A wide solid solution of lithium manganese chromium oxides, LiMn x Cr 1Ϫx O 2 (0 р x р 0.6), having the layered ␣-NaFeO 2 structure, was synthesized by employing the emulsion drying method, and the Mn and Cr oxidation states of the prepared powders were identified by combination of the Rietveld analysis of the X-ray diffraction ͑XRD͒ data and X-ray absorption near edge spectroscopic ͑XANES͒ analysis. A reversible structural change of LiMn 0.6 Cr 0.4 O 2 was observed using the in situ XRD technique after the first charge. With increasing Mn contents, the reversible capacity increased due to the redox couples of Mn 3ϩ/4ϩ and Cr 3ϩ/6ϩ , as observed by the XANES spectra measured as a function of the Li contents during the first cycle. The rechargeable capacity for LiMn 0.6 Cr 0.4 O 2 was about 140 mAh g Ϫ1 between 4.3 and 2.7 V vs. Li for 30 cycles. The measured chemical diffusion coefficient for LiMn 0.6 Cr 0.4 O 2 was much higher than those for LiAl x Mn 2Ϫx O 4 and LiAl x Co 1Ϫx O 2 . This emulsion drying synthesis is an excellent powder preparation alternative method of high capacity cathode materials to be used in a Li-ion secondary battery.The Li-Mn-Cr-O system has been studied extensively by several research groups. 1-7 Earlier studies have shown that the partial substitution of the Mn sites of the tetragonal spinel Li 2 Mn 2 O 4 by Cr produced a continuous solid solution of Li 2 Cr x Mn 2Ϫx O 4 . 1-3 The final products of this system depend on the Cr doping amount and calcination conditions; different Cr doping amounts resulted in different crystal systems, such as tetragonal (I4 1 /amd), distorted hexagonal (C2/m), and hexagonal (R3 m). 2,3 The corresponding electrochemical properties of the prepared powders were also quite different. For example, a lower Cr doping level in the tetragonal Li 2 Cr x Mn 2Ϫx O 4 showed a two-step Li ϩ deintercalation/intercalation during cycling with two potential plateaus at 3 and 4 V, which were mainly caused by the effect of the Jahn-Teller ion, Mn 3ϩ . A dilution of the effect was achieved by higher level Cr 3ϩ doping in Li 2 Cr x Mn 2Ϫx O 4 where crystallization occurred to produce a distorted hexagonal system. A much higher level doping led to increased symmetry from distorted hexagonal (C2/m) to hexagonal (R3 m) where the cooperative Jahn-Teller distortion was absent. Obviously, the layered compounds showed simple S-shaped charge/ discharge curves and stable cycling behavior. According to the obtained capacity, one is able to postulate that both the Mn 3ϩ and Cr 3ϩ elements were electrochemically active. Unfortunately, the pure hexagonal structured compound, LiCr 0.75 Mn 0.25 O 2 , delivered a capacity of about 100 mAh g Ϫ1 ͑current density: 3.6 mA g Ϫ1 at 25°C͒.Li 3 MnCrO 5 ͑can also be written as Li 1.2 Cr 0.4 Mn 0.4 O 2 ) is a solid solution series, Li 2 MnO 3 -LiCrO 2 . 4,5,7 Obviously, both compounds are famous as electrochemically inactive materials. Nonetheless, once Li 1.2 Cr 0.4 Mn 0.4 O 2 is formed, the hexagonal structured layer compound provides excellent cap...

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The melt-drawing behavior of poly(tetrafluoroethylene) (PTFE) with ultrahigh molecular weight (UHMW) was analyzed using in situ measurements composed of stress-strain curves and wide-angle X-ray diffraction with synchrotron radiation. The stress-strain behavior of the melt-drawing of UHMW-PTFE was quite different from that of the solid drawing. In particular, the former exhibited a plateau stress region, followed by a rapid increase in stress with strain. No crystalline reflection appeared in the plateau stress region. However, oriented crystallization was observed in the later strain-hardening region. Correspondingly, the resultant mechanical properties and transparency of the melt-drawn films are much better than those of the solid-drawn films. Optimizing the melt-drawing conditions elongated the plateau stress region, which successfully achieved further property development. The effects of sample MW on melt-drawing behavior and resultant properties were also discussed. The lower MW film produced a longer plateau region. Subsequent oriented crystallization in the strain-hardening region also exhibited a rapid increase of the crystalline reflection intensity, compared to that for the higher MW film. However, the resultant properties were lower than those for the higher MW film, due to the higher content of the chain ends, even if a higher resultant crystallinity was achieved.