Zircon to scheelite phase transition induced by pressure and magnetism in TbCrO4
نویسندگان
چکیده
The scheelite form of the TbCrO4 oxide has been obtained by treating TbCrO4-zircon at 4 GPa and 823 K. X-ray and neutron diffraction data reveal that the high-pressure polymorph of TbCrO4 crystallizes with tetragonal symmetry space group I41 /a and lattice parameters a=5.036 74 10 Å and c=11.3734 4 Å. Although bisdisphenoids TbO8 and tetrahedra CrO4 are present in both scheelite and zircon polymorphs, the remarkable changes observed in both polyhedra appear to support the reconstructive model for the zircon-scheelite first-order phase transition. Specific heat and neutron diffraction measurements confirm the antiferromagnetic ordering previously proposed from magnetic susceptibility measurements, in which both Tb3+ and Cr5+ sublattices are involved. The magnetic structure has been determined and can be described on the basis of the coincidence between the chemical and magnetic cells, k= 0,0 ,0 , where the magnetic moments of the Tb3+ and Cr5+ cations are antiferromagnetically aligned along the c axis of the structure, with TN=29 K. Their values at 2 K are 8.97 3 B and 1.089 9 B, respectively.
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