Reversible and repeatable phase transition at a negative temperature regime for doped and co-doped spin coated mixed valence vanadium oxide thin films

Abstract

Smooth, uniform mixed valance vanadium oxide (VO) thin films are grown on flexible, transparent Kapton and opaque Al6061 substrates by the spin coating technique at a constant rpm of 3000. Various elements e.g., F, Ti, Mo and W are utilized for doping and co-doping of VO. All the spin coated films are heat treated in a vacuum. Other than the doping elements the existence of only V 4+ and V 5+ species is noticed in the present films. Transmittance as a function of wavelength and the optical band gap are also investigated for doped and co-doped VO thin films grown on a Kapton substrate. The highest transparency ($75%) is observed for the Ti, Mo and F (i.e., Ti-Mo-FVO) co-doped VO system while the lowest transparency ($35%) is observed for the F (i.e., FVO) doped VO system. Thus, the highest optical band gap is estimated as 2.73 eV for Ti-Mo-FVO and the lowest optical band gap (i.e., 2.59 eV) is found for the FVO system.The temperature dependent phase transition characteristics of doped and co-doped VO films on both Kapton and Al6061 are studied by the differential scanning calorimetry (DSC) technique. Reversible and repeatable phase transition is noticed in the range of À24 to À26.3 C. 80 2508 3203; Tel: +91 80 2508 3214 † Electronic supplementary information (ESI) available. See

Закономерности Формирования Электропроводящих Свойств Окислов Ряда Магнели

“…Если спаривание происходит вдоль одного из выделенных направлений, то при образовании π-димеров произойдет структурный ФП с сильным понижением симметрии кристаллической решетки ввиду одномерности направления спаривания [22]. Структурный ФП во всем кристалле совершается при достижении критической концентрации образовавшихся пар, после чего процесс спаривания захватывает весь объем нанокристаллита ввиду коллективного характера волновых функций, описывающих поведение в периодическом поле решетки как невзаимодействущих, так и сильно коррелированных электронов [23]. Если в различных точках монокристалла присутствуют хаотически ориентированные одномерные поля механических напряжений (например, вблизи дефектов в виде примесей или точек нестехиометрии), то возможно образование в макроскопическом свободном монокристалле VO отдельных доменов с различной ориентацией димеров.…”

Patterns of formation of electrically conductive properties of oxides of the Magneli series

“…If pairing takes place along one of dedicated directions, then in the course of π-dimers formation a structural PT takes place with a strong lowering of the crystal lattice symmetry due to the one-dimensional nature of the pairing direction [22]. The structural PT in the whole crystal takes place upon achievement of the critical concentration of formed pairs, after which the process of pairing is expanded onto the entire volume of the nanocrystallite due to the collective character of wave functions that describe the behavior of both non-interacting and strongly correlated electrons in the periodic field of the lattice [23].…”

Demystifying the Semiconductor‐to‐Metal Transition in Amorphous Vanadium Pentoxide: The Role of Substrate/Thin Film Interfaces

“…For example, a V 2 O 5 ‐MoO x composite system shows a transition temperature of ≈45 °C [ 9 ] but co‐doping by F with Mo and Ti induced a transition temperature of ≈−24 to −26 °C. [ 15 ] In conclusion, for both metal‐doped VO 2 [ 16–18 ] and V 2 O 5 [ 9 ] systems, a reduction of the MIT down to near room temperature and even sub‐zero Celsius temperatures was reported. V 2 O 5 exhibits semiconductor behavior and theoretically is expected to attain metallic behavior above the transition temperature, thus the transition in V 2 O 5 is referred to as Semiconductor‐to‐Metal Transition (SMT) in the current study.…”

“…However, the existing literature reports the occurrence of SMT at different temperatures. Despite the diversity in thickness [32] and substrates investigated, there remains a lack of clear explanation or direct correlation [4,[6][7][8][9][11][12][13][14][15][16][17][18] which demands the examination of factors influencing the SMT in V 2 O 5 . This includes understanding the SMT in different forms of vanadium oxide, such as crystalline, multilayered, doped, and composite materials.…”