resumo
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.
palavras-chave
THERMAL-EXPANSION ANISOTROPY; TITANATE-MULLITE COMPOSITES; MANGANITES; BEHAVIOR; GEL
categoria
Science & Technology - Other Topics; Materials Science; Metallurgy & Metallurgical Engineering
autores
Tomczyk, M; Senos, AM; Vilarinho, PM; Reaney, IM
nossos autores
Ana Maria de Oliveira e Rocha Senos
Professor associado
Monika Malgorzata Tomczyk
Estudante de doutoramento
Paula Maria Lousada Silveirinha Vilarinho
Vice-DiretorGrupos
2 - nanoestruturas e cerâmicos ferróicos multifuncionais
3 - materiais de carbono, compósitos e revestimentos funcionais
agradecimentos
The authors acknowledge the financial support from FEDER, QREN, COMPETE, and FCT within the project PTDC/CTM/67575/2006.