Liang Jingkui

ANISOTROPIC THERMAL-EXPANSION OF LIB3O5

The anisotropic thermal expansion of LiB3O5 has been studied along the principal crystallographic directions over the temperature range of 17 to 790 degrees C by means of high-temperature X-ray powder diffraction. This orthorhombic crystal exhibits strongly anisotropic expansion with coefficients of 108.2*10-6 K-1 for (100), 33.6*10-6 K-1 for (010) and -88.0*10-6 K-1 for (001) at 50 degrees C. The coefficients tend to zero when the temperature approaches the crystals peritectic reaction point.

Studies on flux systems for the single crystal growth of β-BaB2O4

Abstract The phase equilibrium relationships in the BaB 2 O 4 NaCl, BaB 2 O 4 CaF 2 and BaB 2 O 4 Na 2 SO 4 systems have been investigated by means of X-ray and thermal analysis. The systems of BaB 2 O 4 with other alkali and alkali-earth metal inorganic salts have also been reviewed. Rules governing the selection of fluxes for single crystal growth of β-BaB 2 O 4 have been summarized.

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.

Phase relations and compounds in the Sm2O3-BaO-CuO system at 950 °C in air

Abstract The subsolidus phase relations of the Sm2O3-BaO-CuO system at 950 °C in air were investigated. The system can be divided into eight three-phase regions and two two-phase regions. There is one ternary compound Sm2BaCuO5, a solid solution Sm1+xBa2−xCu3Oy, and three binary compounds Sm2CuO4, BaCuO2, and Sm2BaO4. Sm2BaO4 was isolated with orthorhombic unit cell, space group Pbna, and lattice constants a = 12.313 A , b = 10.535 A and c = 3.564 A . The solid solution range of Sm1+xBa2−xCu3Oy was determined from x = 0 to 0.4, and a phase transition from orthorhombic to tetragonal symmetry occurs at x = 0.25. With an increase in x, Tc decreases monotonically from 94 K (onset), and the compounds of Sm1+xBa2−xCu3Oy finally become semiconducting.

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.

The role of precursors in making Bi(Pb)-Sr-Ca-Cu-O superconductors

Sr-Ca-Cu-O compounds were used as precursors to prepare Bi system superconductors. When Sr2Ca2Cu3O7 and Sr2Ca2Cu4O8 react with Bi2O3 (PbO) for 30 h, samples of Tc(0) higher than 100 K were obtained. Bi2O3 may have been directly inserted into the layered structures of Sr-Ca-Cu-O compounds and hence Bi-system superconductors formed; the authors found that the existence of Ca7Bi10O22 in the Bi system superconductors reduced Tc(0), and extra CuO assisted the formation of the superconducting phase.

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.

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.