First-principles study of ferroelectric, dielectric, and piezoelectric properties in the nitride perovskites CeB N3 (B=Nb, Ta)

The nitride perovskite family has attracted widespread attention since the experimental synthesis of polar nitride perovskite LaWN3. In this work, we investigated the ferroelectric, dielectric, and piezoelectric properties of two nitride perovskites CeBN3 (B5+=Nb, Ta) using the first-principles calculation. Our results show that the polarization values of CeNbN3 (CNN) and CeTaN3 (CTN) approach those of typical perovskites LiNbO3 and BaTiO3, respectively. Interestingly, the A-site cation contributes significantly to the polarization of CNN and CTN, despite the lack of lone pair electrons in Ce4+. 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 d24 over 70 pC/cm2. Our research provides insights for understanding the origin of ferroelectricity in nitride perovskites and their potential piezoelectric applications.