High Dielectric Permittivity of ?-NaFeO2-Type Layered Nitrides br

The exploration of new high-dielectric materials is crucialfor the advancement of modern electronic applications. Most previousresearch on high dielectrics has been limited to oxides. Here, thestructures of nitrides SrHfN2and SrZrN2were investigated by neutronpowder diffraction, which confirmed their alpha-NaFeO2-type layeredstructure without showing apparent preferences of octahedral distortionor polar structure. The SrHfN2and SrZrN2ceramics were found topossess high dielectric permittivities (epsilon r) of approximately 290-650 at106Hz from 5 to 280 K. Impedance spectroscopy measurements indicatethe ceramics could contain conducting grains and less conducting grainboundary regions with extremely small activation energies, inducing theinternal barrier capacitance effect and therefore extrinsically highdielectric permittivities. Density functional theory calculations indicate that both SrHfN2and SrZrN2are semiconductors with similar to 1.0 eV band gaps and possess high bulk epsilon rvalues of 280 and 470, respectively. The exceptionally high epsilon rvalues of these layerednitrides originate from the anisotropic and large ionic polarization within thea-bplane due to the low-frequency infrared activephonon modes concomitant with a large mode effective charge. Our study not only sheds light on the potential of high-epsilon rmaterialsbut also provides a reference for the study of the dielectric mechanism of layered nitrides