Synthesis and characterization of AgBiO₃ with the cubic KSbO₃ structure

Abstract

AgBiO₃, isotypic with cubic (<i>Im-3</i>) KBiO₃, has been prepared by K⁺/Ag⁺ ion-exchange starting from KBiO₃, ^1/3H₂O. Rietveld refinement of the structure from powder X-ray diffraction data shows that AgBiO₃ [<i>a </i>= 9.7852(2) Å; Z = 12; space group <i>Im-3</i>] consists of pairs of edge-shared BiO₆ octahedra connected by common corners wherein the Ag+ reside in the tunnels along <111> direction. The BiO₆ octahedra are distorted and the average Bi-O bond distance (2.117Å) is longer than the Bi- O distance (2.099 Å) in the parent. In addition, the Ag(2)-O(2) bond distance (2.429 A) is considerably short, signaling covalent interaction between Ag⁺ and BiO₃ˉ framework. These structural changes are reflected in the optical

properties as well ; while the brick red parent shows an absorption edge corresponding to ~2 eV band gap, black AgBiO₃ shows free carrier absorption in the 400-800 nm range. Similar difference is also seen in the IR spectra.