本文分析了在不同衬底上生长无极性GaN薄膜的情况,这些衬底主要包括-γL iA lO2、r面蓝宝石等。通常在蓝宝石上制备的GaN外延膜是沿c轴生长的,而c轴是GaN的极性轴,导致GaN基器件有源层量子阱中出现很强的内建电场,发光效率会因此降低,...本文分析了在不同衬底上生长无极性GaN薄膜的情况,这些衬底主要包括-γL iA lO2、r面蓝宝石等。通常在蓝宝石上制备的GaN外延膜是沿c轴生长的,而c轴是GaN的极性轴,导致GaN基器件有源层量子阱中出现很强的内建电场,发光效率会因此降低,发展非极性面外延,有望克服这一物理现象,使发光效率提高。展开更多
A New Niobate Ba 6 LaTi 3 Nb 3 O 21 was synthesized by high temperature solid state reaction in the BaO - La 2 O 3 - TiO 2 - Nb 2 O 5 system.The chemical compositions,crystal structure,microstructure,density and melti...A New Niobate Ba 6 LaTi 3 Nb 3 O 21 was synthesized by high temperature solid state reaction in the BaO - La 2 O 3 - TiO 2 - Nb 2 O 5 system.The chemical compositions,crystal structure,microstructure,density and melting point of the new compound were characterized by EPMA,XRD,DTA and so on.Ba 6 LaTi 3 Nb 3 O 21 crystallizes the rhombohedral system with unit cell parameters a=0.57388(2)nm,c=4.9283(3)nm,and space group R3m,Z=3.The structure may be described as six(Nb,Ti)O 6 octahedra corner - sharing along c - axis to form perovskite layer connected by Ba atoms.The Ba 6 LaTi 3 Nb 3 O 21 ceramics exhibits high dielectric of74.1,low dielectric loss of4.7 × 10 -4 and small temperature coefficient of dielectric constant of-69ppm · K -1 at1MHz due to its close structure and relative high dielectric polarizabilities of Ba 2+ ,La 3+ ,Ti 4+ and Nb 5+ .Ba 6 LaTi 3 Nb 3 O 21 might be a suitable candidate of highε r mi - crowave dielectric ceramics.展开更多
Two compounds Ba 6 Zn 0.67 Nb 9.33 O 3 and Ba 6 Zn 0.67 Ta 9.33 O 30 with tungsten bronze structure were synthesized in the BaO-ZnO-Nb 2 O 5 /Ta 2 O 5 systems by the conventional high temperature solid-state reaction....Two compounds Ba 6 Zn 0.67 Nb 9.33 O 3 and Ba 6 Zn 0.67 Ta 9.33 O 30 with tungsten bronze structure were synthesized in the BaO-ZnO-Nb 2 O 5 /Ta 2 O 5 systems by the conventional high temperature solid-state reaction.The stru cture and dielectric properties of Ba 6 Zn 0.67 Nb 9.33 O 3 and Ba 6 Zn 0.67 Ta 9.33 O 30 were determined by X-ray powder diffraction,scanning electron microscope a nd dielectric measurements.The results show that Ba 6 Zn 0.67 Ta 9.33 O 30 belongs to paraelectric phase of fully filled tetragonal tungsten bronze str ucture at room temperature with unit cell parameters a=1.26256(4)nm, c=0.39698(2)nm.The room temperature dielectric constant( ε )of Ba 6 Zn 0.67 Ta 9.33 O 30 ceramic reached108combined with a low dielectric loss of0.005at1MHz .While Ba 6 Zn 0.67 Nb 9.33 O 3 belongs to fully filled tetragonal tungsten bronze structure at room tempera ture with the unit cell parameters a=1.25940(3)nm,c=0.40008 (2)nm.Ba 6 Zn 0.67 Nb 9.33 O 30 ceramic shows significant relaxor behaviors,and the phase transition from f erroelectric to paraelectric occurred at55℃(at1MHz).The room temperature dielectric constant( ε )of ceramic reached570at1MHz.展开更多
This paper reports that the m-plane GaN layer is grown on （200）-plane LiAlO2 substrate by metal-organic chemical wpour deposition （MOCVD） method. Tetragonal-shaped crystallites appear at the smooth surface. Raman ...This paper reports that the m-plane GaN layer is grown on （200）-plane LiAlO2 substrate by metal-organic chemical wpour deposition （MOCVD） method. Tetragonal-shaped crystallites appear at the smooth surface. Raman measurement illuminates the compressive stress in the layer which is released with increasing the layer＇s thickness. The high transmittance （80%）, sharp band edge and excitonic absorption peak show that the GaN layer has good optical quality. The donor acceptor pair emission peak located at -3.41 eV with full-width at half maximum of 120 meV and no yellow peaks in the photoluminescence spectra partially show that no Li incorporated into GaN layer from the LiAlO2 substrate.展开更多
文摘本文分析了在不同衬底上生长无极性GaN薄膜的情况,这些衬底主要包括-γL iA lO2、r面蓝宝石等。通常在蓝宝石上制备的GaN外延膜是沿c轴生长的,而c轴是GaN的极性轴,导致GaN基器件有源层量子阱中出现很强的内建电场,发光效率会因此降低,发展非极性面外延,有望克服这一物理现象,使发光效率提高。
文摘A New Niobate Ba 6 LaTi 3 Nb 3 O 21 was synthesized by high temperature solid state reaction in the BaO - La 2 O 3 - TiO 2 - Nb 2 O 5 system.The chemical compositions,crystal structure,microstructure,density and melting point of the new compound were characterized by EPMA,XRD,DTA and so on.Ba 6 LaTi 3 Nb 3 O 21 crystallizes the rhombohedral system with unit cell parameters a=0.57388(2)nm,c=4.9283(3)nm,and space group R3m,Z=3.The structure may be described as six(Nb,Ti)O 6 octahedra corner - sharing along c - axis to form perovskite layer connected by Ba atoms.The Ba 6 LaTi 3 Nb 3 O 21 ceramics exhibits high dielectric of74.1,low dielectric loss of4.7 × 10 -4 and small temperature coefficient of dielectric constant of-69ppm · K -1 at1MHz due to its close structure and relative high dielectric polarizabilities of Ba 2+ ,La 3+ ,Ti 4+ and Nb 5+ .Ba 6 LaTi 3 Nb 3 O 21 might be a suitable candidate of highε r mi - crowave dielectric ceramics.
文摘Two compounds Ba 6 Zn 0.67 Nb 9.33 O 3 and Ba 6 Zn 0.67 Ta 9.33 O 30 with tungsten bronze structure were synthesized in the BaO-ZnO-Nb 2 O 5 /Ta 2 O 5 systems by the conventional high temperature solid-state reaction.The stru cture and dielectric properties of Ba 6 Zn 0.67 Nb 9.33 O 3 and Ba 6 Zn 0.67 Ta 9.33 O 30 were determined by X-ray powder diffraction,scanning electron microscope a nd dielectric measurements.The results show that Ba 6 Zn 0.67 Ta 9.33 O 30 belongs to paraelectric phase of fully filled tetragonal tungsten bronze str ucture at room temperature with unit cell parameters a=1.26256(4)nm, c=0.39698(2)nm.The room temperature dielectric constant( ε )of Ba 6 Zn 0.67 Ta 9.33 O 30 ceramic reached108combined with a low dielectric loss of0.005at1MHz .While Ba 6 Zn 0.67 Nb 9.33 O 3 belongs to fully filled tetragonal tungsten bronze structure at room tempera ture with the unit cell parameters a=1.25940(3)nm,c=0.40008 (2)nm.Ba 6 Zn 0.67 Nb 9.33 O 30 ceramic shows significant relaxor behaviors,and the phase transition from f erroelectric to paraelectric occurred at55℃(at1MHz).The room temperature dielectric constant( ε )of ceramic reached570at1MHz.
文摘This paper reports that the m-plane GaN layer is grown on （200）-plane LiAlO2 substrate by metal-organic chemical wpour deposition （MOCVD） method. Tetragonal-shaped crystallites appear at the smooth surface. Raman measurement illuminates the compressive stress in the layer which is released with increasing the layer＇s thickness. The high transmittance （80%）, sharp band edge and excitonic absorption peak show that the GaN layer has good optical quality. The donor acceptor pair emission peak located at -3.41 eV with full-width at half maximum of 120 meV and no yellow peaks in the photoluminescence spectra partially show that no Li incorporated into GaN layer from the LiAlO2 substrate.
