A new alkaline-earth metal borate SrB3O4(OH)3·H2O with UV cutoff edge below 190 nm

Abstract

A new alkaline-earth metal borate SrB3O4(OH)3·H2O, has been successfully synthesized using the hydrothermal method. Single-crystal X-ray diffraction analysis reveals that it crystallizes in the centrosymmetric space group P21/c, a=6.249(4) Å, b=11.459(6) Å, c=8.749(5) Å, β=108.493(6)°, Z=4. SrB3O4(OH)3·H2O contains infinite [B3O4(OH)3]2− chains along the c axis direction extended by the B3O8 units with Sr2+ cations filling the space between these chains. There are inter-chain hydrogen-bonds leading to a compact 3D structure. SrB3O4(OH)3·H2O possesses a large experimental band gap of 6.15eV and a short wavelength cutoff edge lower than 190nm (183nm) as found by the UV–vis-NIR diffuse reflectance spectrum. The calculated band structure and the density of states of SrB3O4(OH)3·H2O suggest that its indirect energy gap is 5.76eV which agrees with the experimental result. The thermal behavior and the IR spectrum of SrB3O4(OH)3·H2O are also reported in this work.