The temperature and frequency dependence of the permittivity in some h
alogen boracites has been measured in the polar and non polar phases.
Mn3B7O13Cl showed the typical dielectric anomaly of most boracites whe
reas Mn3B7O13I and Mn3B7O13Br exhibited a different dielectric behavio
r. The results are discussed using a phenomenological theory of the im
proper ferroelectric phase transition in these compounds.