The Study On Synthesis,Structure And Physical Properties Of NbMoO₄

This thesis mainly discusses the synthesis,structure and physical properties of tran-sition metal oxide NbMoO₄.The compound NbMoO₄was synthesized by using the solid-state reaction method.The synthesis conditions are sintering at 950? for 48h,then at 1150? for 48h,and finally at 1000? for 48h.The grain size of the sample was observed to be around 5m by scanning electron microscope.We performed powder X-ray diffraction measurement on the sample,and then refined the structure.Refined re-sults show that NbMoO₄has a Ti O₂ rutile structure.Transmission electron microscopy results are in good agreement with the XRD data.We studied the physical properties of the sample.The experimentally obtained temperature dependence of resistivity indicates that our synthesized NbMoO₄shows semiconducting behavior,while band strucuture calculations suggest that the compound appears metallic at ground state.The difference between the experimental and theoretical results may come from the fact that the sample used in the measurements is a poly-crystalline having grain boundary effect.Magnetic measurements show that NbMoO₄exhibits weak ferromagnetism at low temperatures,while paramagnetism at room tem-perature.X-ray photoelectron spectroscopy measurements show that Nb appears three valence states of+4,+3 and+2,and Mo appears three valence states of+4,+5 and+6in NbMoO₄.The multiple valence states of Nb and Mo in NbMoO₄ may be caused by possible local ordering of Nb and Mo in the compound.