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YCrO3/Al2O3 Core‐Shell Design: The Effect of the Nanometric Al2O3‐Shell on Dielectric Properties

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We report a novel strategy to improve the dielectric properties of the biferroic YCrO3 ceramic compound through interface conduction control by means of an insulating Al2O3 using a core‐shell design. The YCrO3 particles were covered with several layers of insulating Al2O3 using the atomic layer deposition technique to produce the core‐shell structure. TEM images reveal homogeneous and well‐defined Al2O3 coatings of ~8, ~60, and ~130 nm thickness. XRD shows the Al2O3‐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 Al2O3‐shell thickness covering the YCrO3 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 Al2O3 layer becomes thicker. This behavior is explained because the insulating Al2O3‐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 YCrO3/Al2O3 interface. These results also reveal that the Al2O3‐shell induces another conductive mechanism when the insulating Al2O3 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.
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Keywords: core‐shell structures; dielectric materials/properties; electrical conductivity; interfaces; multiferroics

Document Type: Research Article

Publication date: October 1, 2016

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