Novel Cr–Mn–Fe–Co–Ni oxide composites fabricated by in situ spark plasma sintering for high-temperature applications

Spinel composite is being considered for electrode materials in molten salt electrolysis, aiming to improve high-temperature stability and conductivity. Multi-phase composites with the general formula of (Fe 1-3 x - y Ni y Co x Cr x Mn x ) 3 O 4 ( x  = 0.03, 0.06, 0.09, y = [1-2 x ]/3) were prepared via in situ SPS method. The composites were confirmed to consist of spinel and rock-salt phases through XRD and SEM analysis. Compared to the Ni–Fe–O system, the doping of Cr, Mn and Co improved the phase stability of the spinel during SPS, but hindered the shrinkage process. These composite exhibited low thermal diffusivity (1.236–2.481 m 2 /s, room temperature) and low coefficient of thermal expansion (9.8 - 14.4 × 10 −6  K −1 , 400–800 °C). Moreover, the composite with x  = 0.06 and y  = 0.29 exhibit 94.4 % lower permittivity, 7 times higher dielectric loss (at 40 Hz) and 26.6 % lower high-temperature conductivity (at 800 °C) than that of Ni–Fe–O system. This work demonstrates the enhanced thermal and electrical properties of spinel-based composites, which can provide inspiration to researchers and promote the development of high-temperature electrodes.