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.

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