Entropy of vacancy formation in solidHe3

The free energy of formation of vacancies in solid ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ is discussed in the thermal-activation regime, i.e., for temperatures sufficiently high for the vacancies to obey the statistics of ideal Boltzman defects. It is argued on both experimental and theoretical grounds that the entropy of formation is negative and appreciably large in magnitude. As a consequence the energy of formation is much smaller than the free energy of formation and is in fact consistent with the notion of "ground state" vacancies.