Crystal structure and characterization of mixed anion compounds Rb2Bi(PO4)(MO4) (M=Mo, W)

Two new phosphates Rb2Bi(PO4)(MO4) (M=Mo, W) were grown from congruent melt, and their crystal structures were determined by a single crystal X-ray diffraction technique. In the structure, BiO8 dodecahedra share an edge to form zig-zag chains which are linked by edge sharing with the PO4 tetrahedra to build two dimensional ( Bi 2 P 2 O 12 ) 8 − ∞ 2 planes. The MO4 tetrahedra are attached to the plane in both sides by corner sharing with the apical O atoms of the BiO8 dodecahedra. The expansion coefficients of αa=9.15×10−5 Å °C−1, αb=2.57×10−4 Å °C−1 and αc=3.83×10-4 Å °C−1 for Rb2Bi(PO4)(MoO4), and αa=8.53×10−5 Å °C−1, αb=2.54×10-4 Å °C−1 and αc=3.41×10-4 Å °C−1 for Rb2Bi(PO4)(WO4) were obtained by variable temperature X-ray diffraction measurement. They are both transparent in the range of 400–2500 nm with a UV absorption edge of 290 nm for Rb2Bi(PO4)(MoO4) and 311 nm for Rb2Bi(PO4)(WO4) according to the reflection spectra. Similar to the sheelite crystals, Rb2Bi (PO4)(MO4) may be promising stimulated Raman scattering crystals with narrow linewidths due to isolated MO4 groups.