14721-18-7Relevant articles and documents
Effect of nitrogen substitution on the structural and magnetic ordering transitions of NiCr2O4
Liu, Xin,Yin, Nan,Thomas, Tiju,Yang, Minghui,Wang, Junhu,Shi, Quan
, p. 112140 - 112147 (2016)
The nitrogen (N) doped spinel NiCr2O4 has been synthesized at 773 K (N500) and 873 K (N600) by ammonolysis of NiCr2O4 powders to study the effect of anion doping on its structural and magnetic properties. The N contents are determined by thermogravimetric oxidation, yielding a composition that can be described as NiCr2O3.68N0.21 (N500) and NiCr2O3.55N0.30 (N600). X-ray photoelectron spectroscopic studies suggest that N3? species partly substitute the oxygen in the lattice and oxygen vacancies exist in the N doped samples. There is evidence that in the nitrided sample, the Cr ion is most likely in a mixed oxidation state. As the N content increases, the structure at room temperature changes from tetragonal to the cubic phase; N500 is only partially tetragonal; N600 is completely cubic. Such structural change is the consequence of the depression of the cooperative Jahn-Teller effect of Ni2+ in the tetrahedral A site caused by the presence of N3?. Combined heat capacity and temperature dependent magnetic susceptibility measurements give clear evidence of the magnetic and structural transitions in the N doped NiCr2O4. The Jahn-Teller transition temperatures decrease with increasing N content; this is likely due to increased covalency and hence enhanced contribution of the angular momentum and the spin-orbit coupling to local chemical bonding around Ni2+. Antiferromagnetic transitions are observed at TS = 23 K and 22 K for N500 and N600, respectively. Hence there is indeed a lowering of transition when compared to pure NiCr2O4 (28 K). The magnetic loops at different temperatures confirm that the material behaves as a paramagnet over a wide range of temperatures T ～ 80-350 K. The material also exhibits a canted ferrimagnetic structural transition between 30 and 70 K. We also report evidence for increased frustration and lowered correlation length in N doped compounds compared to the parent NiCr2O4. The present study on N? doping effects on the structure and magnetic properties of this NiCr2O4 is expected to be useful for tailoring the ferric phase transitions through anion substitutions.
Xanes and crystal field spectroscopy of five-coordinated nickel(II) in potassium-nickel phosphate
Galoisy,Calas
, p. 221 - 228 (1993)
The first spectroscopic data on KNiPO4 used as reference compound for 5-coordinated nickel in crystalline oxide compounds are presented. The Ni-K edge X-ray Absorption Near Edge Structure (XANES) spectrum is compared to those of 4- and 6-coordinated Ni in NiCr2O4 and CaNiSi2O6, respectively. The intensity of the pre-edge increases from 6- to 4-coordination while that of the main-edge decreases. Both features are thus sensitive indicators of the Ni coordination state. Crystal field spectra are also different for the three nickel coordination states. The KNiPO4 crystal field spectrum exhibits a position and relative intensity of the absorption bands similar to those found in the spectra of pentacordinated Ni complexes. They are interpreted using the electron energy level diagram of Ni(II), in a distorted square pyramid crystal field. Criteria for the use of XANES and crystal field spectroscopy to characterize the presence of 5-coordinated Ni in oxide compounds are given. The similar crystal field stabilization energy encountered in 5- and 6-coordinated nickel explains the stability of 5-coordinated nickel in phosphates.
Structural transition of spinel compound NiCr2 O4 at ferrimagnetic transition temperature
Ishibashi,Yasumi
, p. e610-e612 (2007)
Magnetic properties and crystal structure of spinel compound NiCr2 O4 have been investigated by magnetization and high-resolution X-ray powder diffraction measurements. The structural transition from tetragonal to orthorhombic symmet
Dielectric relaxation and small polaron hopping transport in sol-gel-derived NiCr2O4 spinel chromite
Javed, Muhammad,Khan, Ayaz Arif,Kazmi, Jamal,Mohamed, Mohd Ambri,Khan, Muhammad Nasir,Hussain, Mubushar,Bilkees, Rehana
, (2021)
Herein, we have synthesized NiCr2O4 chromite by the sol-gel auto-combustion route. The refined X-ray powder diffraction pattern confirmed the single-phase formation of the material, which crystallized in a cubic normal spinel structure with space group Fd3m. The complex impedance study indicated the existence of relaxation phenomenon and predicted the semiconducting nature of the material. The frequency-dependent Nyquist plot modeled by (RGBCGB) (RGQG) equivalent circuit exhibited the effects of grain and grain boundary to the electrical response of the compound over the measured temperature range of 263-393 K. The experimental AC conductivity data followed Jonscher's double power-law behavior, and the frequency exponent profile suggested small polaron hopping as the most probable transport mechanism for the sample. The complex modulus analysis showed the non-Debye type behavior of the material. In contrast, the dielectric constant exhibited dispersion in the low-frequency regime with a large tangent loss directly related to temperature.
Oxygen-sensing properties of spinel-type oxides for stoichiometric air/fuel combustion control
Shimizu,Kusano,Kuwayama,Tanaka,Egashira
, p. 818 - 824 (1990)
The temperature dependence of electrical resistance of several spinel-type oxides was measured in exhaust gases of air-methane combustion, to evaluate the potential of the oxides as an air/fuel stoichiometric oxygen sensor. The results are discussed in te
Magnetic structure of NiCr2O4 studied by neutron scattering and magnetization measurements
Tomiyasu, Keisuke,Kagomiya, Isao
, p. 2539 - 2542 (2004)
The magnetic ordering of the normal spinel ferrimagnet NiCr 2O4 below TC = 74 K was reinvestigated by neutron scattering and magnetization measurements on a powder specimen. We found another magnetic transition at TS = 31 K besides TC in both experiments. The ordering of a ferrimagnetic (longitudinal) component and that of an antiferromagnetic (transverse) component occur at TC and TS, separately. A new magnetic structure model of NiCr 2O4 below TS with a spontaneous magnetization of about 0.3 μB/formula is proposed based on experimental neutron scattering intensity. 2004 The Physical Society of Japan.
Spin glass and exchange bias behavior in magnetically frustrated Ni1?xMgxCr2O4 (x = 0.0–0.50)
Borah, Ritupan,Ravi
, (2020)
Single-phase polycrystalline samples of Ni1?xMgxCr2O4 (x = 0.0–0.50) were prepared by sol gel route and their structural and magnetic properties were studied. Structural transformation from tetragonal (I41/amd) to cubic (Fd3-m) phase is observed at room temperature due to Mg substitution. Mg substitution gives rise to reduction in ferrimagnetic and antiferromagnetic transition temperatures along with a signature of spin glass like phase in samples of intermediate compositions, i.e., for x = 0.10, 0.20 and 0.30. The observed stretched exponential type relaxation of thermoremanent magnetization and the highly frustrated magnetic behavior confirm the glassy magnetic phase. Significant increase in exchange bias field under field cooled condition for the Mg substituted samples is observed. The origin of exchange bias in theses samples is explained by considering exchange anisotropy between the ferrimagnetic and antiferromagnetic components of canted spin. The training effect of exchange bias field is also observed.
New co-precipitation technique for the preparation of mixed-oxides
Pathak,Mukhopadhyay,Pramanik
, p. 155 - 159 (1992)
Fine ceramic oxide powders of the composition MN2O4 [spinels, where M = Ni(II), Zn(II), Co(II), Cd(II) and N = Fe(III), Cr(III)], M3Fe5O12 [garnets, where M = Y, Gd] and RBa2Cu3O7+δ [ceramic superconductors, where R = rare earths] have been synthesized through a novel coprecipitation technique. The novelty of this route lies in its simplicity and cost-effectiveness. The coprecipitation has been done using a mixture of (NH4)2CO3/(NH4)HCO3, triethylamine and formaline in the presence of soluble polymers such as polyvinyl alcohol (PVA). The final product formation is confirmed and characterized by X-ray diffraction (XRD) and energy dispersive X-ray spectroscopy (EDX).
Catalytic Decomposition of Isopropanol over Chromite Spinels MCr2O4 (M=Ni, Mn and Mg)
Balasubramanian, Krithivasa,Krishnasamy, Vengaimuthu
, p. 2665 - 2672 (1986)
The decomposition of isopropanol over nickel, manganese and magnesium chromite spinel catalysts has been investigated in the vapour phase in an integral reactor.Its decomposition follows first-order kinetics.Kinetic and thermodynamic parameters have been calculated using the Arrhenius and Eyring equations.The activity pattern is found to be NiCr2O4>MnCr2O4>MgCr2O4.The chromite spinels have been characterised by X-ray studies, i.r. spectral analysis, conductivity and thermoelectric potential measurements.All three chromites were found to be p-type semiconductors in the temperature range 150-400 deg C.Exclusive dehydrogenetion is shown by NiCr2O4 and MnCr2O4, whereas MgCr2O4 functions as a dehydrogenation and dehydration catalyst.A linear correlation exists between the entropy of activation and the activation energy for electrical conduction for the chromite spinels studied.
Subsolidus of the MO-Cr2O3-V2O5 systems, where M=Ni, Mg
Rychlowska-Himmel,Bosacka
, p. 1193 - 1197 (2007)
Phase relations in the system: MO-Cr2O3-V2O5, where M=Ni and Mg, were determined up to the solidus lines over the whole components concentration range. On the basis of this, a division of both systems into subsidiary subsystems was performed. The melting temperatures of individual areas were also established.
