Paper TF-ThM3
Electrical Conductivity and Thermopower of Ti_nO_2n-1 Thin Films grown by Pulsed Laser Deposition

Thursday, October 23, 2008, 8:40 am, Room 302

Reduced titanium dioxide (TiO₂) in thin film forms are investigated as a new class of oxide materials for thermoelectric applications. Deposition of thin films was carried out at temperature of 800 °C and oxygen partial pressure of 10^-7 torr on both SrTiO₃ (001) and LaAlO₃ (001) substrates by pulsed laser deposition (PLD). Initial X-ray diffraction characterizations indicate that thin films are crystallized into a mixture of polycrystalline and texture Magneli phases, Ti_nO_2n-1 where n = 4, 5, 6… Electrical conductivity (Σ) and Thermopower (S) of the samples were measured over a temperature range from 10 K to 500 K, from which power factors (S²σ) were evaluated as a function of temperature. It was found that Ti_nO_2n-1 thin films deposited on SrTiO₃ yielded unusually large power factors, at room temperature and bellow. These values were at least several times larger than those found on Ti_nO_2n-1 films deposited on LaAlO₃ and typical bulk thermoelectric materials such as Na_xCo₂O₄ and Bi₂Te₃ at room temperature, and by an order magnitude around T~100K. In addition, the thermopower from thin films deposited on SrTiO₃ exhibits large deviation from a small polaron hopping transport mechanism, suggesting that interface defects in a form of oxygen vacancies introduced during PLD play an important role in thermoelectric transport process.