Phase transition induced by pressure in TbCrO4 oxide: Relationship structure–properties

Terbium chromate TbCrO4, which has been described as belonging to the zircon-type structure showing tetragonal symmetry, space group I41/amd, has been prepared as a dimorphic compound. When the zircon-type TbCrO4 polymorph is treated at 40kbar and 833K takes place a phase transition to the tetragonal scheelite-type TbCrO4 polymorph, space group I41/a, with lattice parameters a=5.0315(10)Å and c=11.3740(2)Å. Magnetic susceptibility measurements reveal dramatic changes concerning the magnetic behavior of these two polymorphs. In this sense, the zircon-type TbCrO4 polymorph behaves as ferromagnetic with a Curie temperature of 22K, while the scheelite-type TbCrO4 polymorph is antiferromagnetic with TN=29K. M vs. H plots at different temperatures show the presence of a metamagnetic transition for the scheelite-type TbCrO4 polymorph with a critical field of 2.6T. The change of the sign of the magnetic interaction has been explained taking into account the differences found in the distances and bond angles of the superexchange Tb–O–Cr pathway through these interactions take place in both zircon and scheelite polymorphs.