Crystal growth and spontaneous polarization mechanism of polar metal borate halides: Mn3B7O13Cl†

Spontaneous polarization plays a crucial role in manifesting unprecedented properties in polar materials, yet its mechanism remains relatively unexplored. We lack certainty regarding how asymmetric groups distort to generate spontaneous polarization, and the understanding of how spontaneous polarization changes with temperature is incomplete. In this study, we have grown a high-quality crystal of metal borate halides, specifically Mn₃B₇O₁₃Cl, as a proof of principle for spontaneous polarization in polar materials. Our results for Mn₃B₇O₁₃Cl indicate that approximately 80% of spontaneous polarization originates from [MnCl₂O₄], and the magnitude of spontaneous polarization associated with [MnCl₂O₄] remains nearly constant with temperature. Meanwhile, the temperature-dependent variation in spontaneous polarization is entirely governed by the [BO₄–BO₃] groups. These findings provide insight into the mechanism of spontaneous polarization in polar materials, particularly metal borate halides, and offer a new pathway for inducing properties related to spontaneous polarization in this class of materials.