Effect of stoichiometry on the dielectric properties and soft mode behavior of strained epitaxial SrTiO_3 thin films on DyScO_3 substrates

摘要

The effect of stoichiometry on the dielectric properties and soft mode behavior of strained epitaxial Sr_(1+x)Ti_(3+δ) films grown on DyScO_3 substrates is reported. Direct comparisons between nominally stoichiometric and non-stoichiometric films have been performed through measurements of lattice parameters, temperature-dependent permittivities, second harmonic generation, and terahertz dielectric spectra. The nominally stoichiometric film shows dispersion-free low-frequency permittivity with a sharp maximum and pronounced soft mode behavior. Our results suggest that strained perfectly stoichiometric SrTiO_3 films should not show relaxor behavior and that relaxor behavior emerges from defect dipoles that arise from non-stoichiometry in the highly polarizable strained SrTiO_3 matrix.