Synthesis and phase transition behavior of w-doped VO2(A) nanorods

Abstract

In this paper, pure and w-doped VO 2 (A) nanorods were synthesized via the reduction of V 2 O 5 with oxalic acid through hydrothermal treatment and characterized by XRD, SEM and DSC. The study about the influence of w-doping on its phase transition and stability properties was carried out for the first time on the best of our knowledge. The doping of tungsten decreased the phase transition temperature of VO 2 (A) just as it does in the case of rutile VO 2 (R). The doping limitation of tungsten for pure VO 2 (A) was estimated to be about 0.50.75 at. %, whereas over doping of tungsten led to the destabilization of VO 2 (A) phase. Based on the experimental results, the solution reaction process should be such that VO 2 (B) was first formed at lower temperature or shorter time, and then transformed to VO 2 (A) or VO 2 (R) during hydrothermal treatment. Furthermore, inhomogeneous doping of tungsten in VO 2 during the crystallization from the solution was revealed by DSC measurements.

Hydrothermal Synthesis of VO2 Polymorphs: Advantages, Challenges and Prospects for the Application of Energy Efficient Smart Windows

“…VO 2 (A) can be obtained by compressing or grinding VO 2 (B), and a simple crystallographic‐slip‐phase transition mechanism was proposed to explain this transformation . In recent studies, Jin et al synthesized pure and W‐doped VO 2 (A) nanorods, and proved the phase transition exothermic peak at 135 °C in DSC during the cooling process, for the first time . Figure a,b shows the SEM images of VO 2 (A) ultralong nanobelts prepared by Li et al The TEM image in Figure c shows the rectangular top of the nanobelt, and the HRTEM image and SAED pattern in Figure d confirm the phase structure and single crystalline property of VO 2 (A).…”

Thermochromic Property of Tungsten Doped VO2Prepared by Hydrothermal Method

“…VO2의 합성법 에는 졸-겔법 [2], 스퍼터링 [3][4][5][6], 열분해법 [7,8], 수열 합성법 [9,10], 등 이 있다. 바나듐 산화물에는 다양한 산화 상태인 VO, VO2, V2O3, V2O5, V2O7, V6O13 등이 있으며, 특히 VO2는 6개의 동질이상(polymorph)인 tetragonal rutile상, monoclinic rutile상, triclinic상, 3개의 불안정상인 VO2(A), VO2(B) 및 VO2(C)로 존재하지만, 이들 중에서 tetragonal rutile상과 monoclinic rutile상은 약 68 ℃에서 완전한 가역적인 semiconductor-to-metal phase transition (SMT) 특성을 나타낸다고 보고된 다 [11][12][13]. VO2는 68 ℃의 상전이 온도 이하에서 monoclinic 결정상으 로 존재하지만, 상전이 온도 이상에서는 monoclinic 결정상의 비틀어 져 있는 바나듐 원자 쌍들의 결합이 축을 따라 팽창하게 되고 바나듐 원자들 간의 거리가 서로 같게 되어 tetragonal 결정상으로 존재하게 된다 [14][15][16].…”

Study on the Growth of Monoclinic VO₂ Phase Applicable for Thermochromic Ceramic Tile

“…[6][7][8][9] VO 2 exists in a total of 7 types of polymorphism including Monoclinic(VO 2 (M)), Tetragonal Rutile(VO 2 (B)), Orthorhombic(VO 2 (O)), Triclinic as well as 3 unstable phases of VO 2 (A), VO 2 (B) and VO 2 (C). [10][11][12][13] While VO 2 exists as VO 2 (M) phase below 68 o C, and as VO 2 (R) above 68 o C, since distances between twisted vanadium atoms in the VO 2 (M) phase become equal to each other. [14][15][16] Since the VO 2 (M) phase below 68 o C has a high electrical resistance value exhibiting the characteristics of an insulator, it is referred to as an insulator phase and transmits visible light and infrared rays.…”

“…On th other hand, since electrical conductivities are exponentially increased in the VO 2 (R) phase as compared with the VO 2 (M) phase so as to have very low electrical resistance values and exhibit characteristics of a metal, it is called a metal phase and shows characteristics of transmitting visible light while blocking infrared ray. [11][12][13] Such reversible phase transition phenomenon at 68 o C 17) is called Metal-Insulator Phase Transition (MIPT) ( Fig. 1), showing a drastic change in specific resistance in the phase transition section.…”