The crystallographic and magnetic characteristics of Sr2CrO4 (K2NiF4-type) and Sr10(CrO4)6F2 (apatite-type)

Solid-state reaction between SrCO3, Cr2O3 and SrF2 has produced the apatite phase Sr-10(CrO4)(6)F-2 and Sr2CrO4 which adopts the K2NiF4-type structure. The reaction outcome was very sensitive to the heating rate with rapid rise times favouring the formation of Sr2CrO4, which has been synthesised at ambient pressure for the first time. Powder X-ray diffraction and electron diffraction confirmed that Sr-2,CrO4 adopts a body centred tetragonal cell (space group I4/mmm) with lattice parameters a = 3.8357(l) angstrom and c = 12.7169(l) angstrom, while a combination of neutron and X-ray diffraction verified Sr-10(CrO4)(6)F-2, is hexagonal (space group P6(3)/m) with lattice parameters a = 9.9570(l) angstrom and c = 7.4292(l) angstrom. X-ray photoelectron spectroscopy and magnetic measurements were used to characterise the oxidation states of chromium contained within these phases. (C) 2007 Elsevier Inc. All rights reserved.