A First-Principles Analysis of Metal Fluorides with Polar Crystal Structures as Candidates for New Ferroelectric Materials

High Resolution Image Download MS PowerPoint Slide We present a systematic first-principles screening of metal fluorides reported in polar crystallographic point groups to identify new candidates for ferroelectric materials. From an initial set of 57 distinct polar structure types collected from crystallographic databases, we classified each entry by crystallographic group-subgroup analysis, hybrid density functional theory (DFT) calculations, and machine-learning-based similarity search into one of the three categories: potentially ferroelectric structures, pyroelectric but nonferroelectric compounds, and structures likely based on wrong polar structure models. Our analysis yields 20 potentially ferroelectric compounds, including 14 new structure types that are further ranked by a one-class support vector machine (SVM) similarity analysis. Promising ferroelectric candidates include KNaSnF 6, NaSrAlF 6, KYF 4 and the possibly multiferroic RbCrF 5 . With tetragonal antiprismatic coordinated Hf atoms the compound Pb 2 HfF 8 introduces a new structural motive for ferroelectricity, whereas Mn 3 F 8 is a new candidate for a charge-ordered ferroelectric. Together, these compounds expand the structural chemistry of fluoride ferroelectrics beyond the classical BaZnF 4 type. We further report 14 pyroelectric candidates that lack centrosymmetric reference phases and are therefore structurally precluded from ferroelectric switching. In addition, we identified 23 structure types based on possibly wrong polar models. For these compounds, DFT structure optimizations systematically relax into centrosymmetric crystal structures, in line with earlier corrections reported in the literature. Among them, Sr 4 Zn 3 F 14, NaMn 3 F 10, RbTlF 4 and δ-Na 2 UF 6 remain uncorrected in crystallographic databases and require experimental reinvestigation. Our findings highlight that about 40% of the reported polar fluorides are likely misassigned, underlining the need for critical crystal structure validation prior to high-throughput searches. At the same time, the newly identified ferroelectric candidates offer promising directions for expanding the family of fluoride-based functional materials.