Structures and Properties of KxCryNi1-x-yO Dielectric Materials Prepared by an Ultrasonic-Assisted Sol-Gel Method

KxCryNi1-x-yO (x = 0.05-0.20, y = 0.02) dielectric materials were prepared using a facile simple green ultrasonic-assisted sol-gel method. All samples have a main phase consisting of a cubic NiO structure and with nanoscale crystallite sizes (28.58-37.51 nm). However, secondary phases were also observed for the samples with x values exceeding 0.10. The fractured surface microstructures of the samples with x values less than 0.15 exhibited uniformly distributed spherical grains. Other samples showed irregularly shaped grains. The grain sizes were larger when x was increased to 0.15 and exhibited increased grain growth probably due to substitution of K ions into the NiO lattice. However, a reduction of grain sizes was observed in the sample with x = 0.20, possibly due to inhibition of the grain growth by the secondary phase. At room temperature and a frequency of 1013 Hz, the highest dielectric constant of 2.25 x 10(4) was obtained for the samples with x = 0.15.