The Preparation And Properties Of Sodium Tungsten Bronze By Electrochemical Intercalation

In this paper,sodium tungsten thin film was prepared by electrochemical intercalation method,and its preparation process,crystallization and magnetic properties were studied.Firstly nano-porous WO3 thin film was prepared on the surface of tungsten substrate by electrochemical anodic oxidation.The effects of NH4F concentration,anodization voltage,reaction time and reaction temperature in fabrication process of WO3 thin film were analyzed by a series of comparative experiments.The WO3 thin film with high specific surface area was prepared.The crystal structure of WO3 was studied through XRD,composition and morphology were analyzed by means of SEM and AFM.The electrochemical properties were tested by linear sweep voltammetry curve,cyclic voltammetry curve and current-time curve in electrochemical workstation to confirm that the nano-porous WO3 thin film can be used to prepare sodium tungsten bronze.The prepared nano-porous WO3 film was subjected to electrochemical intercalation reaction to prepare sodium tungsten bronze.By changing the electrochemical intercalation time,the concentration of electrolyte and light intensity during the preparation,comparing the influence of different preparation conditions on the intercalated sodium ion content,high sodium content of sodium tungsten bronze thin film was prepared.The XRD,SEM,EDS and other means were used to analyze the crystal structure changes and composition of the thin film after electrochemical intercalation.The performance of the sodium tungsten bronze thin film after intercalation was tested by SQUID.The main findings are as follows:1.The preconditions of nano-porous WO3 thin film prepared by electrochemical anodic oxidation was to keep the rate of oxide reaction and oxide dissolution reaction rate balance.The SEM,AFM and other detection methods were used to investigate the most suitable conditions for preparation of nano-porous WO3 thin film in electrolyte environment of NH4F solution:anodization voltage of 60 V,0.05 wt.%NH4F aqueous solution,the anodization 20 min at a water bath temperature of 20 ?.2.Nano-porous WO3 film prepared by electrochemical anodic oxidation went through different heat treatment processes.Comparing the XRD patterns and SEM images after heat treatments.Analysis which heat treatment can be used to obtained monoclinic WO3:the temperature was raised to 450? at a heating rate of 5?/min and incubated for 3 hours and then cooled in the furnace.3.In the linear sweep voltammetry and cyclic voltammetry curves of nano-porous WO3 films,the current density increased with the increase of the number of measurements,and there were clear oxidation peaks.According to the experimental process,the appearance of the oxidation peak was due to the metal tungsten as a substrate in heat treatment leaded the generation of W5+ and W4+ ions.Oxidation reaction occurred in the electrochemical process.The increase of current density was due to the intercalation reaction.Photogenerated electron,sodium ion and WO3 generate tungsten bronze with smaller resistivity.Thus the current density increased.The current density in the current-time curve increased steadily over time for the same reason.Electrochemical analysis of the nanoporous WO3 thin film confirmed that the prepared nano-porous WO3 thin film can be used to prepare sodium tungsten bronze.4.The magnetic properties of the sample was tested by SQUID.Due to the sample was thick,the sample after intercalation presented an similar M(T)curve with the metallic tungsten.Therefore,thinned the substrate of sample and retested.The sample exhibited paramagnetic-diamagnetic transition at H=100 Oe,65 K.This phenomenon indicates that sodium tungsten bronze thin film prepared by electrochemical intercalation reaction may have superconductivity.