A second example is provided by the family of hexagonal rare earth manganites (h-"R"MnO3 with "R"=Ho-Lu, Y), which have a structural phase transition at around 1300 K consisting primarily of a tilting of the MnO5 bipyramids. While the tilting itself has zero polarization, it couples to a polar corrugation of the "R"-ion layers which yields a polarisation of ~6µC/cm². Since the ferroelectricity is not the primary order parameter it is described as "improper". The multiferroic phase is reached at ~100K when a triangular antiferromagnetic order due to spin frustration arises.