ELECTRICAL-PROPERTIES AND STRUCTURAL CHARACTERIZATIONS OF POLYPHENYLQUINOXALINE PYROLYZED AT HIGH-TEMPERATURE

Insulating polyphenylquinoxaline (PPQ) was converted into an electrica l conductor by pyrolysis at high temperature in nitrogen. Room tempera ture conductivity was measured as a function of pyrolytic conditions, and it was found that it strongly depends on the pyrolytic temperature and time. A maximum of room temperature conductivity about 177 S cm(- 1) for PPQ film pyrolyzed at 1200 degrees C for 1 h was obtained, whic h is 18 orders of magnitude greater than that of the original PPQ film . The current voltage (I-V) curve of pyrolyzed PPQ films follows Ohm's law characteristics of metals. Anisotropy in conductivity along and p erpendicular to the surface of the film indicates the formation of a g raphite-like structure in pyrolyzed PPQ films. The structure of the py rolyzed PPQ films was investigated by elemental analysis, X-ray photoe lectron spectroscopy spectra, X-ray diffraction, and scanning electron microscopic image. The electrical property and the structural charact erizations suggest that the pyrolysis of PPQ films consists of two pro cesses (i.e., carbonization and graphitization), and the critical temp erature is at about 800 degrees C. During carbonization (T-p < 800 deg rees C), some H, N, and O atoms are removed and the temperature depend ence of conductivity of pyrolyzed PPQ film can be expressed by the thr ee-dimensional Variable-Range Hopping (3-D VRH) model. During graphiti zation (T-p > 800 degrees C), most H, N, and O atoms are removed from the residue, and a polyconjugated structure forms in it. The temperatu re dependence of conductivity deviates somewhat from the 3-D VRH model and can befitted with a modified 3-D VRH model. (C) 1998 John Wiley & Sons, Inc.