High dielectric constant in Al-doped ZnO ceramics using high-pressure treated powders

Pure and Al-doped ZnO ceramics were prepared by conventional sintering high pressure treated nano powders at 1150 degrees C for 2 h, and the effect of Al-doping on the microstructure and dielectric properties were mainly investigated. X-ray diffraction (XRD) and scanning electron microscopy (SEM) results revealed that Al reacted with ZnO and formed ZnAl2O4 nano-precipitates on the grain boundaries. Small amount of ZnAl2O4 nano-precipitates (i.e. < 1 mol%) enhanced the grain growth of ZnO, while larger amount suppressed the grain growth. AC impedance analysis indicated that Al-doping decreases the resistivity of ZnO ceramics. Dielectric studies revealed that the incorporation of Al in ZnO can significantly enhance the dielectric constant (1.39 x 10(4) at 1 kHz) of ZnO ceramics. And the dielectric behavior can be well-explained by Maxwell-Wagner relaxation. (C) 2015 Elsevier B.V. All rights reserved.