Dielectric relaxation and electrical conduction in (Bi_xNa_1−x)_0.94Ba_0.06TiO₃ ceramics

Abstract

The dielectric relaxation and electrical conduction were investigated in (BixNa1−x)0.94Ba0.06TiO3 (Abb. xBNBT6, x = 0.5, 0.495, 0.485, and 0.475) ceramics prepared by solid state reaction. With a decrease in x, the dielectric properties of the ceramics decreased, whereas the electrical conduction increased, resulting in a transition from insulator to oxide‐ions conductor. When x = 0.475, the ceramics exhibited large conductivity (~10−3 S cm−1 at 575°C) and low activation energy (~0.45 eV), indicating their potential application in solid oxide fuel cells. A mixed conduction mechanism with oxide‐ions, electrons, and holes was proposed. With a decrease in x from 0.495 to 0.475, it was found that the p‐type conduction was switched to n‐type conduction. The dielectric relaxation of the x = 0.495 sample was associated with short‐range hopping of oxygen vacancies. However, the dielectric properties of the x = 0.485 and 0.475 samples can be explained by Maxwell‐Wagner interface relaxation.

Dielectric Relaxor and Conductivity Mechanism in Fe-Substituted PMN-32PT Ferroelectric Crystal

“…Based on the Arrhenius formula (Equation 6), the relationship between the frequency and temperature was plotted, as shown in Figure 7. It can be seen that the relaxor activation energy of P h peaks is 1.2 eV, which is in agreement with Figure 5, indicating that the dielectric relaxation and electrical conduction in bulk derive from the same physical mechanism, that is, oxygen vacancies [13,21]. For the low-frequency P l peak (300-400 • C), the relaxor activation energy is 1.28 eV, close to the migration energy of oxygen vacancy.…”

“…vacancies [13,20,21,24]. At this point, oxygen vacancy acts as a polaron, and its hopping process can be regarded as the reorientation of the dipole, which leads to dielectric relaxation.…”

“…Therefore, the conduction mechanism controlled by oxygen vacancy hopping is ruled out [13][14][15][16][17]20,21]. It can be seen that the relaxation activation energy E relax is 1.2 eV, indicating that the high-temperature dielectric relaxation peak III is related to the short-range hopping of oxygen vacancies [13,20,21,24]. At this point, oxygen vacancy acts as a polaron, and its hopping process can be regarded as the reorientation of the dipole, which leads to dielectric relaxation.…”

“…Two abnormal peaks in Z"(f ) curves are observed in Figure 6a, corresponding to a high-frequency P h peak and a low-frequency P l peak, respectively. Usually, the high-frequency P h peak is related to the bulk, while the low-frequency P l peak is associated with interface, and they can be described by an equivalent circuit with two pairs of parallel R-C series [13,20]. With decreasing temperature from 700 to 250 • C, the position of the P h peak shifts gradually toward low frequency, indicating its relaxation characteristics.…”

“…However, the intensity of the P l peak decreases gradually with increasing temperature, and it can be hardly observed at 450 • C. It is very interesting that the P l peak rises again when the temperature is above 500 • C, but the frequency where the Z" is up to maximum almost does not change with increasing temperature, except for when the peak intensity decreases. The phenomena suggest that the P l peak depends on temperature rather than frequency in the temperature range from 500 to 700 • C. Therefore, the conduction mechanism controlled by oxygen vacancy hopping is ruled out [13][14][15][16][17]20,21]. To explore the physical mechanism of the Pl and Ph peaks, we extracted the position of the Ph peak (250-650 °C) and Pl peak (300-400 °C) from Figure 6b.…”