Grain growth in 8 mol% Y 2 O 3 -stabilized zirconia ceramics (8YSZ) under an electric current has been investigated. Enhanced grain growth on the cathode side starts at 1150°C, well below the conventional sintering temperature, while grain growth is dormant on the anode side until 1400°C. In fully dense samples, the grain size undergoes an abrupt transition, differing by a factor of more than 10 on the two sides. Porous samples also experience faster densification on the cathode side, but grain growth is postponed until full density is first reached. Estimated grain boundary diffusivity on the cathode side has an apparent activation energy about 1 eV lower than that of normal grain boundary diffusion. These results are attributed to supersaturated oxygen vacancies accumulated on the cathode side, causing cation reduction that lowers their migration barrier.

Insulators and conductors with periodic structures can be readily distinguished, because they have different band structures, but the differences between insulators and conductors with random structures are more subtle. In 1958, Anderson provided a straightforward criterion for distinguishing between random insulators and conductors, based on the 'diffusion' distance ζ for electrons at 0 K (ref. 3). Insulators have a finite ζ, but conductors have an infinite ζ. Aided by a scaling argument, this concept can explain many phenomena in disordered electronic systems, such as the fact that the electrical resistivity of 'dirty' metals always increases as the temperature approaches 0 K (refs 4-6). Further verification for this model has come from experiments that measure how the properties of macroscopic samples vary with changes in temperature, pressure, impurity concentration and applied magnetic field, but, surprisingly, there have been no attempts to engineer a metal-insulator transition by making the sample size less than or more than ζ. Here, we report such an engineered transition using six different thin-film systems: two are glasses that contain dispersed platinum atoms, and four are single crystals of perovskite that contain minor conducting components. With a sample size comparable to ζ, transitions can be triggered by using an electric field or ultraviolet radiation to tune ζ through the injection and extraction of electrons. It would seem possible to take advantage of this nanometallicity in applications.

Tensile and compressive solid-solution thin films based on LaAlO 3 and CaZrO 3 compositions were grown on perovskite oxide substrates using pulsed laser deposition to study growth mode transitions and strain relaxation. A buried layer of SrRuO 3 between the thin film and the SrTiO 3 substrate was also introduced to provide an auxiliary embedded strain gauge, which helps identify the critical conditions for the onset of catastrophic strain relaxation events -cracking and dislocation cascades. The results are compared with theoretical predictions to provide guidelines on some general deposition conditions that may be used to obtain smooth, crystalline and defect-free thin films of interest to perovskite-based heterostructures. Tensile and compressive solid-solution thin films based on LaAlO 3 and CaZrO 3 compositions were grown on perovskite oxide 9 substrates using pulsed laser deposition to study growth mode transitions and strain relaxation. A buried layer of SrRuO 3 between 10 the thin film and the SrTiO 3 substrate was also introduced to provide an auxiliary embedded strain gauge, which helps identify the critical 11 conditions for the onset of catastrophic strain relaxation events -cracking and dislocation cascades. The results are compared with 12 theoretical predictions to provide guidelines on some general deposition conditions that may be used to obtain smooth, crystalline 13 and defect-free thin films of interest to perovskite-based heterostructures.