Synthesis and magnetic properties of the high-pressure scheelite-type GdCrO4 polymorph

• Published in: Journal of solid state chemistry Vol. 194; pp. 119 - 126
• Main Authors: Dos santos-García, A.J., Climent-Pascual, E., Gallardo-Amores, J.M., Rabie, M.G., Doi, Y., Romero de Paz, J., Beuneu, B., Sáez-Puche, R.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier Inc 01-10-2012; Elsevier
• Subjects: 3d–4f interactions; Antiferromagnetism; Condensed matter: electronic structure, electrical, magnetic, and optical properties; Condensed matter: structure, mechanical and thermal properties; Crystalline state (including molecular motions in solids); Crystallographic aspects of phase transformations; pressure effects; Diffraction; Exact sciences and technology; Group theory; High pressure synthesis; Inorganic compounds; Magnetic permeability; Magnetic properties; Magnetic properties and materials; Magnetization; Metamagnetism; Order disorder; Physics; Polymorphism; Scheelite-type structure; Structure of solids and liquids; crystallography; Structure of specific crystalline solids; Studies of specific magnetic materials; Thermal decomposition; Zircon-type structure; Zircon-type structure; Metamagnetism; High pressure synthesis; Scheelite-type structure; 3d–4f interactions; Polymorphism; Antiferromagnetism; High-pressure effects; Scheelite structure; Space groups; Neutron diffraction; Zirconium silicate; XRD; Symmetry groups; Zircon; Magnetic susceptibility; Specific heat; Magnetic properties; Crystal structure; Magnetization; Tetragonal lattices; Thermal decomposition; Group theory; Magnetic moments; Perovskites; High pressure; Magnetic measurement; Powder pattern; Long range interaction; 3d―4f interactions; Thermodynamic properties; Exchange interactions
• ISSN: 0022-4596; 1095-726X
• DOI: 10.1016/j.jssc.2012.04.044

The scheelite-type polymorph of GdCrO4 has been obtained from the corresponding zircon-type compound under high pressure and temperature conditions, namely 4GPa and 803K. The crystal structure has been determined by X-ray powder diffraction. This GdCrO4 scheelite crystallizes in a tetragonal symmetry with space group I41/a (No. 88, Z=4), a=5.0501(1)Å, c=11.4533(2)Å and V=292.099(7)Å3. The thermal decomposition leads to the formation of the zircon–polymorph as intermediate phase at 773K to end in the corresponding GdCrO3 distorted perovskite-structure at higher temperatures. Magnetic susceptibility and magnetization measurements suggest the existence of long-range antiferromagnetic interactions which have been also confirmed from specific heat measurements. Neutron powder diffraction data reveal the simultaneous antiferromagnetic Gd3+ and Cr5+ ordering in the scheelite-type GdCrO4 with a TN∼20K. The magnetic propagation vector was found to be k=(000). Combined with group theory analysis, the best neutron powder diffraction fit was obtained with a collinear antiferromagnetic coupling in which the mCr5+ and mGd3+ magnetic moments are confined in the tetragonal basal plane according to the mixed representation Γ6 ⊕ Γ8.
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Thermal decomposition of the GdCrO4 high pressure polymorph, from the scheelite-type through the zircon-type structure as intermediate to end in the GdCrO3 perovskite.
► New high pressure GdCrO4 polymorph crystallizing in the scheelite type structure. ► It is an antiferromagnet with a metamagnetic transition at low magnetic fields. ► We have determined its magnetic structure from powder neutron diffraction data. ► Otherwise, the room pressure zircon–polymorph is a ferromagnet. ► The paper will be a great contribution in the study of 3d–4f magnetic interactions.