No abstract

The densification and grain growth of ZnO doped with Al from 0.08 to 1.2 mol% were investigated during isothermal sintering between 1100 and 1400°C. The Al dopant significantly inhibited the grain growth of ZnO and increased the grain growth exponent from 3 for pure ZnO to 4-6 for Al-doped ZnO. The grain growth activation energy was also changed from approximately 200 kJ/mol for pure ZnO to approximately 480 kJ/mol for Al-doped ZnO. The results of x-ray diffraction, scanning electron microscopy, and transmission electron microscopy showed that a ZnAl 2 O 4 spinel phase existed as a second phase at the ZnO grain boundaries in Al-doped ZnO specimens. The spinel particles exerted an effective drag (pinning) on the migration of ZnO grain boundaries. The analyses of the Al doping effect on the densification rate provided evidence that the driving force for densification was reduced by the second-phase particles. A mechanism of pore surface drag (pinning) on densification equivalent to the observed drag (pinning) of grain boundaries on grain growth was proposed.

No abstract

No abstract

No abstract

The (Sr1−1.5xBix)TiO3 (0.0133⩽x⩽0.133) ceramic system reveals several sets of dielectric permittivity peaks in different temperature ranges. Dielectric permittivity and dielectric loss peaks were detected in the temperature range 500–800 K and in the present article the dielectric polarization behavior is presented and discussed. The activation energy of the dielectric relaxation is in the range of 0.99–1.12 eV. It is suggested that the permittivity peaks are related to the movement of oxygen ions or oxygen vacancies.

No abstract

The dc and ac conductivities of Mn-doped ZnO were investigated at temperatures from 10 to 100 K. The temperature dependence of the dc conductivity from 10 to 100 K shows an abrupt change at ϳ18 K, manifesting a much lower activation energy for conduction below 18 K. From 10 to 18 K, the ac conductivity, ac (), varies as ac ()ϭA s in the frequency range from 10 2 to 10 6 Hz with s in the range of 0.6-1. The dc and ac conductivity observations suggest that the dominant conduction mechanism at temperatures between 10 to 18 K in these samples is a hopping conduction.