Comparing the Pressure-Induced Structural Behavior of CuCr₂O₄ and CuCr₂Se₄ Spinels

Abstract

We have conducted high-pressure measurements on the CuCr 2 O 4 and CuCr 2 Se 4 spinels to unravel the structural systematics of these materials under compression. Our studies have revealed diverse structural behavior in these two compounds. In particular, CuCr 2 O 4 retains its ambient-pressure I4 1 /amd structure up to 50 GPa. Close inspection of the lattice and interatomic parameters reveals a compressibility change near 23 GPa, which is accompanied by an expansion of the apical Cr−O bond distances. We speculate that an outer Cr 3+ 3d orbital reorientation might be at play in this system, manifesting as the change in compressibility at that pressure point. On the other hand, CuCr 2 Se 4 undergoes a structural transformation from the starting Fd3̅ m phase toward a monoclinic structure initiated at ∼8 GPa and completed at ∼20 GPa. This highpressure behavior resembles that of ZnCr 2 Se 4 , and it appears that, unlike similar chalcogenide Cr spinels, steric effects take a leading role in this pressure-induced Fd3̅ m → monoclinic transition. Close comparison of our results with the reported literature yields significant insights behind the pressure-induced structural systematics of this important family of materials, thus both allowing for the careful manipulation of the structural/physical properties of these systems by strain and promoting our understanding of similar pressure-induced effects in relevant systems.

From Semiconducting to Metallic: Jahn–Teller-Induced Phase Transformation in Skyrmion Host GaV4S8

“…The errors in the fitting results come from the fitting process without including the propagation of uncertainties from pressure and volume. The bulk modulus of the cubic phase of this lacunar spinel compound is different from other conventional spinels, such as ZnGa 2 O 4 , ZnCr 2 Se 4 , CoCr 2 O 4 , CuCr 2 O 4 , ZnCr 2 S 4 , MnCr 2 O 4 , NiCr 2 O 4 , CdCr 2 Se 4 , and so on. The discrepancies are predominantly caused by the different crystal structures, F 4̅3 m versus Fd 3̅ m , in these two systems.…”

Universal link of magnetic exchange and structural behavior under pressure in chromium spinels

“…We can immediately observe a linear dependence of the two parameters, with the exception of CuCr 2 O 4 which does not show any transition up to 50 GPa, whereas the P Tr = 25 GPa in this case indicates an isostructural transition, most likely resulting from a pressureinduced orbital reorientation 24 . We note also that the calculated magnetic exchange interactions of CuCr 2 O 4 are much larger compared to the rest of the spinels ( Table S8 in the Supplement 46 ), possibly accounting for the absence of any structural transition up to 50 GPa 24 . On the other hand, CoCr 2 O 4 undergoes a structural distortion at about 16 GPa, attributed to magnetic frustration 45 .…”

“…In particular, we have shown that the ratio of the next-nearest neighbor (K nnn ) over the nearest neighbor (J nn ) magnetic interactions is proportional to the structural transition pressure (P Tr ) from the starting cubic Fd3 m phase towards a tetragonal modification 21,22 . Notable exceptions from this trend are ZnCr 2 Se 4 23 and CuCr 2 Se 4 24 , as their high-pressure behavior appears to be dictated by the similar ionic radii of tetrahedrally coordinated Zn 2+ and Cu 2+ with the octahedrally coordinated Cr 3+ , and the higher covalency of the larger-sized Se anions [for a more detailed discussion see Ref. 24 ].…”

“…Notable exceptions from this trend are ZnCr 2 Se 4 23 and CuCr 2 Se 4 24 , as their high-pressure behavior appears to be dictated by the similar ionic radii of tetrahedrally coordinated Zn 2+ and Cu 2+ with the octahedrally coordinated Cr 3+ , and the higher covalency of the larger-sized Se anions [for a more detailed discussion see Ref. 24 ].…”

Preparation and Characterization of Copper Chromium Oxide Nanoparticles Using Modified Sol‐Gel Route and Evaluation of Their Microwave Absorption Properties

“…Copper chromite composite oxide is a versatile catalyst and has been employed as a catalyst for chemical reactions such as hydrogenation, dehydrogenation, oxidation, alkylation, etc. Accordingly, it finds a wide range of commercial applications . Recently, we have reported the photocatalytic property of CuCr 2 O 4 nanoparticles .…”