Influence of Mo doping on the microstructure and dielectric property of alumina ceramic/metal composites

Mo-doped alumina (Al₂O₃/Mo) ceramic composites were prepared by a powder metallurgical process. The influence of Mo doping amount on the microstructure and dielectric properties of the composites were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM) and other testing analysis methods. The results show that the composites are composed of Al₂O₃ and Mo phases, and no new phases appear. Mo mainly disperses in the Al₂O₃ grain boundary. With increasing the Mo content, Al₂O₃ grain size declines and the porosity increases gradually. When the amount of Mo is below 20 wt%, there are no obvious changes in resistivity (>10¹² Ω·cm) and in permisittvity (8~9) for the composites. When the doping amount is over 20 wt%, Mo transforms from the dispersed phase into the continuous phase while volume resistivity decreases to 10¹⁰ Ω·cm sharply. When the doping amount is 40 wt%, since the throughout matrix of Mo is formed, the volume resistivity decreases slowly, and becomes steady at about 10 Ω·cm. Therefore, ceramic/metal composite materials with different resistivities can be prepared by adjusting the amount and phase distribution of Mo in Al₂O₃ matrix.