On the green density, sintering behavior and electrical property of tape cast Ce0.9Gd0.1O1.95 electrolyte films

Gadolinia doped ceria (Ce_0.9Gd_0.1O_1.95, GDC) electrolyte films were tape cast from oxalate coprecipitated GDC powders, gelcast GDC powders and their mixtures, respectively, to evaluate the effects of the original particle size and distribution on the properties of the green and sintered GDC cast tapes. The apparent density of different original powders, as well as the green density, sintered behavior, and electrical conductivity of tapes cast from the various starting powders were investigated. Mixing the coprecipitated and the gelcast GDC powders not only results in a higher packing efficiency of particles in the loose powders, but also results in higher green and sintered densities of cast tapes. Furthermore, tapes cast from the 50/50 powder mixtures can be sintered to 96.2% of theoretical density at relatively low sintering temperature of 1400°C, whereas those from the oxalate coprecipitated and from the gelcast powders were only 89.7 and 94.1% dense, respectively. The ac impedance measurement shows that GDC films cast from the 50/50 powder mixture exhibit good electrical conductivity (4.2 and 6.0 S m⁻¹ at 700 and 800°C in air, respectively). The test results have revealed that high-density GDC films can be fabricated by tape casting technique at relatively low sintering temperature by optimizing the particle size distribution of the starting powders.     

Study on properties of CaO-SiO2-B2O3 system glass-ceramic

Low temperature co-fired ceramic (LTCC) is prepared by sintering a glass selected from CaO-SiO₂-B₂O₃ system, and its sintered bodies are characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS). It is found that the optimal sintering temperature for this glass-ceramic is 820 °C for 15 min, and the major phases of this material are CaSiO₃, CaB₂O₄ and SiO₂. The glass-ceramic possesses excellent dielectric properties: ?_r = 6.5, tan δ < 2 × 10⁻³ at 10 MHz, temperature coefficient of dielectric constant about −51 × 10⁻⁶ °C⁻¹ and coefficient of thermal expansion about 8 × 10⁻⁶ °C⁻¹ at 20-400 °C. Thus, this material is supposed to be suitable for the tape casting process and be compatible with Ag electrode, which could be used as the LTCC materials for the application in wireless communications.     

Physical properties of electrically conductive Sb-doped SnO2 transparent electrodes by thermal annealing dependent structural changes for photovoltaic applications

We have investigated the optical and electrical characteristics of antimony (Sb)-doped tin oxide (SnO₂) films with modified structures by thermal annealing as a transparent conductive electrode. The structural properties were analyzed from the relative void % by spectroscopic ellipsometry as well as the scanning electron microscopy images and X-ray diffraction patterns. As the annealing temperature was raised, Sb-doped SnO₂ films exhibited a slightly enhanced crystallinity with the increase of the grain size from 17.1 nm at 500 °C to 34.3 nm at 700 °C. Furthermore, the refractive index and extinction coefficient gradually decreased due to the increase in the relative void % within the film during the annealing. The resistivity decreased to 8.2 × 10⁻³ Ω cm at 500 °C, but it increased rapidly at 700 °C. After thermal annealing, the optical transmittance was significantly increased. For photovoltaic applications, the photonic flux density and the figure of merit over the entire solar spectrum were obtained, indicating the highest values of 5.4 × 10¹⁴ cm⁻² s⁻¹ nm⁻¹ at 1.85 eV after annealing at 700 °C and 340.1 μA cm⁻² Ω⁻¹ at 500 °C, respectively.     

Deposition of transparent conductive mesoporous indium tin oxide thin films by a dip coating process

Cetyltrimethyl ammonium bromide (CTAB) templated mesoporous indium tin oxide (ITO) thin films were deposited on quartz plates by an evaporation-induced self-assembly (EISA) process using a dip coating method. The starting solution was prepared by mixing indium chloride, tin chloride, and CTAB dissolved in ethanol. Five to fifty mole percent Sn-doped ITO films were prepared by heat-treatment at 400 °C for 5 h. The structural, adsorptive, electrical, and optical properties of mesoporous ITO thin films were investigated. Results indicate that the mesoporous ITO thin films have an ordered two-dimensional hexagonal (p6mm) structure, with nanocrystalline domains in the inorganic oxide framework. The continuous thin films have highly ordered pore sizes (>20 Å), high Brunauer-Emmett-Teller (BET) surface area up to 340 m²/g, large pore volume (>0.21 cm³/g), outstanding transparency in the visible range (>80%), and show a minimum resistivity of ρ = 1.2 × 10⁻² Ω cm.     

Dielectric properties of Ba3−xKxCaNb2O9−δ (0.5 < x < 1.25) (KBCN) double perovskites

We report synthesis, structure and dielectric properties of double perovskite-type Ba_3−xK_xCaNb₂O_9−δ (x = 0.5, 0.75, 1, 1.25) (KBCN). Powder X-ray diffraction (XRD) confirmed the formation of double perovskite-type structure and lattice constant decreases with increasing K in KBCN. AC impedance study showed a single semicircle over the investigated temperatures and frequencies in dry H₂, H₂ + 3% H₂O, 3% H₂O + N₂, while two semicircles were observed at low temperatures in air, which could be attributed to bulk and grain-boundary contributions. Unlike un-doped BCN, KBCN exhibits negligible grain-boundary and electrode effects to the total electrical properties and is consistent with perovskite-type K-doped BaZrO₃. The bulk dielectric constant and dielectric loss were found to increase with increasing K content in KBCN and also found to change with sintering temperature. Among the samples investigated, Ba_1.75K_1.25CaNb₂O_9−δ sintered at 1100 °C showed the highest dielectric constant of 65 at 10⁶ Hz and dielectric loss of 0.14 at 400 °C in air. Isothermal dielectric constant and electrical conductivity at 1 MHz were found to be independent at elevated temperatures, while vary at low-frequency and low temperatures. Below 700 °C, dielectric constant and dielectric loss decreases with increasing frequency, whereas an opposite trend was observed for the electrical conductivity.     

The effect of nitrogen on the properties of zinc nitride thin films and their conversion into p-ZnO:N films

Zinc nitride thin films were deposited by magnetron sputtering using ZnN target in plasma containing either N₂ or Ar gases. The rf-power was 100 W and the pressure was 5 mTorr. The properties of the films were examined with thermal treatments up to 550 °C in N₂ and O₂ environments. Films deposited in Ar plasma were opaque and conductive (ρ ∼ 10^− 1 to 10^− 2 Ω cm, N_D ∼ 10¹⁸ to 10²⁰ cm^− 3) due to excess of Zn in the structure. After annealing at 400 °C, the films became more stoichiometric, Zn₃N₂, and transparent, but further annealing up to 550 °C deteriorated the electrical properties. Films deposited in N₂ plasma were transparent but very resistive even after annealing. Both types of films were converted into p-type ZnO upon oxidation at 400 °C. All thermally treated zinc nitride films exhibited a shoulder in transmittance at around 345 nm which was more profound for the Ar-deposited films and particularly for the oxidized films. Zinc nitride has been found to be a wide band gap material which makes it a potential candidate for transparent optoelectronic devices.     

Synthesis and microwave dielectric properties of CaO-MgO-SiO2 submicron powders doped with Li2O-Bi2O3 by sol-gel method

Using Ca(NO₃)₂·4H₂O, Mg(NO₃)₂·6H₂O, Si(OC₂H₅)₄, LiNO₃ and Bi(NO₃)₃·5H₂O as raw materials, CaO-MgO-SiO₂ submicron powders were prepared at low temperature by sol-gel method. The crystallization temperature was decreased enormously by the introduction of Li-Bi liquid phase sintering aids into Ca-Mg-Si sol, and the powders with average particle sizes of 80-100 nm and 200-400 nm were obtained at the calcining temperature of 750 °C and 800 °C, respectively. The sintering characteristic and dielectric properties of powders calcined at 750 °C with different content of powders calcined at 800 °C were studied. When the content of powders calcined at 800 °C was 10 wt%, the dielectric ceramic sintered at 890 °C had compact structure, and possessed excellent microwave dielectric properties: ?_r = 7.16, Q × f = 25630 GHz, τ_f = −69.26 ppm/°C.     

Electrical and optical properties of nanocrystalline yttrium-doped hafnium oxide thin films

Yttrium-doped hafnium oxide (YDH) films have been produced by sputter-deposition by varying the growth temperature (T_s) from room-temperature (RT) to 400 °C. The electrical and optical properties of YDH films have been investigated. Structural studies indicate that YDH films grown at T_s = RT − 200 °C were amorphous and those grown at 300-400 °C are nanocrystalline. The crystalline YDH films exhibit the high temperature cubic phase of HfO₂. Spectrophotometry analysis indicates that all the YDH films are transparent. The band gap of YDH films was found to be in the range of 6.20-6.28 eV. Frequency variation of frequency dependent resistivity indicates the hopping conduction mechanism operative in YDH films. While the electrical resistivity (ρ_ac) is ~ 1 Ω-m at low frequencies (100 Hz), ρ_ac decreases to ~ 10^− 4 Ω-cm at higher frequencies (1 MHz).     

Growth and characterization of Bi2Se3 thin films by pulsed laser deposition using alloy target

Bi₂Se₃ thin films were deposited on the (100) oriented Si substrates by pulsed laser deposition technique at different substrate temperatures (room temperature −400 °C). The effects of the substrate temperature on the structural and electrical properties of the Bi₂Se₃ films were studied. The film prepared at room temperature showed a very poor polycrystalline structure with the mainly orthorhombic phase. The crystallinity of the films was improved by heating the substrate during the deposition and the crystal phase of the film changed to the rhombohedral phase as the substrate temperature was higher than 200 °C. The stoichiometry of the films and the chemical state of Bi and Se elements in the films were studied by fitting the Se 3d and the Bi 4d5/2 peaks of the X-ray photoelectron spectra. The hexagonal structure was seen clearly for the film prepared at the substrate temperature of 400 °C. The surface roughness of the film increased as the substrate temperature was increased. The electrical resistivity of the film decreased from 1 × 10⁻³ to 3 × 10⁻⁴ Ω cm as the substrate temperature was increased from room temperature to 400 °C.     

Preparation of LiFePO4/C composite powders by ultrasonic spray pyrolysis followed by heat treatment and their electrochemical properties

LiFePO₄ powders could be successfully prepared from a precursor solution, which was composed of Li(HCOO)·H₂O, FeCl₂·4H₂O and H₃PO₄ stoichiometrically dissolved in distilled water, by ultrasonic spray pyrolysis at 500 °C followed by heat treatment at sintering temperatures ranging from 500 to 800 °C in N₂ + 3% H₂ gas atmosphere. Raman spectroscopy revealed that α-Fe₂O₃ thin layers were formed on the surface of as-prepared LiFePO₄ powders during spray pyrolysis, and they disappeared after sintering above 600 °C. The LiFePO₄ powders prepared at 500 °C and then sintered at 600 °C exhibited a first discharge capacity of 100 mAh g⁻¹ at a 0.1 C charge-discharge rate. To improve the electrochemical properties of the LiFePO₄ powders, LiFePO₄/C composite powders with various amounts of citric acid added were prepared by the present method. The LiFePO₄/C (1.87 wt.%) composite powders prepared at 500 °C and then sintered at 800 °C exhibited first-discharge capacities of 140 mAh g⁻¹ at 0.1 C and 84 mAh g⁻¹ at 5 C with excellent cycle performance. In this study, the optimum amount of carbon for the LiFePO₄/C composite powders was 1.87 wt.%. From the cyclic voltammetry (CV) and AC impedance spectroscopy measurements, the effects of carbon addition on the electrochemical properties of LiFePO₄ powders were also discussed.     

Electrical and optical properties of indium tin oxide films prepared on plastic substrates by radio frequency magnetron sputtering

The influence of deposition power, thickness and oxygen gas flow rate on electrical and optical properties of indium tin oxide (ITO) films deposited on flexible, transparent substrates, such as polycarbonate (PC) and metallocene cyclo-olefin copolymers (mCOC), at room temperature was studied. The ITO films were prepared by radio frequency magnetron sputtering with the target made by sintering a mixture of 90 wt.% of indium oxide (In₂O₃) and 10 wt.% of tin oxide (SnO₂). The results show that (1) average transmission in the visible range (400-700 nm) was about 85%-90%, and (2) ITO films deposited on glass, PC and mCOC at 100 W without supplying additional oxygen gas had optimum resistivity of 6.35 × 10⁻⁴ Ω-cm, 5.86 × 10⁻⁴ Ω-cm and 6.72 × 10⁻⁴ Ω-cm, respectively. In terms of both electrical and optical properties of indium tin oxide films, the optimum thickness was observed to be 150-300 nm.     

Formation, sintering, and electrical conductivity of (Nd1−xCax)CrO3 (0≤x≤0.25) using citric acid as a gelling agent

In Ca²⁺-substituted NdCrO₃, single-phase perovskite compounds (Nd_1−xCa_x)CrO₃, where x=0-0.25, have been formed by a citric acid processing. (Nd_1−xCa_x)CrO₃ powders consisting of submicrometer-size particles are sinterable; dense materials can be fabricated by sintering for 2 h at 1700°C under atmospheric pressure. The relative densities, grain sizes, and electrical conductivities increase with increased Ca²⁺ content. (Nd_0.75Ca_0.25)CrO₃ materials show an excellent electrical conductivity of 1.9×10 S m⁻¹ at 1000°C.     

Dielectric and pyroelectric anisotropy in melt-quenched BaBi2(Nb1 − xVx)2O9 ceramics

The (0 0 l) textured BaBi₂(Nb_1 − xV_x)₂O₉ (where x = 0, 0.03, 0.07, 0.1 and 0.13) ceramics were fabricated via the conventional melt-quenching technique followed by high temperature heat-treatment (800-1000 °C range). The influence of vanadium content and sintering temperature on the texture development and relative density were investigated. The samples corresponding to the composition x = 0.1 sintered at 1000 °C for 10 h exhibited the maximum orientation of about 67%. The Scanning electron microscopic studies revealed the presence of platy grains having the a-b planes perpendicular the pressing axis. The dielectric constant and the pyroelectric co-efficient values in the direction perpendicular to the pressing axis were higher. The anisotropy in the dielectric constant is about 100 (at 100 kHz) at the dielectric maximum temperature and anisotropy in the pyroelectric co-efficient is about 50 μC cm⁻² °C⁻¹ in the vicinity of pyroelectric anomaly for the sample corresponding to the composition x = 0.1 sintered at 1000 °C. Higher values of the dielectric loss and electrical conductivity were observed in the direction perpendicular to the pressing axis which is attributed to the high oxygen ion conduction in the a-b planes.     

Microstructure and electrical conductivity of LaNi0.6Fe0.4O3 prepared by combustion synthesis routes

The continuing development of new materials suitable for solid oxide fuel cells operating at about 650-800 °C is of great interest in recent days. The present investigation deals with the development of a perovskite composition-LaNi_0.6Fe_0.4O₃ (LNF)-prepared following two combustion synthesis routes: citrate-gel (LNC) and urea (LNU). The powders were sintered over a wide temperature range (900-1400 °C) and sintering behavior for LNC and LNU was compared. The thermal expansion coefficient (TEC), electrical and microstructural characteristics of LNF was thoroughly investigated. Electrical conductivities were found to be one and a half times higher than that of most commonly used cathode material, La(Sr)MnO₃. Moreover, the TEC value of LNF was found to be ≈11.4×10⁻⁶ K⁻¹ at 800 °C. The study opens up a possibility of using LNF as a promising cell component for SOFC.     

From tin oxalate to (Fe, Co, Nb)-doped SnO2: Sintering behavior, microstructural and electrical features

Highly reactive SnO₂-doped nanocrystalline powders with average particle size of 20 nm and specific surface areas above 30 m²/g were obtained through the polymeric precursor method with tin oxalate (SnC₂O₄) as a chloride-free precursor for SnO₂. Powders and sintered discs were characterized by means of X-ray powder diffraction (XRD), SEM and TEM. The influence of Co and Fe on the microstructure development and on the electrical properties of dense SnO₂-based ceramics was studied. Co and Fe species were found to decrease in more than 70 °C the sintering temperature of SnO₂ with respect to mixed oxide procedures. Secondary phases enriched in Co and Fe were detected and identified in sintered samples with XRD. Current-voltage curves were registered for electrical characterization. Doping with iron increased the electrical breakdown field and a nonlinearity coefficient of 20 was achieved.     

Study on properties of BaxSmyTi7O20 ceramics with CaO-SiO2-B2O3 glass

The effect of CaO-SiO₂-B₂O₃ (CSB) glass addition on the sintering temperature and dielectric properties of Ba_xSm_yTi₇O₂₀ ceramics has been investigated using X-ray diffraction, scanning electron microscopy and differential thermal analysis. The CSB glass starts to melt at about 970 °C, and a small amount of CSB glass addition to Ba_xSm_yTi₇O₂₀ ceramics can greatly decrease the sintering temperature from about 1350 to about 1260 °C, which is attributed to the formation of liquid phase. It is found that the dielectric properties of Ba_xSm_yTi₇O₂₀ ceramics are dependent on the amount of CSB glass and the microstructures of sintered samples. The product with 5 wt% CSB glass sintered at 1260 °C is optimal in these samples based on the microstructure and the properties of sintering product, when the major phases of this material are BaSm₂Ti₄O₁₂ and BaTi₄O₉. The material possesses excellent dielectric properties: ?_r = 61, tan δ = 1.5 × 10⁻⁴ at 10 GHz, temperature coefficient of dielectric constant is −75 × 10⁻⁶ °C⁻¹.     

Structural and electrical properties of sputtered indium-zinc oxide thin films

In this study, indium-zinc oxide (IZO) thin films have been prepared at a room temperature, 200 and 300 °C by radio frequency magnetron sputtering from a In₂O₃-12 wt.% ZnO sintered ceramic target, and their dependence of electrical and structural properties on the oxygen content in sputter gas, the substrate temperature and the post-heat treatment was investigated. X-ray diffraction measurements showed that amorphous IZO films were formed at room temperature (RT) regardless of oxygen content in sputter gas, and micro-crystalline and In₂O₃-oriented crystalline films were obtained at 200 and 300 °C, respectively. From the analysis on the electrical and the structural properties of annealed IZO films under Ar atmosphere at 200, 300, 400 and 500 °C, it was shown that oxygen content in sputter gas is a critical parameter that determines the local structure of amorphous IZO film, stability of amorphous phase as well as its eventual crystalline structure, which again decide the electrical properties of the IZO films. As-prepared amorphous IZO film deposited at RT gave specific resistivity as low as 4.48 × 10^− 4 Ω cm, and the highest mobility value amounting to 47 cm²/V s was obtained from amorphous IZO film which was deposited in 0.5% oxygen content in sputter gas and subsequently annealed at 400 °C in Ar atmosphere.     

Preparation and electrochemical properties of multiwalled carbon nanotubes-nickel oxide porous composite for supercapacitors

Porous nickel oxide/multiwalled carbon nanotubes (NiO/MWNTs) composite material was synthesized using sodium dodecyl phenyl sulfate as a soft template and urea as hydrolysis-controlling agent. Scanning electron microscopy (SEM) results show that the as-prepared nickel oxide nanoflakes aggregate to form a submicron ball shape with a porous structure, and the MWNTs with entangled and cross-linked morphology are well dispersed in the porous nickel oxide. The composite shows an excellent cycle performance at a high current of 2 A g⁻¹ and keeps a capacitance retention of about 89% over 200 charge/discharge cycles. A specific capacitance approximate to 206 F g⁻¹ has been achieved with NiO/MWNTs (10 wt.%) in 2 M KOH electrolyte. The electrical conductivity and the active sites for redox reaction of nickel oxide are significantly improved due to the connection of nickel nanoflakes by the long entangled MWNTs.     

Preparation and characterization of Y2O3–Sm2O3 co-doped ceria electrolyte for IT-SOFCs

Y₂O₃–Sm₂O₃ co-doped ceria (YSDC) powder was synthesized by a gel-casting method using Ce(NO₃)₃·6H₂O, Sm₂O₃ and Y₂O₃ as raw materials. Phase structure of the synthesized powders was characterized by X-Ray diffraction analysis. Sinterability of the powders was investigated by testing the relative density and observing the microstructure of the sintered YSDC samples. Electrical conductivity of the sintered YSDC samples was measured using impedance spectra method. Single solid oxide fuel cells based on the YSDC electrolyte were also assembled and tested. The results showed that YSDC powders with single-phase fluorite structure can be obtained by calcining the dried gelcasts at temperature above 800 °C. Average particle size of the YSDC powder is 50–100 nm. Relative density of more than 95% of the theoretical can be achieved by sintering the YSDC compacts at temperature above 1400 °C. The sintered YSDC sample has an ionic conductivity of 4.74 × 10⁻² S cm⁻¹ at 800 °C in air. Single fuel cells based on the YSDC electrolyte with 50 μm in thickness were tested using humidified hydrogen as fuel and air as oxidant, and maximum power densities of about 190 and 112 mW cm⁻² were achieved at 700 and 600 °C, respectively.     

Synthesis and characterization of nanocrystalline CdZnO thin films prepared by sol-gel dip-coating process

Nanocrystalline Cd_xZn_1 − xO thin films with different Cd volume ratios in solution (x = 0, 0.25, 0.50, 0.75 and 1) have been deposited on glass substrate by sol-gel dip-coating method. The as-deposited films were subjected to drying and annealing temperatures of 275 °C and 450 °C in air, respectively. The prepared films were characterized by X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy, UV-vis spectroscopy and dc-electrical measurements. The results show that the samples are polycrystalline and the crystallinity of the films enhanced with x. The average grain size is in the range of 20-53 nm. The atomic percent of Cd:Zn was found to be 9.50:1.04, 6.20:3.77 and 4.42:6.61 for x = 0.75, 0.50 and 0.25, respectively. It was observed that the transmittance and the band gap decreased as x increased. All the films exhibit n-type electrical conductivity. The resistivity (ρ) and mobility (μ) are in the range of 3.3 × 10² − 3.4 × 10^− 3 Ω cm, and 1.5 − 45 cm² V^− 1 s^− 1 respectively. The electron density lies between 1.26 × 10¹⁶ and 0.2 × 10²⁰ cm^− 3.