Rao Guanghui

New intermetallic compounds RCo9Si4 (R=Pr, Nd) with a tetragonal NaZn13-derivative structure

Abstract Two new intermetallic compounds RCo 9 Si 4 (R = Pr, Nd) with tetragonal NaZn 13 -derivative structure have been synthesized. Their crystal structures have been determined by X-ray powder diffraction and refined by the Rietveld technique. The space group for the tetragonal structure is I 4/ mcm . The lattice parameters are a = 7.789(1) A , c = 11.509(2) A and a = 7.791(2) A , c = 11.516(3) A for PrCo 9 Si 4 and NdCo 9 Si 4 respectively. The Si atoms strongly prefer to occupy the crystallographic 161(2) position.

Synthesis and superconductivity of Nd0.7Sr1.3Cu(O,F)4−δ with Tc = 44 K

Abstract Superconducting cuprate fluorides Nd 0.7 Sr 1.3 Cu(O,F) 4−δ with T c = 44 K were obtained by solid phase fluorination of the T-structure Nd 0.7 Sr 1.3 CuO 4− y at low temperature (200–300°C) using CuF 2 as fluorinating reagent. The oxyfluoride has K 2 NiF 4 structure with S.G. 14/mmm as its precursors, but the evident lattice expansions were observed. The a -axis expands from 3.7257(2) A to 3.9288 (5) A and c -axis from 12.8240 (3) A to 12.9630 (2) A. No trace of SrF 2 was detected in these fluorinated products. XRD and magnetic measurement revealed that the superconductivity in the fluorinated products originated from the oxyfluorides with reduced CuO 2 plane and in the presence of the apical anion.

Subsolidus phase relations in BiO3/2–GdO3/2–CuO system

The subsolidus phase relations of BiO3/2-GdO3/2-CuO ternary systems, its binary systems and crystallographic parameters of compounds are investigated by X-ray powder diffraction. The room temperature section of the phase diagram of the BiO3/2-GdO3/2-CuO system can be divided into four two-phase regions and six three-phase regions. No ternary compound was found. There exists three solid solutions (theta, alpha and gamma) in the (BiO3/2 )(1-x)-(GdO3/2)(x) system. The solid solution theta (0.03 less than or equal to x less than or equal to 0.09) has space group P (4) over bar 2(1)c, the solid solutions alpha (0.1 less than or equal to x less than or equal to 0.12) and gamma (0.58 less than or equal to x less than or equal to 0.7) have space group R (3) over bar m with lattice parameters n=3.9590(7) Angstrom, and c=27.895(5) Angstrom for Bi9GdO15(alpha phase) and a=3.8174(5), c=9.5445(2) Angstrom for Bi2Gd3O7.5 (gamma phase). For Bi2Gd3O7.5, the Rietveld structure refinement reveals that Bi/Gd atoms occupy the 3a site statistically, O atoms and vacancies occupy the 6c site.

Phase relations in the system La2O3B2O3P2O5

Abstract The subsolidus phase relations in the system La 2 O 2 B 2 O 3 P 2 O 5 were investigated. The system can be divided into 12 three-phase regions. There are nine binary compounds and one ternary compound in this system. The ternary compound La 7 O 6 (BO ? )(PO 4 ) 2 has a monoclinic structure, space group P 2 1 /n, with lattice constants a = 7.0172A, b = 17.9125A, c = 12.6500A, β = 97.516°, V = 1576.39A, and Z = 4.

STRUCTURE AND MAGNETIC PROPERTIES OF NDCO13-XSIX

NdCo13-xSix (2.5 less than or equal to x less than or equal to 4.0) compounds have been prepared by are melting and subsequent annealing. X-ray powder diffraction indicated that they crystallized in a tetragonal NaZn13-derivative structure. Thermomagnetic measurements in an applied held of 1.2 T revealed that the compounds are ferromagnetic. From the magnetization at 1.5 K a value of 2.2 mu(B) is obtained for the magnetic moment of Nd3+, and this value is about 1.4 mu(B) smaller than the value of a free Nd3+ ion, i.e., the Nd3+ moment in these compounds seems to be significantly quenched

SUBSOLIDUS PHASE-RELATIONS OF THE LA-FE-AL TERNARY-SYSTEM

The subsolidus phase relations of the La-Fe-Al ternary system have been investigated by X-ray powder diffraction. In this ternary system, there exist six kinds of ternary compounds and their solid solutions, i.e. A (La/Fe/Al (at.%)=10/12/78), B (36/44/20), LaFe4Al8, LaFe13-xAlx (2.34 less than or equal to x less than or equal to 7.28), La2Fe7Al10 and LaAl2-xFex (0 less than or equal to x less than or equal to 0.4). A and B are two kinds of new ternary compounds with unknown crystal structures. For the LaFe13-xAlx solid solution with cubic NaZn13-type structure, the solid solubility has been determined by a parametric method. The ternary system can be divided into 17 three-phase and four two-phase regions. The subsolidus phase relations of the La-Fe-Al ternary system are presented.

Structure, dielectric and magnetodielectric properties of Bi(1-x)Gd(x)FeO(3) Ceramics

Different magnetodielectric effects were observed in Bi(1-x)Gd(x)FeO(3) ceramics depending on gadolinium content. A positive one was observed in the samples with x = 0 : 3 at room temperature. Temperature-dependent dielectric response and x-ray diffraction confirm the occurrence of a structural transition in the Pbnm phase at low temperature for the samples with x <= 0.4. While the positive magnetodielectric effects can be attributed to a coupling of magnetic and crystallographic structures of the R 3 c phase, the observed negative magnetodielectric effect in the Pbnm phase can be associated with a low-temperature modification of the Pbnm structure. The observed dual-signed magnetodielectric effects suggest that the Bi(1-x)Gd(x)FeO(3) oxides are a good prototype for understanding the magnetodielectric coupling mechanism in this kind of materials.

Crystal structure and magnetic properties of Nd(Mn1 xFex)2Si2 compounds

X-ray powder diffraction, resistivity and magnetization studies have been performed on polycrystalline Nd(Fe(x)Mn(1-x))(2)Si(2) (0 <= x <= 1) compounds which crystallize in a ThCr(2)Si(2)-type structure with the space group 14/mmm. The field-cooled temperature dependence of the magnetization curves shows that, at low temperatures, NdFe(2)Si(2) is antiferromagnetic, while the other compounds show ferromagnetic behaviour. The substitution of Fe for Mn leads to a decrease in lattice parameters a, c and unit-cell volume V. The Curie temperature of the compounds first increases, reaches a maximum around x = 0.7, then decreases with Fe content. However, the saturation magnetization decreases monotonically with increasing Fe content. This Fe concentration dependent magnetization of Nd(Fe(x)Mn(1-x))(2)Si(2) compounds can be well explained by taking into account the complex effect on magnetic properties due to the substitution of Mn by Fe. The temperatures square dependence on electrical resistivity indicates that the curve of Nd(Fe(0.6)Mn(0.4))(2)Si(2) has a quasi-linear character above its Curie temperature, which is typical of simple metals.X-ray powder diffraction, resistivity and magnetization studies have been performed on polycrystalline Nd(Fe(x)Mn(1-x))(2)Si(2) (0 <= x <= 1) compounds which crystallize in a ThCr(2)Si(2)-type structure with the space group 14/mmm. The field-cooled temperature dependence of the magnetization curves shows that, at low temperatures, NdFe(2)Si(2) is antiferromagnetic, while the other compounds show ferromagnetic behaviour. The substitution of Fe for Mn leads to a decrease in lattice parameters a, c and unit-cell volume V. The Curie temperature of the compounds first increases, reaches a maximum around x = 0.7, then decreases with Fe content. However, the saturation magnetization decreases monotonically with increasing Fe content. This Fe concentration dependent magnetization of Nd(Fe(x)Mn(1-x))(2)Si(2) compounds can be well explained by taking into account the complex effect on magnetic properties due to the substitution of Mn by Fe. The temperatures square dependence on electrical resistivity indicates that the curve of Nd(Fe(0.6)Mn(0.4))(2)Si(2) has a quasi-linear character above its Curie temperature, which is typical of simple metals.

MAGNETORESISTANCE BEHAVIOR OF LA(2-X)/3BIX/3CA1/3MNO3 (X = 0.4)

The magnetoresistance (MR) behavior of La(2-x/)3Bi(x/3)Ca(1/3)MnO(3) (x = 0.4) compound was investigated. The compound exhibits complex magnetic transitions, i.e., paramagnetic-canted ferromagnetic-ferromagnetic-spin glass transitions. The temperature dependence of resistivity of the compound indicates a semiconducting behavior, and no semiconductor-metal transition was associated with these magnetic transitions. The magnetoresistance ratio exhibits a critical maximum corresponding to the canted ferromagnetic transition. A MR ratio as large as 86% was observed at 85 K. The temperature dependence of MR ratio is well described by the relation of (rho(o)-rho(H))/rho(o) = A(M/M-s)(2).