Enhanced negative permittivity by A-site heterovalent ion doping in La1−x−yCaxKyMnO3 perovskites†

Adjusting the concentration of free carriers is a direct strategy to achieve ideal negative permittivity. Employing chemical methods for atypical ion doping is an effective approach to regulate the concentration of free carriers. Owing to the A-site tunability of perovskite manganese oxides, doping with multi-valent ions becomes particularly favorable. In this study, to realize temperature-stable negative permittivity, mono-phase La_1−x−yCa_xK_yMnO₃ (named LCKMO) perovskite crystals having diverse compositions were prepared using an ultra-high-alkaline hydrothermal method. Heterovalent ion doping (La³⁺, Ca²⁺, and K⁺) at the A site within the perovskite crystal structure occurred with the help of the disproportionation reaction of Mn ions at the B site under extreme hydrothermal conditions. By adjusting the La/Ca ratio, we can vary the doping content of K⁺. Experimental results demonstrate that as the concentration of K⁺ increases, so does the concentration of Mn oxide states, indicating that the increase in free carriers contributes to enhanced negative permittivity and reduced dielectric loss. This work thus pioneers a novel synthetic pathway for the creation and design of materials having negative permittivity.