STUDY ON THE DYNAMIC BEHAVIOR OF SURFACE-LOCATED AND BULK-LOCATED DOPING IONS IN CR2O3 SAMPLES USING SN-119 DIAMAGNETIC PROBE MOSSBAUER SPECTROMETRY

In order to compare the dynamical properties of surface- and bulk-located dopant ions, Mossbauer spectra of several Cr2O3 samples corresponding to the same chemical composition (Cr1.9934Sn0.0066O3) but with different Sn-119(4+) ion distributions have been investigated over the temperature range 294 K less-than-or-equal-to T less-than-or-equal-to 615 K. The Mossbauer lattice temperature THETA(M) probed by surface-located Sn-119(4+) is shown to be considerably lowered (THETA(M) = 314 K) if compared to that for bulk positions (THETA(M) = 400 K). The greater thermal vibration amplitude of surface-located ions is related to the reduced effective coordination sphere of the surface sites. The Neel temperature probed by Sn-119(4+) (T(N) = 305 +/- 2 K), in surprisingly good agreement with that of undoped Cr2O3 (308 K), does not depend upon the Sn-119(4+) distribution with respect to the surface, which shows that the ordering temperature is the same for surface Cr3+ as for bulk ones.