Phase Relations in the K2W2O7—K2WO4 —KPO3—Bi2O3 System and Structure of K6.5Bi2.5W4P6O34.

The phase relations in the cross-section of the K{sub 2}W{sub 2}O{sub 7}-K{sub 2}WO{sub 4}-KPO{sub 3} containing 15 mol% Bi{sub 2}O{sub 3} were undertaken using flux method. Crystallization fields of K{sub 6.5}Bi{sub 2.5}W{sub 4}P{sub 6}O{sub 34}, K{sub 2}Bi(PO{sub 4})(WO{sub 4}), Bi{sub 2}WO{sub 6}, KBi(WO{sub 4}){sub 2} and their cocrystallization areas were identified. Novel phase K{sub 6.5}Bi{sub 2.5}W{sub 4}P{sub 6}O{sub 34} was characterized by single-crystal X-ray diffraction: sp. gr. P-1, a=9.4170(5), b=9.7166(4), c=17.6050(7) A, {alpha}=90.052(5){sup o}, {beta}=103.880(5){sup o} and {gamma}=90.125(5){sup o}. It has a layered structure, which contains {l_brace}K{sub 7}Bi{sub 5}W{sub 8}P{sub 12}O{sub 68}{r_brace}{sub {infinity}} layers stacked parallel to ab plane and sheets composed by potassium atoms separating these layers. Sandwich-like {l_brace}K{sub 7}Bi{sub 5}W{sub 8}P{sub 12}O{sub 68}{r_brace}{sub {infinity}} layers are assembled from [W{sub 2}P{sub 2}O{sub 13}]{sub {infinity}} and [BiPO{sub 4}]{sub {infinity}} building units, and are penetrated by tunnels with K/Bi atoms inside. FTIR-spectra of K{sub 2}Bi(PO{sub 4})(WO{sub 4}) and K{sub 6.5}Bi{sub 2.5}W{sub 4}P{sub 6}O{sub 34} were discussed on the basis of factor group theory. - Graphical abstract: Sandwich-like architecture of K{sub 6.5}Bi{sub 2.5}W{sub 4}P{sub 6}O{sub 34} prepared during high-temperature investigation of K{sub 2}W{sub 2}O{sub 7}-K{sub 2}WO{sub 4}-KPO{sub 3} system. It is organized from {l_brace}K{sub 7}Bi{sub 5}W{sub 8}P{sub 12}O{sub 68}{r_brace}{sub {infinity}} layers andmore » potassium atom sheets.« less