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Formation mechanism and growth of MN bO 3 , M=K, Na by in situ X‐ray diffraction
Author(s) -
Skjærvø Susanne Linn,
Sommer Sanna,
Nørby Peter,
Bøjesen Espen Drath,
Grande Tor,
Iversen Bo B.,
Einarsrud MariAnn
Publication year - 2017
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.14932
Subject(s) - crystallite , orthorhombic crystal system , hydrothermal synthesis , nucleation , hydrothermal circulation , crystallography , stoichiometry , crystallization , tetragonal crystal system , x ray crystallography , materials science , chemistry , diffraction , mineralogy , crystal structure , chemical engineering , physics , organic chemistry , optics , engineering
Hydrothermal synthesis is a well‐established method to produce complex oxides, and is a potential interesting approach to synthesize stoichiometric lead‐free piezoelectric K 0.5 Na 0.5 NbO 3 . Due to challenges in obtaining the desired stoichiometry of this material, more knowledge is needed on how the end‐members, KN bO 3 and NaNbO 3 , are nucleating and growing. Here, we report on the formation mechanisms and growth during hydrothermal synthesis of KN bO 3 and NaNbO 3 by in situ synchrotron powder X‐ray diffraction. We show that tetragonal KN bO 3 crystallites form from dissolved T‐Nb 2 O 5 at 250°C‐300°C and 250 bar while orthorhombic NaNbO 3 forms via several crystalline intermediate phases at 225°C‐325°C and 250 bar. The crystallite size of KN bO 3 is decreasing while the crystallite size of NaNbO 3 is increasing with increasing temperature, demonstrating that the presence of intermediate phases is highly important for the nucleation and growth of the final product. The different crystallization schemes explain the challenge in obtaining stoichiometric K 0.5 Na 0.5 NbO 3 by hydrothermal synthesis.