Premium
Hydrothermal Synthesis and Formation Mechanisms of Lanthanum Tin Pyrochlore Oxide
Author(s) -
Moon Jooho,
Awano Masanobu,
Maeda Kunihiro
Publication year - 2001
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/j.1151-2916.2001.tb01048.x
Subject(s) - pyrochlore , lanthanum , crystallization , dissolution , hydrothermal circulation , hydrothermal synthesis , materials science , crystallite , precipitation , tin , chemical engineering , phase (matter) , oxide , mineralogy , inorganic chemistry , crystallography , chemistry , metallurgy , physics , organic chemistry , meteorology , engineering
Well‐defined La 2 Sn 2 O 7 with a phase‐pure pyrochlore structure was produced by hydrothermal synthesis at temperatures as low as 200°C. Production of phase‐pure La 2 Sn 2 O 7 requires a pH above 10, and higher pH accelerates the crystallization process. The synthesis produced spherical particles of average particle size ∼0.59 μm (±0.12) and surface area ∼14.1 m 2 /g. SEM and TEM observation for morphologic evolution and kinetic analysis during crystallization indicated that La 2 Sn 2 O 7 formation probably proceeds via a two‐step reaction. First a transient dissolution–precipitation occurs. Then the primary crystallites aggregate because of their colloidal instability, and heterocoagulation with the lanthanum hydrous oxide precursor particles also occurs. The sluggish reaction rate at the later stage of reaction is characterized by an in situ transformation, where the soluble tin species is diffused through the porous La 2 Sn 2 O 7 aggregates to react with entrapped lanthanum precursors.