Fabrication and characterization of (Mg1−xFex)O (0.05≤x≤0.25) ceramics

Highly dense (Mg1−xFex)O (0.05≤x≤0.25) ceramics (relative density >98%) were prepared by ultrasonic assisted oxalate co-precipitation method together with spark plasma sintering. Mechanical measurements indicate that Young’s modulus decreases monotonously from 312 to 268.5±5.2 GPa with increasing Fe content x from 0 to 0.25. In contrast, the Vickers hardness first increases from 6.8 to 8.50±0.11 GPa as x increases from 0 to 0.1, and then decreases monotonously with further increasing x. The increase and decrease in the hardness with x can be mainly attributed to the solid solution strengthening and weakening of Peierls–Nabarro stress, respectively. Thermal analyses reveal that heat capacity Cp decreases (from 0.896±0.018 to 0.816±0.016 (J K)−1 g−1 at 323 K, for instance) with increasing x (from 0.05 to 0.25) due to the lower Cp of FeO. Similarly, thermal conductivity κ of the samples decreases (say, from 24.8±1.0 to 3.7±0.1 (W K)−1 m−1 at 323 K) with the increasing x (from 0.05 to 0.25), which could be ascribed to the decreasing melting point and increasing mean atomic weight resulting from substitution of Mg for Fe.