Zircon to scheelite phase transition induced by pressure and magnetism in TbCrO4

7 páginas, 6 figuras, 3 tablas.-- PACS number(s): 75.25.-j, 62.50.-p, 61.66.Fn, 75.30.Cr.-- et al.
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)μB and 1.089(9)μB, respectively.
The authors are grateful to Spanish MICINN and FEDER for financial support under Research Projects No. MAT2007- 63497 and No. MAT2007-61621, CONSOLIDER-Ingenio 2010 (Grant No. CSD 2007-00010).