JOURNAL OF MATERIALS SCIENCE LETTERS 10 (1991) 406-407 Sol-gel processing for BaTiO3 and application to an a.c. powder electroluminescence device Y. NOSAKA, M. JIMBO, M. AIZAWA, N. FUJII Department of Chemistry, Nagaoka University of Techno/ogy, Kamitomioka, Nagaoka 940-21, Japan R. IGARASHI R & D Division, Nippon Seiki Co. Ltd, Higashi-Zaoh, Nagaoka 940, Japan In the fabrication of powder electroluminescence (EL) devices, organic binders such as cyanoethyl cellulose are currently used. The application of silicate sol-gel processing to the binder in an a.c. powder EL device has been demonstrated [1]. One of the advantages of the silicate binder is its purity, which comes from the purity of starting materials and the adaptability of high temperaturefor the drying process. The high dielectric constant of the binder is favourable for low-voltage operation. Since the relative dielectric constant of silicate is as low as about 4, we tried to use a material of high dielectric constant as a binder formed by sol-gel processing. Since barium titanate (BaTiO3) powder is already used in EL devices, sol-gel processing of this material was investigated. Sakka and Kokubo have already reported a sol-gel preparation of BaTiO3 and shown that it crystallized at 600 °C [2]. Although the crystallization is necessary for high dielectricity, this temperature is not convenient for EL devices because of the possible degradation of phosphor and melting of the indium-tin oxide (ITO) glass plate. We found that the crystallization occurs at 200 °C when the n-propanol is used as solvent in place of isopropanol. The procedure for the preparation of binder sol is shown in Fig. 1. Typical amounts of chemicals (2.76 g barium and 8.86 g titanium tetra-n-prop- oxide, each in 100 ml n-propanol) were mixed and 4.67 g acetylacetone was added to moderate the reaction rate. The reaction temperature under reflux conditions was 90 °C, which is higher than the 80 °C in the case of isopropanol solvent [2]. For sol formation 100 ml n-propanol solution containing 85.7g glacial acetic acid and 1.13 g water were mixed dropwise. The reaction was performed under nitrogen atmosphere. Finally the reaction mixture was concentratedwith a rotating evaporator to supply a viscous binder solution. The procedure of silicate sol was the same as reported in [1]. The test specimen for the a.c. powder EL device was fabricated with ZnS : Cu phosphor (grain dia- meter 23 gin). The phosphor powder was mixed with binder sol and sandwiched between pieces of ITO glass ( l c m x 2cm). The device was heated at 200 °C for 3 h in the air. The thickness of the binder ranged from 50 to100 Mm. The EL intensity was measured with a luminance meter (Topcom, BM-3) under the application of a sinusoidal a.c. voltage. Fig. 2 shows an X-ray diffraction pattern for the powder obtained by heating the sol at 200 °C for 3 h. Although there are some by-products Ba(OH)2 and n- c H °H,.l 1 Ne bubbllng heat 80°C TI(OCaHT)4 l IBa(oc H ) I I o-CaH~OH, I I I ICH COCH COCH I Ne bubbling heat g0°C stirring 2h I BaTIO So'l CHaCOOH I HaO n - CaHTOH Figure 1 Flowchart for the preparation of BaTiO3 sol. 406 O , ~ O 0 I ,%0 L I I I L I 20 30 40 50 60 70 20 (degrees) Figure2 X-ray diffraction pattern for the powders prepared by heating sol at 200 °C for 3 h. ((7)) BaTiO3, (0) Ba(OH)~ an (A) TiO2. 0261-8028/91 $03.00 + .12 © 1991 Chapman and Hall Ltd.