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Neutron diffraction study of (K x Na 1− x )NbO 3 ‐based ceramics from low to high temperatures
Author(s) -
Mgbemere Henry,
Schneider Gerold,
Hoelzel Markus,
Hinterstein Manuel
Publication year - 2016
Publication title -
journal of applied crystallography
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.429
H-Index - 162
ISSN - 1600-5767
DOI - 10.1107/s1600576716005197
Subject(s) - monoclinic crystal system , rietveld refinement , orthorhombic crystal system , crystallography , neutron diffraction , tetragonal crystal system , materials science , natural bond orbital , curie temperature , space group , phase diagram , crystal structure , phase (matter) , x ray crystallography , chemistry , analytical chemistry (journal) , diffraction , physics , condensed matter physics , density functional theory , computational chemistry , organic chemistry , ferromagnetism , optics , chromatography
A neutron diffraction study of (K x Na 1− x )NbO 3 ‐based ceramics has been carried out from 5 K to high temperatures well above the Curie temperature. The diffraction data were analysed using Rietveld refinement. For pure KNN samples, especially at the Na‐rich side of the phase diagram, the low‐temperature structure of simple rhombohedral symmetry changes to a highly complex monoclinic structure at a higher temperature. Chemical analysis on the samples showed good agreement of the expected and actual compositions. Trigonal, monoclinic, orthorhombic, tetragonal and cubic phase models as well as two‐phase mixtures are observed depending on the temperature of measurement. Space groups R 3 c , P 1 m 1, P 11 m , Amm 2, P 4 mm , and their combinations are used to refine the trigonal, monoclinic, orthorhombic, tetragonal, cubic and mixed phases, respectively. For the (K 0.48 Na 0.48 Li 0.04 )(Nb 0.86 Ta 0.1 Sb 0.04 )O 3 sample at temperatures between 5 and 300 K, the monoclinic P 11 m space group gives the best refinement fit. For the (K 0.17 Na 0.83 )NbO 3 sample, a two‐phase refinement using the trigonal R 3 c and monoclinic Pm space groups gave the best fit at 300 K, while at 5–150 K the trigonal R 3 c space group gives the best fit. The understanding of the structure of these lead‐free ceramics will help in the optimization of their piezoelectric properties.