SYNTHESIS AND X-RAY-DIFFRACTION STUDY OF POTASSIUM, RUBIDIUM, AND CESIUM POLYTUNGSTATES WITH DEFECT PYROCHLORE AND HEXAGONAL TUNGSTEN BRONZE STRUCTURES

Based on x-ray diffraction data for the A(2)WO(4)-WO3 (A = K, Rb, Cs) systems, the existence of K2W2O7, A(2)W(3)O(10), K2W4O13, and Cs6W11O3 6 was confirmed, and the new phases A(4)W(11)O(35) and A(2)W(7)O(22) ( A = K, Rb, Cs) were identified. It was found that A(2)W(3)O(10) (A = R b, Cs) and Cs6W11O36 have pyrochlorerelated structures, while A(4)W(11 )O(35) and A(2)W(7)O(22) (A = K, Rb, Cs) are structurally related to h exagonal tungsten bronzes (HTB). All of these structures can be derive d from the parent structure by removing, in an ordered manner, certain structural units from the tungsten-oxygen framework. Comparison of th e structures of HTB-related polytungstates suggests that there exist h omologous series A(2n)B(1-y)M(4n-1)X(12n) (n = 3 for Cs6W11O36) and A( n+3-x)M(3n+5)X(9n+17) (n = 2 and 3 for A(4)W(11)O(35) and A(2)W(7)O(22 ), respectively).