4d-5p orbital mixing and asymmetric In4d-O2p hybridization in InMnO ₃: A new bonding mechanism for hexagonal ferroelectricity

Recent studies on the ferroelectricity origin of YMnO₃, a prototype of hexagonal manganites (h-RMnO₃, where R is a rare-earth-metal element), reveal that the d0-ness of a Y³⁺ ion with an anisotropic Y 4d-O 2p hybridization is the main driving force of ferroelectricity. InMnO₃ (IMO) also belongs to the h-RMnO₃ family. However, the d0-ness-driven ferroelectricity cannot be expected because the trivalent In ion is characterized by a fully filled 4d orbital. Here we propose a new bonding mechanism of the hexagonal ferroelectricity in IMO: intra-atomic 4d_z2-5p_z orbital mixing of In followed by asymmetric 4d_z2(In)-2p_z(O) covalent bonding along the c axis.