  In this paper, using the entropy production inequality of Green and Laws, the
theory of thermopiezoelectricity is presented, in which the second gradient of
displacement and the second gradient of electric potential are included in the
set of independent constitutive variables. At first, the appropriate
thermodynamic restrictions and constitutive equations are obtained. Then, the
basic equations of linear theory are derived and a uniqueness result for the
mixed boundary-initial value problem is presented.
