Ferroelectric and dielectric properties of improper ferroelectric Ca_8−xSr_x[Al₁₂O₂₄ ](MoO₄)₂ multilayer capacitors

Improper ferroelectric Ca_8−xSr_x[Al₁₂O₂₄](MoO₄)₂ (x = 0–2) multilayer capacitors (MLCs) were fabricated to study their dielectric and ferroelectric properties for their potential practical applications and reversible switching of electric polarization by an electric field. The substitution of Sr for Ca caused a structural change from polar orthorhombic to non-polar cubic phases at 297 K and decreased the ferroelectric phase transition temperature (T_c). Spontaneous polarization up to ∼0.6 μC/cm² was performed at 297 K in Ca_7.5Sr_0.5[Al₁₂O₂₄](MoO₄)₂ and Ca₇Sr[Al₁₂O₂₄](MoO₄)₂ MLCs by poling with an electric field of 10 MV/m. Furthermore, ferroelectric hysteresis loops from the electric polarization switching were successfully demonstrated in Ca₈[Al₁₂O₂₄](MoO₄)₂ MLCs above 469 K by the application of a high electric field over 50 MV/m, and remnant electric polarization of ∼0.59 μC/cm² was obtained at 573 K. The results introduce a new avenue for possible applications and new functionalities of improper ferroelectrics with an MLC structure.