Temperature-dependent x-ray diffraction of the low-dimensional spin 1/2 quantum magnet TiOCl shows that the phase transition at T_{c2} = 90 K corresponds to a lowering of the lattice symmetry. Below T_{c1} = 66 K a twofold superstructure develops, that indicates the formation of spin-singlet pairs via direct exchange between neighboring Ti atoms, while the role of superexchange is found to be negligible. TiOCl thus is identified as a spin-Peierls system of pure 1D chains of atoms. The first-order character of the transition at T_{c1} is explained by the competition between the structurally deformed state below T_{c2} and the spin-Peierls state below T_{c1}.Comment: Phys. Rev. B (Rapid Communications) in pres

The present investigation describes the hydrogen sorption (de/absorption) behavior of MgH2 catalyzed by graphene sheet templated Fe3O4 nanoparticles (Fe3O4@GS).

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The charge-density-wave ͑CDW͒ transitions in compounds R 5 Ir 4 Si 10 (Rϭrare-earth element͒ have been studied by x-ray-diffraction and electrical conductivity experiments for temperatures between 20 and 300 K. At T CDW incommensurate CDW's ͓q ជ ϭ(Ϯ0.25Ϯ␦)c ជ * with ␦Ϸ0.03] develop in compounds with RϭHo, Er, Tm, and (Lu 0.16 Er 0.84 ), while commensurate CDW's ͓q ជ ϭ(n/7)c ជ *͔ develop in compounds with RϭLu and (Lu 0.34 Er 0.66 ). T CDW varies between 83 K in RϭLu and 161.4 K in RϭHo. The compounds with an incommensurate CDW exhibit a second transition at T lock-in ϽT CDW , with T lock-in between 55 K in RϭEr and 111.5 K in RϭTm. In Ho 5 Ir 4 Si 10 and Er 5 Ir 4 Si 10 this is a pure lock-in transition at which ␦ becomes zero. In Tm 5 Ir 4 Si 10 and (Lu 0.16 Er 0.84 ) 5 Ir 4 Si 10 ␦ also becomes zero, but below T lock-in additional satellite reflections have been discovered, at commensurate positions (n/8)c ជ * in Tm 5 Ir 4 Si 10 and at incommensurate positions (n/8Ϯ␦ 2 )c ជ * with ␦ 2 Ϸ0.01 in (Lu 0.16 Er 0.84 ) 5 Ir 4 Si 10 . The development of this second CDW can be understood by a two-step mechanism similar to the mechanism for the development of the primary CDW in Er 5 Ir 4 Si 10 ͓Galli et al., Phys. Rev. Lett. 85, 158 ͑2000͔͒. At T lock-in the primary CDW becomes commensurate, leading to a partly restoration of the Fermi surface, as evidenced by an anomalous decrease of the electrical resistivity for T below T lock-in in Ho 5 Ir 4 Si 10 and Er 5 Ir 4 Si 10 . The modified Fermi surface then provides the favorable nesting conditions for the development of a second CDW in Tm 5 Ir 4 Si 10 and (Lu 0.16 Er 0.84 ) 5 Ir 4 Si 10 . The electronic character of this transition is suggested by the anomalous increase of the resistivity for T below T lock-in .

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Herein, we demonstrate a facile one pot synthesis of graphene nanosheets by electrochemical exfoliation of graphite. In the present study, we report a significant increase in the yield of graphene by electrolyte heating assisted electrochemical exfoliation method. The obtained results of heating assisted electrochemically exfoliated graphene (utilizing H 2 SO 4 + KOH + DW) synthesis clearly exhibit that the yield increases $4.5 times i.e. from $17% (room temperature) to $77% (at 80 C). A plausible mechanism for the enhanced yield based on lattice expansion and vibration of intercalated ions has been put forward and discussed in details. The quality of graphene was examined by Raman, XPS, FTIR, AFM, SEM, TEM/HRTEM and TGA techniques. The Raman as well as morphogenesis results confirm the quality of the graphene nanosheets. We have used this graphene as electromagnetic interference shielding material where a comparatively large quantity of graphene is required. This graphene exhibits enhanced shielding effectiveness (46 dB at 1 mm thickness of stacked graphene sheets in frequency region 12.4 to 18 GHz) as compared to conventional electromagnetic interference shielding materials, which is greater than the recommended limit ($30 dB) for techno-commercial applications. Thus the present work is suggestive for future studies on enhancement of yield of high quality graphene by proposed method and the use of synthesized graphene in electromagnetic interference shielding and other possible applications.