Behavior of the Pyroelectric Coefficient at Low Temperatures

The third law of thermodynamics is used to show that the primary pyroelectric coefficient as $T\to 0$ K cannot have a linear temperature dependence when the coefficient is negative and when the specific heat is proportional to $T^3$. The argument is consistent with previous microscopic theories that predict a cubic temperature dependence for the pyroelectric coefficient but not with those that predict a linear temperature dependence. Electrocaloric cooling effects in lithium sulfate monohydrate below 1 K must then be smaller than predicted earlier.