Fig. 5. Bode plot of imaginary part impedance of cubic garnet specimen in temperature range of 303–353 K (specimen dimensions: diameter 0.9885 cm, height 0.1216 cm) and equivalent circuit used to fit data (inset).Figure optionsDownload full-size imageDownload as PowerPoint slide
Fig. 6 shows the fitted Nyquist plots of the sintered sample at two selected temperatures (303 K (highest temperature measured) and 353 K (lowest temperature measured)). The Nyquist plots show the beginning of Purvalanol B semicircle in the high frequency region and one clearly resolved semicircle as well as an ascending tail in the low frequency region. The first semicircle at high frequencies can be attributed to the bulk resistance. It is clearly visible at low temperatures and becomes less pronounced at high temperatures as the ionic conductivity rises. The second semicircle is related to the Li+-ion movement through grain boundaries in the crystal. This process is enhanced at higher temperatures, which leads to a reduction of the impedance. Overall, the impedance of the pellet becomes smaller with rising temperature. From the total resistance the lithium ion conductivity can be calculated (Table 2).