On the Problem of Metal-Insulator Transitions in Vanadium Oxides

The problem of metal-insulator transition is considered. It is shown that the Mott criterion <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" id="M1"><mml:msub><mml:mrow><mml:mi>a</mml:mi></mml:mrow><mml:mrow><mml:mtext>B</mml:mtext></mml:mrow></mml:msub><mml:msup><mml:mrow><mml:mrow><mml:mo stretchy="false">(</mml:mo><mml:mrow><mml:msub><mml:mrow><mml:mi>n</mml:mi></mml:mrow><mml:mrow><mml:mtext>c</mml:mtext></mml:mrow></mml:msub></mml:mrow><mml:mo stretchy="false">)</mml:mo></mml:mrow></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>/</mml:mo><mml:mn>3</mml:mn></mml:mrow></mml:msup><mml:mo>≈</mml:mo><mml:mn>0.25</mml:mn></mml:math> is applicable not only to heavily doped semiconductors but also to many other materials, including some transition-metal compounds, such as vanadium oxides (particularly, VO 2 and V 2 O 3 ). The low-temperature transition (“paramagnetic metal—antiferromagnetic insulator”) in vanadium sesquioxide is described on the basis of this concept in terms of an intervening phase, between metal and insulator states, with divergent dielectric constant and effective charge carrier mass. Recent communications concerning a possible “metal-insulator transition” in vanadium pentoxide are also discussed.

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