Wide gap brazing（WGB） experiments using the butted specimen with a 1.5 mm gap were carried out for the repair of the failed K418B superalloy low-pressure turbine vanes.The high temperature creep rupture strengths of...Wide gap brazing（WGB） experiments using the butted specimen with a 1.5 mm gap were carried out for the repair of the failed K418B superalloy low-pressure turbine vanes.The high temperature creep rupture strengths of the brazed joints were tested,and the microstructures and fracture surfaces of the joints were observed.The results show that the microstructure of K418B alloy joint is composed of dense equiaxed grain,small and discrete compounds with a few micro-pores.During the creep rupture test,the cracks initiate preferentially at the micro-pore or the grain boundary,then propagate along the grain boundary till the fracture happens.The creep rupture strength at 700 ℃ of the brazed joints with 50% braze metal in the working part could exceed 90% that of the K418B superalloy,and the joints with 100% braze metal in the working part achieve 70% to 80% of the creep rupture strengths for the K418 B base metal.展开更多
This paper presents a self-consistent nonlinear theory of the current and energy modulations when an electron beam propagates through an inductively-loaded wide gap cavity. The integro-differential equations axe obtai...This paper presents a self-consistent nonlinear theory of the current and energy modulations when an electron beam propagates through an inductively-loaded wide gap cavity. The integro-differential equations axe obtained to describe the modulation of the beam current and kinetic energy. A relativistic klystron amplifier （RKA） model is introduced, which uses an inductively-loaded wide gap cavity as an input cavity. And a numerical code is developed for the extended model based on the equations, from which some relations about the modulated current and modulated energy are numerically given.展开更多
Applications like solid oxide fuel cells and sensors increasingly demand the possibility to braze ceramics to metals with a good resistance to high temperatures and oxidative atmospheres. Commonly used silver based ac...Applications like solid oxide fuel cells and sensors increasingly demand the possibility to braze ceramics to metals with a good resistance to high temperatures and oxidative atmospheres. Commonly used silver based active filler metals cannot fulfill these requirements, if application temperatures higher than 600℃ occur. Au and Pd based active fillers are too expensive for many fields of use. As one possible solution nickel based active fillers were developed. Due to the high brazing temperatures and the low ductility of nickel based filler metals, the modification of standard nickel based filler metals were necessary to meet the requirements of above mentioned applications. To reduce thermally induced stresses wide brazing gaps and the addition of A1203 and WC particles to the filler metal were applied. In this study, the microstructure of the brazed joints and the thermo-chemical reactions between filler metal, active elements and WC particles were analyzed to understand the mechanism of the so called wide gap active brazing process. With regard to the behavior in typical application oxidation and thermal cycle tests were conducted as well as tensile tests.展开更多
The design of pnictide nonlinear optical crystals is quite different from chalcogenide and oxide those in which a new paradigm need be developed to regulate the band gap,one of key optical parameters In this work,two ...The design of pnictide nonlinear optical crystals is quite different from chalcogenide and oxide those in which a new paradigm need be developed to regulate the band gap,one of key optical parameters In this work,two non-centrosymmetric halidepnictides,[Cd_(2)P]_(2)[CdBr_(4)](CPB)and[Cd_(2)As]_(2)[CdBr_(4)](CAB) were reported.The complete octet binding electrons of pnictogens were constructed by four Cd-P pola covalent bonds under the anchoring effect of halogens,creating an extremely flat valence band maximum with band dispersion of only 0.17 eV.As expected,the balance of the covalency and ionicity in CPB and CAB was successfully realized,leading to a wide band gap of 2.58 eV and 1.88 eV.Remarkably,CPB no only has a widest band gap among Cd-containing pnictides,but also exhibits a SHG effect of 1.2×AgGaS_(2).moderate birefringence(0.088@visible light and calcd.0.043@2050 nm)and a wide IR transmission range.This is the first time that the octet binding electrons construction strategy was utilized to design non diamond like NLO pnictides with excellent performances.展开更多
The rapid pace of change in the wide band gap(WBG)power semiconductor area has led to an explosion in potential uses for WBG devices in a huge variety of applications.The applications include automotive,aerospace and ...The rapid pace of change in the wide band gap(WBG)power semiconductor area has led to an explosion in potential uses for WBG devices in a huge variety of applications.The applications include automotive,aerospace and traction applications,as well as grid related or charging systems,with the potential to provide paradigm shifts in performance and efficiency over Silicon devices in current use today.Despite these exciting developments,however,there are still many outstanding challenges for both researchers and industry to solve before WBG technology becomes pervasive.In this paper we will explore some of these challenges and highlight the strengths of WBG devices,some of the specific issues for machine drives and develop some potential solutions for future developments in power electronics.展开更多
Laser-assisted simulation technique has played a crucial role in the investigation of dose rate effects of silicon-based devices and integrated circuits,due to its exceptional advantages in terms of flexibility,safety...Laser-assisted simulation technique has played a crucial role in the investigation of dose rate effects of silicon-based devices and integrated circuits,due to its exceptional advantages in terms of flexibility,safety,convenience,and precision.In recent years,wide band gap materials,known for their strong bonding and high ionization energy,have gained increasing attention from researchers and hold significant promise for extensive applications in specialized environments.Consequently,there is a growing need for comprehensive research on the dose rate effects of wide band gap materials.In response to this need,the use of laser-assisted simulation technology has emerged as a promising approach,offering an effective means to assess the efficacy of investigating these materials and devices.This paper focused on investigating the feasibility of laser-assisted simulation to study the dose rate effects of wide band gap semiconductor devices.Theoretical conversion factors for laser-assisted simulation of dose rate effects of GaN-based and SiC-based devices were been provided.Moreover,to validate the accuracy of the conversion factors,pulsed laser and dose rate experiments were conducted on GaN-based and SiC-based PIN diodes.The results demonstrate that pulsed laser radiation andγ-ray radiation can produce highly similar photocurrent responses in GaN-based and SiC-based PIN diodes,with correlation coefficients of 0.98 and 0.974,respectively.This finding reaffirms the effectiveness of laser-assisted simulation technology,making it a valuable complement in studying the dose rate effects of wide band gap semiconductor devices.展开更多
In this paper, the zero voltage switching (ZVS) region of a dual active bridge (DAB) converter with wide band-gap (WBG) power semiconductor device is analyzed. The ZVS region of a DAB converter varies depending on out...In this paper, the zero voltage switching (ZVS) region of a dual active bridge (DAB) converter with wide band-gap (WBG) power semiconductor device is analyzed. The ZVS region of a DAB converter varies depending on output power and voltage ratio. The DAB converters operate with hard switching at light loads, it is difficult to achieve high efficiency. Fortunately, WBG power semiconductor devices have excellent hard switching characteristics and can increase efficiency compared to silicon (Si) devices. In particular, WBG devices can achieve ZVS at low load currents due to their low parasitic output capacitance (C<sub>o,tr</sub>) characteristics. Therefore, in this paper, the ZVS operating resion is analyzed based on the characteristics of Si, silicon carbide (SiC) and gallium nitride (GaN). Power semiconductor devices. WBG devices with low C<sub>o,tr</sub> operate at ZVS at lower load currents compared to Si devices. To verify this, experiments are conducted and the results are analyzed using a 3 kW DAB converter. For Si devices, ZVS is achieved above 1.4 kW. For WBG devices, ZVS is achieved at 700 W. Due to the ZVS conditions depending on the switching device, the DAB converter using Si devices achieves a power conversion efficiency of 91% at 1.1 kW output. On the other hand, in the case of WBG devices, power conversion efficiency of more than 98% is achieved under 11 kW conditions. In conclusion, it is confirmed that the WBG device operates in ZVS at a lower load compared to the Si device, which is advantageous in increasing light load efficiency.展开更多
The recent claim of potential room-temperature superconductivity in Pb_(10−x)Cu_(x)(PO_(4))_(6)O has attracted widespread attention.However,the signature of superconductivity is later attributed to the Cu_(2)S impurit...The recent claim of potential room-temperature superconductivity in Pb_(10−x)Cu_(x)(PO_(4))_(6)O has attracted widespread attention.However,the signature of superconductivity is later attributed to the Cu_(2)S impurity formed during the multiple-step synthesis procedure.Here we report a simple one-step approach for synthesizing single-phase chloride analogue Cu-doped Pb10(PO_(4))_(6)Cl_(2) using PbO,PbCl_(2),CuCl_(2),and NH_(4)H_(2)PO_(4) as starting materials.Irrespective of the initial stoichiometry,Cu doping always leads to a lattice expansion in Pb10(PO_(4))_(6)Cl_(2).This indicates that Cu prefers to reside in the hexagonal channels rather than as substitutes at the Pb sites,and the chemical formula is expressed as Pb10(PO_(4))_(6)Cu_(x)Cl_(2).All the Pb10(PO_(4))_(6)Cu_(x)Cl_(2)(0≤x≤1.0)samples are found to be semiconductors with wide band gaps of 4.46–4.59 eV,and the Cu-doped ones(x=0.5 and 1.0)exhibit a paramagnetic behavior without any phase transition between 400 and 1.8 K.Our study calls for a reinvestigation of the Cu location in Pb_(10−x)Cu_(x)(PO_(4))_(6)O and supports the absence of superconductivity in this oxyapatite.展开更多
Recently,non-centrosymmetric(NCS)Hg-based chalcogenides have garnered significant interest due to their strong second-harmonic-generation intensities(deff),making them attractive candidates for infrared nonlinear opti...Recently,non-centrosymmetric(NCS)Hg-based chalcogenides have garnered significant interest due to their strong second-harmonic-generation intensities(deff),making them attractive candidates for infrared nonlinear optical(IR-NLO)application.However,achieving both wide band gaps(Eg)and large phasematched deffsimultaneously in these materials remains a challenge due to their inherent constraints on each other.In this research,we have successfully obtained two quaternary NCS Hg-based chalcogenides,Rb2HgGe_(3)S_(8)and Cs_(2)HgGe_(3)S_(8),by implementing a bandgap engineering strategy that involves alkali metal introduction and Hg/Ge ratio regulation.Both compounds consist of 2D[Hg Ge_(3)S_(8)]_(2)–anionic layers made of 1D[HgGeS_(6)]^(6–)chains and dimeric[Ge_(2)S_(6)]_(4–)polyhedra arranged alternately,and the charge-balanced Rb+/Cs+cations located between these layers.Remarkably,Rb_(2)HgGe_(3)S_(8)and Cs_(2)HgGe_(3)S_(8)exhibit overall properties required for promising IR-NLO materials,including sufficient PM deff(0.55–0.70×AgGaS_(2)@20_(5)0 nm),large Eg(3.27–3.41 e V),giant laser-induced damage thresholds(17.4–19.7×AgGaS_(2)@1064 nm),broad optical transmission intervals(0.32–17.5μm),and suitable theoretical birefringence(0.069–0.086@2050 nm).Furthermore,in-depth theoretical analysis reveals that the exceptional IRNLO performance is attributed to the synergy effects of distorted[HgS_(4)]and[GeS_(4)]tetrahedra.Our study provides a useful strategy for enhancing the Eg and advancing Hg-based IR-NLO materials,which is expected to extended and implemented in other chalcogenide systems.展开更多
Much effort has been devoted to the discovery of novel birefringent crystals that display considerable birefringence(Δn)in the infrared(IR)region.However,the simultaneous achievement of a wide energy gap(E_(g)>3.1...Much effort has been devoted to the discovery of novel birefringent crystals that display considerable birefringence(Δn)in the infrared(IR)region.However,the simultaneous achievement of a wide energy gap(E_(g)>3.1 eV)and a largeΔn(>0.2)in a heteroanionic chalcogenide system remains a formidable challenge.To address this bottleneck,we applied the partial-substitution strategy and successfully designed and synthesized two new quaternary oxychalcogenides,namely AEGe_(2)O_(4)Se(AE=Sr and Ba).These two isomorphic compounds belong to the monoclinic space group P2_(1)/c(no.14),featuring a structure composed of two-dimensional(2D)[Ge_(2)O_(4)Se]^(2−)layers with an antiparallel arrangement,which are separated by charge-balanced Ba^(2+)cations.Remarkably,they exhibit the coexistence of largeΔn values(0.209 and 0.238@2050 nm based on the generalized gradient approximation)and wide E_(g)values(3.57 and 3.81 eV).Furthermore,theoretical calculations were performed to elucidate the interplay between optical properties and electronic structures.These results reveal that the significantly improvedΔn value(approximately 15–17 times that of the parent compound BaGe_(2)O_(5))can mainly be attributed to the newly discovered[GeO_(3)Se]heteroanionic motif.In brief,this study provides a simple chemical substitution method to overcome the trade-off between wide E_(g)and largeΔn values in heteroanionic chalcogenides.展开更多
文摘Wide gap brazing（WGB） experiments using the butted specimen with a 1.5 mm gap were carried out for the repair of the failed K418B superalloy low-pressure turbine vanes.The high temperature creep rupture strengths of the brazed joints were tested,and the microstructures and fracture surfaces of the joints were observed.The results show that the microstructure of K418B alloy joint is composed of dense equiaxed grain,small and discrete compounds with a few micro-pores.During the creep rupture test,the cracks initiate preferentially at the micro-pore or the grain boundary,then propagate along the grain boundary till the fracture happens.The creep rupture strength at 700 ℃ of the brazed joints with 50% braze metal in the working part could exceed 90% that of the K418B superalloy,and the joints with 100% braze metal in the working part achieve 70% to 80% of the creep rupture strengths for the K418 B base metal.
文摘This paper presents a self-consistent nonlinear theory of the current and energy modulations when an electron beam propagates through an inductively-loaded wide gap cavity. The integro-differential equations axe obtained to describe the modulation of the beam current and kinetic energy. A relativistic klystron amplifier （RKA） model is introduced, which uses an inductively-loaded wide gap cavity as an input cavity. And a numerical code is developed for the extended model based on the equations, from which some relations about the modulated current and modulated energy are numerically given.
文摘Applications like solid oxide fuel cells and sensors increasingly demand the possibility to braze ceramics to metals with a good resistance to high temperatures and oxidative atmospheres. Commonly used silver based active filler metals cannot fulfill these requirements, if application temperatures higher than 600℃ occur. Au and Pd based active fillers are too expensive for many fields of use. As one possible solution nickel based active fillers were developed. Due to the high brazing temperatures and the low ductility of nickel based filler metals, the modification of standard nickel based filler metals were necessary to meet the requirements of above mentioned applications. To reduce thermally induced stresses wide brazing gaps and the addition of A1203 and WC particles to the filler metal were applied. In this study, the microstructure of the brazed joints and the thermo-chemical reactions between filler metal, active elements and WC particles were analyzed to understand the mechanism of the so called wide gap active brazing process. With regard to the behavior in typical application oxidation and thermal cycle tests were conducted as well as tensile tests.
基金supported by the National Natural Science Foundation of China(Nos.22305174,22375147,52332001,51890862,51902308 and 21921001)the Natural Science Foundation of Fujian Province(No.2021J05097)the Natural Science Foundation of Tianjin City(No.22JCYBJC01380)。
文摘The design of pnictide nonlinear optical crystals is quite different from chalcogenide and oxide those in which a new paradigm need be developed to regulate the band gap,one of key optical parameters In this work,two non-centrosymmetric halidepnictides,[Cd_(2)P]_(2)[CdBr_(4)](CPB)and[Cd_(2)As]_(2)[CdBr_(4)](CAB) were reported.The complete octet binding electrons of pnictogens were constructed by four Cd-P pola covalent bonds under the anchoring effect of halogens,creating an extremely flat valence band maximum with band dispersion of only 0.17 eV.As expected,the balance of the covalency and ionicity in CPB and CAB was successfully realized,leading to a wide band gap of 2.58 eV and 1.88 eV.Remarkably,CPB no only has a widest band gap among Cd-containing pnictides,but also exhibits a SHG effect of 1.2×AgGaS_(2).moderate birefringence(0.088@visible light and calcd.0.043@2050 nm)and a wide IR transmission range.This is the first time that the octet binding electrons construction strategy was utilized to design non diamond like NLO pnictides with excellent performances.
文摘The rapid pace of change in the wide band gap(WBG)power semiconductor area has led to an explosion in potential uses for WBG devices in a huge variety of applications.The applications include automotive,aerospace and traction applications,as well as grid related or charging systems,with the potential to provide paradigm shifts in performance and efficiency over Silicon devices in current use today.Despite these exciting developments,however,there are still many outstanding challenges for both researchers and industry to solve before WBG technology becomes pervasive.In this paper we will explore some of these challenges and highlight the strengths of WBG devices,some of the specific issues for machine drives and develop some potential solutions for future developments in power electronics.
基金National Natural Science Foundation of China(12205028)Natural Science Foundation of Sichuan Province(2022NSFSC1235)Young and Middle-aged Backbone Teacher Foundation of Chengdu University of Technology(10912-JXGG2022-08363)。
文摘Laser-assisted simulation technique has played a crucial role in the investigation of dose rate effects of silicon-based devices and integrated circuits,due to its exceptional advantages in terms of flexibility,safety,convenience,and precision.In recent years,wide band gap materials,known for their strong bonding and high ionization energy,have gained increasing attention from researchers and hold significant promise for extensive applications in specialized environments.Consequently,there is a growing need for comprehensive research on the dose rate effects of wide band gap materials.In response to this need,the use of laser-assisted simulation technology has emerged as a promising approach,offering an effective means to assess the efficacy of investigating these materials and devices.This paper focused on investigating the feasibility of laser-assisted simulation to study the dose rate effects of wide band gap semiconductor devices.Theoretical conversion factors for laser-assisted simulation of dose rate effects of GaN-based and SiC-based devices were been provided.Moreover,to validate the accuracy of the conversion factors,pulsed laser and dose rate experiments were conducted on GaN-based and SiC-based PIN diodes.The results demonstrate that pulsed laser radiation andγ-ray radiation can produce highly similar photocurrent responses in GaN-based and SiC-based PIN diodes,with correlation coefficients of 0.98 and 0.974,respectively.This finding reaffirms the effectiveness of laser-assisted simulation technology,making it a valuable complement in studying the dose rate effects of wide band gap semiconductor devices.
文摘In this paper, the zero voltage switching (ZVS) region of a dual active bridge (DAB) converter with wide band-gap (WBG) power semiconductor device is analyzed. The ZVS region of a DAB converter varies depending on output power and voltage ratio. The DAB converters operate with hard switching at light loads, it is difficult to achieve high efficiency. Fortunately, WBG power semiconductor devices have excellent hard switching characteristics and can increase efficiency compared to silicon (Si) devices. In particular, WBG devices can achieve ZVS at low load currents due to their low parasitic output capacitance (C<sub>o,tr</sub>) characteristics. Therefore, in this paper, the ZVS operating resion is analyzed based on the characteristics of Si, silicon carbide (SiC) and gallium nitride (GaN). Power semiconductor devices. WBG devices with low C<sub>o,tr</sub> operate at ZVS at lower load currents compared to Si devices. To verify this, experiments are conducted and the results are analyzed using a 3 kW DAB converter. For Si devices, ZVS is achieved above 1.4 kW. For WBG devices, ZVS is achieved at 700 W. Due to the ZVS conditions depending on the switching device, the DAB converter using Si devices achieves a power conversion efficiency of 91% at 1.1 kW output. On the other hand, in the case of WBG devices, power conversion efficiency of more than 98% is achieved under 11 kW conditions. In conclusion, it is confirmed that the WBG device operates in ZVS at a lower load compared to the Si device, which is advantageous in increasing light load efficiency.
基金support from the Foundation of Westlake University,Prof.
文摘The recent claim of potential room-temperature superconductivity in Pb_(10−x)Cu_(x)(PO_(4))_(6)O has attracted widespread attention.However,the signature of superconductivity is later attributed to the Cu_(2)S impurity formed during the multiple-step synthesis procedure.Here we report a simple one-step approach for synthesizing single-phase chloride analogue Cu-doped Pb10(PO_(4))_(6)Cl_(2) using PbO,PbCl_(2),CuCl_(2),and NH_(4)H_(2)PO_(4) as starting materials.Irrespective of the initial stoichiometry,Cu doping always leads to a lattice expansion in Pb10(PO_(4))_(6)Cl_(2).This indicates that Cu prefers to reside in the hexagonal channels rather than as substitutes at the Pb sites,and the chemical formula is expressed as Pb10(PO_(4))_(6)Cu_(x)Cl_(2).All the Pb10(PO_(4))_(6)Cu_(x)Cl_(2)(0≤x≤1.0)samples are found to be semiconductors with wide band gaps of 4.46–4.59 eV,and the Cu-doped ones(x=0.5 and 1.0)exhibit a paramagnetic behavior without any phase transition between 400 and 1.8 K.Our study calls for a reinvestigation of the Cu location in Pb_(10−x)Cu_(x)(PO_(4))_(6)O and supports the absence of superconductivity in this oxyapatite.
基金supported by the National Natural Science Foundation of China(Nos.22175175 and 22193043)Natural Science Foundation of Fujian Province(Nos.2022L3092 and 2023H0041)+1 种基金Fujian Science&Technology Innovation Laboratory for Optoelectronic Information of China(No.2021ZR118)the Youth Innovation Promotion Association CAS(No.2022303)。
文摘Recently,non-centrosymmetric(NCS)Hg-based chalcogenides have garnered significant interest due to their strong second-harmonic-generation intensities(deff),making them attractive candidates for infrared nonlinear optical(IR-NLO)application.However,achieving both wide band gaps(Eg)and large phasematched deffsimultaneously in these materials remains a challenge due to their inherent constraints on each other.In this research,we have successfully obtained two quaternary NCS Hg-based chalcogenides,Rb2HgGe_(3)S_(8)and Cs_(2)HgGe_(3)S_(8),by implementing a bandgap engineering strategy that involves alkali metal introduction and Hg/Ge ratio regulation.Both compounds consist of 2D[Hg Ge_(3)S_(8)]_(2)–anionic layers made of 1D[HgGeS_(6)]^(6–)chains and dimeric[Ge_(2)S_(6)]_(4–)polyhedra arranged alternately,and the charge-balanced Rb+/Cs+cations located between these layers.Remarkably,Rb_(2)HgGe_(3)S_(8)and Cs_(2)HgGe_(3)S_(8)exhibit overall properties required for promising IR-NLO materials,including sufficient PM deff(0.55–0.70×AgGaS_(2)@20_(5)0 nm),large Eg(3.27–3.41 e V),giant laser-induced damage thresholds(17.4–19.7×AgGaS_(2)@1064 nm),broad optical transmission intervals(0.32–17.5μm),and suitable theoretical birefringence(0.069–0.086@2050 nm).Furthermore,in-depth theoretical analysis reveals that the exceptional IRNLO performance is attributed to the synergy effects of distorted[HgS_(4)]and[GeS_(4)]tetrahedra.Our study provides a useful strategy for enhancing the Eg and advancing Hg-based IR-NLO materials,which is expected to extended and implemented in other chalcogenide systems.
基金National Natural Science Foundation of China(21771179)Fujian Science&Technology Innovation Laboratory for Optoelectronic Information of China(2021ZR118)Natural Science Foundation of Fujian Province(2022L3092 and 2023H0041)。
文摘Much effort has been devoted to the discovery of novel birefringent crystals that display considerable birefringence(Δn)in the infrared(IR)region.However,the simultaneous achievement of a wide energy gap(E_(g)>3.1 eV)and a largeΔn(>0.2)in a heteroanionic chalcogenide system remains a formidable challenge.To address this bottleneck,we applied the partial-substitution strategy and successfully designed and synthesized two new quaternary oxychalcogenides,namely AEGe_(2)O_(4)Se(AE=Sr and Ba).These two isomorphic compounds belong to the monoclinic space group P2_(1)/c(no.14),featuring a structure composed of two-dimensional(2D)[Ge_(2)O_(4)Se]^(2−)layers with an antiparallel arrangement,which are separated by charge-balanced Ba^(2+)cations.Remarkably,they exhibit the coexistence of largeΔn values(0.209 and 0.238@2050 nm based on the generalized gradient approximation)and wide E_(g)values(3.57 and 3.81 eV).Furthermore,theoretical calculations were performed to elucidate the interplay between optical properties and electronic structures.These results reveal that the significantly improvedΔn value(approximately 15–17 times that of the parent compound BaGe_(2)O_(5))can mainly be attributed to the newly discovered[GeO_(3)Se]heteroanionic motif.In brief,this study provides a simple chemical substitution method to overcome the trade-off between wide E_(g)and largeΔn values in heteroanionic chalcogenides.
