The Electrical Conductivity of Lead Chromate

Abstract

The conductivity of sintered pellets of lead chromate varies with the temperature in accordance with the Boltzmann‐type law ${\sigma }^{\propto }\exp \text{(−1.48}\mathrm{ev}\mathrm{/kT)}$ in the temperature range 700°C to 350°C and with the law ${\sigma }^{\propto }\exp \text{(−0.60}\mathrm{ev}\mathrm{/kT)}$ at lower temperatures. At constant temperature the conductivity increases with decreasing oxygen pressure, ${\sigma }^{\propto }{P}_0^{\text{−1/3.1}}$ , which indicates that lead chromate probably dissociates in accordance with the equations: 2PbCrO₄→Pb(CrO₂)₂+Pb⁰+2O₂ and Pb⁰→Pb⁺+e. The energies of these reactions are 5.28 and 1.20 electronvolts, respectively. These same reactions would explain optical and thermal darkening as well as the conductivity, and they indicate along with transport measurements and Seebeck effect measurements that lead chromate is an excess electronic semiconductor.