An in situ Raman spectroscopic study of pressure induced dissociation of spinel NiCr2O4

An in situ Raman spectroscopic study was conducted to investigate the pressure induced phase transformation of spinel NiCr2O4 to pressures of 57.1 GPa. Results indicate that NiCr2O4 spinel dissociates to the mixture of Cr2O3 and NiO at 13.1 GPa. Such a dissociation is complete at 25.1 GPa. The coexistence of Cr2O3 and NiO remains up to the peak pressure of 57.1 GPa. Upon release of pressure to 33.3 GPa, the Cr2O3 Starts to react with NiO to form the spinel phase, and such a reaction is complete at 18.9 GPa. The recovered spinel phase may exhibit an inverse spinel structure, which differs from the initial normal spinel structure. Combined with the results obtained from other end member chromites, it is suggested that the variation of high-pressure behavior of chromites (ACr(2)O(4)) significantly depends on the average A-O bond length of the A-O tetrahedron. (C) 2002 Elsevier Science Ltd. All rights reserved.