The oxide ZrW_2O_8 displays unusual property of isotropic negative thermalexpansion in a large wide temperature range, which makes it have a number of important potentialapplications. The cubic Zr_(1-x)Hf_xW_2O_8 (x v...The oxide ZrW_2O_8 displays unusual property of isotropic negative thermalexpansion in a large wide temperature range, which makes it have a number of important potentialapplications. The cubic Zr_(1-x)Hf_xW_2O_8 (x velence 0,0.3, 0.5, 0.7, and 1.0) were synthesized bystandard solid state reaction technique. The high and low temperature X-ray diffraction analysisindicate that the substitution of the Hf^(4+) for Zr^(4+) only leads to reducing the latticeconstants, and the changes of negative thermal expansion coefficients are not obvious. The linearexpansion coefficients of Zr_(1-x)Hf_xW_2O_8 (x velence 0,0.3, 0.5, 0.7, and 1.0) are about -6 X 10^(-6) K^(-1) in the temperature range of 298 to 973 K, while that of Zr_(0.5)Hf_(0.5)W_2O_8 is -9.6X 10^(-6) K_(-1) from 83 to 298 K. The phase transition temperatures from alpha-ZrW_2O_8 tobeta-ZrW_2O_8 structure were also determined by X-ray diffraction method. Thermogravimetric analysis(TGA) exhibits that Zr_(1-x)Hf_xW_2O_8 is not hygroscopic in air.展开更多
A temperature stable Li2Zn0.95(SrxCa1-x)0.05Ti3O8(0≤x≤1)ceramics were fabricated using a conventional solid-state route sintered at 1100℃for 4 h.The XRD results indicate that the main phase Li2ZnTi3O8 and secondary...A temperature stable Li2Zn0.95(SrxCa1-x)0.05Ti3O8(0≤x≤1)ceramics were fabricated using a conventional solid-state route sintered at 1100℃for 4 h.The XRD results indicate that the main phase Li2ZnTi3O8 and secondary phase including SrxCa1-xTiO3(0≤x≤1)solid solution and TiO2 co-exist in composite and form a stable composite system when the(CaxSr1-x)(0≤x≤1)substitutes for Zn of Li2ZnTi3O8 ceramic.As x is increased from 0 to 1,the relative permittivity(εr)increases from 26.65 to 27.12,and the quality factor(Q×f)increases from 63300 to 66600 GHz.With the increased of x,the temperature coefficient of resonant frequency(τf)increases from 0.27 to 8.23 ppm/℃,and then decreases to 3.51 ppm/℃.On the whole,the Li2Zn0.95(SrxCa1-x)0.05Ti3O8(0≤x≤1)ceramics show excellent comprehensive properties of middleεr=25-27,higher Q×f≥60000 GHz andτf≤±8.5 ppm/℃.展开更多
The effect of Y substitution for Ca on the crystal structure and electronic states of Bi_2Sr_2CaCu_2O_(8+y) was studied. It is found that the modulation period of the incommensurate superlattice along b axis decreases...The effect of Y substitution for Ca on the crystal structure and electronic states of Bi_2Sr_2CaCu_2O_(8+y) was studied. It is found that the modulation period of the incommensurate superlattice along b axis decreases from 4.7b to about 4.0b gradually, which implies the change of the extra oxygen atoms residing within double Bi-O layers. Two kinds of modulation structures with periods of 4b and 8b exist in the same compound as Ca is completely substituted by Y. XPS was employed to study the change in the electronic structure. The results suggest that the variation of superconductivity is not caused by the slight change in crystal structure, but rather by the hole filling in O2p orbitals in CuO_2 layers. For this substituted system, it is still the case where one hole in Cu3d orbital (3d^9) is corresponding to the strong correlation antiferromaguetic insulator, and an extra hole in O2p orbital in CuO_2 layer (3d^9L) to the superconductor.展开更多
基金This project is financially supported by the National Natural Science Foundation of China (No. 50002001) the Natural Science Foundation of Yunnan Province (No. 2000E0006Q)
文摘The oxide ZrW_2O_8 displays unusual property of isotropic negative thermalexpansion in a large wide temperature range, which makes it have a number of important potentialapplications. The cubic Zr_(1-x)Hf_xW_2O_8 (x velence 0,0.3, 0.5, 0.7, and 1.0) were synthesized bystandard solid state reaction technique. The high and low temperature X-ray diffraction analysisindicate that the substitution of the Hf^(4+) for Zr^(4+) only leads to reducing the latticeconstants, and the changes of negative thermal expansion coefficients are not obvious. The linearexpansion coefficients of Zr_(1-x)Hf_xW_2O_8 (x velence 0,0.3, 0.5, 0.7, and 1.0) are about -6 X 10^(-6) K^(-1) in the temperature range of 298 to 973 K, while that of Zr_(0.5)Hf_(0.5)W_2O_8 is -9.6X 10^(-6) K_(-1) from 83 to 298 K. The phase transition temperatures from alpha-ZrW_2O_8 tobeta-ZrW_2O_8 structure were also determined by X-ray diffraction method. Thermogravimetric analysis(TGA) exhibits that Zr_(1-x)Hf_xW_2O_8 is not hygroscopic in air.
基金Funded by the Open Project Program of Key Laboratory of Inorganic Functional Materials and Devices,Chinese Academy of Sciences(No.KLIFMD201606)the Open Fund of National Innovation Platform(No.2017YJ163)+1 种基金the National Natural Science Foundation of China(Nos.51502220,51521001,and 51672197)the Open Foundation of Hubei Key Laboratory of Theory and Application of Advanced Materials Mechanics(Wuhan University of Technology)(No.TAM201802)。
文摘A temperature stable Li2Zn0.95(SrxCa1-x)0.05Ti3O8(0≤x≤1)ceramics were fabricated using a conventional solid-state route sintered at 1100℃for 4 h.The XRD results indicate that the main phase Li2ZnTi3O8 and secondary phase including SrxCa1-xTiO3(0≤x≤1)solid solution and TiO2 co-exist in composite and form a stable composite system when the(CaxSr1-x)(0≤x≤1)substitutes for Zn of Li2ZnTi3O8 ceramic.As x is increased from 0 to 1,the relative permittivity(εr)increases from 26.65 to 27.12,and the quality factor(Q×f)increases from 63300 to 66600 GHz.With the increased of x,the temperature coefficient of resonant frequency(τf)increases from 0.27 to 8.23 ppm/℃,and then decreases to 3.51 ppm/℃.On the whole,the Li2Zn0.95(SrxCa1-x)0.05Ti3O8(0≤x≤1)ceramics show excellent comprehensive properties of middleεr=25-27,higher Q×f≥60000 GHz andτf≤±8.5 ppm/℃.
基金Project supported by the National Natural Science Foundation of China and by the Laboratory of Structure and Element Analysis, Academia Sinica
文摘The effect of Y substitution for Ca on the crystal structure and electronic states of Bi_2Sr_2CaCu_2O_(8+y) was studied. It is found that the modulation period of the incommensurate superlattice along b axis decreases from 4.7b to about 4.0b gradually, which implies the change of the extra oxygen atoms residing within double Bi-O layers. Two kinds of modulation structures with periods of 4b and 8b exist in the same compound as Ca is completely substituted by Y. XPS was employed to study the change in the electronic structure. The results suggest that the variation of superconductivity is not caused by the slight change in crystal structure, but rather by the hole filling in O2p orbitals in CuO_2 layers. For this substituted system, it is still the case where one hole in Cu3d orbital (3d^9) is corresponding to the strong correlation antiferromaguetic insulator, and an extra hole in O2p orbital in CuO_2 layer (3d^9L) to the superconductor.
