Transport and optical properties of pulsed laser deposited BaPb1-xBixO3 thin films

Epitaxial thin films of BaPb1-xBixO3 (x = 0.0, 0.25, 0.3, 0.4, 0.6, 0.8, and 1.0) were grown on MgO substrates by the pulsed-laser-deposition method. Dc resistance measurements confirmed that the films experienced a metal-semiconductor transition with variation of the Bi concentration, and that the BaPb0.75Bi0.25O3 film exhibited a superconducting transition at 10 K. The metallic BaPbO3 films with x less than or equal to 0.35 were characterized by small carrier densities, and for the semiconducting films with 0.4 less than or equal to x less than or equal to 1.0 de activation energy increased as x increased. The reflectance spectra also showed a metal-semiconductor transition: the screening of phonons in the IR region by free carriers became prominent as x decreased. The reflectance spectra of semiconducting films showed four infrared-active transverse optical phonon peaks and an interesting feature around 730 cm(-1) which was attributed to a longitudinal optical phonon of the MgO substrate.