JOURNAL OF OPTOELECTRONICS AND ADVANCED MATERIALS Vol. 9, No. 7, July 2007, p. 2245 - 2250 Structural characterization of Nb and La doped nanostructured titania powders and coatings M. M. MALETIN, R. R. ĐENADIĆ, L. M. NIKOLIĆ, V. V. SRDIĆ, Department of Materials Engineering, Faculty of Technology, University of Novi Sad, Bulevar cara Lazara 1, Novi Sad, Serbia The aim of this part of research was to elucidate the complex effect of different parameters and phenomena on obtained nanostructured titania powders and coatings suitable for various applications. Through this work we showed that titania coatings exhibit a distinct behavior in respect to their powder counterparts. We have investigated the strong influence of the substrate, temperature, type and concentration of dopants (Nb and La) on nanostructure development in titania coatings. The obtained results were compared to the results of titania powders prepared under the same conditions. (Received February 7, 2007; accepted June 27, 2007) Keywords: Nanostructured Titania, Anatase Coatings, Titania Powders, Doping Effect 1. Introduction Nanostructured titania is one of the most studied semiconducting materials from fundamental and practical point of view, due to their excellent properties, which are useful in many applications such as: optical, sensors and solar devices, photocatalysis, biomaterials etc. Properties of titania depend on many parameters, such as method and conditions of preparation, crystalline phase type (anatase, rutile), grain size, surface area, the presence of dopants or impurities. Since anatase is more suitable than rutile in many fields of applications (monitoring some gases, pollutant photodegradation etc.) it is necessary to stabilize anatase phase at higher temperatures and hinders anatase to rutile transformation [1,2,3,4]. The addition of different concentrations and type of dopants can be a useful way to prevent anatase to rutile transition and to inhibit its grain growth. Although the studies have been attempting to understand how dopants affect titania properties [5,6], there is still limited information concerning the effect of dopants on the phase formation, microstructural development and thus the properties of titania. Expansion of nanostructured materials, especially coatings, has opened the new opportunities in tailoring of titania properties. However, the application of the titania/anatase coatings in different devices faces the problem of complicated investigations concerning effects of substrate, dopants, and heat treatment on its performances. A great number of results, reported on this subject, are based mostly on the titania powders. However, as expected, the titania properties are quite different depending on whether they are obtained as a powder or in a form of a coating. The results obtained on titania powders concerning application should be used very carefully in the field of titania coatings. Therefore, we found interesting and necessary to deal with a preparation of titania powders and coatings and with comparison of their structural characteristics, pointing out the fact that coatings exhibit a distinct behavior in respect to their powder counterparts. The aim of this work was to investigate the influence of the substrate, temperature, type and concentration of Nb and La as dopants on nanostructure development in titania coatings. The obtained results were compared to the results of titania powders prepared under the same conditions. 2. Experimental procedure The sol-gel method was used to obtain titania powders and coatings, starting from transparent titania sols, undoped and doped with 2, 4 and 6 at% of Nb or La. For the prepartion of titania sols, as starting materials were used: titanium-butoxide (Ti(OC 4 H 9 ) 4 - Fluka, Switzerland), isobutanol, distilled water and appropriate acid (HCl was used for Nb-doped samples and HNO 3 for La-doped ones). Titania sols were prepared according to the procedure proposed in earlier work [7]. The final molar ratio of starting materials, in all titania sols, was Ti(OC 4 H 9 ) 4 : H 2 O : C 4 H 9 OH : HCl or HNO 3 = 1 : 2 : 5 : 0.5 and pH value was about 2. As a dopant source were used NbCl 5 (Merck, Germany) aqueos solution which was added to the HCl and La(NO 3 ) 3 ×6H 2 O (Riedel-de Haën-Germany) which was dissolved in HNO 3 . Undoped and doped titania sols, prepared for titania coatings, were deposited on α-alumina substrate by dip technique with withdrawal speed of 0.02 cm/s. Prior to coatings deposition, the gold comb shaped electrodes were deposited on substrates by physical vapor deposition