Phase transitions in lead-free piezoelectric ceramics: Study of local atomic structureM. 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
Local atomic structure of the piezoelectric ceramics ( x=0.00, 0.05, 0.30, 0.40, 0.50 and 0.65) is studied in all phase regions (10 K1023 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 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 octahedra does not depend on the x value at each temperature, whereas the octahedra rotation angles do.
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