| Transition metal oxides are oxide materials formed by transition metal element and oxygen element.Due to the different d orbital electron distribution in the outer shell of transition metal elements,there are many lone electrons that are easily lost in the electronic structure,so that various valence states can be formed.Combines with elemental oxygen under certain conditions to form various structures that may have superconducting,semiconducting or metallic electronic states.At the same time,transition metal oxides usually have high relative permittivity,wide band gap and low intrinsic carrier concentration,capacitors,gas sensors,electronic devices and other applications are of great value.In this paper,the typical transition metal oxide materials?-Mo O3 and Mo O2 were taken as the research object.Firstly,the controllable preparation process of?-Mo O3 was studied.Secondly,the Raman vibration behavior of?-Mo O3 under atmospheric pressure and temperature change was systematically studied.Finally,the crystal lattice structure changes of?-Mo O3 and Mo O2 under high pressure were obtained by using diamond anvil and high pressure Raman test.The following results were obtained:Firstly,a physical vapor deposition method was presented to synthesize centimeter-sized?-Mo O3 single crystals and whose ultraviolet-visible light absorption,polarization Raman and temperature-variable Raman were investigated.It has been shown that increasing the synthesis temperature and accelerating the evaporation rate of the reactants will affect the morphology of the samples,thus allowing the preparation of centimetre-sized?-Mo O3 single crystals by optimising the evaporation source temperature.The single crystal grows preferentially along the[001]direction,and the out-of-plane consistently oriented,highly crystalline.The ultraviolet-visible light absorption test showed that the sample has a forbidden band width of 3.17 e V;the Agand B2g vibration modes were identified by polarized Raman.Mo O2 samples were prepared by pyrolytic reduction of?-Mo O3 crystal.The results showed that the conditions for the preparation of Mo O2 by reduction of?-Mo O3 crystal are as follows:a mixture of hydrogen and argon(5%H2+95%Ar),reaction time 480 min,and reaction temperature ranging from 600?to 750?.Secondly,high pressure Raman spectroscopy was carried out on bulk?-Mo O3single crystals at a maximum pressure of 35.12 GPa.The study showed that the first phase transition started near 8.64 GPa and the second phase transition started near 24.29GPa.Both piezoelectric phase transitions of?-Mo O3 single crystals were found to be reversible structural phase transitions during the unloading process.No new phase transitions were observed in the?-Mo O3 single crystal in the temperature range of-190°C to 445°C by variable temperature Raman testing.Finally,high pressure Raman spectroscopy of Mo O2 was carried out at a maximum pressure of 42.86 GPa,and the results showed that the first phase transition of Mo O2started at around 15.00 GPa and the second phase transition at 27.63 GPa.No amorphous phenomena were found at the maximum pressure of 42.86 GPa.The structural phase transition of Mo O2 was found to be reversible during the unloading process. |
PDF Full Text Request