Preparation of TeO2 based thin films by nonhydrolytic sol–gel process

To solve the problem of the extremely high hydrolytic reactivity of tellurium alkoxides in hydrolytic sol–gel method, the nonhydrolytic sol–gel process has been applied as a novel route for producing TeO₂ based thin films. The transition of nonhydrolytic sol–gel was monitored by means of ¹H NMR, FT-IR and Raman techniques. These results show that the formation of Te–O–Te bonds in gel networks mainly resulted from the nonhydrolytic cross-condensation reaction between different Te–OR groups. The decomposition process and structure evolution of the nonhydrolytic gel products were investigated and managed. Results from DTA and XRD analyses show that metallic tellurium, β-TeO₂ and α-TeO₂ phase appeared in the film during heat-treatment process at around 300, 350 and 400 °C, respectively. The formation of metallic tellurium can be alleviated through preheating the gel films under O₂ atmosphere or by additions of the second component. Crystallization of α-TeO₂ could be retarded by additions of TiO₂ or Al₂O₃, and the transparent, homogeneous amorphous TeO₂ based thin films were obtained by the methods above. The nonhydrolytic sol–gel process developed in this study offers a simple and practical method for fabricating TeO₂ based thin film devices.