Preparation Of Vanadium Oxides V₂O₃/VO₂ Via V₂O₅ Reduction

Materials exhibiting metal-insulator/semiconductor phase transitions (MIPT/MSPT for short, also Mott phase transition and MPT) have been extensively studied ever since Mott suggested the possibility of this many-body phenomenon. The materials which have received most attention are low valenced vanadium oxides, in particular vanadium dioxide VO2 (also V2O4) and vanadium sesquioxide V2O3. VO2/V2O3 undergoing MIPT on cooling/heating accompanied by lattice distortions and fantastic changes in magnetic susceptibility, electrical resistivity and optical properties are of interest for producing starting-current limiters, thermistors, thermochromic window coatings and so on. That is why lately there has been much interest in synthesizing and characterizing new vanadium oxides doped composites (for instance, ceramics, polymers, glasses).In this thesis, VO2 and V2O3 were prepared by the reduction reaction. The V2O5 powder of a high purity was used as a starting material. Initially, vanadium oxide V2O3 was prepared through direct reduction using high purity hydrogen. Vanadium oxide VO2 was prepared by several methods as follows.1) Directly reduced V2O5 using hydrogen of a high purity or mixed with N2/Ar.2) Synthesized from a formulated mixture of V2O5 and Carbon/Graphite by the reaction:2V2O5+C→4VO2+CO23) Other reductants, Cu for instance, were also used in our study.What is more, thermal dissociation of V2O5 in N2/Ar of a high purity was employed as a try.The research was carned out by the XRD, DSC/TGA and Resistance-Temperature Testing (RTT for short). The XRD method was applied to analyze the phases of the products. The DSC/TGA was used to study the routine of the reduction reaction. And the RTTwas employed to testify that the materials synthesized will undergo the MSPT .From XRD patterns analysis, at different temperatures, V2O5 was reduced by H2 to various vanadium oxides: V6O13, VO2, V3O5, V2O3. By Carbon: V6O13, VO2. By Graphite: V6O13, VO2, V3O5. By Cu: CUV2O5+V3O5+VO2.And from DSC/TGA analysis, the reaction routine was defined as: H2: V2O5→V6O13→VO2→V3O5→V2O3. Carbon: V2O5→V6O13→VO2 Graphite:From resistance-temperature testing, the VO2/V2O3 doped LAS glass based ceramics underwent aMIPT accompanied by fantastic resistance jumps on cooling/heating.