A New Lanthanum and Calcium Borate La₂CaB₁₀O₁₉

A new lanthanum calcium borate with the composition La 2 CaB 10 O 19 has been synthesized. Single crystals have been grown from a melt close to the stoichiometric composition. The compound crystallizes in the monoclinic system, space group C 2, with a = 11.043(3) Å, b = 6.563(2) Å, c = 9.129(2) Å, α = γ = 90°, β = 91.47°, and two formula units per cell. The crystal structure contains B 5 O 12 double-ring pentaborate groups, which are linked together to form an infinite two-dimensional double layer. The layer runs almost perpendicular to the c axis of the crystal. The La atoms are located in layers, while the Ca atoms are located between two layers. La 2 CaB 10 O 19 exhibits an optical second-harmonic generation effect about twice as large as that of KDP (KH 2 PO 4 ).