Synthesis and crystal chemistry of two new fluorite-related bismuth phosphates, [Bi.sub.4.25][(PO4)2[O.sub.3.375] and [Bi.sub.5][(PO4)2[O.sub.4.25], in the series [Bi.sub.4+x][(PO4)2[O.sub.3+3x/2] (0.175<=x<=1)

Two new phosphates, [Bi.sub.4.25][(PO4)2[O.sub.3.375] and [Bi.sub.5][(PO4)2[O.sub.4.25], are synthesized and analyzed by single-crystal X-ray diffraction in the series of [Bi.sub.4+x][(PO4)2[O.sub.3+3x/2] (0.175