BackgroundDielectric properties and ac conductivity were studied and correlated with the structure of a series of YBCO ceramic, doped with different doping levels ranging from 0.1 to 0.5 wt.% of magnetic nano-metal oxides, namely Mn3O4, Co3O4, and Cr2O3. The most important feature of this study was the ultrahigh values of dielectric constants at a low frequency, exactly 50 Hz. We found that the undoped YBCO has a value of ε′ equal to 6.99 × 106 at 50 Hz at room temperature which was increased to 1.09 × 108 at 120 °C, higher than any other ferroelectric material. Moreover, the value of ε′ depends on the nature and the value of the magnetic moment of the doped metal oxides. The value of ε′ is at least three orders of magnitude greater than any previously studied composites which suggest that this perovskite ceramic material can be used to create electrostatic capacitors with energy far better than the best electrode double-layer capacitors (EDLC). Additionally, ac electrical conductivity has two frequency-dependent regions, the low frequency, where σac is independent of frequency, and the high-frequency region where dispersion occurs. The ac conductivity measurement with frequency leads us to conclude that the conduction mechanism in the studied samples can be correlated barrier hopping (CBH) model.ResultsThe dielectric properties of undoped YBCO ceramics at 50 Hz in temperature ranging from room temperature to 120°C were studied. It is obvious that the dielectric constant and dielectric loss of YBCO decrease with increase in frequency and temperature. It can be noticed that dielectric constant of YBCO increases at 50 Hz from 6.99 × 106 at room temperature to 1.09 × 108 at 120°C.The high values of ε′ recorded for YBCO doped with Mn3O4 varied from 9.45 × 105 to 15.5 at room temperature and 1.34 × 105 to 9.242 at 1 MHz at 120°C. For doped YBCO with Co3O4, the values of ε\\ varied from 9.5 × 105 at 50 Hz to 13.24 at 1 MHz at room temperature, with changes from7.8 × 104 at 50 Hz to 53.42 at 1 MHz. For YBCO ceramic samples doped with Cr2O3, ε′ varied from 1.138 × 106 at 50 Hz to 8.38 × 103 at 1 MHz at room temperature and from 5.935 × 105 at 50 Hz to 3.53 × 103 at 1 MHz at 120°C.The ac conductivity was further studied for undoped YBCO and doped YBCO with 0.1 wt.% of nano-metal oxide of Cr2O3, Co3O4, and Mn3O4 samples. For all the studied samples, we found σac is typically specified to the hopping conduction and ac conductivity has a power law behavior in terms of frequency (ω). In general, there are two frequency-dependent regions for all the studied ceramic samples; in the low-frequency region, σac is independent of frequency whereas in the high-frequency region, dispersion occurs. The change in microwave conductivity of the studied samples with frequency (1–5 MHz) is shown in Fig. 5. It is observed that for all samples, the conductivity increases with temperatures and depends on the doped metal oxide. The values of σac at 5 MHz varied from − 0.4 to 1.2 for undoped YBCO, from − 0.98 to − 0.75 for 0.1 wt.%Mn3O4-YBCO sample, from − 0.25 to 0.2 for 0.1 wt.% Co2O3-YBCO sample, and from − 0.4 to 0.6 for 0.1 Wt.% Cr3O4-YBCO sample.ConclusionThe primary finding in this paper is of empirical investigation. YBCO, which is a high-temperature superconductor, has a high dielectric constant ε′ ranging from 6.99 × 106 at room temperature to 1.09 × 108 at 120°C. This value is at least three orders of magnitude greater than any previously studied composites which suggest that this perovskite ceramic material can be used to create electrostatic capacitors with energy far more efficient than the best electrode double layer capacitors (EDLC).
Read full abstract
Jan 16, 2020
María C Gélvez-Rueda + 5
Open Access
