Publication
Title
Mössbauer effect study of anapaite, $Ca_{2}Fe^{2+}(PO_{4})_{2}.4H_{2}O$, and of its oxidation products
Author
Abstract
 Mossbauer spectra (MS) of anapaite (Ca-2 Fe2+ (PO4)(2) . 4H(2)O) and of a sample after being immersed in a 4% H2O2 solution at room temperature (RT) over 12 days (hereafter an4ox) were collected at temperatures in the range 4.2 to 420 K and 11 to 300 K respectively. All MS consist of symmetrical doublets. hence magnetic ordering was not observed. The Fe2+ centre shifts of temperature dependencies of the Fe2+ centre shifts of anapaite and an4ox were analysed with the Debye model for the lattice vibrations. The characteristic Mossbauer temperatures were found as 370 K +/- 25 K and 340 K +/- 25 It. and the intrinsic isomer shifts as 1.427 +/- 0.005 mm/s and 1.418 +/- 0.005 mm/s respectively. From the external-field (60 kOe) MS recorded at 4.2 and 189 K for the non-treated sample, the principal component V-zz of the electric field gradient (EFG) is determined to be positive and the asymmetry parameter eta approximate to 0.2 and 0.4 respectively. The temperature variations of the quadrupole splittings, Delta E-Q(T), cannot be interpreted on the basis of the thermal population of the D-5 electronic levels resulting from the tetragonal compression of the O-6 co-ordination. The low-temperature linear behaviour of Delta E-Q(T) is attributed to a strong orbit-lattice coupling. A field of 60 kOe applied to anapaite at 4.2 K produces magnetic hyperfine splitting with effective hyperfine fields of -136. -254 and -171 kOe along the principal axes Ox, Oy and Oz of the EFG tensor respectively. Additional oxidation treatments in solutions with various H2O2 concentrations up to 20% and subsequent Mossbauer experiments at room temperature, have revealed that the anapaite structure is not sensitive to oxidation since eventually only a small amount of Fe2+ (similar to 6.5%) is converted into Fe3+.
Language
English
Source (journal)
Physics and chemistry of minerals. - Berlin
Publication
Berlin : 1999
ISSN
0342-1791
Volume/pages
26:6(1999), p. 506-512
ISI
000081850100011
Full text (Publisher's DOI)
Full text (publisher's version - intranet only)
UAntwerpen
 Faculty/Department Research group Publication type Subject Affiliation Publications with a UAntwerp address