Journal of The Less Common Metals最新文献

Tetragonal ZrO₂-SiC whisker composite powders have been synthesized by the sol-gel method. Analysis reveals that SiC whiskers are homogeneously dispersed in the composite powder, the matrix being ultrafine metastable tetragonal ZrO₂. The sintering properties of the composite have been investigated. SiC whiskers favour an increase in content of metastable tetragonal ZrO₂. When the SiC whisker content is high, the critical stress intensity factor (K_IC) decreases.

Dark red-brown CsUCl₄ · 3H₂O crystallizes in the monoclinic crystal system (a = 711.6(1) pm, b = 867.2(2) pm, c = 807.1(2) pm; β = 99.28(3)°, space group $\text{P2}{}_1\text{m}$, Z = 2). Uranium has a coordination number of nine (tricapped trigonal prism) consisting of six chlorine atoms and three oxygen atoms (representing water) with mean distances of 295.7 and 255.2 pm respectively. Caesium is surrounded by eight chlorine atoms in the shape of a distorted cube which is capped by two water ligands, the mean Cs-Cl distance being 360.2 pm.

The solid solution system U(Mn_1−xFe_x)₂Si₂ (0 ⩽ x ⩽ 1) was synthesized by direct melting of the UMn₂Si₂ and UFe₂Si₂ components and investigated by X-ray diffraction, magnetometric and Mössbauer effect methods. The series investigated behaves similarly in many respects to the isostructural ones formed with other elements. The values of the lattice constants obey Vegard's law. The isomer shift and quadrupole splitting vary gradually across the range of iron concentration. The quadrupole splitting reflects a deviation from the ideal tetrahedral coordination of iron site neighbours. The manganese-rich samples (x ⩽ 0.3) were found to be ferromagnets at 78 K while the others behave as Pauli paramagnets above 78 K. The Curie temperature and hyperfine magnetic field decrease strongly with increasing iron concentration. The composition dependence of the Curie temperature is well described by the Heisenberg model in which the magnetic interactions between nearest neighbours and the uniaxial magnetic anisotropy were taken into account.

Silver-tantalum with the composition Ag₇TaS₆ has been prepared by a sealed silica tube method at 500 °C for 4 days. The compound Ag₇TaS₆ crystallizes in the cubic system with the unit cell dimension $\text{a = 10.5139 ± 0.0003}\text{A}\text{̊}$. The observed density is D_obs = 6.55 ± 0.03 g cm⁻³. The unit cell contains four formula units of Ag₇TaS₆. The space group $\text{F}\text{4}\text{̄}\text{3m}$ is proposed by analogy with the structure of the similar group of silver-containing ternary chalcogenides. Refinement was performed by using X-ray powder diffraction data, the positional parameters for Ag₇TaS₆ being determined. In the structure of Ag₇TaS₆ the sulphur atoms form centred, interpenetrating, distorted icosahedra and the 11.23, 9.77 and 7.00 silver atoms are statistically distributed over 96i and two 48h sites respectively. This compound is a mixed conductor. The ionic conductivity σ_ag+ reaches $\text{1.8 × 10}{}^{\mathrm{-1}}\text{Ω}{}^{\mathrm{-1}}\text{cm}{}^{\mathrm{-1}}$ at 200 °C.

Previous observations have shown smaller grain sizes and higher strengths in W-Ni-Fe heavy alloys containing molybdenum. This study focuses on the microstructure and grain growth kinetics for the W-Mo-Ni-Fe system processed at 1500 °C. The initial rate of grain growth follows an approximate square root time dependence in contrast to the cube root dependence typical for W-Ni-Fe alloys. Microprobe measurements show that chemical gradients are present in the solid grains, with high molybdenum content cores. The retarded grain growth from molybdenum additions is the result of a decreased tungsten solubility in the liquid during the early stages of sintering.