Peak of a gyration tensor component of boracite crystals

摘要

According to HAUP measurements, two ferroelectric boracites, Fe_3B_7O_(13)I and Cu_3B_7O_(13)Cl, manifest peaks of a gyration component g_(11) at each Curie point. These phenomena are entirely unintelligible from the usual concepts of the origin of ferroelectricity. Besides, the electrogyration effects of both crystals are also quite different. As has already been determined boracite crystals exhibit characteristic features of being improper ferroelectric. A phenomenological theory of improper ferroelectricity developed by Kobayashi is applied to these anomalous phenomena, and qualitative interpretations are successfully obtained.