Crystal Structure of Gd(Ca_3.319Sr_0.681)O[BO₃]₃ and Gd(Ca_2.592Sr_1.408)O[BO₃]₃

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 disorder with the earth alkaline cation positions X and Z . To study whether a stabilization of the cation occupation is possible without disorder, calcium oxoborates are chemically modified using the Ca substitutes, Sr, Na, Y, Gd on the X and Z positions. No oxoborate phases can be synthesized by coupled substitution of Ca with Sr, Na, and a rare‐earth element. Only with single substitution of Sr the oxoborate phases can be synthesized. It is found that up to 35% Sr can be incorporated into the structure. From the synthesized Gd(CaSr x )O[BO 3 ] 3 precursor material, single crystals have been grown and used for the refinement of the first structure model. The structures have been refined in space group . A replacing only of Ca with Sr, mainly on the X position, has been observed. The stoichiometry resulting from the refinement is Gd(Ca 3.319 Sr 0.681 )O[BO 3 ] 3 and Gd(Ca 2.592 Sr 1.408 )O[BO 3 ] 3 .