VARIABLE ELECTRICAL-PROPERTIES IN COMPOSITES - APPLICATION TO VANADIUM DIOXIDE PIGMENTS IN A POLYETHYLENE HOST

Composite pellets were prepared from low-density polyethylene (LDPE) a nd vanadium dioxide powders. The VO2 pigments are used for their insul ating-to-metaltic transition at 341 K in order to obtain electrically variable composite materials. The volume fractions of VO2 powders vary from phi = 0 to phi = 0.55. The composite samples are characterized b y X-ray diffraction and scanning electron microscopy. Complex impedanc e analysis in the frequency range 10(-1) to 10(6) Hz is carried out at room temperature and at T = 363 K, to observe the insulator-metal tra nsition of VO2 pigments dispersed in the polymer host. The variation o f the complex impedance modulus Absolute value of Z with frequency and with VO2 volume fraction (phi) is discussed. A specific (R, C) impeda nce model permits interpretation of the experimental results in terms of percolation; the observed variations can be accounted for. (C) 1994 Academic Press, Inc.