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Abstract: The structural features of the “5M” martensitic phase in Ni2FeGa alloys have been determined by electron diffraction using the multi-slice least-squares (MSLS) method. The results demonstrate that the “5M” phase contains an evident cooperative effect of monoclinic distortion and sinusoidal modulation along the [110] c direction. Theoretical simulations based on our refined data suggest that the “5M” martensitic phase observed in Ni–Fe–Ga and Ni–Mn–Ga has visible common behaviors in both stacking sequence and local structural distortion. Considering the cooperative effect of monoclinic distortion and sinusoidal modulation, we demonstrate that the “7M” martensitic phase could adopt two equivalent structural phases corresponding with the stacking sequences of and , respectively. [Copyright &y& Elsevier]

Abstract: Polycrystalline and single crystalline samples of CaFe2As2 were prepared by using different fabrication routes. These samples show evident differences in both phase transition temperatures and transport properties depending on fabrication conditions. TEM observations reveal a rich variety of structural phenomena in these materials, such as a tweed-like pattern in self-flux samples, a structural modulation along the 〈110〉tetra direction in the polycrystalline sample, and complex dislocation networks in the Sn-flux samples. Careful analysis shows that the twinning domains arising from the tetragonal-to-orthorhombic phase transition belong to the δ-type. [Copyright &y& Elsevier]

Abstract: SrMn2As2 single crystals were grown by the Sn flux method. Structural features of these crystals were characterized by means of X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The XRD results show that the single crystal has a rhombohedral structure and grows along the c-axis direction. The microstructure and layered structural features of this material have been examined by SEM and high-resolution TEM observations. The measurements of in-plane resistivity as a function of temperature demonstrate that SrMn2As2 undergoes a phase transition of semiconductor–insulator at a low temperature; the active energies are estimated to be Δ=0.64 and 0.29eV for two distinct regions. Magnetic measurements show a clear antiferromagnetic (AFM) transition at about T N =125K. Therefore, the SrMn2As2 material is an AFM insulator at low temperatures and could be a potential parent compound for superconductors. [Copyright &y& Elsevier]

Abstract: A new inverse spinel ScMn2O4 has been synthesized and characterized by measurements of structural and physical properties. The crystal structure of ScMn2O4, similar with the spinel Mn3O4, is made up of Mn2+ located at tetrahedral site and Mn3+/Sc3+ ions randomly located at the octahedral site. Experimental results of magnetic susceptibility and heat capacity demonstrate that ScMn2O4 undergoes a ferrimagnetic phase transition at the temperature of about 58K. Extensive analyses on the data obtained from structural refinement, electronic structural calculation and EELS spectra measurement suggests that substitution of Sc for Mn in MnO6 octahedron could greatly suppress Jahn–Teller distortions in comparison with what observed in Mn3O4. [Copyright &y& Elsevier]

Abstract: The fine structures of the electron energy-loss spectra (EELS) for the B-K edge have been examined in NbB2 and superconducting Nb0.75Mg0.25B2. The experimental results are analyzed based on the calculations of density functional theory (DFT) using the Wien2k code. The results of the EELS spectra and the angular decomposition of the density of states (DOS) reveal that both the B p z and B p x +p y states in NbB2 have large weights at the Fermi energy due to intersheet covalent bonding with notable hybridization between the Nb 4d and B 2p states. This kind of hybridization also results in different core-hole behaviors for the B-K edge in two orthogonal crystallographic orientations. The best fit between experimental and theoretical data is achieved with consideration of the core-hole effect of the B 1s states, in particular for the q⊥c spectra. Analysis of the electronic structure of the Nb1− x Mg x B2 superconductors suggests that confinement of the intersheet covalent bonding is likely to be favorable for the improvement of superconductivity in this kind of materials. [Copyright &y& Elsevier]

Abstract: A new dual-phase nanocomposite magnet, made up of the well-coupled Sm3(Fe,Ti)29N x and α-Fe nano-crystals, has been successfully fabricated by the melt-spun technique. Measurements of magnetic properties reveal that the hysteresis loop shows up the notable characteristics of single hard magnet in the well-crystallized samples. The electron microscopy investigations indicate that the grain sizes in our samples in general range from 30 to 60nm for Sm3(Fe,Ti)29N x and from 10 to 20nm for α-Fe, grain boundaries between the Sm3(Fe,Ti)29N x and α-Fe phases are clean without any impurities. These structural features are fundamentally compatible with direct exchange-coupling between these two magnetic phases. [Copyright &y& Elsevier]

Structural distortions arising from the condensations of two essential kinds of phonon modes: the triply degenerate rotational modes (ϕx,ϕy,ϕz) of MnO6 and the doubly degenerate Jahn–Teller active modes (Q1,Q2) have been systematically investigated in the perovskite manganites. Microstructural features associated with certain types of distortions have been observed by transmission electron microscopy (TEM). In RMnO3 and La(Sr)2NiO4, we characterize the local structure, charge ordered states and orbital ordering by means of low-temperature TEM. We present direct evidence that the stripe modulation in La(Sr)2NiO4 is indeed one-dimensional within each NiO2 plane. Several typical kinds of defect structures, including antiphase boundaries and the 90°-twin domains, appear commonly in the charge-ordered states. [Copyright &y& Elsevier]