Study On Doping Effect Of 3d Transition Metal In VO₂ System

Vanadium dioxide,as a typical thermochromic oxide,experienced the reversible transition from metallic phase to insulating phase at around 68?,this transition will lead to abrupt change of the electrical,magnetic and optical properties of VO₂,making it have a wide application prospect.Besides,the origin of metal-insulator transition for this material involves many basic physical problems,many theory and models have been raised while the real mechanism is not clear.The preparation of VO₂ bulks and the influence of electrical and magnetic properties of 3d transition metal doping for V_1-xT_xO₂?T=Ti?Cr?Mn?Fe?Co?Ni?Cu?Zn?,the main research contents and results include several respects as followed:?1?The preparation process of monoclinic phase VO₂ bulk at room temperature is explored.Results show that on the condition of hydrol-thermal synthesis and vaccum annealing treatment,samples sintered at 900?are pure monoclinic VO₂.?2?3d transition metal doping is comparatively studied when the doping concentration is fixed at x=0.02.Results state that all samples show the abrupt change of magnetic susptibility and metal-insulator transition at³40K while different element doping has not obvious effect on the transition.However,except the abrupt change at³40K,the magnetic susptibility-temperature curves of Cr?Fe and Co doped samples are different from others,Cr and Fe doped samples show abrupt change of magnetic susptibility at²80K while Co doped sample shows abrupt change of magnetic susptibility at¹60K.?3?To understand the reason for abnormal magnetic susptibility caused by Cr?Fe and Co doping,Co doped sample is taken for example,the influence of electrical and magnetic properties of V_1-xCo_xO₂ bulks are studied by different Co concentration.Research states that Co doping has not obviously influenced the metal-insulator transition and abrupt change of magnetic susptibility at 340K when x<0.05,but magnetic susptibility changes obviously at low temperature,the magnetic susptibility increases with the increase of doping concentration at¹60K,which may be caused by little ferromagnetic Co₂VO₄ in the samples.XRD and XPS analysis states that doped samples contain little Co₂VO₄ when x?0.02,and Co₂VO₄ is ferromagnetic below 160K,we therefore conclude that abnormal magnetic susptibility at low temperature is caused by little ferromagnetic Co₂VO₄.