ESR evidence for chemically assisted thermal incorporation of Mn2+ centresinto aluminium fluoride lattices

The incorporation of Mn2+ ions into the bulk of polycrystalline AlF3 is rep orted for the first time as a result of combined chemical and thermal treat ments. Mn-55-hyperfine (hfs) and Mn-55-F-19-superhyperfine (shfs) structure s appear to be sensitive tools to indicate structural reorganization proces ses. ESR spectroscopic X-band in situ investigations of powder samples in t he temperature range 4 K less than or equal to T less than or equal to 1473 K led to well defined ESR spectra even at 1473 K as a result of specific c hemical and physical processes taking place at distinct intervals of the te mperature range. Two coupled conditions appear to be necessary prerequisite s for the appearance of the well resolved Mn-55-F-19 shfs structure of MnF6 4- subunits: (i) temperature treatments covering the range above 673 K, and (ii) the presence of water traces in the educts. In addition to X-band, Q- band measurements were performed to verify the coordination of Mn2+ ions by six F- ions using the better spectral resolution at this frequency. Finall y, it can be stated that the formation and stabilization of regular MnF64- units critically depend on the state of the order of the matrix. Therefore, the shfs pattern can advantageously be used as an order parameter. All exp erimental ESR powder spectra could be simulated by diagonalization of the s pin hamiltonian matrix for the S = 5/2 and I = 5/2 spin problem (Mn2+). (C) 1998 Elsevier Science Ltd. All rights reserved.