Beschreibung:
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Optical gyration studies on Co<jats:sub>3</jats:sub>B<jats:sub>7</jats:sub>O<jats:sub>13</jats:sub>I and Cu<jats:sub>3</jats:sub>B<jats:sub>7</jats:sub>O<jats:sub>13</jats:sub>Cl were conducted by the high accuracy universal polarimeter (HAUP) method. Temperature dependences of the gyration tensor <jats:italic>g</jats:italic>
<jats:sub>12</jats:sub> manifested sharp peaks at improper ferroelectric transition points. The electrogyration coefficient of Co<jats:sub>3</jats:sub>B<jats:sub>7</jats:sub>O<jats:sub>13</jats:sub>I also exhibited a sharp peak at the transition point. Taking our previous work of Fe<jats:sub>3</jats:sub>B<jats:sub>7</jats:sub>O<jats:sub>13</jats:sub>I into account, it was concluded that peculiar temperature dependences of gyration and the electrogyration coefficient are a common nature of ferroelectric boracite crystals.
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