We have studied YMnO3 by high-temperature synchrotron x-ray powder diffraction, and have carried out differential thermal analysis and dilatometry on a single crystal sample. These experiments show two phase transitions at about 1100 K and 1350 K, respectively. This demonstrates the existence of an intermediate phase between the room temperature ferroelectric and the high-temperature centrosymmetric phase. This study identifies for the first time the different high-temperature phase transitions in YMnO3.
Nénert, G., Polleto, M., Marinel, S., Blake, G. R., Meetsma, A., & Palstra, T. T. M. (2007). Experimental evidence for an intermediate phase in the multiferroic YMnO3. Journal of physics: Condensed matter, 19, . https://doi.org/10.1088/0953-8984/19/46/466212