= Pyroelectricity
{title2=$p=(\partial P_s/\partial T)$}
<Pyroelectricity> is a change in spontaneous <electric polarization> with <temperature>. When electrodes collect the corresponding change of surface <electric charge>, a changing <temperature> can produce an <electric current> even without an applied voltage.
For electrode area $A$, coefficient $p$ and sufficiently uniform sample <temperature>, the ideal short-circuit signal is $I=pA\,dT/dt$. Heating and cooling reverse its sign. A constant elevated <temperature> does not sustain that ideal current once the <temperature> stops changing. Thermal gradients, leakage and mechanical <strain> can add signals, motivating the distinction between <primary pyroelectric effect> and <secondary pyroelectric effect>.
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