the SDC electrolyte layer for the SDC powder calcined at 800 °C. When the calcinations temperature increased to 1000 °C, strongly bonded SDC electrolyte film/anode substrate bilayer structures were achieved. An open-circuit voltage (OCV) of 0.82–0.84 V and maximum power density of ～1 W cm^?2 were obtained at 600 °C using hydrogen as fuel and stationary air as the oxidant. The results indicate that the matching of the onset sintering temperature and maximum sintering rate temperature is most critical for the development of a dense and flat Ni/SDC supported SDC thin electrolyte cells for intermediate temperature solid oxide fuel cells.     

Low-firing of BiSbO4 microwave dielectric ceramic with V2O5–CuO addition

Effects of 1.0 wt.% V₂O₅–CuO mixture addition on the sintering behavior, phase composition and microwave dielectric properties of BiSbO₄ ceramics have been investigated. BiSbO₄ ceramics can be well densified below temperature about 930 °C with 1.0 wt.% V₂O₅–CuO mixtures addition with different ratios of CuO to V₂O₅. The formation of BiVO₄ phase and substitution of Cu²⁺ can explain the decrease of sintering temperature. Dense BiSbO₄ ceramics sintered at 930 °C for 2 h exhibited good microwave dielectric properties with permittivity between 19 and 20.5, Qf values between 19,000 and 40,000 GHz and temperature coefficient of resonant frequency shifting between ?71.5 ppm °C^?1 and ?77.8 ppm °C^?1. BiSbO₄ ceramics could be a candidate for microwave application and low temperature co-fired ceramics technology.