Structural and magnetic properties of hydrides R3Fe29-xVxHy (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and intrinsic magnetic properties of the hydrides R3Fe29 - xVxHy (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed in this work. The lattice constants a, b, and c and the unit cell volume of R3Fe29 - xVxHy decrease with increasing rare-earth atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Hydrogenation results in regular anisotropic expansions along the a-, b-, and c-axes in this series of hydrides. Abnormal crystallographic and magnetic properties of Ce3Fe27.5V1.5H6.5, like Ce3Fe27.5V1.5, suggest that the Ce ion is non-triply ionized. Hydrogenation leads to the increase in both Curie temperature for all the compounds and in the saturation magnetization at 4.2 K and RT for R3Fe29 - xVx with R = Y, Ce, Nd, Sm, Gd, and Dy, except for Tb. Hydrogenation also leads to a decrease in the anisotropy field at 4.2 K and RT for R3Fe29 - xVx with R = Y, Ce, Nd, Gd, Tb, and Dy, except for Sm. The Ce3Fe27.5V1.5 and Gd3Fe28.4V0.6 show the larger storage of hydrogen with y = 6.5 and 6.9 in these hydrides. (C) 1998 Elsevier Science B.V. All rights reserved.

Crystallographic and magnetic properties of the hydrides R3Fe29-xCrxHy (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic study of the structural and intrinsic magnetic properties of the hydrides R3Fe29-xCrxHy (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed. Hydrogenation lends to a relative volume expansion of the unit cell and a decrease in x-ray density for each compound. Anisotropic expansions mainly along the n- and b-axes rather than along the c-axis for all of the compounds upon hydrogenation are observed. The lattice constants and the unit-cell volume of R3Fe29-xCrx and R3Fe29-xCrxHy decrease with increasing R atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Hydrogenation results in an increase in the Curie temperature and a corresponding increase in the saturation magnetization at room temperature for each compound. After hydrogenation a decrease of 0.34 mu(B)/Fe in the average Fe atomic magnetic moment and a slight increase in the anisotropy field for Y3Fe27.2Cr1.8 are achieved at 4.2 K. First-order magnetization processes (FOMP) occur in magnetic fields of around 1.5 T and 4.0 T at 4.2 K for Nd3Fe24.5Cr4.5H5.0 and TD3Fe27.0Cr2.0H2.8, and around 1.4 T at room temperature for Gd3Fe28.0Cr1.0H4.2. The abnormal crystallographic and magnetic properties of Ce3Fe25.0Cr4.0 and Ce3Fe25.0Cr4.0H5.4 suggest that the Ce ion non-triply ionized.

Crystallographic and magnetic properties of nitride R3Fe29-xCrxN4 (R = Y, Ca, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and magnetic properties of nitride R3Fe29-xCrxN4 (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed. The lattice constants and unit cell volume decrease with increasing rare earth atomic number from Nd to Dy, reflecting the lanthanide contraction. After nitrogenation the relative volume expansion of each nitride is around between 5% and 7%. The nitrogenation results in a good improvement in the Curie temperature, the saturation magnetization and anisotropy fields at 4.2 K, and room temperature for R3Fe29-xCrxN4. Magnetohistory effects of R3Fe29-xCrxN4 and R3Fe29-xCrx (R=Nd and Sm) are observed in a low field of 0.04 T. First order magnetization process occurs in Sm3Fe24.0Cr5.0N4 in magnetic fields of 2.8 T at 4.2 K. After nitrogenation, the easy magnetization direction of Sm3Fe24.0Cr5.0 is changed from the easy-cone structure to the uniaxial. The good intrinsic magnetic properties of Sm3Fe24.0Cr5.0N4 make this compound a hopeful candidate for new high-performance hard magnets. (C) 1998 American Institute of Physics.

Crystallographic and magnetic properties of R3Fe29-xVxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy)

A systematic investigation of crystallographic and magnetic properties of nitride R3Fe29-xVxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed. Nitrogenation leads to a relative volume expansion of about 6%. The lattice constants and unit cell volume decrease with increasing rare-earth atomic number from Nd to Dy, reflecting the lanthanide contraction. On average, the Curie temperature increases due to the nitrogenation to about 200 K compared with its parent compound. Generally speaking, nitrogenation also results in a remarkable improvement of the saturation magnetization and anisotropy fields at 4.2 K and room temperature for R3Fe29-xVxN4 compared with their parent compounds. The transition temperature indicates the spin reorientations of R3Fe29-xVxN4 for R = Nd and Sm are at around 375 and 370 K which are higher than that of R3Fe29-xVx, for R = Nd and Sm 145 and 140 K, respectively. The magnetohistory effects of R3Fe29-xVxN4 (R = Ce, Nd, and Sm) are observed in low fields of 0.04 T. After nitrogenation the easy magnetization direction of Sm3Fe26.7V2.3 is changed from an easy-cone structure to the b-axis. As a preliminary result, a maximum remanence B-r of 0.94 T, an intrinsic coercivity mu(0)H(C) of 0.75 T, and a maximum energy product (B H)(max) of 108.5 kJ m(-3) for the nitride magnet Sm3Fe26.7V2.3N4 are achieved by ball-milling at 293 K.

Structure and magnetic properties of nitrides R3Fe29-xCrxN4

A systematic investigation of nitrides R3F29-xCrxN4 (R = Y, Ce, Nd, Sm, Gd, Tb, and Dy) has been performed. The nitrogen concentration in the nitride R3Fe29-xCrxNy was determined to be y = 4. Nitrogenation leads to a relative volume expansion of about 5.3%. The lattice constants and unit cell volume decrease with increasing rare earth atomic number from Nd to Dy, reflecting the lanthanide contraction. In average, the increase of Curie temperature upon nitrogenation is about 200 K, compared with its parent compound. The nitrogenation also results in a remarkable improvement in the saturation magnetization and anisotropy fields for R3Fe29-x CrxN4 at 4.2 K and room temperature, compared with their parent compounds. A spin reorientation of Nd3Fe24.5Cr4.5N4 occurs at around 368 K, which is 138 K higher than that of Nd3F24.5Cr4.5. Magnetohistory effects of R3Fe29-xCrxN4 (R = Nd and Sm) are observed in a low field of 0.04 T. First-order magnetization process occurs in Sm3Fe24.0Cr5.0N4 in magnetic fields of around 3.0 T at 4.2 K. After nitrogenation the easy magnetization direction of Sm3Fe24.0C5.0 is changed from the easy-cone structure to the uniaxial. The excellent intrinsic magnetic properties of Sm3Fe24.0Cr5.0N4 make this compound a hopeful candidate for new high-performance permanent magnets.

Formation, structure and fluorescence of CdS clusters in a mesoporous zeolite

CdS clusters are formed in the pores of a mesoporous zeolite in which the size of the clusters may be adjusted. The size of the clusters increases as the CdS loading is increased. X-ray diffraction investigation shows that the lattice constants of the clusters contract upon increasing size. This contraction is attributed to an increase of the static pressure exercised by the zeolite framework as the clusters grow bigger. Both the excitonic and trapped emission bands are detected and become more intensive upon decreasing size. Three absorption bands appear in the photoluminescence excitation (PLE) spectra and they shift to the blue as cluster size decreases. Based on the effective-mass approximation, the three bands are assigned to the 1S-1S, 1S-1P and 1S-1D transitions, respectively. The size-dependence of the PLE spectra can also be explained. (C) 1997 Elsevier Science Ltd.

Evaluation of both composition and strain distributions in InGaN epitaxial film using x-ray diffraction techniques

The composition and stain distributions in the InGaN epitaxial films are jointly measured by employing various x-ray diffraction (XRD) techniques, including out-of-plane XRD at special planes, in-plane grazing incidence XRD, and reciprocal space mapping (RSM). It is confirmed that the measurement of (204) reflection allows a rapid access to estimate the composition without considering the influence of biaxial strain. The two-dimensional RSM checks composition and degree of strain relaxation jointly, revealing an inhomogeneous strain distribution profile along the growth direction. As the film thickness increases from 100 nm to 450 nm, the strain status of InGaN films gradually transfers from almost fully strained to fully relaxed state and then more in atoms incorporate into the film, while the near-interface region of InGaN films remains pseudomorphic to GaN.

Assessment of the structural properties of GaAs/Si epilayers using X-ray (004) and (220) reflections

We improved the method previously used to determine the lattice constants and misorientation of GaAs/Si by recording the patterns of X-ray (004) and (220) reflections. The (220) reflection was measured from the (110) cross section of a GaAs/Si epilayer. The structural properties of the GaAs/Si epilayers grown by metal-organic chemical-vapor deposition (MOCVD) using an ultrathin a-Si buffer layer were investigated. The rotation angle of GaAs/Si epilayers grown by MOCVD using an a-Si buffer layer is very small and the lattice constants of these GaAs/Si epilayers agree quite well with elastic theory.

A study on GaP/Si heterostructures grown by GS-MBE

GaP/Si is a promoting heterostructure for Si-based optoelectronic devices since lattice constants of GaP and Si are so closed that they can match with each other. GaP was successfully grow on (100) Si subtracts by Gas-Source Molecular Bean Epitaxy (GS-MBE) in the study. The GaP/Si heterostructure was characterized by X-ray double crystal diffraction, Anger electron spectrograph, X-ray photonic spectrograph and photoluminescence (PL) measurements. The results showed that the epitaxial GaP layers are single crystalline, in which a parallel to and a (perpendicular to)are 0.54322 and 0.54625 nm, respectively. The peaks in PL spectra of GaP epitaxial layer grown on Si are 650, 627 and 640 nm, respectively. The study demonstrated that GaP/Si is a kind of lattice matched heterostructures and will be a promoting materials for future integrated photonics.

Crystallographic and magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb and Dy; T=V and Cr)

The crystallographic and intrinsic magnetic properties of hydride R3Fe29-xTxHy (R=Y, Ce, Nd, Sm, Gd, Tb, and Dy; T=V and Cr) have been investigated. The lattice constants and the unit cell volume of R3Fe29-xTxHy decrease with increasing R atomic number from Nd to Dy, except for Ce, reflecting the lanthanide contraction. Regular anisotropic expansions, mainly along the a- and b-axis rather than along the c-axis, are observed for all the compounds upon hydrogenation. Hydrogenation leads to an increase in Curie temperature. First-order magnetization processes (FOMP) occur in magnetic fields of around 1.5 T and 4.0 T at 4.2 K for Nd3Fe24.5Cr4.5H5.0 and Tb(3)Fc(27.0)Cr(2.0)H(2.8), and around 1.4 T at room temperature for Gd3Fe28.0Cr1.0H4.2 Abnormal crystallographic and magnetic properties of Ce3Fe29-xTxHy suggest that the Ce ion is non-triply ionized.

Preparation and upconversion luminescence of nanocrystalline Gd2O3 : Er3+, Yb3+

Nanocrystalline Gd1.77Yb0.2 Er0.03O3 samples were prepared by combustion and precipitation methods. Structures and upconversion luminescence properties of samples were studied. The results of XRD show that all samples are cubic structure, the average crystallite size could be calculated as 23 nm and 39 nm, respectively. The lattice constants were obtained. The FT-IR spectra were measured to investigate the vibrational feature of the samples.

Study on structure and oxide ionic conductivity for new compound Ce(6-x)Ln(x)MoO(15-delta)

A new compound Ce(6-x)Ln(x)MoO(15-delta) has been synthesized by wet-chemistry method. Their crystal structure and oxide ionic conductivity were characterized by powder X-ray diffraction, Raman, IR spectrum and A.C. impedance technique. The XRD results showed that Ce6MO15-delta, Ce(5)LnMoO(15-delta) have cubic symmetry with Fm3m space group. The refined lattice parameters showed that their lattice constants decrease with the decrease of the ionic radius of Ln(3+). The electrochemical measurements showed that the ionic conductivity of resulting oxides Ce(6-x)Ln(x)MoO(15-delta) have an enhance, which may be a kind of promising material for SOFCs.

Structural and magnetic properties of (PrxSm1-x)Mn2Si2

Crystallographic and magnetic properties of intermetallic compounds (PrxSm1-x) Mn2Si2 (x = 0 similar to 0.80) have been investigated by X-ray powder diffraction, XPS and magnetic measurements. All the compounds crystallize in ThCr2Si2-type structure. Substitution of Pr for Sm leads to the increase of the lattice constants and the transition from antiferromagnetism (AFM) to ferromagnetism (FM). The valence-fluctuation in the compounds was observed and the relation between the change of electron binding energy and magnetic properties was also discussed preliminarily.

Synthesis, structure and properties of alpha-Keggin-type of K6H3[ZnW11O40Al]center dot 9.5H(2)O

A new heteropolycomplex, K6H3[ZnW11O40Al] . 9.5H(2)O was prepared and characterized by means of elemental analysis, IR, UV spectroscopy, Al-27 NMR, electrochemistry and X-ray crystallography. The crystal of K6H3[ZnW11O40Al] . 9.5H(2)O is cubic, space group Fm-3m, with lattice constants a=b=c=2. 144 8(2) nm, V = 9.866(2) nm(3), Mo radiation, R = 0.057 8 for 497 independent data with [I>2 delta(I)]. The anion is of alpha-type Keggin structure with C-s symmetry.

PREPARATION, STRUCTURE AND INFLUENCE OF VALENCE STATE ON LASR2-XCAXV3O9+/-Y

New compounds LaSr2-xCa-(x)V3O9+/-y (x = 0.0, 0.67, 1.0, 1.33 and 2.0) have been synthesized with a simple new method X ray powder diffraction results indicate that they are single compound. Their lattice constants are calculated. The structure of LaSr2-xCa(x)V39+/-y changed from cubic to orthorhombic and back to cubic with the increase of calcium content. The results of weight gain in TG and XPS curves show that vanadium with lower valent state is oxidized to higher valent state at higher temperature. The oxygen content of new compounds are calculated from the weight gain. It is shown that V3+ and V4+ may coexist in LaSr2-xCa(x)V3O9+/-y. These compounds show that low resistivity.