Crystal structure and phase transitions of sodium potassium niobate perovskites

• Published in: Solid state sciences Vol. 11; no. 2; pp. 320 - 324
• Main Authors: Tellier, J., Malic, B., Dkhil, B., Jenko, D., Cilensek, J., Kosec, M.
• Format: Journal Article
• Language: English
• Published: Issy-les-Moulineaux Elsevier Masson SAS 01-02-2009; Elsevier Masson; Elsevier
• Subjects: Chemical Sciences; Condensed matter: structure, mechanical and thermal properties; Crystal structure; Crystalline state (including molecular motions in solids); Exact sciences and technology; KNN; Material chemistry; Phase transitions; Physics; Rietveld method; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Theory of crystal structure, crystal symmetry; calculations and modeling; X-ray diffraction; X-ray diffraction; Rietveld method; KNN; Phase transitions; Crystal structure; Temperature dependence; Cubic lattices; Potassium niobates; Symmetry property; Phase transformations; Morphotropic phase boundary; Sodium niobates; Distortion; Perovskites; XRD; Lattice parameters; Monoclinic lattices; Trigonal lattices; Potassium; crystal structure; phase transitions; X-Ray diffraction
• ISSN: 1293-2558; 1873-3085
• DOI: 10.1016/j.solidstatesciences.2008.07.011

This paper presents the crystal structure and the phase transitions of K
x
Na
1−
x
NbO
3 (0.4
≤
x
≤
0.6). X-ray diffraction measurements were used to follow the change of the unit-cell parameters and the symmetry in the temperature range 100–800
K. At room temperature all the compositions exhibited a monoclinic metric of the unit cell with a small monoclinic distortion (90.32°
≤
β
≤
90.34°). No major change of symmetry was evidenced in the investigated compositional range, which should be characteristic of the morphotropic phase-boundary region. With increasing temperature, the samples underwent first-order monoclinic–tetragonal and tetragonal–cubic transitions. Only the potassium-rich phases were rhombohedral at 100
K.
Evolution of the unit-cell parameters of K
x
Na
1−
x
NbO
3 compounds in the range
x
=
[0.4–0.6] at room temperature.
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