Origin of microcracking in YMnO3 ceramics

YMnO3 is a multiferroic with a high-temperature ferroelectric phase transition (T-C = 913 K) and a subambient Neel temperature (T-N = 70 K). Ferroelectricity has been reported for single crystals and epitaxial thin films but to date not for ceramics. We postulate that the absence of direct evidence of ferroelectricity in ceramic YMnO3 might be attributed to microcrack formation (3.2 vol.%) on cooling. We show that microcracking originates from a combination of 3.7 vol.% change and strong anisotropy in the thermal expansion coefficient (a) of the hexagonal structure (alpha(a)-alpha(c)vertical bar approximate to 4.57 x 10(-5)degrees C-1) between 600 and 1000 degrees C. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.