High dielectric constant associated with the strain-induced phase transition of an ordered assembly of BaTiO 3 nanocubes under three-dimensional clamping

Numerical calculations of the Gibbs function for an ordered assembly of BaTiO 3 nanocubes (nanocrystals) under three-dimensional clamping have revealed that the phase transition from a tetragonal to cubic crystal structure can take place at room temperature at some misfit strain associated with a tilt angle of the attached nanocubes. The phase transition is second-order due to the three-dimensional clamping. Near and at the phase transition, the dielectric constant becomes extremely high owing to the second-order transition. This is considered to be the reason for the high dielectric constant of an assembly at room temperature, which has been experimentally observed. An ordered assembly of BaTiO 3 nanocubes under rigid three-dimensional clamping is a completely different system from the normal nanocrystalline (polycrystalline) BaTiO 3 ceramics under elastic clamping and from a BaTiO 3 epitaxial thin film under two-dimensional clamping.