Study of the overtones and combination bands in the Raman spectra of polyparaphenylene-based carbons
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Study of the overtones and combination bands in the Raman spectra of polyparaphenylene-based carbons A. Marucci, M.A. Pimenta,a) S.D.M. Brown, M.J. Matthewsb) Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
M.S. Dresselhaus Department of Electrical Engineering and Computer Science and Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139
M. Endo Faculty of Engineering, Shinshu University, 500 Wakasato, Nagano 380-0092, Japan (Received 28 December 1998; accepted 19 May 1999)
A detailed study of the second-order Raman spectrum of the polymer polyparaphenylene (PPP) prepared according to the Kovacic method and heat treated at temperatures THT between 650 and 750 °C is presented. The Raman experiments have been performed with five different laser excitation energies in the visible range between 1.92 and 3.05 eV. Several Raman bands in the region between 2400 and 3400 cm−1 have been detected and assigned to the overtones and combination bands of the two conformations of the PPP polymer (benzenoid and quinoid) that co-exist in our samples. Due to the carbonization process, these bands broaden and decrease in intensity with increasing heat treatment temperature, as is also observed for the corresponding first-order Raman features. The complete absence of these high-frequency Raman bands for PPP with heat treatment temperatures in excess of 750 °C indicates complete transformation of the polymer into a disordered carbon material.
I. INTRODUCTION
Much attention has for some time been focused on polyparaphenylene (PPP), mainly because it is an organic conducting polymer.1,2 In the past few years, however, the discovery of its remarkable properties as a host material for fabrication of the anode of a lithium-ion rechargeable battery3 has greatly increased the interest in this polymer. Lithium-ion rechargeable batteries have become an essential element in the development of some portable electronic devices, because they exhibit a highenergy density, a relatively low cost, and quite a long shelf life.4,5 Carbon materials in general have exhibited very good properties as a host material for lithium,6 and a lot of work has been done recently in search of the best form of carbon that could react reversibly with the largest amount of lithium.7 PPP prepared according to the Kovacic method8 and heat treated at temperature THT ⳱
a)
Permanent address: Departamento de Fisica, Universidade Federal de Minas Gerais, Belo Horizonte, 31023-970 Brazil. e-mail: [email protected] b) Permanent address: Lucent Technologies, Bell Laboratories, Murray Hill, New Jersey 07974. e-mail: [email protected] J. Mater. Res., Vol. 14, No. 8, Aug 1999
http://journals.cambridge.org
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700 °C showed one of the highest Li uptake capacities9 (1170 mAh/g, equivalent to Li:C ⳱ 1:2), nearly three times greater than that exhibited by some ordered carbon materials, such as graphite intercalation compo
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