Noncentrosymmetric mixed-cation borate: Crystal growth, structure and optical properties of Cs2Ca[B4O5(OH)4]2·8H2O

A single crystal of the new noncentrosymmetric material Cs2Ca[B4O5(OH)4]2·8H2O has been grown by a slow evaporation method with sizes up to 10×10×5 mm3 using an aqueous acetone solution as a solvent. The crystal structure of this compound was determined by single crystal X-ray diffraction. It crystallizes in the Orthorhombic space group P212121 with lattice parameters a=11.5158(7) Å, b=12.8558(7) Å, c=16.7976(10) Å and Z=4. The optical transmittance spectrum was measured on the Cs2Ca[B4O5(OH)4]2·8H2O crystal, which exhibits an absorption edge at about 190 nm in the UV region. The powder second-harmonic generation (SHG) measurement indicates that Cs2Ca[B4O5(OH)4]2·8H2O is phase-matchable and the signal is about half that of a KDP (KH2PO4) standard. Theoretical calculation shows it has moderate birefringence, and identifies the contribution of cations to the optical properties.