Synthesis, structure determination and electrical properties of beta-K0.399V2.623W0.377O7.5 with mixed occupation of vanadium and tungsten elements

International audienceThe title compound vanadium-tungsten mixed oxide bronze K0.399V2.623W0.377O7.5 was prepared by solid state reaction at 700 degrees C in an evacuated silica ampoule. The single crystal K0.399V2.623W0.377O7.5 crystallizes in the monoclinic system, C-2/m (no12) space group, with cell parameters a =15.7123 (3) angstrom, b =3.6796 (6) angstrom, c =10.2092 (2) angstrom and beta=108.994 degrees (4).This phase is isostructural to beta-KxV2O5 called Bannermanite family with x ranging between 0.19 and 0.4. The structure determination shows that the framework consists of tunnels which are created by the junction of two kind of connection by the edge and the corners of VO5 square pyramid and (VO6, MO6) octahedra. The "M" metal site is statistically occupied by 62.3% of vanadium and 37.7% of tungsten. The vanadium atoms are observed in irregular octahedra forming a short bond (1.6-1.67 angstrom) related to the double bond character ((VO)-O-=)). The structure refinement led to reliability factors R=0.046, R-w=0.0377 and GOF = 1.23. According to the calculated values of the activation energy, the electrical conductivity measurement as function of various temperatures ranging (between 400 and 625 K) and frequency (100-10(5) Hz) shows a semiconductor behavior for K0.399V2.623W0.377O7.5