Transparent conducting oxides (TCOs) have wide range of application areas in transparent electrode for display devices, Transparent coating for solar energy heat mirrors, and electromagnetic wave shield. SnO2 is intrinsically an n-type semiconductor due to oxygen deficiencies and has a high energy-band gap more than 3.5eV. It is known as a transparent conducting oxide because of its low resistivity of 10-3Ωcm and high transmittance over 90% in visible region. In this study, co-doping effects of Al and Y on the properties of SnO2 were investigated. The addition of Y in SnO2 was tried to create oxygen vacancies that increase the diffusivity of oxygen ions for the densification of SnO2. The addition of Al was expected to increase the electron concentration. Once, we observed solubility limit of SnO2 single-doped with Al and Y. {(x/2) Al2O3+(x/2) Y2O3}-SnO2 was used for the source of Al and Y to prevent the evaporation of Al2O3 and for the charge compensation. And we observed the valence changes of aluminium oxide because generally reported of valence changes of aluminium oxide in Tin - Aluminium binary system. The electrical properties, solubility limit, densification and microstructure of SnO2 co-doped with Al and Y will be discussed.

Nd and Ti co-doped bismuth ferrite (Bi1-xNdx)(Fe1-yTiy)O3 (x, y=0, 0.05, 0.1, 0.2) ceramics and thin films were synthesized through the conventional mixed-oxide process and pulsed laser deposition (PLD), respectively. Nd and Ti co-doping effect was examined with emphasis on how these impurities affect phase formation behavior as there could be the improvement in leakage current problems often associated with multiferroic BiFeO3 (BFO) thin films. The lattice constants of BFO ceramics decreased with Nd doping concentration up to 10mol%, while they further decreased with Nd and Ti co-doping to about 20%. BFO thin films obtained by the PLD process revealed random polycrystalline structure. Similar to bulk BFO ceramic, Nd and Ti co-doping effectively suppressed the formation of unwanted secondary phase and thus stabilized the perovskite phase in BFO thin films.