  Long-range ordering of magnetic dipoles in bulk materials gives rise to a
broad range of magnetic structures, from simple collinear ferromagnets and
antiferromagnets, to complex magnetic helicoidal textures stabilized by
competing exchange interactions. In contrast, in the context of dipolar order
in dielectric crystals, only parallel (ferroelectric) and antiparallel
(antiferroelectric) collinear alignments of electric dipoles are typically
considered. Here, we report an observation of incommensurate helical ordering
of electric dipoles by light hole-doping of the quadruple perovskite BiMn7O12.
In analogy with magnetism, the electric dipole helicoidal texture is also
stabilized by competing instabilities. Specifically, orbital ordering and lone
electron pair stereochemical activity compete, giving rise to phase transitions
from a non-chiral cubic structure, to an incommensurate electric dipole and
orbital helix, via an intermediate density wave.
