Low-temperature synthesis of solid-solution Ba_xSr _1-xTiO₃ nanocrystals

The very low-temperature synthesis (20-80°C) of sub-15 nm Ba _xSr_1-xTiO₃ (0 ≤ x ≤ 1) nanocrystals and characterization of their dielectric properties as a function of composition are reported. A series of Ba_xSr_1-xTiO₃ nanocrystals were synthesized under ultrabenign conditions (i.e., low temperatures, ambient pressure and neutral pH) using a vapor diffusion sol-gel technique, whereby water is slowly diffused into a mixture of bimetallic alkoxides to yield the solid-solution nanocrystals in quantitative yield on the gram scale. The unsintered 12 nm Ba_0.69Sr_0.31TiO ₃ nanocrystals synthesized at 20°C possess a maximized dielectric constant (ε′ = 341 at 1 kHz) for the solid solution series, and is more than an order of magnitude greater than the dielectric constant for SrTiO₃ (ε′ = 11.0 at 1 kHz). The observed non-monotonic dependence of the dielectric constant on solid solution composition for these small nanocrystals is consistent with theoretical and empirical studies for bulk Ba_xSr_1-xTiO₃ ceramics, proving this dielectric effect holds for small nanocrystals.