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Phase stability of rare earth sesquioxides with grain size controlled in the nanoscale
Author(s) -
Kimmel Giora,
Shneck Roni Z.,
Lojkowski Witold,
Porat Ze'ev,
Chudoba Tadeusz,
Mogilyanski Dmitry,
Gierlotka Stanislaw,
Ezersky Vladimir,
Zabicky Jacob
Publication year - 2019
Publication title -
journal of the american ceramic society
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.9
H-Index - 196
eISSN - 1551-2916
pISSN - 0002-7820
DOI - 10.1111/jace.16396
Subject(s) - ionic radius , monoclinic crystal system , materials science , crystallite , nanocrystal , grain size , grain growth , annealing (glass) , crystallography , phase (matter) , crystal structure , chemical engineering , mineralogy , nanotechnology , chemistry , ion , metallurgy , organic chemistry , engineering
Rare earth oxides are important materials due to their chemical and physical properties. The rare earth sesquioxides (RESOXs) possess a cubic, monoclinic, or hexagonal structure, depending on pressure, temperature and ionic radius. When RESOXs take the form of single crystalline grains with diameter in the nanoscale range (nanocrystals), it is suspected that the grain size determines the phase stability as well. RESOXs with medium ionic radius such as Gd 2 O 3 , Eu 2 O 3 and Sm 2 O 3 in the low temperature range up to 900°C may take the monoclinic structure or the cubic structure, depending on the synthesis process. The structure determining factor can be, besides temperature, also the grain size. In order to determine the stable structure taking into account grain size as a parameter, we produced Gd 2 O 3 and Sm 2 O 3 nanocrystals embedded in a neutral MgO matrix. This way, we prevented grain growth during annealing. For comparison, we annealed pure Gd 2 O 3 and Sm 2 O 3 nanocrystals in which temperature increase caused grain growth, as in traditional experiments for phase stability determination. We have shown that for coarse grained materials at low temperature monoclinic is the stable structure. For nano‐sized crystallites, cubic is the stable structure. This explains the controversial results as far as which phase is the stable one below 900°C and permits to program the needed structure by controlling crystallization kinetics and grain growth.