Metal-Insulator Transition Temperatures and Excitonic Phases in Vanadium Oxides

A L Pergament

doi:10.5402/2011/605913

Abstract

The possibility of applying the excitonic insulator model to the description of metal-insulator transitions in vanadium oxide Magneli phases is investigated. Based on the Animalu transition metal model potential, the equation for the constant of Coulomb interaction in the theory of excitonic insulator is modified. It is shown that this theory allows the transition temperatures of all the oxides to be calculated. The conformity of the theory with the experimental data concerning the effective mass values for electrons in vanadium oxides is discussed.

Highlights

Studies of metal-insulator transitions (MITs) challenged the well-established division of materials into metals and dielectrics according to the type of electron spectrum and occupation of a band by collective electrons [1]
Vanadium dioxide could be formally included in this pattern with n = ∞, whereas V6O13 belongs to another homology series, the limiting term of which with n = ∞ is the insulator V2O5
In the present work I will try to give some particular formulae allowing the MIT temperature to be calculated for transition metal compounds, vanadium oxides, in the first place

Summary

Introduction

Studies of metal-insulator transitions (MITs) challenged the well-established division of materials into metals and dielectrics according to the type of electron spectrum and occupation of a band by collective electrons [1]. One can find quite a few examples of materials “violating” the abovementioned division. Among those are compounds exhibiting MITs and revealing properties of either a metal in certain external conditions (temperature, pressure) or an insulator in other conditions. The transition between these two states is generally followed by a drastic change of electrical conduction (by a few orders of magnitude) as well as of other physical characteristics. In the present work I will try to give some particular formulae allowing the MIT temperature to be calculated for transition metal compounds, vanadium oxides, in the first place. My intention here is to provide some general formulae for calculating Tt of vanadium oxides on the basis of the excitonic insulator model [2,3,4,5,6,7,8], using the model pseudopotential concept [8]

General Theory of an Excitonic Insulator

Conclusion