Abstract

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 4dz2−5pz orbital mixing of In followed by asymmetric 4dz2(In)–2pz(O) covalent bonding along the c axis.