*2.3. Testing Methods*

Solid State Impedance Spectroscopy

The SSIS results were obtained from HIOKI IMPEDANCE ANALYZER IM3570 (AC) using LCR sample application software. The GRGC specimens were investigated using the two-probe method with electrodes, as depicted in Figure 1b, in a dry state under ambient laboratory conditions. The values for different parameters, such as impedance, capacitance and tan delta over a frequency range of 101 to 10<sup>5</sup> Hz, were obtained from the instrument. The values of the dielectric constant, dielectric loss and conductivity were calculated from Equations (1) to (4) [17–19]:

$$
\varepsilon\_I = \frac{\mathbb{C}\_P t}{\varepsilon\_0 A} \tag{1}
$$

$$\mathbf{D} = \frac{\mathbf{e}\_r''}{\mathbf{e}\_r} \tag{2}$$

$$
\omega = 2\pi f \tag{3}
$$

$$
\sigma = \varepsilon\_0 \varepsilon\_r^\prime \omega \tag{4}
$$

where


*σ = conductivity*.
