The Electrical Transport Properties Of Molybdenum Trioxide Under High Pressure

Molybdenum trioxides (MoO3) is a kind of transition metal oxide, which iscomposed of transition metal molybdenum (Mo) and the VI main group elementoxygen (O). MoO3is also an unusual transition metal oxide because of the uniquelayered structure which makes it easy for other ions, or small molecules embed in it,and the particular properties make it a new type of potential function material in manyfields: information storage, sensor, etc; meanwhile, the properties of electrochromism,photocatalytic degradation have siginicifant application in fast ionic conductorsynthsis, battery electrode and so on. The excellent properties of MoO3broaden itsapplied range, and MoO3gradully become a international research hotspot insemiconductor materials field.In recent years, most studies focus on high pressure structure phase transition,doping and nano-MoO3. The research of the electrical properties is scarce forbulk-MoO3especially under high pressure. It is well known that the electricalproperties of MoO3are the important factors to influnce its application value.Therefore, in this paper we systematically study the electrical preperties ofbulk-MoO3under high pressure.The main study results are listed as follow:1. By the pressure induced AC impedance spectrum of MoO3, we found thatthere was no obvious grain boundary conduction in bulk-MoO3.The grain resistanceof bulk-MoO3decreases with the increase of pressure and the bulk resistance presenta sudden change at around10.6GPa, the relaxation frequency of MoO3increased by2orders of magnitude and the relaxation strength dramatically reduced. We consideredthat the discontinuous changes of these electrical parameters are in correspondencewith the phase transition from orthorhombic phase (α-MoO3) to monoclinic phase(MoO3-II). After13GPa, although we have no the data for resistance of MoO3. wecan still get the DC resistivities of MoO3after13GPa as complement for electrical parameters of MoO3under high pressure.2. Through the pressure dependence of electrical resistivity of MoO3, during thecompression process, we find that the electrical resistivity presents a discontinuouschange at around10.9GPa. We figure out the sudden change of the electricalresistivity represents the phase transition from orthorhombic phase (α-MoO3) tomonoclinic phase (MoO3-II). At the same time, the sharp decrease of the electricalresistivity around20.8GPa is caused by the phase transition from monoclinic phase(MoO3-II) to another monoclinic phase (MoO3-III). During the decompressionprocess, two discontinuous changes of the resistivity are in consistent with the suddenchange points of the compression process. It means that the high pressure phasetrasition of MoO3is a reversible structure transition which is in good agreement withthose described content in the previous literatures.3. The first principle calculation of MoO3: the calculation results of bandstructure indicate that three different structures of MoO3(α-MoO3, MoO3-II, MoO3-III)are all indirect gap semiconductor. With the increase of pressure, all of the conductionbands and valence bands are broadened and close to each other. The rates of descent(dEg/dP) of these three structures with pressure are-0.012,-0.017and-0.007eV/GPa,respectively. The density of electronic states shows that: the lowest valence state isoccupied by O-2s state. The main contribution of conduction bands and valence bandsare from Mo-4d and O-2p states. With the increasing of pressure, the electroniccoupling and hybridization become more and more intensive, which result in thebroaden and diffusion of the upper valence bands and finally lead to the decrease ofthe band gap.