ABSTRACT: A series of mixed-metal oxide structures based on the stacking of α-U3O8 type pentagonal bipyramid layers have been investigated for symmetry lowering distortions and photocatalytic activity. The family of structures contains the general composition Am+((n+1)/m)B(3n+1)O(8n+3) (e.g., A = Ag, Bi, Ca, Cu, Ce, Dy, Eu, Gd K, La, Nd, Pb, Pr, Sr, Y; B = Nb, Ta; m=1-3 ; n=1 , 1.5, 2), and the edge-shared BO7 pentagonal pyramid single, double, and/or triple layers are differentiated by the average thickness, (i.e., 1 ≤ n ≤ 2), of the BO7 layers and the local coordination environment of the "A" site cations. Temperature dependent polymorphism has been investigated for structures containing single layered ( n=1 ) monovalent ( m=1 ) "A" site ca
