YCrO 3 /Al 2 O 3 Core‐Shell Design: The Effect of the Nanometric Al 2 O 3 ‐Shell on Dielectric Properties

We report a novel strategy to improve the dielectric properties of the biferroic YCrO 3 ceramic compound through interface conduction control by means of an insulating Al 2 O 3 using a core‐shell design. The YC rO 3 particles were covered with several layers of insulating Al 2 O 3 using the atomic layer deposition technique to produce the core‐shell structure. TEM images reveal homogeneous and well‐defined Al 2 O 3 coatings of ~8, ~60, and ~130 nm thickness. XRD shows the Al 2 O 3 ‐shell to be amorphous. The dielectric characteristics of the sintered nano‐composite were investigated in the 100 Hz–1 MHz frequency range and temperature between 300 and 580 K. As the Al 2 O 3 ‐shell thickness covering the YC rO 3 particles is increased, a decrease of the dielectric permittivity, loss tangent and AC conductivity values was found in the whole range of temperatures and frequencies. Furthermore, the rounded hysteresis loop, typical of conductive ceramic is restored as the insulating Al 2 O 3 layer becomes thicker. This behavior is explained because the insulating Al 2 O 3 ‐shell acts as internal barrier layer localizing the surface charges on the sintered grain boundaries. This fact was confirmed by Electron Beam Induced Current technique where a clear contrast at the grain boundaries confirms the charge localization at the YC rO 3 /Al 2 O 3 interface. These results also reveal that the Al 2 O 3 ‐shell induces another conductive mechanism when the insulating Al 2 O 3 layer becomes thicker. Nonetheless, this new strategy is an effective approach to suppress the parasitic conductivity in polycrystalline multiferroic ceramics and increasing thus the multifuncionality.