Revisiting NaNbO₃ structural phase diagram through first principles studies

NaNbO₃ is typically coined as the most complex perovskite system due to its intricate temperature-induced structural phase diagram, with applications for high-density optical storage [1] and high output piezoelectricity [2]. The structural phase diagram of NaNbO₃ is generally believed to possess seven preeminent phases that include paraelectric, antiferroelectric and ferroelectric states in a temperature range from 0 to 913 K. Although experimental and theoretical studies have been carried out to understand the structural changes of NaNbO₃, there is still discussion about its exact phase diagram. Inspired by Ref. [3] that used first principles calculations (at the LDA and GGA level) along with an effective Hamiltonian approach to study the phase diagram of NaNbO₃, we perform here first principles calculations of NaNbO₃ at the meta-GGA level using the SCAN [4] and r²SCAN [5] density functionals that have been showed with superior performance on complex materials, aiming to provide more insights in the understanding of the complex phase diagram of NaNbO₃.