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Issue
EPL
Volume 77, Number 2, January 2007
Article Number 26003
Number of page(s) 5
Section Condensed Matter: Structural, Mechanical and Thermal Properties
DOI http://dx.doi.org/10.1209/0295-5075/77/26003
Published online 11 January 2007
EPL, 77 (2007) 26003
DOI: 10.1209/0295-5075/77/26003

Phase transitions in lead-free piezoelectric ceramics: Study of local atomic structure

M. P. Lemeshko1, E. S. Nazarenko1, 2, A. A. Gonchar1, L. A. Reznichenko1, O. Mathon3, Y. Joly2 and R. V. Vedrinskii1

1  Institute of Physics, Rostov State University - 194 Stachky Ave., 344090 Rostov-on-Don, Russia
2  Laboratoire de Cristallographie, CNRS associé à l'Université Joseph Fourier - BP 166, F-38042 Grenoble Cedex 9, France
3  BM29, European Synchrotron Radiation Facility - BP 220, F-38043 Grenoble Cedex 9, France


received 16 August 2006; accepted in final form 20 November 2006; published January 2007
published online 11 January 2007

Abstract
Local atomic structure of the piezoelectric ceramics ${\rm K}_{x}{\rm Na}_{1-x}{\rm NbO}_{3}$ ( x=0.00, 0.05, 0.30, 0.40, 0.50 and 0.65) is studied in all phase regions (10 K$\hbox{--} $1023 K) using Nb K-edge extended X-ray absorption fine-structure (EXAFS) spectroscopy. We have shown the validity of a new spherical model for phase transitions on the basis of both fitting of EXAFS signal in the R-space and differential EXAFS analysis. Within this model the Nb atoms are located on the surfaces of small spheres of constant radii surrounding centers of ${\rm NbO}_{6}$ octahedrons in all phases. The distri- bution of the Nb atom on this surface changes during phase transitions. Besides, the analysis of local structure reveals that the geometry of ${\rm NbO}_{6}$ octahedra does not depend on the x value at each temperature, whereas the octahedra rotation angles do.

PACS
61.10.Ht - X-ray absorption spectroscopy: EXAFS, NEXAFS, XANES, etc. .
77.84.Dy - Niobates, titanates, tantalates, PZT ceramics, etc. .
64.90.+b - Other topics in equations of state, phase equilibria, and phase transitions .

© Europhysics Letters Association 2007