Abstract
Over the past decade, the most commonly studied nanocrystalline electroceramic system has been cerium oxide. Ionic conduction is traditionally introduced into this system via homogeneous doping, though the maximum conductivity is limited by carrier mobility at high doping levels. In this work, heterogeneous doping is explored as a potential means for enhanced ionic conductivity. Nanocrystalline CeO2 thin films were deposited by pulsed laser deposition and modified by in-diffusion of Ni and Gd along columnar grain boundaries. To separate the ionic and electronic contributions to the conductivity, electron-blocking microelectrodes, consisting of dense yttria-stabilized zirconia and porous Pt layers, were fabricated on the microscale. After in-diffusion, both the ionic and electronic partial conductivities decreased relative to the as-deposited state. This result is analyzed in terms of the grain boundary chemistry and space charge potential, as well as segregation of acceptor impurities within the ceria thin films.