The Euler-Kockel-Heisenberg Lagrangian at Finite Temperature
  In the present work we investigate temperature effects on the spinor and scalar effetive QED in the context of Thermo Field Dynamics. Following Weisskopf's zero-point energy method, the problem of charge renormalization is reexamined and high temperature contributions are extracted from the thermal correction for the Lagrangian densities. 
J. L. Tomazelli and L. C. Costa