Artificial ferroelectricity in paraelectric superlattices

SrZrO₃/SrTiO₃ (SZO/STO) artificial superlattices were fabricated on STO substrates by the molecular beam epitaxy. The lattice distortion in the superlattices is dependent on stacking periodicity and is maximum in the [(SZO)₁₀/(STO)₁₀]₄ superlattice. The dielectric properties were measured using interdigital electrodes at frequencies up to 110 MHz, and dielectric relaxation was observed in the [(SZO)₁/(STO)₁]₄₀ and [(SZO)₁₀/(STO)₁₀]₄ superlattices in the low-frequency domain. The dielectric permittivities of all superlattices were more than 10,000 at 110 MHz. The charge vs voltage (Q-V) measurement revealed that the SZO/STO superlattices show distinct hysteresis curves, which indicated that ferroelectricity is induced by the superlattices. The origin of the ferroelectricity seems to be related to the anisotropic lattice distortion incorporated into the superlattice structure.