Synthesis of indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) nano-powder by sol–gel

combustion hybrid method

Chi-Hwan Hana, Sang-Do Hana, Jihye Gwaka, S.P. Khatkar b

a Photo- and Electro-Materials Research Center, Korea Institute of Energy Research, 71-2 Jangdong Yuseong, Daejeon 305-343, Republic of Koreab Department of Chemistry, Maharshi Dayanand University, Rohtak-124 001, India

指導教授：林克默 博士報告學生：郭俊廷報告日期： 99/5/28

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Outline

Introduction Experimental procedure Results and discussions Summary

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Introduction

Tin-doped indium oxide, ITO, and fluorine-doped tin oxide, FTO are used to make transparent conductive coatings. It is an advanced ceramic material with many optical and electronic applications due to its high electrical conductivity.

There are various processes for preparation of ITO or FTO powders such as co-precipitation[8–10], vapor–liquid–solid (VLS)[12,13], sol–gel[2,14], emulsion technique[15], ion exchange and hydrothermal process[1].

However, still there is a need to develop a simple and efficient method to obtain nanoparticles with narrow size distribution.

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Sol–gel combustion is a novel method, with a unique combination of the chemical sol–gel process and the combustion process, based on the gelling and subsequent combustion of an aqueous solution containing salts of the desired metals and inorganic fuel like acetylene black, giving a voluminous and fluffy product with a large surface area.

In the present study, the possibility of obtaining indium tin oxide (ITO) and fluorine-doped tin oxide (FTO) nano-powders with the uniform particle size by sol–gel combustion process has been investigated.

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Experimental procedure

SnCl4(99.995%), In(NO3)3·5H2O (99.999%), and HF 50% in water (semiconductor grade) were purchased from Aldrich and used as starting materials.

Acetylene black was purchased from Chevron Phillips Chemical Company.

The flow scheme for the sol–gel combustion process employed for the synthesis of nanocrystalline ITO or FTO powder.

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For the synthesis of ITO nano-powder, indium tin solution was prepared by dissolving 4.752g of In(NO3)3·5H2O and 0.648g of SnCl4 in 20 ml of deionized water.

The quantity of metal ion in the solution was adjusted as the final oxide composition: 90:10 weight ratio of In2O3/SnO2.

0.4 g of acetylene black was added to this indium tin solution and then NH4OH aqueous solution was added drop by drop under constant stirring until it turned to a sol at ambient condition.

This sol was heated at 120°C to get the sol transferred into dried gel.

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Being ignited in air at 650°C, an auto-combustion process took place and as-burnt powder was obtained.

The powder was further calcined at 750°C for 30 min in air to get the ITO nano-powder.

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For the synthesis of FTO nano-powder, 5.2 g of SnCl4 and 0.38 g of HF 50% solution were dissolved in 20 ml of deionized water. 0.4 g of acetylene black was added to this solution.

The other process for the synthesis of FTO nano-powder was the same as the process for the synthesis of ITO.

The chemical composition of the synthesized FTO powder was determined by inductively coupled plasma (ICP; Perkin Elmer, Optima 4300 DV) and ion chromatography (IC; Dionex, ICS-1500): powder calcined at 750°C; (exptl) wt.% Sn=74.1, wt.% F=0.18.

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ITO and FTO nano-powders were examined by powder X-ray diffraction (XRD; Rigaku, Ultimaplus diffractometer D/Max 2000).

Particle morphology and size were investigated by field emission scanning electron microscope (FE-SEM; Hitachi, S-4300).

Thermal analysis was carried out using a simultaneous thermal analyzer (STA; Scinco, STA S-1500) with a heating rate of 5°C/min.

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Results and discussions

Fig. 2 shows the thermogravimetric and differential thermal analysis (TG/DTA) plot of the dried gel precursor of ITO.

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Fig. 2. TG and DTA plots of ITO dried gel between 30 and 800°C recorded for a heating rate of 5°C/min.

There was only one large exothermic peak at temperature 636°C, which belongs to the formation of the indium tin oxide nano-powder.

The TG analysis showed a continuous mass loss from 550°C to 700°C.

Usually, combustion reaction lasts only a few seconds and its reaction is too violent to control in conventional combustion method. However in this sol–gel combustion hybrid method using acetylene black, the reaction was not very violent.

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XRD patterns of the specimens calcined at 750°C show the formation of pure ITO (cubic structure In2O3) and FTO (cassiterite structure SnO2) nanocrystals, and all the peaks can be well indexed to the pure phase patterns.

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No impurity phases are detected. Calculated from the broadening of the diffraction peaks using Scherrer formula, mean crystals' size of the indium tin oxide and fluorine-doped tin oxide crystals are 26 and 28 respectively.

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15Fig. 4. SEM images of (a) ITO and (b) FTO nano-powders.

It can be seen in Fig. 4a that the ITO powder consists of very uniform size cuboid particles of 26–28 nm size. This is in agreement with the results obtained from the XRD analysis.

A slightly broader particle size distribution (16–38 nm) of FTO than that of ITO was observed in Fig. 4b.

Clearly, the sol–gel combustion method could be employed to synthesize ITO and FTO nano-powders with narrow size distribution.

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Summary

利用溶膠凝膠法製作 ITO 與 FTO 粉末，並在過程中加入乙炔炭黑，成功的製做出奈米粉體，其晶粒尺寸介於16~33nm 。藉由這樣的低溫的製程方式，可以安全又簡單快速的做出高微細的粉末。

因此，溶膠凝膠法的燃燒過程，提供一個簡單有效的合成 ITO 和 FTO 導電納米粉體的方法，是可以有用的大規模生產應用的材料和光學產業。

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Thank you for your attention

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