Facile synthesis of AlOx dielectrics via mist-CVD based on aqueous solutions

Aluminum oxide (AlO_x) thin films were synthesized by mist-chemical vapor deposition (mist-CVD) using aluminum acetylacetonate (Al(acac)₃) dissolved in an aqueous solvent mixture of acetone and water. Nitrogen gas was used to purge the precursor solution and growth rates between 7.5–13.3 nm/min were achieved at substrate temperatures of 250–350 °C. The AlO_x layers deposited at temperatures below 350 °C exhibit 3–5 at% residual carbon levels, however those grown at 350 °C exhibit only 1–2 at% carbon impurity. Reasonable dielectric properties were obtained in the latter, with a dielectric constant (κ) of ~ 7.0, breakdown field of ~ 9 MV/cm and relatively low leakage current density of ~ 8.3×10⁻¹⁰ A/cm².     

Semiconducting properties of cold sintered V2O5 ceramics and Co-sintered V2O5-PEDOT:PSS composites

Recently we established a sintering approach, namely Cold Sintering Process (CSP), to densify ceramics and ceramic-polymer composites at extraordinarily low temperatures. In this work, the microstructures and semiconducting properties of V₂O₅ ceramic and (1-x)V₂O₅-xPEDOT:PSS composites cold sintered at 120 °C were investigated. The electrical conductivity (25 °C), activation energy (25 °C), and Seebeck coefficient (50 °C) of V₂O₅ are 4.8 × 10⁻⁴ S/cm, 0.25 eV, and −990 μV/K, respectively. The conduction mechanism was studied using a hopping model. A reversible metal-insulator transition (MIT) was observed with V₂O₅ samples exposed to a N₂ atmosphere, whereas in a vacuum atmosphere, no obvious MIT could be detected. With the addition of 1–2 Vol% PEDOT:PSS, the electrical conductivity (50 °C) dramatically increases from 10⁻⁴ to 10⁻³ ∼ 10⁻² S/cm, and the Seebeck coefficient (50 °C) shifts from −990 to −(600 ∼ 250) μV/K. All the results indicate that CSP may offer a new processing route for the semiconductor electroceramic development without a compromise to the all-important electrical properties.     

Carbon oxidation characteristics of yttrium manganate catalyst prepared via urea decomposition

YMnO₃ is a hexagonal crystal characterized by high carbon oxidation activity. In this study, carbon black powder has been directly oxidized at temperatures as low as 250 °C with the active oxygen species generated by YMnO₃ catalyst. The activation energies measured for the non-catalyzed and YMnO₃-catalyzed carbon oxidation reactions were 160 kJ mol⁻¹ and 131 kJ mol⁻¹, respectively. During combustion testing of particulate matter in a ceramic form coated with YMnO₃, the captured soot was continuously purified at a temperature of 350 °C.     

Crystal structure,thermal expansion and electrical conductivity of perovskite oxides BaxSr1−xCo0.8Fe0.2O3−δ (0.3 ≤ x ≤ 0.7)

Ba_xSr_1−xCo_0.8Fe_0.2O_3−δ (0.3 ≤ x ≤ 0.7) composite oxides were prepared and characterized. The crystal structure, thermal expansion and electrical conductivity were studied by X-ray diffraction, dilatometer and four-point DC, respectively. For x ≤ 0.6 compositions, cubic perovskite structure was obtained and the lattice constant increased with increasing Ba content. Large amount of lattice oxygen was lost below 550 °C, which had significant effects on thermal and electrical properties. All the dilatometric curves had an inflection at about 350–500 °C, and thermal expansion coefficients were very high between 50 and 1000 °C with the value larger than 20 × 10⁻⁶ °C⁻¹. The conductivity were larger than 30 S cm⁻¹ above 500 °C except for x > 0.5 compositions. Furthermore, conductivity relaxation behaviors were also investigated at temperature 400–550 °C. Generally, Ba_0.4Sr_0.6Co_0.8Fe_0‘2O_3−δ and Ba_0.5Sr_0.5Co_0.8Fe_0.2O_3−δ are potential cathode materials.     

Synthesis,characterization, and electrical conduction of 10 mol% Dy2O3-doped CeO2 ceramics

Well-densified 10 mol% Dy₂O₃-doped CeO₂ (20DDC) ceramics with average grain sizes of ∼0.12–1.5 μm were fabricated by pressureless sintering at 950–1550 °C using a reactive powder thermally decomposed from a carbonate precursor, which was synthesized via a carbonate coprecipitation method employing nitrates as the starting salts and ammonium carbonate as the precipitant. Electrical conductivity of the ceramics, measured by the dc three-point impedance method, shows a V-shape curve against the average grain size. The sample with the smallest grain size of 0.12 μm exhibits a high conductivity of ∼10^−1.74 S/cm at the measurement temperature of 700 °C, which is about the same conduction level of the micro-grained 10 mol% Sm₂O₃- or Gd₂O₃-doped CeO₂, two leading electrolyte materials.     

Preparation of dual-phase composite BaCe0.8Y0.2O3/Ce0.8Y0.2O2 and its application for hydrogen permeation

Dual-phase ceramic membranes composed of BaCe_0.8Y_0.2O₃ (BCY) and Ce_0.8Y_0.2O₂ (CYO) were successfully synthesized by solid state reaction method for hydrogen permeation. The influences of the BCY/CYO volume ratios on phase composition, microstructure, chemical stability and electrical property were investigated. The hydrogen permeation of the dual-phase composite was characterized as a function of temperature and feed side hydrogen partial pressure. The results showed that there was no reaction between the two constituent oxides observed under the preparation conditions. The dual-phase composite with different BCY/CYO volume ratios after sintering at 1550 °C exhibited dense structure, as well as good stability in 4% H₂/Ar, wet Ar and pure CO₂ atmosphere. The conductivity of the dual-phase composite increased with the content of CYO increasing and 30BCY–70CYO exhibited the highest total conductivity of 2.6×10⁻² S cm⁻¹ at 800 °C in 4% H₂/Ar. The hydrogen permeability of 30BCY–70CYO sample was improved as the temperature and the hydrogen partial pressure in feed gas increased. The hydrogen permeation flux of 1.7 μmol cm⁻² s⁻¹ was achieved at 850 °C.     

Investigation of the electrical conductivity of sintered monoclinic zirconia (ZrO2)

High-density monoclinic ZrO₂ was manufactured through sintering at ~1200 °C by using nanosized powders. Then, the electrical conductivity was measured at a range of high temperatures (700–900 °C) by electrical impedance spectroscopy (EIS). For the as-sintered monoclinic ZrO₂, the measured electrical conductivity was 3.2×10⁻⁵ s/cm (for 80% TD) and 4.4×10⁻⁵ s/cm (for 89% TD) at 900 °C. After aging at 900 °C for 100 h, the electrical conductivity of the monoclinic ZrO₂ of 80%-TD decreased by more than 50%. However, after reheating at 1200 °C for 1 h, approximately 80% of the conductivity was recovered compared to the value of the as-sintered monoclinic ZrO₂. The pure monoclinic crystal structure was retained despite the aging and reheating treatment. Based on microstructural observations of the aged and reheated monoclinic ZrO₂, the changes in electrical conductivity after aging and reheating were explained by the formation and recovery of micro-cracks, respectively.     

Structural and electrical properties of Sr2NaNb4O13 thin film grown by electrophoretic method using nanosheets synthesized from K(Sr2Na)Nb4O13 compound

Sr₂NaNb₄O₁₃⁻ (SNNO⁻) nanosheets were exfoliated from the K(Sr₂Na)Nb₄O₁₃ compound that was synthesized at 1200 °C. The SNNO⁻ nanosheets were deposited on a Pt/Ti/SiO₂/Si substrate at room temperature by the electrophoretic method. Annealing was conducted at various temperatures to remove organic defects in the SNNO film. A crystalline SNNO phase without organic defects was formed in the film annealed at 500 °C. However, a SrNb₂O₆ secondary phase was formed in the films annealed above 600 °C, probably due to the evaporation of Na₂O. The SNNO thin film annealed at 500 °C showed a dielectric constant of 74 at 1.0 MHz with a dielectric loss of 2.2%. This film also exhibited a low leakage current density of 9.0 × 10⁻⁸ A/cm² at 0.6 MV/cm with a high breakdown electric field of 0.72 MV/cm.     

Synthesis of BaCeO3 and BaCe0.9Y0.1O3−δ from mixed oxalate precursors

An oxalate precipitation route is proposed for the synthesis of BaCe_1−xY_xO₃ (x = 0 and 0.1) after calcination at 1100 °C. The precipitation temperature (70 °C) was a determinant parameter for producing a pure perovskite phase after calcination at 1100 °C for 1 h. TG/DTA measurements showed that the co-precipitated (Ba, Ce and Y) oxalate had a different thermal behaviour from single oxalates. Despite a simple grinding procedure, sintered BaCe_0.9Y_0.1O_3−δ pellets (1400 °C, 48 h) presented 90.7% of relative density and preliminary impedance measurements showed an overall conductivity of around 2 × 10⁻⁴ S cm⁻¹ at 320 °C.     

Sintering,microstructural development,and electrical properties of gadolinia-doped ceria electrolyte with bismuth oxide as a sintering aid

A considerable reduction (≥250 °C) in the sintering temperature, enhancement of the sintering density, and a slight improvement of the electrical properties, can be achieved by using bismuth oxide in the range of 0.2 to 2 wt.%, as a sintering aid for gadolinia-doped ceria (GDC) ceramic electrolytes. Dilatometric experiment (CHR) and SEM observations indicate that a liquid phase-assisting sintering mechanism contributes to the improvement in sintering density for bismuth oxide concentrations exceeding 0.5 wt.%. The addition of small amount of Bi₂O₃ ≤0.5 wt.% also results in the achievement of highly dense ceramic bodies (≥99% of theoretical density) after sintering at 1200 °C for 4 h, which indicates that the addition of Bi₂O₃ to gadolinia-doped ceria promoted the sintering process by a cooperating volume diffusion-liquid phase-assisting mechanism. Based on the lattice constant data, the solid solubility limit of Bi₂O₃ in gadolinia-ceria is, probably, lower than 1.0 wt.%. Grain size also increased with increasing Bi₂O₃ content up to 0.5 wt.% and then it decreased with further addition of Bi₂O₃. The addition of the smaller amounts of bismuth oxide, i.e., ≤1.0 wt.% Bi₂O₃ slightly enhanced the total ionic electrical conductivity of the gadolinia-doped ceria electrolyte. The sintering temperature strongly influenced the electrical conductivity of the doped-GDC ceramics. The best sample was that containing 1.0 wt.% Bi₂O₃ sintered at 1400 °C for 2 h which had an ionic electrical conductivity of 4 S m⁻¹ at 700 °C, and an activation energy of 0.58 eV for the oxide-ion conduction process in air.     

Temperature dependence of electrical conductivity of a green porcelain mixture

AC conductivity of a green porcelain body was investigated using impedance spectroscopy over a temperature range of 100–950 °C. The results showed that during the heating, conductivity at 100–200 °C increased mainly arising from H⁺ and OH⁻ ions generated from adsorbing physical water. The activation energy increased below the dehydroxylation of clay resulting from movement of monovalent ions. At the dehydroxylation of clay, a combination of H⁺, OH⁻ and monovalent ions dominated the conductivity. The activation energy rose to 1.14 eV (600–950 °C) controlled by diffusion of Na⁺, and K⁺ ions. During the cooling, conductivity showed single activation energy with 0.86 eV resulting from denser microstructure and change in mineralogical constituents and the heat treated porcelain sample showed higher electrical conductivity at the same temperature. Understanding conduction behaviour of the green porcelain enabled more accurate control of furnace temperature in flash sintering, a process which relies on electrical conductivity at high temperatures.     

Synthesis and characterization of NH4PO3 based composite with superior proton conductivity for intermediate temperature fuel cells

In this work, we prepared NH₄PO₃/MO₂ (MSi, Ti) composite materials with various amounts of TiO₂ using a sol–gel method, which are potential for application as electrolytes for intermediate temperature fuel cells (150–250 °C). The effect of the amount of TiO₂ on the conductivities of the composite was investigated systematically by an impedance spectroscopy within the temperature range of 50–275 °C under different atmospheres. The composite SiTiO10APP (10 mol% TiO₂) showed high proton conductivity, 0.001–0.043 S cm^?1 at 150–250 °C. The maximum conductivities are 0.043 S cm^?1 at 225 °C under humid H₂ and 0.0085 S cm^?1 at 175 °C under humid air, respectively. A thermogravimetric analysis showed the composite had high thermal stability below 300 °C. Moreover, it was found that the microstructure has significant effect on the conductivity of the composites at higher temperature.     

Enhanced thermal conductive 3D-SiC/Al-Si-Mg interpenetrating composites fabricated by pressureless infiltration

A high thermal conductive 3D-SiC/Al-Si-Mg interpenetrating composite (IPC) with three dimensional mutually interpenetrated structure was fabricated by mold-forming and pressureless infiltration method. Al-15Si-10Mg was used as the infiltration aluminum alloy. The obtained composite was treated with a T6 procedure. The composed phases, microstructure, thermal conductivity, mechanical strength and fractography of the prepared 3D-SiC/Al-Si-Mg IPC were either analyzed or measured with X-ray diffraction (XRD), optical metallography, laser thermal conductivity instrument, universal testing machine, field emission electron scanning microscopy (SEM) with energy dispersive spectroscopy (EDS), high-resolution transmission electron microscopy (HRTEM), and etc. The results showed that both SiC ceramic and aluminum alloy phases distribute evenly and form a three-dimensional mutually interpenetrated structure in the obtained IPC. No clear brittle and harmful Al₄C₃ phase was found in the composite. The obtained IPC contains a SiC volume fraction of 67 vol% and has the properties of a density of 3.02 g/cm², a thermal conductivity of 233.6 W/(m °C), a thermal expansion coefficient (RT~300 °C) of 7.03×10⁻⁶/°C and a bending strength of 288 MPa.     

Deformation behavior and joining of a MgF2 optical ceramic

Compressive deformation behavior of a polycrystalline magnesium fluoride (MgF₂) ceramic was investigated at temperatures ranging from 760 to 830 °C in an argon atmosphere at strain rates between 2 × 10⁻⁶ and 4 × 10⁻⁵ s⁻¹. Steady-state flow stresses increased with increasing strain rates and ranged between 2 and 38 MPa. Stress exponents of ≈1.4 ± 0.2 were determined at temperatures >760 °C, indicative of a viscous diffusion-controlled deformation mechanism. Activation energy, determined from flow stress as a function of temperature, at a constant strain rate, was ≈476 ± 60 kJ/mol. Self-joining by plastic deformation of MgF₂ was demonstrated at 830 °C at a strain rate of 5 × 10⁻⁶ s⁻¹. The joined samples were characterized by optical transmission measurements and their transmittivity was ≈80% of the unjoined sample in the 2.5–8 μm wavelength range.     

Colossal dielectric constant and extremely low loss in T-type La2CuO4−δ ceramics

In this paper, we present the colossal dielectric behavior of T-type La₂CuO_4-δ (LCO) ceramics synthesized in fine grained form using wet chemical “Pechini” process, followed by annealing in argon (Ar) atmosphere. The colossal dielectric constant (CDC) (10³≤ε_r′≤10⁴) displayed over a wide frequency (1 Hz ≤f ≤ 1 MHz) and temperature (−100–150 °C) ranges was equally complimented by the remarkably low dielectric losses (0.01≤ tan δ≤0.1) for LCO ceramics, which are the lowest reported dielectric losses for the T-type La₂CuO₄ system, so far. This substantial decrease in losses could be attributed to the enhanced resistivity (10⁸−10⁹ Ω.cm) of the sample. Further, the origin of CDC, in this non-ferroelectric LCO, was investigated using combined ac impedance and modulus spectroscopy. The study revealed heterogeneity in electrical microstructure of LCO, with semiconducting grains and insulating grain boundaries. This electrically heterogeneous microstructure could give rise to the Internal Barrier Layer Capacitance (IBLC) mechanism, thus leading to apparent CDC in LCO.     

Synthesis and electrical properties of Ce1−xGdxO2−x/2 (x = 0.05–0.3) solid solutions prepared by a citrate–nitrate combustion method

Ce_1?xGd_xO_2?x/2 (GDC) powders with different Gd³⁺ contents (x = 0.05–0.3) were prepared by a simple citrate–nitrate combustion method. The influence of the Gd³⁺ doping content on the crystal structure and the electrical properties of GDC were examined. Many analysis techniques such as thermal analysis, X-ray diffraction, nitrogen adsorption analysis, scanning electron microscopy and AC impedance analysis were employed to characterize the GDC powders. The crystallization of the GDC solid solution occurred below 350 °C. The GDC powders calcined at 800 °C showed a typical cubic fluorite structure. The lattice parameter of GDC exhibited a linear relationship with the Gd³⁺ content. As compared with that sintered at other temperatures, the GDC pellet that sintered at 1300 °C had a high relative density of 97%, and showed finer microstructure. The conductivity of GDC was firstly increased and then decreased with the increase of the Gd³⁺ content. The sintered GDC sample with the Gd³⁺ content of 0.25 exhibited the highest conductivity of 1.27 × 10^?2 S cm^?1 at 600 °C.     

Reprint of "Palladium Ohmic contact on hydrogen-terminated single crystal diamond film"

Contact properties of Palladium (Pd) on the surface of hydrogen-terminated single crystal diamond were investigated with several treatment conditions. 150 nm Pd pad was deposited on diamond surface by thermal evaporation technique, which shows good Ohmic properties with the specific contact resistivity (ρ_c) of 1.8 × 10^− 6 Ω cm² evaluated by Transmission Line Model. To identify the thermal stability, the sample was annealed in Ar ambient from 300 to 700 °C for 3 min at each temperature. As the temperature increased, ρ_c firstly decreased to 4.93 × 10⁻⁷ Ω cm² at 400 °C and then increased. The barrier height was evaluated to be − 0.15 eV and − 0.03 eV for as-deposited and 700 °C annealed sample by X-ray photoelectron spectroscopy analysis. Several surface treatments were also carried out to determine their effect on ρ_c, among which HNO₃ vapor treated sample indicates a lower value of 5.32 × 10⁻⁶ Ω cm².     

Synthesis and characterisation of MnGaxCr2−xO4 (0.1≤x≤1) spinels as potential electrode support materials for intermediate-temperature solid oxide fuel cells

MnGa_xCr_2−xO₄ (MGCO, x=0.1, 0.2, 0.4, 0.8, 1) oxides are synthesised using a citric acid nitrate combustion method. The influence of Ga substitution on the structure, electrical conductivity and electrochemical performance are systematically investigated. The chemical and thermal compatibility of MGCO materials with yttrium-stabilised zirconia (YSZ) are also studied. All the samples exhibit a single phase spinel structure. Thermal expansion coefficients (TECs) of the MGCO oxides are in the range of 9–12×10⁻⁶ K⁻¹, indicating a good thermal match with the YSZ electrolyte. No chemical reactions are detected between MGCO materials and YSZ, indicating their good chemical compatibility with YSZ. The magnitude of electrical conductivity of all the obtained samples is in the order of about 10⁻³ S cm⁻¹at 800 °C measured in air. The polarisation resistance reaches a value as low as 5.2 Ω cm² for x=0.4 at 800 °C. The preliminary results demonstrate that MGCO materials could be used as electrode support materials for intermediate-temperature solid oxide fuel cells (IT-SOFCs).     

Effect of substrate temperature on structural and electrical properties of BaZr0.2Ti0.8O3 lead-free thin films by pulsed laser deposition

Barium zirconate titanate (BaZr_0.2Ti_0.8O₃, BZT) 250 nm thick thin films were fabricated by pulsed laser deposition and the influence of the substrate temperature on their preferred orientation, microstructure, morphology and dielectric properties was investigated. Dielectric measurements indicated the (1 1 0)-oriented BZT thin films deposited at 750 °C to show good dielectric properties with high dielectric constant (~500 at 100 kHz), low loss tangent (<0.01 at 100 kHz), and superior tunability (>70% at 400 kV/cm), while the largest figure of merit was 78.8. The possible microstructural background responsible for the high dielectric constant and tenability is discussed. In addition, thin films deposited at 750 °C with device quality factor of 8738 and dielectric nonlinearity coefficient of 1.66×10⁻¹⁰ J/C⁴m⁵ were demonstrated.     

Structural,optical, and electrical properties of conducting p-type transparent Cu–Cr–O thin films

Cu–Cr–O films were prepared by DC magnetron co-sputtering using Cu and Cr targets on quartz substrates. The films were then annealed at temperatures ranging from 400 °C to 900 °C for 2 h under a controlled Ar atmosphere. The as-deposited and 400 °C-annealed films were amorphous, semi-transparent, and insulated. After annealing at 500 °C, the Cu–Cr–O films contained a mixture of monoclinic CuO and spinel CuCr₂O₄ phases. Annealing at 600 °C led to the formation of delafossite CuCrO₂ phases. When the annealing was further increased to temperatures above 700 °C, the films exhibited a pure delafossite CuCrO₂ phase. The crystallinity and grain size also increased with the annealing temperature. The formation of the delafossite CuCrO₂ phase during post-annealing processing was in good agreement with thermodynamics. The optimum conductivity and transparency were achieved for the film annealed at approximately 700 °C with a figure of merit of 1.51×10⁻⁸ Ω⁻¹ (i.e., electrical resistivity of up to 5.13 Ω-cm and visible light transmittance of up to 58.3%). The lower formation temperature and superior properties of CuCrO₂ found in this study indicated the higher potential of this material for practical applications compared to CuAlO₂.