(Invited) Ferroelectric Materials Study Using Materials Informatics and First-Principles Calculation-a Computational Search for Wurtzite-Structured Ferroelectrics with Low Coercive Voltages

Abstract

In this talk, I will explain our resent achievements for ferroelectric materials studies using first-principles calculations and materials informatics. Especially focusing on wurtzite-structured ferroelectrics materials. Ferroelectricity has recently been observed in wurtzite-structured Sc-doped AlN thin films, five years after our initial prediction of ferroelectricity in wurtzite compounds based on first-principles calculations. The thin films, however, exhibited a much higher coercive voltage (3 MV/cm) than that of conventional perovskite-structured ferroelectric material PbTiO3, making it difficult to switch the films’ polarity and limiting their practical application. To identify tetrahedral ferroelectric materials with low coercive voltages, we have carried out a wider exploration of candidate binary compounds, from halides to chalcogenides to pnictogenides, using first-principles methods. Our calculations results are summarized in Fig.1. The overall trend is for polarization switching barriers to decrease with decreasing anion-to-cation radius ratio, with the lowest barriers found in monovalent compounds such as the copper and silver halides; e.g., CuCl is calculated to have a switching barrier of 0.17 eV/f.u. and AgI of 0.22 eV/f.u., values similar in magnitude to that of PbTiO3 (0.20 eV/f.u.). Applying an epitaxial tensile strain in the (0001) plane is also calculated to be effective for lowering the potential barrier further, with barriers in both AgI and CuCl decreasing to 0.04 eV/f.u. when a 5% in-plane expansion is applied. The results suggest that tetrahedral ferroelectrics with moderate coercive voltages (below 100 kV/cm) should be achievable. Figure 1