Ba(4)Bi(2)(Si(8–x)B(4+x)O(29)) (x = 0.09): a new acentric metal borosilicate as a promising nonlinear optical material

A new acentric metal borosilicate, namely Ba(4)Bi(2)(Si(8–x)B(4+x)O(29)) (x = 0.09), has been synthesized by a standard solid-state reaction. The title compound crystallizes in noncentrosymmetric (NCS) space group I4[combining macron]2m with lattice parameters a = 11.0254(4) Å and c = 10.3961(9) Å. Structure refinements indicate that mixing of B atoms and Si atoms exists for a few atomic sites. In the “ideal” Ba(4)Bi(2)(Si(8)B(4)O(29)), BO(4) or SiO(4) tetrahedra are inter-connected by corner-sharing to cyclic B(4)O(12) or Si(4)O(12) units. These B(4)O(12) and Si(4)O(12) units are further interconnected via corner-sharing to an “ideal” [Si(8)B(4)O(29)](14–) 3D network. The Ba(2+) and Bi(3+) act as the counter cations and are located at the cavities of the structure. Ba(4)Bi(2)(Si(8–x)B(4+x)O(29)) (x = 0.09) melts incongruently at a high temperature of 929 °C. Powder second-harmonic generation (SHG) measurements reveal that Ba(4)Bi(2)(Si(8–x)B(4+x)O(29)) (x = 0.09) is a type I phase-matching compound with a good SHG response of about 5.1 times that of KDP (KH(2)PO(4)), which is the highest among the borosilicates reported so far. The SHG source has been studied by DFT theoretical calculations. Our preliminary results indicate that Ba(4)Bi(2)(Si(8–x)B(4+x)O(29)) (x = 0.09) is a new second-order nonlinear-optical crystalline material candidate.