Immiscibility in the NiFe2O4–NiCr2O4 spinel binary

Abstract

The solid solution behavior of the Ni(Fe 1-n Cr n ) 2 O 4 spinel binary is investigated in the temperature range 400-1200°C. Non-ideal solution behavior, as exhibited by non-linear changes in lattice parameter with changes in n, is observed in a series of single-phase solids air-cooled from 1200°C. Air-annealing for one year at 600°C resulted in partial phase separation in a spinel binary having n = 0.5. Spinel crystals grown from NiO, The extrapolated solvus is shown to be consistent with that predicted using a primitive regular solution model in which free energies of mixing are determined entirely from changes in configurational entropy at room temperature.

Mixing and non-stoichiometry in Fe–Ni–Cr–Zn–O spinel compounds: density functional theory calculations

“…5 still shows a miscibility gap between the NiFe 1 Cr 1 O 4 compound and the slightly Cr poor FeCr 2 O 4 phase. The measured NiFe 2 O 4 -NiCr 2 O 4 phase diagram 86,87 indicates an almost symmetrical miscibility gap, though there is a slight shift towards the Cr rich side. The latter observation is consistent with the calculations.…”

“…In order to analyze this behavior further we calculated the free energy of mixing by adding the mixing entropy to the calculated mixing energies. We used a model similar to that derived by Ziemniak et al 86 The resulting free energy at 1200 K in Fig. 5 still shows a miscibility gap between the NiFe 1 Cr 1 O 4 compound and the slightly Cr poor FeCr 2 O 4 phase.…”

Up-scalable synthesis of size-controlled copper ferrite nanocrystals by thermal treatment method

“…Spinels have three different cation distribution patterns between sites known as normal, random and inverse. In the ideal normal spinel, A and B cations occupy the tetrahedral and octahedral sites, respectively; in the inverse spinel, half of B cations enter the fourfold coordination, with the consequent migration of all A cations to the octahedral sites [1,2]. Due to ferromagnetic nature, the magnetic properties of the spinel ferrites are dependent upon the cation distribution between A and B-sites [3].…”

Evaluation of metal-ions containing sludges in the preparation of black inorganic pigments

“…These two formulations develop nichromite instead of trevorite, due to the excessive amount of nickel and chromium that results from the use of a higher percentage of galvanizing sludge (>83 wt.%). Its presence is accompanied by free NiO [21,22]. On the opposite side, nonstoichiometric mixtures richer in F-sludge (TF3 and SF3) show hematite (␣-Fe 2 O 3 ).…”

“…The crystalline phases detected in the pigments are listed in [20,21]. In the actual conditions, it can be assigned to trevorite, since it shows the nearest arrangement and composition.…”