Description:
Optical gyration studies on Co3B7O13I and Cu3B7O13Cl were conducted by the high accuracy universal polarimeter (HAUP) method. Temperature dependences of the gyration tensor g 12 manifested sharp peaks at improper ferroelectric transition points. The electrogyration coefficient of Co3B7O13I also exhibited a sharp peak at the transition point. Taking our previous work of Fe3B7O13I into account, it was concluded that peculiar temperature dependences of gyration and the electrogyration coefficient are a common nature of ferroelectric boracite crystals.