High-temperature structural evolution of hexagonal multiferroic YMnO3 and YbMnO3

Neutron powder diffraction studies on the structural evolution of hexagonal multiferroic YMnO3 and YbMnO3 from 1000 K to 1400 K, and from 1000 K to 1350 K, respectively, are presented. The temperature evolution of diffraction patterns suggests that YMnO3 undergoes a phase transition to a non-polar structure above 1200 K, while YbMnO3 remains ferroelectric up to 1350 K. Detailed structural parameters were obtained as a function of temperature from Rietveld refinements. Based on this result, the distinct differences in temperature behaviour between YMnO3 and YbMnO3, and the origin of the ferroelectricity in these hexagonal multiferroics are discussed.