A 4d-4f heterometallic coordination polymer： Synthesis, crystal structure and near-infrared luminescent properties

A 4d-4f heterometallic coordination polymer, [AgNd(pydc)2]?2H2O (1) (H2pydc=pyridine-3,4-dicarboxylic acid), was synthesized under hydrothermal conditions, and further characterized by elemental analysis, IR, thermogravimetric analysis and single-crystal X-ray dif-fraction. Complex 1 featured a three-dimensional (3D) framework containing one-dimensional (1D) channels occupied by free water molecules, which was constructed from 1D inorganic heterometallic chains and linear pydc linkers. To our knowledge, complex 1 represented a rare example of 3D open-framework 4d-4f heterometallic coordination polymer. After removal of the water molecules from complex 1, the remaining material had high thermal stability. Moreover, the near-infrared luminescent properties of 1 were also investigated in the solid state.     

Hydrogen-induced cleavage fracture of Fe3Al-based intermetallics

Hydrogen-induced fracture of ductile Fe₃Al-based intermetallics was studied through mechanical testing, fracture surface observation, andin situ transmission electron microscopy (TEM) tests of tensile specimens. Mechanical properties of ordinary ductile X-80 pipeline steel (low-alloy steel) were tested and compared with Fe₃Al intermetallics. Elongations of the Fe₃Al alloy decreased from 14 to 10 pct, with increases in the strain rate from 10⁻⁶ to 10⁻³/s. The elongation reduction of Fe₃Al was caused by the hydrogen-induced fracture. There was no elongation reduction when the testing was done in mineral oil. Non-necking occurred near the fracture section, and the fracture surfaces mainly consist of cleavage and partial intergranular morphologies. Elongation near the fracture surface of the Fe₃Al intermetallics was about 14 pct, which is the same as the total elongation. For the pipeline steel, however, an elongation near the fracture cross section was greater than 130 pct, which was much higher than its total elongation of 17 pct.In situ TEM observation on a tensile test sample showed crack propagation accompanied by dislocation plasticity. When the Fe₃Al was precharged cathodically, the crack tip was sharp. Its radius was much less than that obtained without hydrogen charging. The crack propagated along the grain boundary for the charged specimens, but penetrated the grain boundary for the specimen without hydrogen charging. Effects of hydrogen on plastic deformation and grain-boundary cracking are discussed in this article.     

Modeling of the atomic ordering processes in Fe3Al intermetallics by the monte carlo simulation method combined with electronic theory of alloys

The evolution of atomic ordering processes in Fe₃Al has been modeled by the Monte Carlo (MC) simulation method combined with the electronic theory of alloys in pseudopotential approximation. The magnitude of atomic ordering energies of atomic pairs in the Fe₃Al system has been calculated by means of electronic theory in pseudopotential approximation up to sixth coordination spheres and subsequently used as input data for MC simulation for more detailed analysis for the first time. The Bragg-Williams long-range order (LRO) and Cowley-Warren short-range order (SRO) parameters have been calculated from the equilibrium configurations attained at the end of MC simulation for each predefined temperature and Al concentration levels, which reveal the evolution of the system from DO₃→B2→disordered state as temperature increases. The variation of ordering parameters with temperature has identified the transition temperature from DO₃→B2 type superlattice, and from B2→disordered (α) solid solution at about 540 °C and >900 °C, respectively, showing good qualitative agreement with experimental results. The results of the present study imply that combination of electronic theory of alloys in pseudopotential approximation with MC simulation can be successfully applied for qualitative or semiquantitative analysis of energetical and structural characteristics of atomic ordering processes in Fe₃Al intermetallics.