Polarization-Induced Temperature Self-Sensing and Self-Powering Behavior of Carbon–Carbon Composites

Pyropermittivity, pyroresistivity, and pyroelectret refer to the effect of temperature on permittivity, resistivity, and inherent electric field. They are emerging thermoanalytical methods that are relevant to capacitance-based, resistance-based, voltage-based temperature self-sensing, and thermal energy harvesting. This work provides the first determination of temperature coefficients of permittivity (associated with ac polarization), resistivity (associated with dc conduction), and inherent electric field (associated with dc polarization) for carbon–carbon composites (C/C). The coefficients are
$-(5.1 \pm 0.2) \times 10^{-3} \mathrm{ \, K}^{-1},(2.0 \pm 0.1) \times 10^{-3} \mathrm{ \, K}^{-1}$
, and
$(0.43 \pm 0.02) \mathrm{K}^{-1}$
in terms of resistivity, permittivity, and inherent electric field, respectively. The highest coefficient for the inherent electric field means that dc polarization is more sensitive to temperature. The activation energy required for the inherent electric field
$[(0.25 \pm 0.01) \mathrm{eV}]$
is significantly higher than for resistivity
$[(56.6 \pm 1.6) \mathrm{meV}]$
and permittivity
$[(21.4 \pm 0.6) \mathrm{meV}]$
, suggesting that the formation of electrets through carrier–atom interaction is more challenging during heating than the interaction under ac conditions and carrier drift under dc conditions. Mild heating increases the volumetric power density (by
$600 \times $
), gravimetric power density (by
$600 \times $
), and current density (by
$28 \times $
) significantly. The pyropermittivity-based energy density is
$(4.96 \pm 0.15) \times 10^{-6} \mathrm{ \, J} / \mathrm{m}^3$
when the temperature increases from 20 °C to 70 °C. The temperature self-sensing and self-powering behavior make C/C a highly promising smart material.