High Dielectric Permittivity of α‑NaFeO₂‑Type Layered Nitrides

The exploration of new high-dielectric materials is crucial for the advancement of modern electronic applications. Most previous research on high dielectrics has been limited to oxides. Here, the structures of nitrides SrHfN₂ and SrZrN₂ were investigated by neutron powder diffraction, which confirmed their α-NaFeO₂-type layered structure without showing apparent preferences of octahedral distortion or polar structure. The SrHfN₂ and SrZrN₂ ceramics were found to possess high dielectric permittivities (ε_r) of approximately 290−650 at 10⁶ Hz from 5 to 280 K. Impedance spectroscopy measurements indicate the ceramics could contain conducting grains and less conducting grain boundary regions with extremely small activation energies, inducing the internal barrier capacitance effect and therefore extrinsically high dielectric permittivities. Density functional theory calculations indicate that both SrHfN₂ and SrZrN₂ are semiconductors with ∼ 1.0 eV band gaps and possess high bulk ε_r values of 280 and 470, respectively. The exceptionally high ε_r values of these layered nitrides originate from the anisotropic and large ionic polarization within the a−b plane due to the low-frequency infrared active phonon modes concomitant with a large mode effective charge. Our study not only sheds light on the potential of high-ε_r materials but also provides a reference for the study of the dielectric mechanism of layered nitrides.