Dielectric behavior and negative capacitance in multidomain ferroelectric/dielectric Pb(Zr0.2Ti0.8)O3/SrTiO3 superlattices

The high domain wall mobility in ferroelectric multidomain state superlattices contributes to an enhancement of the dielectric permittivity and can locally over-respond to an applied charge giving rise to a negative capacitance behavior in the ferroelectric layers. Here the results of dielectric investigations using impedance spectroscopy are reported on $\mathrm{Pb}\left({\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}\right){\mathrm{O}}_3/{\mathrm{SrTiO}}_3$ superlattices made of 5 unit cells of $\mathrm{Pb}\left({\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}\right){\mathrm{O}}_3$, but with varying the thickness of the ${\mathrm{SrTiO}}_3$ in the superlattice period. X-ray diffraction has evidenced the presence of ferroelectric nanodomains consistent with dielectric enhancement. The temperature dependence of the dielectric constant ε′, the dissipation factor tanδ, the ac conductivity σ′, and the electric modulus M″ were investigated. We evidence thermally activated long-range conduction, which is not associated to an interfacial polarization. The temperature behavior of the ac conductivity depends on the STO layer thickness in the period of the superlattice. Regardless of the STO thickness, a Maxwell-Wagner effect occurs for all samples around 600 K. A negative capacitance regime in the superlattices was evidenced in a temperature range where no Maxwell-Wagner relaxation takes place, showing that $\mathrm{Pb}\left({\mathrm{Zr}}_{0.2}{\mathrm{Ti}}_{0.8}\right){\mathrm{O}}_3/{\mathrm{SrTiO}}_3$ superlattices provide an alternative system to ${\mathrm{PbTiO}}_3/{\mathrm{SrTiO}}_3$ superlattices to investigate the relationship between ferroelectric topological structures and related dielectric properties.