For a given compound, the deviation from the exact stoichio-metry is the crucial chemical control parameter. Even if such deviations are small, they are of first order for the charge-carrier concentrations. This means that it is the oxygen nonstoichiometry in oxides that may determine whether a given oxide is n- or p-type, ionically or electronically conducting, or even superconducting. This nonstoichiometry, which is paramount for applications such as superconducting devices, fuel cell electrodes, solid electrolytes, or dielectrics, to name only a few examples, can be tuned by variation of the oxygen partial pressure under equilibrium conditions. Here, we report the striking result that the transition from macroscopic to mesoscopic nanocrystalline SrTiO3, that is, a sheer size effect, is equivalent to a variation in oxygen partial pressure by as much as 12 orders of magnitude. In addition to the opposing variation of n and p conductivity by 3 orders of magnitude, the oxygen vacancy conductivity is depressed by 6 orders of magnitude.
展开▼
