Cesium Tungsten Bronze

Introduction
Cesium tungsten oxide (CsxWO₃) is a kind of functional compound which has nonstoichiometry ratio and oxygen octahedral, it has low electrical resistivity and low temperature superconducting property. CsxWO₃ is discovered to have great near infrared shielding property which is expected to take replace of ITO as raw material for smart window, it has wide application prospect in automobile and architecture field.

Preparation
Citric acid induction thermal synthesis method
According to chemical formula CsxWO₃（0<x<0.33）, valance state of W is at reduction state. With the increasing of Cs ion, low valance state of W ion also increases. It means synthesis of CsxWO₃ needs a certain reduction atmosphere.

During this process, citric acid and ethanol is used as reducing agent, carboxyl and hydroxyl will be oxidation into carbon dioxide under high temperature and pressure. And W⁶⁺ can be reduced into W⁵⁺ and W⁴⁺. Cs ion added into tungsten bronze which the process is like following:

1. Preparation of CsxWO₃ powder
1) Use AR grade sodium tungstate Na₂WO₄·2H₂O as raw material, configurating sodium tungstate solution for concentration of 0.5 mol/L;
2) Obtain tungstic acid solution by ion exchange resin method, adding citric acid solution of concentration 1mol/L or 2 mol/L and 0.3mol/L Cs₂CO₃ solution, stick it evenly, the precursor solution is obtained;
3) Adding precursor solution into autoclave, reacting for 3days under 90℃, after ultrasonic washing, alcohol washing, centrifugal and dry the CSxWO₃ is obtained.

2. Preparation of CsxWO₃ thin film
Grinding CsxWO₃ powder, ultrasonic dispersing it in citric acid solution for 1hour, then add into citric acid solution for ultrasonic dispersing for 1h, then adding 0.1g/ml PVA solution, stirring it for 30min then aging 1day to get latex. Use sol-gcl dip-coating method to prepare CsxWO₃ thin film on glass slide.

Property and application:
Near infrared shielding property and heat insulating property
Near infrared shielding material often refers to a kind of functional thin film material which has strong absorbance or reflect ability of near infrared and won’t affect its visible light transmission. As transparent insulating material, it has wide application prospect in architecture and automobile insulating glass.

CsxWO₃ thin film can shield near infrared for wave length longer than 1100nm. The near infrared shielding property and heat insulating property of glass after coated with CsxWO₃ thin film increases with the Cs content in CsxWO₃. Compared to common glass, the insulating temperature difference can reach 13.5℃. 

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