First XANES evidence of a disorder-order transition in a spinel compound: nanocrystalline ZnFe2O4,

FIGUEROA, S. J. A.; S. J. STEWART

JOURNAL OF SYNCHROTRON RADIATION

WILEY-BLACKWELL PUBLISHING, INC

Año: 2009 vol. 16 p. 63 - 68

0909-0495

In situ Zn K-edge XANES experiments were performed to investigate thethermal evolution of the non-equilibrium state in nano-sized ZnFe2O4. Theinitially disordered ferrite was annealed under oxygen atmosphere and kept attemperatures of 673, 773 and 873 K. Modifications of the XANES featuresallowed the direct detection of the Zn local surrounding changes from Oh to Tdsymmetry. Quantitative analyses of these results were performed by using theprincipal-component analysis approach. The ferrite inversion does not changeuntil the activation barrier is overcome at Ta = 585 K. Above Ta, the Zn ionscontinuously change their environment to their normal equilibrium state.Isothermal treatments confirm that the Zn transference follows a first-orderkinetic process. In addition, the thermal treatment produces a partialrecrystallization that increases the average grain size from 13 to 50 nm andreduces the microstrain. The room-temperature magnetic state changes fromferrimagnetic to paramagnetic, while the blocking temperature increases afterthe treatment.