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
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
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.
