Preparation And Gas Sensing Properties Of Barium Strontium Titanate Modified Titanium Dioxide Thin Films

Physical or chemical adsorption process on the surface of Titanium dioxide?TiO₂?semiconductor exposing to H₂ gas will cause internal carrier concentration and Schottky barrier change,and thus the measured resistivity of TiO₂ will be change accordingly.Resistivity change based TiO₂ hydrogen sensor has the advantage of stable,low cost and easy fabrication,which vests it with a very broad application area.Sensitivity to hydrogen is an important indicator of the performance of TiO₂ materials,various ways such as surface modification,doping,morphology adjusting have been adopted by researchers with the aim of improving the hydrogen sensitivity of TiO₂,among which surface modification has been considered as one of the most popular means.In this paper,barium strontium titanate?BST?nanopowders and oriented TiO₂ thin films were prepared by hydrothermal method.A heterojunction was formed by spin coating the BST nanopowder onto the surface of TiO₂ thin films.The heterojunction was strengthened by the following post annealing.The effects of surfactants and post annealing on the particle size and dispersion of BST nanopowder was analyzed.The influence of the powder annealing on the sensitivity,response and recovery time of the TiO₂ thin film sensor as well as the possible mechanism were discussed.The main results are as follows:1.BST nanoparticles were prepared by hydrothermal method,in which the specific ratio was BT?Ba:Sr:Ti=1:0:1?,BST?Ba:Sr:Ti=2:1:2?,BST?Ba:Sr:Ti=2:3:2?,ST?Ba:Sr:Ti=0:1:1?.Ultrafine nanoparticles with the size of 10-20 nm was obtained by the addition of a certain amount of oleic acid as dispersant.The dispersibility of the nanopowder will be greatly improved as the BST powder was submitted to annealing at 500°C for five hours.2.The BST nanopowder was coated onto the surface of TiO₂ film uniformly by spin coating.After being annealed at 500?for 10 min,a stable BST-TiO₂ heterojunction was fabircated.Comparing to pure TiO₂ film,room temperature sensitivity of the BST-TiO₂heterojunction hydrogen sensor at different hydrogen concentration has been obviously improved,the highest sensitivity of 21%was achieved.3.Post annealing of BST powder has a great influence on the recovery time of hydrogen sensor.In the environment of 100 ppm hydrogen,the recovery time of pure TiO₂ hydrogen sensor is 63.6 s,the recovery time of the unannealed BST powder modified TiO₂ hydrogen sensor is 120.8 s,and the recovery time of the annealed BST powder modified TiO₂ hydrogen sensor is as short as 38.2 s.4.The sensitivity of the BST nanopowder modified TiO₂ thin film was also remarkably improved,the sensitivity of the TiO₂ thin film hydrogen sensors modified with BST?2:1:2?and BST?2:3:2?is better than the one modified with BT and ST.