Properties of tantalum mixed vanadium oxide thin film

Birçok geçiş metal elementleri oksitlerinin ince filmleri elektrokromik özellik göstermektedir. Bugüne kadar üzerinde çok çalışılan elektrokromik malzemelerden bazıları tungsten, vanadyum, molibden, tantalum, titanyum vb. geçiş metal oksitlerdir. Uygulanan bir dış potansiyel altında optik geçirgenliklerini değiştiren ve uygulanan potansiyelin işareti değiştirildiğinde tekrar önceki geçirgenlik değerine dönen cihazlara elektrokromik cihazlar denir. Renklenme mekanizmasının esaslarını anlamak için vanadyum oksit filmler en ideal malzemelerden biridir, çünkü vanadyum oksit filmler; termokromizm, fotokromizm ve elektrokromizm gibi çeşitli tiplerde renklenme özellikleri gösterirler. Vanadyum dioksit bilinen en eski termokromik malzemedir. Vanadyum pentoksit ise hem katodik hem de anodik olarak renklenebilen elektrokromik malzemedir. Vanadyum pentoksit gelişmiş elektrokimyasal özelliğinden dolayı üzerinde çok çalışılmış bir malzemedir. Elektrokromik cihazlarda, termokromik cihazlarda, güneş pillerinin pencerelerinde, yüksek kapasiteli lityum pillerinin elektrotlarında, elektronik ve optik anahtarlama cihazlarında kullanılmaktadır. Literatürde Vanadyum oksit ince filmlerin hazırlanmasında birçok yönteme rastlanmaktadır. Tozutma yöntemi, vakum buharlaştırma, elektrokimyasal yöntemler ve sol jel yöntemi kaplama yöntemlerine bazı örneklerdir. Bu çalışmada Vanadium (V) Oxytriisopropoxide ve Tantalum(V) Ethoxide başlangıç maddeleri ile sol-jel daldırma ve döndürme yöntemi kullanılarak ince filmler hazırlanmıştır. Hazırlanan vanadyum ve tantalum katkılı vanadyum oksit filmler sarı renkte olup elektrolit içerisinde elektrik potansiyeli uygulandığında tersinir olarak önce saydamlaşır, sonra açık kahverengi renge dönüşür. Tantalum katkısı, filmlerin optik ve yapısal özelliklerini değiştirmiş, elektrokromik özelliklerini iyileştirmiştir. Anahtar Kelimeler: Vanadyum, tantalum, sol-jel, ince film, elektrokromik, elektrokromiz.The enormous development of the electronic age after the discovery of solid state bipolar junction transistor, thin film technology made possible to improve the capabilities, reduce the size and cut down the price of many electronic devices. Besides of the capabilities to produce high efficient electronic device in small volumes, they benefit also from low power consumption. Nowadays Resistors, capacitors, inductors, as well as semiconductor such as diode, transistor and integrated circuit in electronic application, reflecting, anti-reflecting, light polarizing, optical band pass filters in optical industry and anti corrosive and anti abrasion coating in mechanical application take use of thin film technology. The use of thin films is extended to lithium battery electrodes, heat, temperature, pressure, humidity and gas sensors. Chromogenic devices comprices also of chromegenic thin film coatings. The influence of ambient condition such as light, temperature, pressure on the color of the material is refered as chromegenic. Chromegenic material returns to its initial state when the ambient conditon returns to its initial condition. Chemocromism, gaschromism, photochromism, thermochromism and electrochromic are some sort of chromogenic effects. The most desirable application of electrochromic (EC) device are smart windows. Electrochromic smart window colors upon applied potential. By reversing the potential it becomes again belached. Smart windows in comparison with other building coating application, can reduce the energy consumption by means of heating and illuminating conditioning for indoor of large buildings. Due to unresolved problems their use is still not widely considered. Heat sensitive coating can also be used to minimize the heating or cooling costs. Some automobile rear  view mirrors and automatically belaching sensor driven devices uses electrochromic coatings. Electrochromic reflecting mirror system can also be continously adjusted to reflect the desired amount of light. It is not always possible to use photochromic device since they change their optical properties due to the incoming light. Electrochromic device colors or bleaches when electric potential is applied to its terminals. By using an external electronic control unit the coloration or bleaching on-demand or dimming can be achived easily at a desirable speed within a maximum and minimum transmittance value. Many works have been carried on most of the electrochromic materials but many of them are interested in vanadium oxide and tungsten oxide. Vanadium is the most studied powerful element which has an oxidation state V5+ up to V2+. Vanadium oxide films possess metal-semiconductor phase transition, photochromic, electrochromic, and thermochromic properties. Vanadium is the rare material which exhibits the three chromogenic properties. The anodic and cathodic coloration of vanadium oxide and the oxidation states resulting in coloration of more then one color makes vanadium oxide preferable to use them in EC application. They can be used as EC active layer and also as complimentary layer in EC devices. This work states the study on vanadium oxide and tantalum oxide mixed vanadium oxide thin films. Material mixture and coating conditions for fabricating high performance EC device has been investigated. Vanadium and tantalum mixed vanadium oxide thin films have been prepared by sol-gel dip and spin coating process from vanadium (V) oxytriisopropoxide and tantalum (V) ethoxide precursors. Heat treatment at 100°C and 300°C has been applied for 2h. Optical, electrochemical and surface analyses have been investigated. Results show that the surface structure and electrochromic properties can be easily adjusted with the ingredient tantalum percentage. Increasing tantalum improves the optical transmittance of the coatings. Charge capacity of the EC film also has been increased with increasing tantalum content in the studied range. The calculated highest diffusion coefficient is 4.11 10-12 cm2/s  which correspond to 10% tantalum mixed vanadium oxide thin films. Increasing heat treatment temperature causes porosity that reveals the improvement of EC performance as a result of easier ion injection. Keywords: Vanadium, tantalum, sol-gel, thin film, electrochromic, electrochromism

Preparation And Characterization Of Vanadium Oxide And Mixed Vanadium Oxide Thin Films

Tez (Doktora) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2008Thesis (PhD) -- İstanbul Technical University, Institute of Science and Technology, 2008Bu çalışmada, elektrokromik cihaz yapımında kullanılacak vanadyum tabanlı elektrokromik aktif tabak üretilmiş ve karakterize edilmiştir. Elektrokromik cihaz, uçlarına uygulanan potansiyel ile optik geçirgenliğini değiştiren, uygulanan potansiyel in yönü ters çevrildiğinde tekrar eski optik geçirgenliğine kavuşan cihazlardır. Vanadyum ve katkılı vanadyum oksit ince filmler sol-jel yöntemi ile hazırlanmıştır. Titanyum, tantalyum, zirkonyum ve tungsten ile katkılanmış vanadyum oksit filmler hazırlanmış, katkı türlerinin ve oranlarının hazırlanan ince film elektrokromik aktif tabakaların elektrokimyasal, yapısal ve optik özelliklerine etkisi incelenmiştir. Uygun bir elektrokromik film yapımı için gereken özellikler belirlenmiştir.In this study, we prepared and characterized vanadium based electrochromic active layer which are used to produce electrochromic device. An electrochromic device changes it optical transmittance when an external potential is applied to its terminal. When the potential is reversed it recovers its initial transmittance. Vanadium and mixed vanadium oxide thin films are prepared by sol-gel method. Titanium, tantalum, zirconium and tungsten mixed vanadium oxide films have been prepared, the effect of mixture type and portion of the vanadium oxide electrochromic active layer on the electrochromic, structural and optical properties have been investigated. The parameters for producing an optimized electrochromic film are stated.DoktoraPh