Single crystals of a new bismuth oxyphosphate were isolated and X-ray investigated, leading to the formula Bi 6.67 (PO 4 ) 4 O 4 . Its crystal structure was refined using 2624 independent reflections in the P1 space group, a ؍ 9.195(15) A s , b ؍ 7.552(5) A s , c ؍ 6.933(4) A s , ؍ 112.2(1)°, ؍ 93.9(1)°, ؍ 106.9(1)°, Z ؍ 1, with the final R ؍ 0.049, R w ؍ 0.060. It consists of infinite chains running parallel to the a axis formed by the linkage of BiO 5 , BiO 6 , and BiO 8 polyhedra. These chains are connected by BiO 8 polyhedra, in which the central atom partially occupies the 1(a) inversion center. That produces (Bi 6.67 O 20 ) 20؊ slabs parallel to the (ac) plane. Finally, the cohesion between the layers is provided by the interconnection of PO 3؊ 4 species. This phase was previously evidenced during the Bi 2 O 3 -BiPO 4 phase diagram study and behaves on cooling as an incongruently melting compound stable above 910°C. It was therefore assigned to the 2Bi 2 O 3 -7BiPO 4 composition very close to our corresponding 2Bi 2 O 3 -6BiPO 4 (Bi 6.67 P 4 O 20 ) revised stoichiometry. Pure polycrystalline samples were room temperature stabilized by substitution of several cations for a substantial part of bismuth. This yielded the new series Bi