First-principles study of ferroelectric, dielectric, and piezoelectric properties in the nitride perovskites CeBN3 ( B=Nb , Ta)

The nitride perovskite family has attracted widespread attention since the experimental synthesis of polar nitride perovskite $\mathrm{LaW}{\mathrm{N}}_{3}$. In this work, we investigated the ferroelectric, dielectric, and piezoelectric properties of two nitride perovskites $\mathrm{Ce}B{\mathrm{N}}_{3}$ (${B}^{5+}=\mathrm{Nb}$, Ta) using the first-principles calculation. Our results show that the polarization values of $\mathrm{CeNb}{\mathrm{N}}_{3}$ (CNN) and $\mathrm{CeTa}{\mathrm{N}}_{3}$ (CTN) approach those of typical perovskites $\mathrm{LiNb}{\mathrm{O}}_{3}$ and $\mathrm{BaTi}{\mathrm{O}}_{3}$, respectively. Interestingly, the $A$-site cation contributes significantly to the polarization of CNN and CTN, despite the lack of lone pair electrons in ${\mathrm{Ce}}^{4+}$. In addition, CTN and CNN exhibit unusually large static dielectric constants (>220) along the $x$ direction, much larger than the $y$ and $z$ directions. This strong anisotropy primarily stems from the dominant infrared-active mode having a lower frequency or larger mode-effective charges along the $x$ direction relative to the other two directions. Finally, we found both CTN and CNN have a comparatively large shear piezoelectric coefficient ${d}_{24}$ over 70 $\mathrm{pC}/\mathrm{c}{\mathrm{m}}^{2}$. Our research provides insights for understanding the origin of ferroelectricity in nitride perovskites and their potential piezoelectric applications.