Search

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]

CNx nanotubes have been synthesized by thermal decomposition of ferrocene/ethylenediamine (Fe(C5H5)2/C2H8N2) mixture at 1053–1353 K. The effect of temperature on the growth and structure has been studied by transmission electron microscopy (TEM) and Raman spectroscopy. With increasing growth temperature, the average diameter of the nanotubes increases and a morphology transition from thinner polymerized ‘pearl-like’ nanobells to thicker ‘bamboo-like’ compartments occurs. The FWHMs of the D, G and D* bands reduce while the normalized intensities of the D and D* bands with respect to G band change conversely with increasing growth temperature. The opposite trends in intensities between the D and D* bands are interpreted by their correlation with K-point phonons in disordered sample. Raman spectroscopic studies showed that the degree of disorder and consequently the nitrogen incorporation decrease with increasing growth temperature. Based on these results, we presented two new parameters to describe the degree of disorder in CNx nanotubes. [Copyright &y& Elsevier]

Abstract: Transmission electron microscopy (TEM) observations reveal the presence of complex superstructures and remarkable phase separation in association with Na-ordering phenomenon in γ-Na0.5CoO2. Resistivity and magnetization measurements indicate that three phase transitions at the temperatures of 25, 53 and 90K, respectively, appear commonly in γ-Na0.5CoO2 samples. Under a high pressure up to 10kbar, the low-temperature transport properties show certain changes below the charge order transition; under an applied magnetic field of 7T, phase transitions at around 25 and 53K, proposed fundamentally in connection with alternations of magnetic structure and charge ordering maintain almost unchanged. [Copyright &y& Elsevier]

• The effect of rapid cooling after continuous heating on the alloy was investigated. • Influence of crystal structures on the mechanical properties of RC450 were studied. • The strengthening and embrittlement mechanism of the crystalline phase was discussed. The effects of rapid cooling after continuous heating on mechanical properties and microstructure of Zr 50 Cu 34 Al 8 Ag 8 amorphous alloy are investigated. The microstructure of the alloy is analyzed by X-ray diffraction, differential scanning calorimetry, scanning electron microscopy and transmission electron microscopy. Experimental results show that the rapid cooling of the amorphous alloy after heating to 450 °C possesses the best comprehensive mechanical properties, which can be attributed to the formation of 4.65% ordered crystal structures in the amorphous matrix. When the heating temperature rises to 480 °C, a large number of hexagonal Al 2 Zr and Ag 2 Al phases precipitate in the amorphous matrix, thereby deteriorating the alloy properties. [ABSTRACT FROM AUTHOR]