Applicability of Field Plate in Double Channel GaN HEMT for Radio-Frequency and Power-Electronic Applications

Silicon - In the present communication, for the first time, applicability of Field Plate (FP) for Double Channel (DC) AlGaN/GaNHEMT is demonstrated. Impact of design space parameters such as field...     

Investigation of Influence of SiN and SiO2 Passivation in Gate Field Plate Double Heterojunction Al0.3Ga0.7N/GaN/Al0.04Ga0.96N High Electron Mobility Transistors

Silicon - This research article reports the operational characteristics of gate field plate double heterojunction (DH) high electron mobility transistors (HEMTs) using SiN (SiO2) passivation...     

Microstructure and electrical conductivity of La0.9Sr0.1 Ga0.8Mg0.2O2.85-Ce0.8Gd0.2O1.9 composite electrolytes for SOFCs

(100-x) wt.% La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 - x wt.% Ce_0.8Gd_0.2O_1.9 (x = 0, 5, 10, 20) electrolytes were prepared by solid-state reaction. The composition, microstructure, and electrical conductivity of the samples were investigated. At 300 ~ 600°C, the pure La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 electrolyte has a higher conductivity compared to the composite electrolytes, but at 650 ~ 800°C the 95 wt.% La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 - 5 wt.% Ce_0.8Gd_0.2O_1.9 composite electrolyte presents the highest conductivity, reaching 0.035 S cm⁻¹ at 800°C. The cell performances based on La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85-Ce_0.8Gd_0.2O_1.9 electrolytes were measured using Sr₂CoMoO₆-La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 as anode and Sr₂Co_0.9Mn_0.1NbO₆ -La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 as cathode, respectively. At 800°C, the measured open-circuit voltages are higher than 1.08 V, and the maximum power density and current density of the fuel cell prepared with 95 wt.% La_0.9Sr_0.1 Ga_0.8Mg_0.2O_2.85 - 5 wt.% Ce_0.8Gd_0.2O_1.9 electrolyte reach 192 mW cm⁻² and 720 mA cm⁻², respectively.     

Performance of IT‐SOFC with Ce0.9Gd0.1O1.95 Functional Layer at the Interface of Ce0.9Gd0.1O1.95 Electrolyte and Ni‐Ce0.9Gd0.1O1.95 Anode

In this paper we present results for a high power density IT‐SOFC and a method for dispersing nanosized Ce_0.9Gd_0.1O_1.95 (GDC) particles at the GDC electrolyte and Ni‐GDC anode interface. Dispersed nanosized particles were deposited to form an anode functional layer (AFL). Anode supports were prepared by tape casting of large micron‐sized NiO powder and sub micron‐sized GDC powder without pore former. For the cathode a La_0.6Sr_0.4Co_0.2Fe_0.8O_{3 – δ} (LSCF)‐GDC composite was used. Without an AFL the open circuit potential (OCP) and the maximum power density were 0.677 V and 407 mW cm^–2, respectively, at 650 °C using 30 sccm of hydrogen and air flow‐rate. With an AFL the OCP and the maximum power density increased to 0.796 V and 994 mW cm^–2, respectively, at the same temperature. Two point probe impedance measurements revealed that the AFL fabricated by the proposed method not only increased the OCP but also reduced the electrode polarisation by 68%. The effect of gas flow‐rate is also present in this paper. When hydrogen and air flow‐rate is increased to 90 sccm, the sample with AFL obtained 1.57 W cm^–2 at 650 °C.     

Synthesis of La0.9Sr0.1Ga0.8Mg0.2O2.85 powder by gel combustion route with two-step doping strategy

A two-step doping strategy was applied to the synthesis of La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85 (LSGM1020) powder by a gel combustion method. The Mg-doped LaGaO₃ powder was prepared in the first step, and Sr incorporation in the Mg-doped LaGaO₃ powder was done in the second step to obtain the final LSGM1020 powder. The two-step procedure is effective in preparing higher purity powders than the traditional one-step procedure. Rietveld refinement of X-ray powder diffraction (XRD) patterns shows that incorporation of Mg in LaGaO₃ in the first step enlarges the LaGaO₃ lattice: this facilitates the incorporation of Sr in the second doping step and thus high purity powder is obtained. Relatively phase pure LSGM1020 powder with only 3.1% of LaSrGaO₄ was obtained after calcination at 1300 °C for 5 h. Therefore, the two-step doping strategy is an effective procedure for the preparation of LSGM powders with high Sr- and Mg-doping levels.     

Theoretical investigation of mechanical and thermal properties of MPO4 (M = Al,Ga)

Minimum lattice thermal conductivities and mechanical properties of polymorphous MPO₄ (M = Al, Ga) are investigated by first principles calculations. The theoretical minimum thermal conductivities are found to be 1.02 W (m K)^?1 for α-AlPO₄, 1.20 W (m K)^?1 for β-AlPO₄, 0.87 W (m K)^?1 for α-GaPO₄ and 0.88 W (m K)^?1 for β-GaPO₄. The lower thermal conductivities in comparison to YSZ can be attributed to the lattice phonon scattering due to the framework of heterogeneous bonds. In addition, the low shear-to-bulk modulus ratio for both β-AlPO₄ (0.38) and β-GaPO₄ (0.30) is observed. Our results suggest their applications as light-weight thermal insulator and damage-tolerant/machinable ceramics.     

Effects of ZrO2 on the photoluminescence of 0.5 at% Eu:(Y0.9La0.1)2O3 transparent ceramics

Zr-codoped 0.5 at% Eu: (Y_0.9La_0.1)₂O₃ ceramics sintered in H₂-reducing atomsphere, together with the ceramics with annealing treatment, were fabricated by solid-state reactions and the effects of Zr codoping on these materials’ photoluminescence examined. The obtained emission spectra showed that Zr codoping adjust the materials’ photoluminescence with UV excitation and a logical explanation was proposed. The results suggested that an Eu-doped, yttrium-lanthanum oxide transparent ceramic with Zr in low concentration appeared to have promising potential in modern lighting applications.     

Deposition of mechanically hard amorphous carbon nitride films with high [N] / ([N] + [C]) ratio

Mechanically hard amorphous carbon nitride films were prepared by a combination of negative radio frequency (RF) bias voltage (− V_RF) applied to a substrate and chemical vapor deposition using a decomposition reaction of BrCN with a microwave discharge flow of Ar. A pulsed operation of − V_RF was effective when − V_RF > 40 V to avoid excess sputtering of films. The [N] / ([N] + [C]) ratios of films were ≈ 0.5 irrespective of the application of − V_RF. The maximum hardness was 36 ± 10 GPa for the film obtained under the conditions of − V_RF = 100 V, a pulse period of 1000 s, and a pulse-on time of 800 s. According to the IR spectra, the intensity of the stretching vibration of the CN bond increased by the application of − V_RF. The Raman spectra showed increases in the relative intensity and width of the D-band. From these observations, the mechanism of film hardening was discussed.     

Computational Analysis of Oxide Ion Conduction in Orthorhombic Perovskite Structured La0.9A0.1InO2.95 (A = Ca,Sr and Ba)

Oxide ion conduction in orthorhombic perovskite structured oxides, La_0.9A_0.1InO_2.95 (A = Ca, Sr and Ba) is analyzed using molecular dynamics simulation. Factors influencing oxide ion conductivity of the compositions considered are analyzed using radial distribution function, bond energies between dopant and oxide ions, and the diffusion path. It is known that perovskite oxides with smaller ion size mismatch between host and dopant ions have higher electrical conductivities. However, exceptions exist, such as a La_0.9A_0.1InO_2.95 (A = Ca, Sr and Ba) system, where high electrical conductivities occur with large ion size mismatches. Based on this study, a dopant with smaller ion than host ion results in the formation of strong ionic bonds with oxide ions, suggesting that the A‐site dopant should be larger than the host ion for forming weaker O–A bonds. Consequently, the trade‐off between ion size mismatch and O–A bond needs to be considered for enhancing oxide ion conductivity of perovskite oxides.     

Mullite-type EMBO4: synthesis,structural, optical,and vibrational properties of rare tin(II) borates with M = Al and Ga

Metal tin-(II)-borates are rarely studied mainly due to the susceptibility of either oxidation into tin(IV) or disproportionation into elemental tin(0) and tin(IV). We report mullite-type SnAlBO₄ and SnGaBO₄ ceramics produced by conventional solid-state synthesis in sealed quartz tubes at low pressure of 10^–7 MPa. Both compounds are isostructural to PbAlBO₄ as confirmed by Rietveld refinements of powder X-ray data. The crystal structures are highly influenced by the stereochemical activity of the 5s² lone electron pair of the Sn²⁺ cation measured by the Wang–Liebau eccentricity parameter. To further consolidate the structural features ¹¹⁹Sn Mössbauer, solid state NMR, Raman, IR and UV/vis spectroscopic measurements are performed. The ¹¹⁹Sn Mössbauer isomer shifts and the quadrupole splitting values confirm the SnO₄ coordination and Sn(II) valence states. Solid state ¹¹B, ²⁷Al and ¹¹⁹Sn NMR spectra provided insights into the local crystal-chemical environment. The vibrational properties are discussed from group theoretical analysis to mode assignments. SnAlBO₄ and SnGaBO₄, respectively, possess an electronic band gap of 3.73(9) and 3.21(4) eV calculated from the diffuse reflectance UV/Vis spectra.     

Comparison of hydrothermal corrosion behavior of SiC with Al2O3 and Al2O3 + Y2O3 sintering additives

Fully dense SiC bulks with Al₂O₃ and Al₂O₃ + Y₂O₃ sintering additives were prepared by spark plasma sintering and the effect of sintering additives on the hydrothermal corrosion behavior of SiC bulks was investigated in the static autoclave at 400°C/10.3 MPa. The SiC specimen with Al₂O₃ sintering additive exhibited a higher weight loss and followed a linear law. However, the SiC specimen with Al₂O₃ + Y₂O₃ additive exhibited a lower weight loss and followed a parabolic law, indicating that the corrosion kinetic and mechanism were different for these two SiC bulks. Further examination revealed that, a deposited layer was formed on the surface of SiC specimen with Al₂O₃ + Y₂O₃ sintering additive after corrosion, which can effectively protect the SiC specimen from further corrosion, and thereby improved the corrosion resistance of the SiC specimen with Al₂O₃ + Y₂O₃ sintering additive.     

Operation of a 10 kWth chemical-looping combustor during 200 h with a CuO–Al2O3 oxygen carrier

Chemical-looping combustion (CLC) is an attractive technology to decrease greenhouse gas emissions affecting global warming, because it is a combustion process with inherent CO₂ separation and therefore without needing extra equipment for CO₂ separation and low penalty in energy demand. The CLC concept is based on the split of a conventional combustion of gas fuel into separate reduction and oxidation reactions. The oxygen transfer from air to fuel is accomplished by means of an oxygen carrier in the form of a metal oxide circulating between two interconnected reactors. A Cu-based material (Cu14Al) prepared by impregnation of γ-Al₂O₃ as support with two different particle sizes (0.1–0.3 mm, 0.2–0.5 mm) was used as an oxygen carrier for a chemical-looping combustion of methane. A 10 kWth CLC prototype composed of two interconnected bubbling fluidized bed reactors has been designed, built in and operated at 800 °C during 100 h for each particle size. In the reduction stage full conversion of CH₄ to CO₂ and H₂O was achieved using oxygen carrier-to-fuel ratios above 1.5. Some CuO losses as the active phase of the CLC process were detected during the first 50 h of operation, mainly due to the erosion of the CuO present in external surface of the alumina particles. The high reactivity of the oxygen carrier maintained during the whole test, the low attrition rate detected after 100 h of operation, and the absence of any agglomeration problem revealed a good performance of these CuO-based materials as oxygen carriers in a CLC process.     

Fabrication of Solid Oxide Fuel Cells with a Thin (La0.9Sr0.1)0.98(Ga0.8Mg0.2)O3–δ Electrolyte on a Sr0.8La0.2TiO3 Support

This paper describes Sr_0.8La_0.2TiO₃ (SLT)‐supported solid oxide fuel cells with a thin (La_0.9Sr_0.1)_0.98Ga_0.8Mg_0.2O_3–δ (LSGM) electrolyte and porous LSGM anode functional layer (AFL). Optimized processing for the SLT support bisque firing, LSGM electrolyte layer co‐firing, and LSGM AFL colloidal composition is presented. Cells without a functional layer yielded a power density of 228 mW cm^–2 at 650 °C, while cells with a porous LSGM functional layer yielded a power density of 434 mW cm^–2 at 650 °C. Cells with an AFL yielded a higher open circuit voltage, possibly due to reduced Ti diffusion into the electrolyte. Infiltration produced Ni nanoparticles within the support and AFL, which proved crucial for the electrochemical activity of the anode. Power densities increased with increasing Ni loadings, reaching 514 mW cm^–2 at 650 °C for 5.1 vol.% Ni loading. Electrochemical impedance spectroscopy analysis indicated that the cell resistance was dominated by the cathode and electrolyte resistance with the anode resistance being relatively small.     

Visible light-induced photocatalytic activity of delafossite AgMO2 (M = Al, Ga, In) prepared via a hydrothermal method

Delafossite-structured oxides AgMO₂ (M = Al, Ga, In) were successfully synthesized using fluoro(ethylene-propylene) (FEP) pouch via a facile hydrothermal method. The obtained samples were characterized by X-ray diffraction (XRD), BET surface area measurement, UV–vis diffuse reflectance spectroscopy (DRS), scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The photocatalytic activity of the as-prepared samples was evaluated by the degradation of rhodamine B (RhB) and methyl orange (MO) under visible light irradiation. All three samples showed photocatalytic activity for RhB and MO degradation under visible light irradiations and their photocatalytic activity followed the order of AgInO₂ > AgGaO₂ > AgAlO₂. The relative high photocatalytic activity of AgInO₂ can be attributed to its high quantity of the surface hydroxyl groups. The photocatalytic mechanism of AgInO₂ was proposed and its stability was also investigated.     

Production and deposition of CN radicals to produce amorphous carbon nitride films with high [N]/([N] + [C]) ratio

The dissociative excitation reaction of BrCN with the microwave discharge flow of Ar was studied on the basis of the laser-induced fluorescence (LIF) spectroscopy and electrostatic-probe analysis. The CN(A²Π_i − X²Σ⁺), 4-0, 5-1, and 7-2 bands were observed by LIF, from which the density of CN(X²Σ⁺) was evaluated as 9.9 × 10¹⁷ m^− 3. The intensities of the LIF spectra of the ³P₁–³P₂ and ³P₂–³P₂ transitions of Ar were negligibly weak under the steady-state condition introducing BrCN. Therefore, the contribution of Ar(³P₂) was negligible to the dissociation process. A kinetic analysis based on the densities of CN(X²Σ⁺) and electrons revealed that the dissociation proceeds almost uniquely via the charge transfer from Ar⁺ followed by the ion–electron recombination and that the dominant quenching process of CN(X²Σ⁺) was reaction with BrCN.     

Residence Time Distribution of Steady and Pulsed Flow in a Parallel‐Plate Channel with Staggered Fins

The residence time distribution (RTD) in a parallel‐plate channel with staggered fins for both steady and pulsed flow conditions was experimentally determined. Dispersion and tank‐in‐series models were also adopted to characterize the system. The process fluid was water and the experiments were performed at room temperature. A steady Reynolds number Re ranging from 100 to 1000 was studied. The pulsating flow was generated using a frequency f of 6–20 Hz and an amplitude A of 0–2.3 mm. A pulse injection of sodium chloride solution was used as a tracer and the response in the form of electrical conductivity was measured at the outlet stream. The flow in the staggered finned channel approaches nearly plug‐flow behavior with either higher steady‐flow velocity or superposition of oscillation at low Re.     

The influence of tetrahedral ordering on the microwave dielectric properties of Sr0.05Ba0.95Al2Si2O8 and (M = Al, Ga, M′ = Si, Ge) ceramics

The feldspars Sr_0.05Ba_0.95Al₂Si₂O₈, BaAl₂Ge₂O₈ and BaGa₂Si₂O₈ with S.G. I2/c, and BaGa₂Ge₂O₈ with S.G. P2₁/a, were studied by means of crystal structural and microstructural analyses and dielectric measurements. All the investigated densely sintered single-phase feldspars exhibited a permittivity () of 7–8 and a temperature coefficient of resonant frequency (τ_f) from −20 to −30 ppm/°C. In contrast to the and τ_f the dielectric losses were found to be dependent on the annealing conditions. In Sr_0.05Ba_0.95Al₂Si₂O₈ the Qxf values increased from 42,500 to 92,600 GHz when the annealing time at 1400 °C was increased from 1 to 162 h. Such a difference in the Qxf values as a result of various annealing conditions was attributed to different degrees of tetrahedral ordering. In contrast to aluminosilicate feldspars, Ge-containing feldspars can be sintered and ordered at low temperature. In BaAl₂Ge₂O₈ the Qxf values decreased when the sintering temperature exceeded the order-disorder I2/c ↔ C2/m phase-transition temperature. The BaGa₂Si₂O₈ and BaGa₂Ge₂O₈ feldspars exhibited a rapid decrease of Qxf values when the annealing temperature approached the melting point. However, the BaAl₂Ge₂O₈ and BaGa₂Ge₂O₈ can regain their high Qxf values by annealing at 1000 °C. The BaGa₂Ge₂O₈ stood out from the other investigated feldspars, with a sintering temperature of 1100 °C, Qxf values of 100,000–150,000 GHz and a τ_f of −26 ppm/°C.     

Electrostrictive and Dielectric Response in Lead Magnesium Niobate–Lead Titanate (0.9PMN · 0.1PT) and Lead Lanthanum Zirconate Titanate (PLZT 9.5/65/35) under Variation of Temperature and Electric Field

In situ measurements of electrostrictive strain and effective dielectric constant for two ferroelectric relaxor materials, lead magnesium niobate–lead titanate (0.9PMN · 0.1PT) and lead lanthanum zirconate titanate (PLZT 9.5/65/35), were performed in the temperature ranges near their respective mean Curie points under the variation of applied electric field. The measurement results show that the polarization-related electrostrictive coefficients Q_ij are not constant under variation of temperature and electric field. The observed anomaly in Q_ij indicates the dynamic behavior of the existing micropolar domains and its coupling to local defect structure. The data also support the idea that at temperatures far above the mean Curie point, there is still a substantial amount of micropolar domain and the response of the relaxor materials at the experimental temperature range is from the combined contributions due to induced polarization and micropolar domain flipping.     

Sintering and Dielectric Properties of Li2O–B2O3–Al2O3–SiO2 Glass‐Added (Ca0.7Sr0.3O)1.03(Ti0.1Zr0.9)O2 for Copper Electrode

When 1.5 wt% of Li₂O–B₂O₃–SiO₂ and 1.5 wt% of Li₂O–B₂O₃–Al₂O₃ glass‐added (Ca_0.7Sr_0.3O)_1.03(Ti_0.1Zr_0.9)O₂ batch was ball milled for 10~30 h followed by sintering at 950°C in flowing N₂‐10%H₂ atmosphere, an apparent density of approximately 4.5 g/cm³, a dielectric constant of approximately 26, and a quality factor of roughly about 3300 GHz were demonstrated. A prolonged ball mill time thereafter significantly decreased both of the dielectric properties because of the enhanced reduction of the specimens during sintering. The apparent evidence of a material reaction between the dielectric material and the copper electrode was not observed.     

Synthesis of Cerium‐Doped Gd3(Al,Ga)5O12 Powder for Ceramic Scintillators with Ultrasonic‐Assisted Chemical Coprecipitation Method

Cerium‐doped Gd₃(Al,Ga)₅O₁₂ powders have been synthesized with ultrasonic‐assisted chemical coprecipitation method (UACC), and the traditional chemical coprecipitation method (CC) was also employed for comparison. The structure and morphology of powders were investigated by XRD, BET, and TEM. The powders were used for preparing ceramics at different temperatures. The specific surface areas of UACC and CC powders calcined at 800°C were 66 and 29 m²/g, respectively. Ceramics derived from UACC and CC powders were sintered at 1600°C, and the densities are 6.67 and 6.48 g/cm³, respectively. UACC is an attractive method for synthesizing GAGG powder for preparing ceramic scintillators.