Samples of manganese oxides La（1-x）2/3Ca1/3MnO3（x 〈 0.10） with Lavacancy were prepared by standard solid-state reaction method. All the samples are single phase, with orthorhombic symmetry （Pnma ）, analyzed by ...Samples of manganese oxides La（1-x）2/3Ca1/3MnO3（x 〈 0.10） with Lavacancy were prepared by standard solid-state reaction method. All the samples are single phase, with orthorhombic symmetry （Pnma ）, analyzed by XRD and with Rietveld Refinement. The effect of different La-site vacancies concentration on electronic transport of La（1-x）2/3Ca1/3MnO3 was investigated. The insulator-metal transition temperature （about 267 K） nearly remains unchanged with the increase of vacancy concentration, which indicates that small La-vacancy does not destroy the double exchange interaction. But the electronic resistance increases and MR value decreases with La-vacancy content x 〉 0.04. The maximum of the MR value （8 T） is about 220% at transition temperature （TMI）.展开更多
As an interconnector of solid oxide fuel cell, La 1-x Ca x CrO 3( x =0 0～0 5) were prepared by sol gel method. The crystal structures of La 1-x Ca x CrO 3 at room temperature are the or...As an interconnector of solid oxide fuel cell, La 1-x Ca x CrO 3( x =0 0～0 5) were prepared by sol gel method. The crystal structures of La 1-x Ca x CrO 3 at room temperature are the orthorhombic perovskite GdFeO 3 type. XPS analysis indicates that chrome ions are in different valence state. The introduction of Ca 2+ into the lattice induces the oxidation of Cr 3+ to Cr 6+ . With x increasing, the amount of Cr 6+ increases. The present of the more Cr 6+ is one of the important factors that effect electric conductivity of La 1-x Ca x CrO 3.展开更多
The influences of W doping at Mn site on the charge order and spin order were studied by measuring M-T curves, M-H curves and ESR spectra of La0.3Ca0.7Mn1?xWxO3 (x = 0.00, 0.04, 0.08, 0.12, 0.15) system. The results s...The influences of W doping at Mn site on the charge order and spin order were studied by measuring M-T curves, M-H curves and ESR spectra of La0.3Ca0.7Mn1?xWxO3 (x = 0.00, 0.04, 0.08, 0.12, 0.15) system. The results showed that: When 0.00≤ x≤0.08, the system exhibits charge ordering (CO) phase, and its spin order experiences the change of paramagnetism (PM)-charge ordering (CO)-antiferro- magnetism (AFM) with decreasing temperature; when x≥0.12, the charge ordering (CO) phase melts, part of charge ordering (CO)phase remains in the paramagnetism (PM)background, the spin order of the system is mainly paramagnetism (PM), and ferromagnetic (FM) clusters appear at low tem- perature.展开更多
Ho^（3＋） doped La_（2（1-x））Yb_（2x）TiO_5 samples were prepared by sol-gel method. Pyrochlore structured powders were obtained under the annealing of the as-prepared samples at 1100 °C for 3 h in the air. Al...Ho^（3＋） doped La_（2（1-x））Yb_（2x）TiO_5 samples were prepared by sol-gel method. Pyrochlore structured powders were obtained under the annealing of the as-prepared samples at 1100 °C for 3 h in the air. All the samples were characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM） and photoluminescent spectroscopy. When x=0, we obtained La_2TiO_5 phosphors. Monitored at 546 nm, the excitation spectrum of Ho^（3＋） activated La_2TiO_5 phosphors consisted of a broad band originating from the charge-transfer band（CTB） between Ho^（3＋） ions and the nearest neighboring O^（2-） ions at 250-280 nm and four sharp bands associated to f-f transitions of Ho^（3＋） ions at 350-500 nm. Under the blue light excitation at 461 nm, Ho^（3＋） ion in La_2TiO_5 emitted an intense green emission band at 546 nm due to the transition of ~5S_2, ~5F_4→~5I_8. Two intense bands were observed at 490 nm（blue, ~5F_3→I_8） and 663 nm（red, ~5F_5→~5I_8） in the up-conversion（UC） spectrum under 980 nm NIR laser excitation in La_2TiO_5 phosphors activated with Ho^（3＋） alone, whereas they were much different from the down-conversion（DC） luminescent samples. When x=7.5 mol.%-17.5 mol.%, the UC emission spectra of them dominated at 546 nm（green, ~5S_2, ~5F_4→~5I_8） and enhanced significantly with the dose of Yb^（3＋） ion. The decay curve also confirmed that the transitions of ~5F_4→~5I_8 and ~5S_2→~5I_8 were merged into one emission band at 546 nm.展开更多
文摘Samples of manganese oxides La（1-x）2/3Ca1/3MnO3（x 〈 0.10） with Lavacancy were prepared by standard solid-state reaction method. All the samples are single phase, with orthorhombic symmetry （Pnma ）, analyzed by XRD and with Rietveld Refinement. The effect of different La-site vacancies concentration on electronic transport of La（1-x）2/3Ca1/3MnO3 was investigated. The insulator-metal transition temperature （about 267 K） nearly remains unchanged with the increase of vacancy concentration, which indicates that small La-vacancy does not destroy the double exchange interaction. But the electronic resistance increases and MR value decreases with La-vacancy content x 〉 0.04. The maximum of the MR value （8 T） is about 220% at transition temperature （TMI）.
文摘As an interconnector of solid oxide fuel cell, La 1-x Ca x CrO 3( x =0 0～0 5) were prepared by sol gel method. The crystal structures of La 1-x Ca x CrO 3 at room temperature are the orthorhombic perovskite GdFeO 3 type. XPS analysis indicates that chrome ions are in different valence state. The introduction of Ca 2+ into the lattice induces the oxidation of Cr 3+ to Cr 6+ . With x increasing, the amount of Cr 6+ increases. The present of the more Cr 6+ is one of the important factors that effect electric conductivity of La 1-x Ca x CrO 3.
基金supported by the National Natural Science Foundation of China(Grant No.19934003)the State Key Project of Fundamental Research of China(No.001CB610604)
文摘The influences of W doping at Mn site on the charge order and spin order were studied by measuring M-T curves, M-H curves and ESR spectra of La0.3Ca0.7Mn1?xWxO3 (x = 0.00, 0.04, 0.08, 0.12, 0.15) system. The results showed that: When 0.00≤ x≤0.08, the system exhibits charge ordering (CO) phase, and its spin order experiences the change of paramagnetism (PM)-charge ordering (CO)-antiferro- magnetism (AFM) with decreasing temperature; when x≥0.12, the charge ordering (CO) phase melts, part of charge ordering (CO)phase remains in the paramagnetism (PM)background, the spin order of the system is mainly paramagnetism (PM), and ferromagnetic (FM) clusters appear at low tem- perature.
基金supported by the National Natural Science Foundation of China(51401130)the Natural Science Foundation of Liaoning Province(2014028015)Fundamental Research Foundation of Central Universities(N142304007)
文摘Ho^（3＋） doped La_（2（1-x））Yb_（2x）TiO_5 samples were prepared by sol-gel method. Pyrochlore structured powders were obtained under the annealing of the as-prepared samples at 1100 °C for 3 h in the air. All the samples were characterized by X-ray diffraction（XRD）, scanning electron microscopy（SEM） and photoluminescent spectroscopy. When x=0, we obtained La_2TiO_5 phosphors. Monitored at 546 nm, the excitation spectrum of Ho^（3＋） activated La_2TiO_5 phosphors consisted of a broad band originating from the charge-transfer band（CTB） between Ho^（3＋） ions and the nearest neighboring O^（2-） ions at 250-280 nm and four sharp bands associated to f-f transitions of Ho^（3＋） ions at 350-500 nm. Under the blue light excitation at 461 nm, Ho^（3＋） ion in La_2TiO_5 emitted an intense green emission band at 546 nm due to the transition of ~5S_2, ~5F_4→~5I_8. Two intense bands were observed at 490 nm（blue, ~5F_3→I_8） and 663 nm（red, ~5F_5→~5I_8） in the up-conversion（UC） spectrum under 980 nm NIR laser excitation in La_2TiO_5 phosphors activated with Ho^（3＋） alone, whereas they were much different from the down-conversion（DC） luminescent samples. When x=7.5 mol.%-17.5 mol.%, the UC emission spectra of them dominated at 546 nm（green, ~5S_2, ~5F_4→~5I_8） and enhanced significantly with the dose of Yb^（3＋） ion. The decay curve also confirmed that the transitions of ~5F_4→~5I_8 and ~5S_2→~5I_8 were merged into one emission band at 546 nm.
