KMBP₂O₈ (M = Sr, Ba): A New Kind of Noncentrosymmetry Borophosphate with the Three-Dimensional Diamond-like Framework

Two new isotypic anhydrous borophosphates, KMBP2O8 (M = Sr, Ba), have been prepared under high temperature solution growth (HTSG). Investigation of single-crystal X-ray diffraction shows that they crystallize in noncentrosymmetric space group I4̅2d with the following lattice parameters: a = 7.1095(18), c = 13.882(5)Å for KSrBP2O8 and a = 7.202(2), c = 14.300(6)Å for KBaBP2O8. The fundamental building block (FBB) of title borophosphates with B:P ratio = 1:2 is 12◻:⟨12◻⟩ (symbol ◻ represents BO4 and PO4 tetrahedra). The FBBs are further interlocked together to form the final 3D diamond-like architecture. Second-harmonic generation (SHG) on powder samples has been measured using Kurtz and Perry technique, which indicates that they are phase-matchable materials, and their SHG coefficients are measured to be about 1/5 (for KSrBP2O8) and 1/3 (for KBaBP2O8) times as large as that of KDP.