High-pressure scheelite-type polymorph of SmCrO sub(4: synthesis, structural characterization and magnetic properties)

The new scheelite form of SmCrO sub(4 oxide was obtained by heating the zircon-type SmCrO) sub(4) oxide at 4 GPa and 803 K. X-ray diffraction revealed that this scheelite SmCrO sub(4 phase crystallized with tetragonal symmetry, S.G. I4) sub(1)/a and lattice parameters: a=0.50776(3) nm and c=1.15606(2) nm. This structural phase transition from zircon to scheelite involved a decreasing of around 10% in the unit cell volume. Although the Cr-O and Sm-O distances did not change very much in both zircon and scheelite polymorphs, the changes occurred in the bond angles were remarkable that appear to support the proposed reconstructive model to explain this structural zircon-scheelite phase transition. Magnetic susceptibility and magnetization measurements revealed that the scheelite SmCrO sub(4 oxide behaved an antiferromagnetic material, where the Sm[super]3+ and Cr[super]5+ were simultaneously ordered. The estimated Neel temperature, T) sub(N), was 16 K and the critical field at 12 K associated with the metamagnetic transition was 3.2 T.