Thermoelectrical properties and optical third harmonic generation of Gd-doped PbTe

Nanocrystalline TiO₂ porous films were prepared by a sol-gel dip coating method from a solution using poly(ethylene glycol) as a template, ethanol as a solvent and terpineol as a highly viscous solvent. The thickness of films increases greatly by increasing the amount of terpineol. However, the overmuch incorporation of terpineol hinders the formation of porous structure and accelerates the crack creation. The crack-free film having a three-dimensionally extended porous structure was obtained at the ethanol/terpineol ratio of 8:1, the film thickness with three depositions being 2.5 μm. Pretreatment of the precursor at an appropriate temperature also plays an important role in pore formation. Single-phase anatase TiO₂ porous films were obtained after calcinations at 550°C for 1 h, and the crystal size increases with an increase in the amount of terpineol. The pore formation mechanism is discussed primarily in relation to the phase separation in the system and self-assembly of PEG.