[en] The phase relations in the cross-section of the K₂W₂O₇-K₂WO₄-KPO₃ containing 15 mol% Bi₂O₃ were undertaken using flux method. Crystallization fields of K_6.5Bi_2.5W₄P₆O₃₄, K₂Bi(PO₄)(WO₄), Bi₂WO₆, KBi(WO₄)₂ and their cocrystallization areas were identified. Novel phase K_6.5Bi_2.5W₄P₆O₃₄ 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, α=90.052(5)^o, β=103.880(5)^o and γ=90.125(5)^o. It has a layered structure, which contains {K₇Bi₅W₈P₁₂O₆₈}_∞ layers stacked parallel to ab plane and sheets composed by potassium atoms separating these layers. Sandwich-like {K₇Bi₅W₈P₁₂O₆₈}_∞ layers are assembled from [W₂P₂O₁₃]_∞ and [BiPO₄]_∞ building units, and are penetrated by tunnels with K/Bi atoms inside. FTIR-spectra of K₂Bi(PO₄)(WO₄) and K_6.5Bi_2.5W₄P₆O₃₄ were discussed on the basis of factor group theory. - Graphical abstract: Sandwich-like architecture of K_6.5Bi_2.5W₄P₆O₃₄ prepared during high-temperature investigation of K₂W₂O₇-K₂WO₄-KPO₃ system. It is organized from {K₇Bi₅W₈P₁₂O₆₈}_∞ layers and potassium atom sheets