The structure family of the rare‐earth calcium oxoborates
O[BO
3]
3 (RCOB) has been investigated mainly with regard to their optical characteristics. Due to their monoclinic‐domatic structure they exhibit pyro‐ and piezoelectric properties, which is not dependent on the numerous possible substitutions of the rare‐earth cation site
R. The rare‐earth cations are known to show partial...