The low-temperature tetragonal phase of NiCr₂O₄

Ferroelectricity in spinel solid solution Co0.8Ni0.2Cr2OБуш1, Shkuratov2, Kamentsev3 et al. 2012Phys. Rev. B141110View full textAdd to dashboardCite

“…[7][8][9][10][11][12] Cobalt CoCr 2 O 4 and nickel NiCr 2 O 4 chromites belong to the spinel family with the general formula AB 2 O 4 in which Co 2+ (3d 7 ) or Ni 2+ (3d 8 ) bivalent cations occupy tetrahedrally coordinated by oxygen A positions and the Cr 3+ trivalent cations-octahedral positions. [6][7][8][9][10][11][12][13][14] These compounds crystallize, at rather high temperatures, into a cubic phase with the space group F d3m (No. 227).…”

Temperature-dependent vibrational spectroscopic and X-ray diffraction investigation of nanosized nickel chromite

“…In spinel chromites, the oxygen atoms form a weak crystal field resulting in low-spin configuration of d orbitals, hence distortion should be expected only in the case where the d 5 , d 6 , d 8 and d 9 cation of transition metal occupy the tetrahedral site A. This assumption is confirmed in the case of nickel (Ni 2+ , d 8 ) [1][2][3][4][5] and copper (Cu 2+ , d 9 ) [1,5,6]. The features of Jahn-Teller transition were studied in the [7,8].…”

“…The temperature-dependent Raman spectra (Fig. 3) contain fluent changes in the whole measured temperature region 350-4 K. The splitting was observed for the band assigned to the mode F 2g (2). This band splits into the two bands with the maxima at 509 and 524 cm À1 at the temperature of 240 K, which can be assigned according to the factor group analysis (Fig.…”

“…In the NiCr 2 O 4 , the lowering of the cubic O h symmetry to the tetragonal D 4h symmetry (I4 1 /amd space group), crystal structure described in [2], which occurs due to Jahn-Teller effect below room temperature, is connected with splitting of the triply degenerate modes F 1u (to A 2u and E u ) and F 2g (to B 2g and E g ), and of doubly degenerate mode E g (to A 1g and B 1g ). Additional E g and 2E u bands can appear arising from the silent modes (in cubic phase) F 1g and 2F 2u in the Raman and infrared spectra, respectively.…”

Study of exchange bias and training effect in NiCr 2 O 4

“…NiCr 2 O 4 is one of the normal spinel oxides having interesting structural and magnetic properties [14,15]. It is known to crystallize in cubic structure with space group Fd m 3 above room temperature (T 4320 K) with Ni 2 þ ions having fully occupied low energy e g states and triply degenerate t 2g state (e t g g 4 2 4 ) at the tetrahedral site and Cr 3 þ ions having non-degenerate t e g g 2 3 0 configuration at the octahedral site.…”