MS16-P01 Synthesis structure determination of béta-K0.399V2.623W0.377O7.5 with mixed  occupation of vanadium and tungsten elements Djillali MEZAOUI (U.S.T.H.B, Laboratoire des Sciences des Matériaux, Faculté de chimie, , Alger, Algeria) Sabrina BELKHIRI (Université de Boumerdès, Laboratoire Sciences des Matériaux, L.S.M, Boumerdès, Algeria) Olivier PEREZ (Laboratoire de cristallographie et Sciences des matériaux, CRISMAT, UMR 6508 CNRS, CAEN, France)email: mezaoui_dji@yahoo.fr The title compound vanadium-tungsten mixed oxide bronze K0.399V2.623W0.377O7.5 was prepared by solid state reaction at 700°C in an evacuated silica ampoule. The single crystal K0.399V2.623W0.377O7.5  crystallizes in the monoclinic system, C 2/m (n°12) space group, with cell parameters a = 15.7123 (3) Å, b = 3.6796 (6) Å, c = 10.2092 (2) Å and b = 108.994° (4) .This phase is isostructural to b-KxV2O5 called: Bannermanite family with x ranging between 0.19 and 0.4.
 
 The idea of this work is to incorporate the vanadium and the tungsten in the same site in order to distort the octahedral polyhedra occupied by the transition metals M (M : vanadium and tungsten elements). The irregular octahedral site is based on the presence of long (M−O) and short bonds (M=O) formed between the transition metal and the oxygen. On the other side, the distortion involves a polarization along the short and long bonds, which can be the origin to improve the electronic delocalization and the no linear optical property. In this context, in 2009 and 2012 we synthesized two single crystals K1.65V1.78W0.22As2O10 (Acta Cryst. (2009). E65, i69) and K2V2As2O10 (Acta Cryst. (2012). E68, i54) isostructural to KTiPO5. The comparison between the MO6 octahedra (M: 78% of vanadium and 22% of tungsten) of K1.65V1.78W0.22As2O10 and VO6 octahedra of K2V2As2O10, showed clearly a strong distortion in “M” site due to the mixed occupation of vanadium and tungsten simultaneously. Furthermore the mixed occupation creates two short bonds, which can have a strong impact on the  no linear optical property.
We are interested in the mixed occupation of vanadium and tungsten to improve the physical properties specially the electronic conduction and the no linear optical property, and explain these physical behavior by the structural arrangement of the atoms. In this context, the electrical conductivity measurement as function of various temperatures ranging (between 400 and 625 K) and frequency (100 - 105 Hz) showed a semi-conductor behavior for K0.399V2.623W0.377O7.5. The flexibility of the investigated structure gives the possibility to substitute the potassium ion by another alkaline ion with small size as lithium, in order to create a new  material used as a rechargeable electrode in the lithium batteries.
References:

S. Sabrina, D. MEZAOUI and T. Roisnel, (2012), Acta Crystallogr, E68 i 54

S. Sabrina, M. KARS and D. MEZAOUI, (2009), Acta Crystallogr. E65, i 69

M. CHAKIR, A. EL JALOULI, J.P. CHAMINADE, F. BOUREE and D. de WAAL, (2006), J. Solid State Chem. 179, 18-28

Keywords: Crystal growth, Structure determination, vanado-tungsto oxide, Semiconductor.