Vacuum hot pressed highly dense, nanograined Mg(Al1−xCrx)2O4 ceramics

Highly dense and nanograined Mg(Al 1− x Cr x ) 2 O 4 ( x   =   0.1, 0.3, 0.5) negative temperature coefficient (NTC) thermistor ceramics have been successfully fabricated by vacuum hot-pressed sintering. The X-ray diffraction analysis has showed that the sintered ceramics crystallize in a cubic spinel structure. The scanning electron microscopy results show the sintered samples to be nanograined with average grain size ranging from 200 to 500   nm. The relative density of the ceramics ranges from 74.2% to 92.3%. The relative density increases and then decreases with increasing Cr content, and reaches its maximum 92.3% at x   =   0.3. The values of ρ 500 , B 500/800 and E a are in the range of 5.49   ×   10 3 –6.06   ×   10 8   Ω   cm, 6847–12808   K, 0.591–1.105   eV, respectively, offer some prospects for potential use as high temperature NTC thermistors.