High Dielectric Permittivity of α-NaFeO₂-Type Layered Nitrides

Abstract

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 SrHfN 2 and SrZrN 2 were investigated by neutron powder diffraction, which confirmed their α-NaFeO 2 -type layered structure without showing apparent preferences of octahedral distortion or polar structure. The SrHfN 2 and SrZrN 2 ceramics were found to possess high dielectric permittivities (ε r ) of approximately 290−650 at 10 6 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 SrHfN 2 and SrZrN 2 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.

Strain-induced giant enhancement of anisotropic dielectric constant in layered nitrides SrHfN2 and SrZrN2

“…As pointed out in our previous work, there are six IR-active modes for the a-NaFeO 2 -type structure, including two A 2u and two E u modes (noting that each E u mode is doubly degenerate). 22 As shown in Fig. 7, the frequency o l of each IR-active mode gradually decreases along with the tensile Fig.…”

“…As shown in Table 1, the calculated dielectric constants e r of SrHfN 2 and SrZrN 2 are only 99.41 and 141.74 for the fully optimized structures, which are significantly smaller than e r calculated for the experimentally determined crystal structure and experimentally measured e r B 290-650. 22 Then, we just optimized the atomic position but fixed the lattice constants of SrHfN 2 and SrZrN 2 as the experimental values, the calculated dielectric constants e r obviously increased to larger values of 175.55 and 302.31 but were still lower than the experimental data. From a theoretical perspective, the partially optimized structures bear strains relative to the fully optimized structures.…”

“…According to group theory, the irreducible representations of the optical modes at the Brillouin zone center (G point) of SrHfN 2 or SrZrN 2 are 22,41…”

“…20,21 We discovered that the layered nitrides SrHfN 2 and SrZrN 2 also possess high e r in a recent report. 22 In contrast to the KCoO 2 -type structure of CaTiN 2 and SrTiN 2 , SrHfN 2 and SrZrN 2 crystallize in an a-NaFeO 2 -type structure, 23 where the Zr and Hf cations are coordinated with six nitrogen anions forming slab-like layers of edge-sharing octahedra (Fig. 1).…”

Bulk Synthesis and Transport Properties of Rocksalt-Type Ti1–xMgxN Solid Solution

“…The B1-L1 1 -type structure is originated from the cubic TiN by replacing the Ti atoms in the (111) plane with Mg atoms; the resultant structure exhibits TiMgTiMg cations ordering in a layered structure with the R 3̅ m space group (no. 166), analogues with SrZrN 2 and SrHfN 2 . In contrast, the LiUN 2 structure has the tetragonal I 4 1 /amd space group (no.…”