Direct Synthesis of Pure Radiative Vo 2 (M) Plate Like Structures Via Hydrothermolysis at Low Temperature
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Direct Synthesis of Pure Radiative Vo2 (M) Plate Like Structures Via Hydrothermolysis at Low Temperature A.Simo1,3, L.C. Edomwonyi-Otu1,2,4, R.Madjoe3, M. Maaza1 1 2 3 4
Nanoscience Laboratories, Materials Physics Dept., iThemba LABS-National Research Foundation, P O Box 722, Somerset West 7129, Faure, South Africa Chemical Engineering Dept, Ahmadu Bello University, Zaria, Nigeria. 870001 Physics Dept., University of Western Cape, Belleville, South Africa Chemical Engineering Department, University College London, WC1E 7JE, UK
ABSTRACT Facile and direct synthesis of radiative VO2 (M) plate-like is reported. The snowflake material presents superstructures plate-like aggregate with an anisotropic orientation in shape governed by V2O5 and NaOH concentration giving high surface energy liable for chemical reactions with the medium. Pure crystalline VO2 (M) has been obtained with a complete hydrothermolysis of the precursor. The morphological, structural, elemental composition, crystallinity and vibrational bands of the powders were characterized by Powder X-ray Diffraction (XRD), Scanning Electron Microscopy (SEM), Selected Area Electron Diffraction (SAED) and Fourier Transform-Attenuated Total Reflection (FTIR-ATR) infrared spectroscopy. INTRODUCTION The unusual properties of the metallic state near the insulating transition have been most extensively studied in d-electron systems. Among these materials, the Vanadium dioxide (VO2) has intrigued researchers for five decades since its discovery by Morin in 1959 with regards to its thermochromic properties [1]. This behavior determines its ability to regulate the infrared radiations at high temperature and so acts as an intelligent window filter. In addition, it has great applications in thermal sensing and switching devices [2], cell electrodes batteries [3] etc. It is accompanied by structural change from monoclinic phase at low temperature (below 680C) with a space group P21/c to tetragonal rutile phase (more stable P4/mnm) due to a single coordinate jump of the V cations[4 -7]. Semi conductor to metal transition has been recently investigated by the femtosecond laser excitation by time resolved-measurements of the characteristic x-rays and optical signatures [8]. Various micro/nanostructures of VO2 such as nanoribbonds, nanobelts, nanorods, nanowires, hollow microspheres by facile template-free process [9] have been prepared. Few reports are available to date on direct synthesis without post heat treatment of pure VO2 (M). Recently Shidong et al [10] prepared VO2 (R) single crystal nanorods by hydrothermal method with a reversible change of surface charge associated with the semiconductor –metal phase transition of the material while Xin-Ping et al [9] reported the synthesis of pure VO2 (M) after annealing at 500˚C for 5h. In our present work, we report for the first time the direct synthesis of pure radiative VO2 (M) plate-like via hydrothermolysis at low temperature without post-annealing. The products were characterized via XRD, SEM, EDX, SAED and FTIR-ATR.
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