(1-x)CoTiNb2O8-x ZnNb2O6 microwave dielectric ceramics were prepared via the conventional solid-state reaction route with the aim of reducing thetf value and improving the thermal stability.The phase composition and t...(1-x)CoTiNb2O8-x ZnNb2O6 microwave dielectric ceramics were prepared via the conventional solid-state reaction route with the aim of reducing thetf value and improving the thermal stability.The phase composition and the microstructure were investigated using X-ray diffraction,Raman spectra,and scanning electron microscopy.A set of phase transitions which were induced by composition had been confirmed via the sequence:rutile structure→coexistence of rutile and columbite phase→columbite phase.For(1-x)CoTiNb2O8-x ZnNb2O6 microwave dielectric ceramics,the addition of ZnNb2O6 content(x=0–1)led to the decrease ofer from 62.98 to 23.94.As a result of the high Q×?of ZnNb2O6 ceramics,the increase of ZnNb2O6 content also led to the lower sintering temperatures and the higher Q×?values.Thetf value was reduced from+108.04(x=0)to–49.31 ppm/℃(x=1).Among them,high density 0.5CoTiNb2O8-0.5ZnNb2O6 ceramics were obtained at 1175℃with excellent microwave dielectric properties of εr 39.2,Q×? 40013 GHz,and tf+3.57 ppm/℃.展开更多
High-purity,homogeneous and ultra fine LaB6 powders were prepared by combustion synthesis.The effects of reactant ratio and molding pressure on the phase and morphology of the combustion products were studied.The comb...High-purity,homogeneous and ultra fine LaB6 powders were prepared by combustion synthesis.The effects of reactant ratio and molding pressure on the phase and morphology of the combustion products were studied.The combustion products and leached products were analyzed by XRD,SEM and EDS.The results indicate that the combustion product consists of LaB6,MgO and a little Mg3B2O6.The combustion product becomes denser and harder when the molding pressure increases.The purity of LaB6 is higher than 99.0%.The LaB6 particle size is in range of 1.92-3.00 μm and the lattice constant of LaB6 is a=0.414 8 nm.展开更多
A new barium aluminoborate, Ba2Al4B6O17, has been synthesized by the hightemperature solution reaction at 780 ℃. The single-crystal XRD analysis shows that it crystallizes in triclinic space group P■ with a = 8.9601...A new barium aluminoborate, Ba2Al4B6O17, has been synthesized by the hightemperature solution reaction at 780 ℃. The single-crystal XRD analysis shows that it crystallizes in triclinic space group P■ with a = 8.9601(5), b = 9.1835(6), c = 10.6574(7) ?, a = 95.050(6)°, b = 111.569(5)°, g = 90.280(6)°, V = 811.71(9) ?3, Z = 2, Mr = 719.46, Dc = 2.944 g/cm3, μ = 5.127 mm-1, F(000) = 660, R = 0.0361 and wR = 0.0855 for 3846 observed reflections and 262 variables. This compound represents a new structure that features a three-dimensional [Al4B6O17]n4n- framework constructed by AlO4 tetrahedra, BO3 triangles, and B2O54-groups composed of two corner-sharing BO3 triangles, with intersecting open channels accommodating Ba2+ cations. It melts incongruently at 849 ℃. The existence of BO3 groups is confirmed by FT-IR and Raman spectra. The insulating nature with an optical band gap of about 3.50 eV is revealed by UV-VIS diffuse reflectance spectrum. Band structure calculations indicate that it is an indirect band material.展开更多
基金financially supported by the National Natural Science Foundation of China (No. 51772022)
文摘(1-x)CoTiNb2O8-x ZnNb2O6 microwave dielectric ceramics were prepared via the conventional solid-state reaction route with the aim of reducing thetf value and improving the thermal stability.The phase composition and the microstructure were investigated using X-ray diffraction,Raman spectra,and scanning electron microscopy.A set of phase transitions which were induced by composition had been confirmed via the sequence:rutile structure→coexistence of rutile and columbite phase→columbite phase.For(1-x)CoTiNb2O8-x ZnNb2O6 microwave dielectric ceramics,the addition of ZnNb2O6 content(x=0–1)led to the decrease ofer from 62.98 to 23.94.As a result of the high Q×?of ZnNb2O6 ceramics,the increase of ZnNb2O6 content also led to the lower sintering temperatures and the higher Q×?values.Thetf value was reduced from+108.04(x=0)to–49.31 ppm/℃(x=1).Among them,high density 0.5CoTiNb2O8-0.5ZnNb2O6 ceramics were obtained at 1175℃with excellent microwave dielectric properties of εr 39.2,Q×? 40013 GHz,and tf+3.57 ppm/℃.
基金Projects (51002025,50644016,5087402) supported by the National Natural Science Foundation of China
文摘High-purity,homogeneous and ultra fine LaB6 powders were prepared by combustion synthesis.The effects of reactant ratio and molding pressure on the phase and morphology of the combustion products were studied.The combustion products and leached products were analyzed by XRD,SEM and EDS.The results indicate that the combustion product consists of LaB6,MgO and a little Mg3B2O6.The combustion product becomes denser and harder when the molding pressure increases.The purity of LaB6 is higher than 99.0%.The LaB6 particle size is in range of 1.92-3.00 μm and the lattice constant of LaB6 is a=0.414 8 nm.
基金Supported by the National Natural Science Foundation of China(No.20871012)
文摘A new barium aluminoborate, Ba2Al4B6O17, has been synthesized by the hightemperature solution reaction at 780 ℃. The single-crystal XRD analysis shows that it crystallizes in triclinic space group P■ with a = 8.9601(5), b = 9.1835(6), c = 10.6574(7) ?, a = 95.050(6)°, b = 111.569(5)°, g = 90.280(6)°, V = 811.71(9) ?3, Z = 2, Mr = 719.46, Dc = 2.944 g/cm3, μ = 5.127 mm-1, F(000) = 660, R = 0.0361 and wR = 0.0855 for 3846 observed reflections and 262 variables. This compound represents a new structure that features a three-dimensional [Al4B6O17]n4n- framework constructed by AlO4 tetrahedra, BO3 triangles, and B2O54-groups composed of two corner-sharing BO3 triangles, with intersecting open channels accommodating Ba2+ cations. It melts incongruently at 849 ℃. The existence of BO3 groups is confirmed by FT-IR and Raman spectra. The insulating nature with an optical band gap of about 3.50 eV is revealed by UV-VIS diffuse reflectance spectrum. Band structure calculations indicate that it is an indirect band material.
