Infrared absorption spectra of La0.67-xPrxCa0.33MnO3 （x= 0, 0.18 and 0.36） are experimentally studied in the temperature range 20 -300K. Absorption peak splitting corresponding to the stretching oscillation of the M...Infrared absorption spectra of La0.67-xPrxCa0.33MnO3 （x= 0, 0.18 and 0.36） are experimentally studied in the temperature range 20 -300K. Absorption peak splitting corresponding to the stretching oscillation of the Mn-O bond, together with a shift of peak position, is observed below the Curie temperature. These features weaken and even disappear as the samples are warmed up to the Curie temperature, which indicates that this anomaly may be a result of phase separation in the compounds.展开更多
Structural properties of the organic-inorganic hybrid(C_(2)H_(5)NH_(3))_(2)CuCl_(4) have been investigated by means of x-ray powder diffraction and Rietveld analysis. A structural phase transition from Pbca to Aba2 oc...Structural properties of the organic-inorganic hybrid(C_(2)H_(5)NH_(3))_(2)CuCl_(4) have been investigated by means of x-ray powder diffraction and Rietveld analysis. A structural phase transition from Pbca to Aba2 occurs at T_(4)= 240 K, which results in a paraelectric–ferroelectric phase transition. The release of the Jahn–Teller distortion with increasing temperature toward T_(4) is revealed by the structural analysis.展开更多
TiO2-δ nanoparticles are synthesized by the sol-gel method and annealed under different reducing atmosphere. The x-ray diffraction patterns show that anatase is the dominant phase with small amounts of the futile pha...TiO2-δ nanoparticles are synthesized by the sol-gel method and annealed under different reducing atmosphere. The x-ray diffraction patterns show that anatase is the dominant phase with small amounts of the futile phase of TiO2-δ for all the samples. Magnetic measurements indicate that the samples annealed in reducing atmosphere exhibit unprecedented room-temperature ferromagnetism, in particular, the saturation magnetization Ms is up to about 8.6 × 10^-3 emu/g for the sample annealed in H2/Ar mixture. Analysis of the x-ray photoelectron spectroscopy spectra for the samples processed under different conditions indicates that the amounts of Ti^3＋ or Ti^2＋ cations, namely, the concentration of oxygen vacancies, increase with intensifying reducing atmosphere during processing, which shows that ferromagnetism in this material strongly depends on the concentration of oxygen vacancies. The relationships between the ferromagnetism and the crystal structure as well as the grain size in this material are also discussed.展开更多
We investigate the electronic structure, chemical bonding and elastic properties of the hexagonal aluminum carbonitride, Al5C3N, by ab initio calculations. Al5C3N is a semiconductor with a narrow indirect gap of 0.81 ...We investigate the electronic structure, chemical bonding and elastic properties of the hexagonal aluminum carbonitride, Al5C3N, by ab initio calculations. Al5C3N is a semiconductor with a narrow indirect gap of 0.81 eV. The valence bands below the Fermi level （EF） originate from the hybridized Al p-C p and A1 p-N p states. The calculated bulk and Young＇s moduli are 201 GPa and 292 GPa, which are slightly lower than those of Ti3SiC2. The values of the bulk-to-shear-modulus and bulk-modulus-to-c44 are 1.73 and 1.97, respectively, which are higher than those of Ti2AlC and Ti2AlN, indicating that Al5C3N is a ductile ceramic.展开更多
The luminescence properties of lanthanum silicon oxynitride （La-Si-O-N） series doped by trivalent Ce ions have been investigated to seek for tunable wavelength-conversion phosphor for white light emitting diode appl...The luminescence properties of lanthanum silicon oxynitride （La-Si-O-N） series doped by trivalent Ce ions have been investigated to seek for tunable wavelength-conversion phosphor for white light emitting diode applications. Four compound hosts of LaSiO2N, La4Si2OTN2, La5Si3012N, and La2Si603N8 were synthesized and examined in this work. Crystallographic examination for the equal amount of Ce^3＋ substitution indicated that the covalency degree decreased in a sequence LaSiO2N 〉 La2Si603Ns 〉 La4Si2OTN2 〉 LasSi3O12N, not simply in correlation to the ratio of N3/O2. Excitation and emission spectrum measurements showed the main features of Ce^3＋ luminescence in the series： the centre of gravity of 5d bands depends on crystal-field splitting more strongly than that on covalency of Ce-N bonding; nephelauxetic effect could not be observed clearly for the investigated series; to some extent Stokes shift was dominated by crystal-field splitting rather than Ce-N covalency degree.展开更多
Polycrystalline samples La0.67-xDyxCa0.3MnO3 (x=0～0.6) were prepared by traditional solid-state reaction method. The magnetization and resistivity of the samples were measured by PPMS (Quantum Design). The infrared a...Polycrystalline samples La0.67-xDyxCa0.3MnO3 (x=0～0.6) were prepared by traditional solid-state reaction method. The magnetization and resistivity of the samples were measured by PPMS (Quantum Design). The infrared absorption spectra (temperature scope: 20～300 K, frequency: 400～4400 cm-1) were collected by WQF-410 Fourier Transform Spectrophotometer. The substitution of Dy on La sites results in a decrease of the Curie temperature Tc and the magnetization, and also induces cluster-glass behaviors. The resistivity of the compounds is enhanced by Dy doped. Infrared absorption spectra provide the evidence of the variety of Mn-O-Mn bond length due to the Dy substitution and temperature changing. These results suggest that all of the magnetic coupling between Dy and Mn sublattice and La-Dy average ionic radius contribute to the magnetic and electronic character.展开更多
Polycrystalline samples of La0.67-xPrxCa0.33MnO3(x=0～0.67) were synthesized by a conventional solid state reaction. X-ray diffraction revealed that the samples were all of single phase with an orthorhombic distorted ...Polycrystalline samples of La0.67-xPrxCa0.33MnO3(x=0～0.67) were synthesized by a conventional solid state reaction. X-ray diffraction revealed that the samples were all of single phase with an orthorhombic distorted perovskite structure. The magnetization depended on temperature measured in FC (field cooling) and ZFC (zero field cooling). It revealed that the compounds mainly underwent a ferromagnetic transition (TC) when the less Pr doped (x<0.4). With increasing doping content (x>0.5), the ferromagnetic transition disappeared and the antiferromagnetic transition (TN) was dominant. Charge ordering (TCO) also emerged when x>0.36. The transition temperatures TN and TCO would change with the Pr doping content. The phase separation could be used to explain these characters occurred in these polycrystalline samples.展开更多
The structure, magnetic properties and magnetostriction of PrxTb1-x(Fe0.6Co0.4)1.9 alloys were investigated. It was found that PrxTb1-x(Fe0.6Co0.4)1.9 alloys with x<0.4 were composed of single cubic Laves phase, wh...The structure, magnetic properties and magnetostriction of PrxTb1-x(Fe0.6Co0.4)1.9 alloys were investigated. It was found that PrxTb1-x(Fe0.6Co0.4)1.9 alloys with x<0.4 were composed of single cubic Laves phase, while a mass of PuNi3-type phase appeared when the Pr concentration was higher than 0.4. The magnetization measurement showed that there were two different magnetic phases in Pr0.2Tb0.8(Fe0.6Co0.4)1.9 alloys. The saturation magnetostriction of Pr0.2Tb0.8(Fe0.6Co0.4)1.9 alloys at 900 kA·m-1 is 1765×10-6, which was higher than that of Tb0.27Dy0.73Fe2(1600×10-6). The spontaneous magnetostriction λ111 showed a maximum value at x=0.3.展开更多
The structure, Curie temperature and magnetostriction of Pr_ 0.1Ce_ 0.6Tb_ 0.3Fe_ 1.9-xB_x compounds were investigated by means of X-ray diffraction using a Vibrating sample magnetometer and a standard strain techniqu...The structure, Curie temperature and magnetostriction of Pr_ 0.1Ce_ 0.6Tb_ 0.3Fe_ 1.9-xB_x compounds were investigated by means of X-ray diffraction using a Vibrating sample magnetometer and a standard strain technique. All the samples show entire MgCu_2-type laves phase structure. The lattice parameter decreases slightly when x≤0.1, and decreases rapidly when x>0.1 with increasing B content. Curie temperature exhibits a peak at x=0.1. The substitution of B for Fe causes the decrease of magnetostriction at room temperature.展开更多
The structural and magnetic properties of Pr0.1CexTb0.9-xFe1.9 alloys were investigated by using X-ray diffraction, AC susceptibility, VSM and standard strain gauge techniques. The lattice parameter exhibits positive ...The structural and magnetic properties of Pr0.1CexTb0.9-xFe1.9 alloys were investigated by using X-ray diffraction, AC susceptibility, VSM and standard strain gauge techniques. The lattice parameter exhibits positive deviation from Vegard’s law with the increasing Ce content in the range of 0.40.6. Curie temperature decreases linearly with increasing Ce content. The saturation magnetization and magnetostriction decrease when 0.2≤x<0.4 and x>0.6, while abnormally increase with Ce content increasing from 0.4 to 0.6. These abnormal changes of （lattice） parameter, saturation magnetization and magnetostriction can be attributed to the valence fluctuation of Ce （ions.）展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos G50225209 and G50271023, the Key Foundation of Education Ministry of China under Grant G02017 and the Natural Science Foundation of Hebei Province under Grant No G503031.
文摘Infrared absorption spectra of La0.67-xPrxCa0.33MnO3 （x= 0, 0.18 and 0.36） are experimentally studied in the temperature range 20 -300K. Absorption peak splitting corresponding to the stretching oscillation of the Mn-O bond, together with a shift of peak position, is observed below the Curie temperature. These features weaken and even disappear as the samples are warmed up to the Curie temperature, which indicates that this anomaly may be a result of phase separation in the compounds.
基金supported by the National Natural Science Foundation of China (Grant No. 51925605)Fujian Institute of Innovation,Chinese Academy of Sciences(Grant No. FJCXY18040303)the Youth Innovation Promotion of the Chinese Academy of Sciences (Grant No. 2013004)。
文摘Structural properties of the organic-inorganic hybrid(C_(2)H_(5)NH_(3))_(2)CuCl_(4) have been investigated by means of x-ray powder diffraction and Rietveld analysis. A structural phase transition from Pbca to Aba2 occurs at T_(4)= 240 K, which results in a paraelectric–ferroelectric phase transition. The release of the Jahn–Teller distortion with increasing temperature toward T_(4) is revealed by the structural analysis.
基金Supported by the National Natural Science Foundation of China under Grant No 50674071, the Tianjin Natural Science Foundation （06YFJZJC01300）, the Programme for New Century Excellent Talents in University （NCET-06-0245）, and the Platform Project of Tianjin for Innovation in Science and Technology and Environmental Construction （06TXTJJC13900）.
文摘TiO2-δ nanoparticles are synthesized by the sol-gel method and annealed under different reducing atmosphere. The x-ray diffraction patterns show that anatase is the dominant phase with small amounts of the futile phase of TiO2-δ for all the samples. Magnetic measurements indicate that the samples annealed in reducing atmosphere exhibit unprecedented room-temperature ferromagnetism, in particular, the saturation magnetization Ms is up to about 8.6 × 10^-3 emu/g for the sample annealed in H2/Ar mixture. Analysis of the x-ray photoelectron spectroscopy spectra for the samples processed under different conditions indicates that the amounts of Ti^3＋ or Ti^2＋ cations, namely, the concentration of oxygen vacancies, increase with intensifying reducing atmosphere during processing, which shows that ferromagnetism in this material strongly depends on the concentration of oxygen vacancies. The relationships between the ferromagnetism and the crystal structure as well as the grain size in this material are also discussed.
基金supported by the National Natural Science Foundation of China (Grant No. 10974041)the Key Project of Science and Technology for Colleges in Hebei Province,China (Grant No. ZD2010120)
文摘We investigate the electronic structure, chemical bonding and elastic properties of the hexagonal aluminum carbonitride, Al5C3N, by ab initio calculations. Al5C3N is a semiconductor with a narrow indirect gap of 0.81 eV. The valence bands below the Fermi level （EF） originate from the hybridized Al p-C p and A1 p-N p states. The calculated bulk and Young＇s moduli are 201 GPa and 292 GPa, which are slightly lower than those of Ti3SiC2. The values of the bulk-to-shear-modulus and bulk-modulus-to-c44 are 1.73 and 1.97, respectively, which are higher than those of Ti2AlC and Ti2AlN, indicating that Al5C3N is a ductile ceramic.
基金Project supported by the National Natural Science Foundation of China (Grant No. 10974041)the Natural Science Foundation of Hebei Province of China (Grant No. E2010000084)
文摘The luminescence properties of lanthanum silicon oxynitride （La-Si-O-N） series doped by trivalent Ce ions have been investigated to seek for tunable wavelength-conversion phosphor for white light emitting diode applications. Four compound hosts of LaSiO2N, La4Si2OTN2, La5Si3012N, and La2Si603N8 were synthesized and examined in this work. Crystallographic examination for the equal amount of Ce^3＋ substitution indicated that the covalency degree decreased in a sequence LaSiO2N 〉 La2Si603Ns 〉 La4Si2OTN2 〉 LasSi3O12N, not simply in correlation to the ratio of N3/O2. Excitation and emission spectrum measurements showed the main features of Ce^3＋ luminescence in the series： the centre of gravity of 5d bands depends on crystal-field splitting more strongly than that on covalency of Ce-N bonding; nephelauxetic effect could not be observed clearly for the investigated series; to some extent Stokes shift was dominated by crystal-field splitting rather than Ce-N covalency degree.
基金the Natural Science Foundation of Hebei Province (E2006000058)Doctor Foundation of Hebei Univ.Tech.
文摘Polycrystalline samples La0.67-xDyxCa0.3MnO3 (x=0～0.6) were prepared by traditional solid-state reaction method. The magnetization and resistivity of the samples were measured by PPMS (Quantum Design). The infrared absorption spectra (temperature scope: 20～300 K, frequency: 400～4400 cm-1) were collected by WQF-410 Fourier Transform Spectrophotometer. The substitution of Dy on La sites results in a decrease of the Curie temperature Tc and the magnetization, and also induces cluster-glass behaviors. The resistivity of the compounds is enhanced by Dy doped. Infrared absorption spectra provide the evidence of the variety of Mn-O-Mn bond length due to the Dy substitution and temperature changing. These results suggest that all of the magnetic coupling between Dy and Mn sublattice and La-Dy average ionic radius contribute to the magnetic and electronic character.
基金the Nature Science Foundation of Hebei Province (E2006000058)Doctor Foundation of Hebei Univ.Tech.
文摘Polycrystalline samples of La0.67-xPrxCa0.33MnO3(x=0～0.67) were synthesized by a conventional solid state reaction. X-ray diffraction revealed that the samples were all of single phase with an orthorhombic distorted perovskite structure. The magnetization depended on temperature measured in FC (field cooling) and ZFC (zero field cooling). It revealed that the compounds mainly underwent a ferromagnetic transition (TC) when the less Pr doped (x<0.4). With increasing doping content (x>0.5), the ferromagnetic transition disappeared and the antiferromagnetic transition (TN) was dominant. Charge ordering (TCO) also emerged when x>0.36. The transition temperatures TN and TCO would change with the Pr doping content. The phase separation could be used to explain these characters occurred in these polycrystalline samples.
基金the Nature Science Foundation of Hebei Province (E2006000063)Foundation of Hebei Education Department (2005216)
文摘The structure, magnetic properties and magnetostriction of PrxTb1-x(Fe0.6Co0.4)1.9 alloys were investigated. It was found that PrxTb1-x(Fe0.6Co0.4)1.9 alloys with x<0.4 were composed of single cubic Laves phase, while a mass of PuNi3-type phase appeared when the Pr concentration was higher than 0.4. The magnetization measurement showed that there were two different magnetic phases in Pr0.2Tb0.8(Fe0.6Co0.4)1.9 alloys. The saturation magnetostriction of Pr0.2Tb0.8(Fe0.6Co0.4)1.9 alloys at 900 kA·m-1 is 1765×10-6, which was higher than that of Tb0.27Dy0.73Fe2(1600×10-6). The spontaneous magnetostriction λ111 showed a maximum value at x=0.3.
文摘The structure, Curie temperature and magnetostriction of Pr_ 0.1Ce_ 0.6Tb_ 0.3Fe_ 1.9-xB_x compounds were investigated by means of X-ray diffraction using a Vibrating sample magnetometer and a standard strain technique. All the samples show entire MgCu_2-type laves phase structure. The lattice parameter decreases slightly when x≤0.1, and decreases rapidly when x>0.1 with increasing B content. Curie temperature exhibits a peak at x=0.1. The substitution of B for Fe causes the decrease of magnetostriction at room temperature.
基金Project(50271023) supported by the National Natural Foundation Science Foundation of China Project(02017) suppor ted by Key Foundation of Education Ministry
文摘The structural and magnetic properties of Pr0.1CexTb0.9-xFe1.9 alloys were investigated by using X-ray diffraction, AC susceptibility, VSM and standard strain gauge techniques. The lattice parameter exhibits positive deviation from Vegard’s law with the increasing Ce content in the range of 0.40.6. Curie temperature decreases linearly with increasing Ce content. The saturation magnetization and magnetostriction decrease when 0.2≤x<0.4 and x>0.6, while abnormally increase with Ce content increasing from 0.4 to 0.6. These abnormal changes of （lattice） parameter, saturation magnetization and magnetostriction can be attributed to the valence fluctuation of Ce （ions.）
