On the preparation and properties of mixed-valence alkali vanadium oxides

Sammanfattning: The phase relations in the systems A2O-V2O5-V2O3 (A = alkali metal) are very complex. The existence of a number of stoichiometric and non-stoichiometric phases complicates phase analysis and preparative work.Preparation methods are described for fairly large single crystals of mixed-valence cesium and rubidium vanadium oxides, grown from melts in a relatively simple apparatus. Oxygen activity control was found to be crucial and could be realized conveniently via the gas phase surrounding the sample.The Cs2O- and Rb2O- V2O5-V2O3 systems were investigated at liquidus temperatures and the relevant oxygen partial pressures and temperatures to initiate growth of the various phases were established. Different thermo-analytical techniques, such as differential thermal analysis (DTA), thermo-gravimetry (TG) and thermo-microscopy (TM) were used.Electric and magnetic properties of single crystals of the compounds are presented and discussed with reference to the crystal structures. An uncritical compilation of reported phases occurring in the systems A2O-V2O5-V2O3 (A = Li-Cs) is also presented, with a brief literature survey of preparative methods.