The structure and disorder-order transformation of NdxFe60.5-x Pt39.5（x = 0, 0.5, 1.0, 1.5） alloys were investigated in situ by high temperature X-ray diffraction. The results show that the lattice parameter a of di...The structure and disorder-order transformation of NdxFe60.5-x Pt39.5（x = 0, 0.5, 1.0, 1.5） alloys were investigated in situ by high temperature X-ray diffraction. The results show that the lattice parameter a of disordered γ phase （FCC, Al structure type） and the lattice parameter ratio c/a of ordered γ1 phase （FCT, L10 structure type） increase linearly with increasing Nd concentration, whereas the c/a ratio decreases with increasing temperature. The transition temperature from ordered FCT to disordered FCC decreases with increasing Nd concentration, but for alloys quenched rapidly from γ phase region into ice-water it increases with increasing Nd.展开更多
The dynamic process of the ionic valence changing from Eu^(2+) to Eu^(3+) in EuF_2 at high temperature has been investigated by ESCA, high,temperature X-ray diffraction, high temperature spectrum, high temperature mag...The dynamic process of the ionic valence changing from Eu^(2+) to Eu^(3+) in EuF_2 at high temperature has been investigated by ESCA, high,temperature X-ray diffraction, high temperature spectrum, high temperature magnetic Isusceptibility and Mssbauer spectrum. It has been shown that the formed Eu^(3+) exists in different compounds when EuF_2 is heated to high temperature in different atmospheres. In air, Eu^(3+) exists in the form of hexagonal EuOF, in nitrogen, in the form of orthogonal EuF_3 and non-hexagon EuOF. This is because decomposition or disproportionation of EuF_2 is different with different atmospheres. The magnetic susceptibility measurement showed quantitatively that the change rate from Eu^(2+) to Eu^(3+) is about 95% in air, and about 75% in nitrogen when it is heated to 900℃. A small amount of Eu^(2+) coexists with Eu^(3+) in the final product.展开更多
Nonstoichiometric series SmF_x (2.0≤x≤3.0) have been synthesized by reduction of samarium trifluoride with hydrogen for several times, and the stoichiometric samarium difluoride has been obtained. The structure of n...Nonstoichiometric series SmF_x (2.0≤x≤3.0) have been synthesized by reduction of samarium trifluoride with hydrogen for several times, and the stoichiometric samarium difluoride has been obtained. The structure of nonstoichiometric samarium fluoride series and the valency of samarium ion are briefly discussed. The valent change process of samarium ion at high temperatures in different atmospheres is investigated.展开更多
The thermal expansion coefficients (TEC) of RuO2 crystallits in thick film resistor (TFR) composites, consisting of RuO2 dispersed in lead-silicate glass of various compositions, were evaluated from X-ray diffraction ...The thermal expansion coefficients (TEC) of RuO2 crystallits in thick film resistor (TFR) composites, consisting of RuO2 dispersed in lead-silicate glass of various compositions, were evaluated from X-ray diffraction patterns at temperatures 298;773;973 and 1123 K corresponding to characteristic temperatures of resistivity and thermopower anomalies of the TFRs. It has been found that TEC of free RuO2 powder along a-axis has an anomaly at T > 973 K (expansion is replaced by constriction), whereas constriction along c-axes remains for all temperatures. This anomaly disappears in doped glass of simplest composition (2SiO2.PbO) but occurs in glasses of some complex compositions. Symmetry of unit cell of RuO2 is not changed in the temperature range investigated.展开更多
In this paper, the phase-formation mechanism of Bi-based superconductors was systematically investigated by using high-temperature X-ray diffraction, differential thermal analysis (DTA) and crystallization of amorphou...In this paper, the phase-formation mechanism of Bi-based superconductors was systematically investigated by using high-temperature X-ray diffraction, differential thermal analysis (DTA) and crystallization of amorphous state. The transformations among Bi-based 2201, 2212 and 2223 phases were observed, and the intergrown phenomenon of the 2201, 2212 and 2223 phases was explained. It was proposed that there exist a composition equilibrium between 2212 phase and Ca2CuO3 and a competition of thermody-namic stability among Ca2CuO3, 2212 and 2223 phases. This is why it is difficult to prepare the 2223 phase. After Pb was doped in Bi-Sr-Ca-Cu-O system, Ca2CuO3 phase in the Bi-Sr-Ca-Cu-O system was replaced by Ca2PbO4, so that the composition equilibrium and competition of thermodynamic stability mentioned above were avoided.展开更多
High-temperature X-ray diffraction (HTXRD) measurements of LaCoO_3 powder was carried out in a temperature range from 298 to 1273 K. The experimental data obtained were adopted to evaluate the lattice parameters and c...High-temperature X-ray diffraction (HTXRD) measurements of LaCoO_3 powder was carried out in a temperature range from 298 to 1273 K. The experimental data obtained were adopted to evaluate the lattice parameters and cell volume. In this temperature range, the linear and volume expansion coefficients calculated using these cell parameters are 24.160～23.610×10^(-6)·K^(-1) and 59.601～63.218×10^(-6)·K^(-1) respectively. There is no discontinuity found in the cell parameters through the proposed first-order transition at 1210 K.展开更多
The sample of cubic lazurite, collected in the Baikal region, with incommensurately 3D modulated (ITM) structure has been studied by the method of high-temperature X-ray powder diffraction. At short time of annealing ...The sample of cubic lazurite, collected in the Baikal region, with incommensurately 3D modulated (ITM) structure has been studied by the method of high-temperature X-ray powder diffraction. At short time of annealing in high-temperature diffraction experiment the modulation recovery proceeds during cooling down the sample to room temperature. The identity of the period of both initial and recovered modulation demonstrates that the system has a structural memory. The acquired results are interpreted through comparison of thermal behavior of lazurite, sodalite and quartz structures. It is supposed that two kinetically different and thermally activated processes proceed under heating: 1) reversible framework expansion due to Si-O-Al angle increase, and 2) equalizing of periodic local distortions via the diffusion-controlled transfer of cage ions between adjacent subcells. The second process seems to be much slower than the first one, especially at lower temperatures. With increasing temperature, both processes are activated. However, the framework expands more rapidly than the cage clusters migrate, and the periodic distortions of the framework are aligned. Under lower temperatures, the framework shrinks and again accommodates to the configuration of cage cations (clusters), which may be changed at high temperature and sufficient time or may not at lower temperature, short time, unfavorable SO2 fugacity values. In the first case the modulation disappears entirely, while in the second case it arises again. The probable reason for ITM formation is the balance of counteracting energetic terms: the elastic strain energy of structure deformation and the energy of cluster ordering providing the state of forced equilibrium. The excess free energy due to structure distortion is compensated by the increment associated with the cluster ordering process. However, no significant variations in sulphur anion speciation for different degrees of modulation retention were observed by XPS S 2p. This may be due to the ordering of Na- 展开更多
文摘The structure and disorder-order transformation of NdxFe60.5-x Pt39.5（x = 0, 0.5, 1.0, 1.5） alloys were investigated in situ by high temperature X-ray diffraction. The results show that the lattice parameter a of disordered γ phase （FCC, Al structure type） and the lattice parameter ratio c/a of ordered γ1 phase （FCT, L10 structure type） increase linearly with increasing Nd concentration, whereas the c/a ratio decreases with increasing temperature. The transition temperature from ordered FCT to disordered FCC decreases with increasing Nd concentration, but for alloys quenched rapidly from γ phase region into ice-water it increases with increasing Nd.
基金Project supported by the National Natural Science Foundation of China.
文摘The dynamic process of the ionic valence changing from Eu^(2+) to Eu^(3+) in EuF_2 at high temperature has been investigated by ESCA, high,temperature X-ray diffraction, high temperature spectrum, high temperature magnetic Isusceptibility and Mssbauer spectrum. It has been shown that the formed Eu^(3+) exists in different compounds when EuF_2 is heated to high temperature in different atmospheres. In air, Eu^(3+) exists in the form of hexagonal EuOF, in nitrogen, in the form of orthogonal EuF_3 and non-hexagon EuOF. This is because decomposition or disproportionation of EuF_2 is different with different atmospheres. The magnetic susceptibility measurement showed quantitatively that the change rate from Eu^(2+) to Eu^(3+) is about 95% in air, and about 75% in nitrogen when it is heated to 900℃. A small amount of Eu^(2+) coexists with Eu^(3+) in the final product.
基金Project supported by the National Natural Science Foundation of China.
文摘Nonstoichiometric series SmF_x (2.0≤x≤3.0) have been synthesized by reduction of samarium trifluoride with hydrogen for several times, and the stoichiometric samarium difluoride has been obtained. The structure of nonstoichiometric samarium fluoride series and the valency of samarium ion are briefly discussed. The valent change process of samarium ion at high temperatures in different atmospheres is investigated.
文摘The thermal expansion coefficients (TEC) of RuO2 crystallits in thick film resistor (TFR) composites, consisting of RuO2 dispersed in lead-silicate glass of various compositions, were evaluated from X-ray diffraction patterns at temperatures 298;773;973 and 1123 K corresponding to characteristic temperatures of resistivity and thermopower anomalies of the TFRs. It has been found that TEC of free RuO2 powder along a-axis has an anomaly at T > 973 K (expansion is replaced by constriction), whereas constriction along c-axes remains for all temperatures. This anomaly disappears in doped glass of simplest composition (2SiO2.PbO) but occurs in glasses of some complex compositions. Symmetry of unit cell of RuO2 is not changed in the temperature range investigated.
文摘In this paper, the phase-formation mechanism of Bi-based superconductors was systematically investigated by using high-temperature X-ray diffraction, differential thermal analysis (DTA) and crystallization of amorphous state. The transformations among Bi-based 2201, 2212 and 2223 phases were observed, and the intergrown phenomenon of the 2201, 2212 and 2223 phases was explained. It was proposed that there exist a composition equilibrium between 2212 phase and Ca2CuO3 and a competition of thermody-namic stability among Ca2CuO3, 2212 and 2223 phases. This is why it is difficult to prepare the 2223 phase. After Pb was doped in Bi-Sr-Ca-Cu-O system, Ca2CuO3 phase in the Bi-Sr-Ca-Cu-O system was replaced by Ca2PbO4, so that the composition equilibrium and competition of thermodynamic stability mentioned above were avoided.
文摘High-temperature X-ray diffraction (HTXRD) measurements of LaCoO_3 powder was carried out in a temperature range from 298 to 1273 K. The experimental data obtained were adopted to evaluate the lattice parameters and cell volume. In this temperature range, the linear and volume expansion coefficients calculated using these cell parameters are 24.160～23.610×10^(-6)·K^(-1) and 59.601～63.218×10^(-6)·K^(-1) respectively. There is no discontinuity found in the cell parameters through the proposed first-order transition at 1210 K.
文摘The sample of cubic lazurite, collected in the Baikal region, with incommensurately 3D modulated (ITM) structure has been studied by the method of high-temperature X-ray powder diffraction. At short time of annealing in high-temperature diffraction experiment the modulation recovery proceeds during cooling down the sample to room temperature. The identity of the period of both initial and recovered modulation demonstrates that the system has a structural memory. The acquired results are interpreted through comparison of thermal behavior of lazurite, sodalite and quartz structures. It is supposed that two kinetically different and thermally activated processes proceed under heating: 1) reversible framework expansion due to Si-O-Al angle increase, and 2) equalizing of periodic local distortions via the diffusion-controlled transfer of cage ions between adjacent subcells. The second process seems to be much slower than the first one, especially at lower temperatures. With increasing temperature, both processes are activated. However, the framework expands more rapidly than the cage clusters migrate, and the periodic distortions of the framework are aligned. Under lower temperatures, the framework shrinks and again accommodates to the configuration of cage cations (clusters), which may be changed at high temperature and sufficient time or may not at lower temperature, short time, unfavorable SO2 fugacity values. In the first case the modulation disappears entirely, while in the second case it arises again. The probable reason for ITM formation is the balance of counteracting energetic terms: the elastic strain energy of structure deformation and the energy of cluster ordering providing the state of forced equilibrium. The excess free energy due to structure distortion is compensated by the increment associated with the cluster ordering process. However, no significant variations in sulphur anion speciation for different degrees of modulation retention were observed by XPS S 2p. This may be due to the ordering of Na-
