Intergrain connectivity of MgB2 ceramics studied by impedance analysis

Abstract

First, by using of the conventional Rowell analysis, we demonstrated that the addition of nano BN particles can effectively eliminate MgO and pores in MgB 2 resulting in a very high density and good connectivity of BN-doped MgB2. Then, another method-low-frequency dielectric impedance analysis-was introduced to characterize the properties of the grain boundaries of MgB 2 . A comparative impedance study was performed in the frequency range from 100 Hz to 100 MHz on pure and nano BN-doped MgB 2 . The study revealed some following interesting results: (1) a dielectric resonance around frequency of 10 8 in both samples was observed, which was argued to be related to an inductance-capacitance and (2) the pure sample has two dielectric relaxations originating from intergrains, while the doped sample has only one intergranular contribution. This convinces that the electric connectivity of the doped sample is really improved by the addition of nano BN particles. Our results indicate that dielectric technique may be a useful tool to characterize the grain boundary properties and grain boundary-related properties of MgB 2 . KeywordsIntergrain, connectivity, MgB2, ceramics, studied, impedance, analysis First, by using of the conventional Rowell analysis, we demonstrated that the addition of nano BN particles can effectively eliminate MgO and pores in MgB 2 resulting in a very high density and good connectivity of BN-doped MgB 2 . Then, another method-low-frequency dielectric impedance analysis-was introduced to characterize the properties of the grain boundaries of MgB 2 . A comparative impedance study was performed in the frequency range from 100 Hz to 100 MHz on pure and nano BN-doped MgB 2 . The study revealed some following interesting results: ͑1͒ a dielectric resonance around frequency of 10 8 in both samples was observed, which was argued to be related to an inductance-capacitance and ͑2͒ the pure sample has two dielectric relaxations originating from intergrains, while the doped sample has only one intergranular contribution. This convinces that the electric connectivity of the doped sample is really improved by the addition of nano BN particles. Our results indicate that dielectric technique may be a useful tool to characterize the grain boundary properties and grain boundary-related properties of MgB 2 .

Effect of Li+ ion mobility on the grain boundary conductivity of Li2TiO3 nanoceramics

“…4. It confirms the spread of relaxation time [26], i.e., the existence of a temperature-dependent electrical relaxation phenomenon in nanocrystalline Li 2 TiO 3 .…”

Effect of different-sized h-BN nano-particles on some properties of MgB2 superconductors

“…The amount of H and OH introduced into MgB2 samples with h-BN doping increases as the particle size decreases due to increasing surface/volume ratio. This may play an important role in the mechanism mentioned above and we suggest that it may provide explanation for the controversy in the literature upon BN doping [26,27]. This discussion is further supported by the fact that when we added 5 % h-BN (not supplemented) which is half of [26] and [27] transport critical transition was broader then 5 K which was our reason to decrease h-BN addition to 3 %.…”

“…This may play an important role in the mechanism mentioned above and we suggest that it may provide explanation for the controversy in the literature upon BN doping [26,27]. This discussion is further supported by the fact that when we added 5 % h-BN (not supplemented) which is half of [26] and [27] transport critical transition was broader then 5 K which was our reason to decrease h-BN addition to 3 %. In the study of Wang et al [27], it has been concluded that 10 % h-BN doping increases the connectivity and improves the high field Jc properties of the MgB2 in contrary to the findings reported in the study of Kovak et al [26].…”

“…Nano particles of h-BN are selected as a dopant due crystallographic structure similarities with carbon containing compounds, especially graphite [21][22][23][24]. In literature, there are a few results on doping of the h-BN into MgB 2 superconductor samples [25][26][27][28]. Since h-BN is stable at high temperatures even in air, in this study, we focus on the probable doping of different sized h-BN nanoparticles in order to search as alternative to carbon related dopants.…”

Superconducting transition width under magnetic field in MgB2 polycrystalline samples

“…2 However, when we extend the study of resistivity to polycrystalline samples, the Rowell relation fails to quantitatively describe the connectivity for this system. 3 Yamamoto et al 4 suggested an improved model by using the packing factor to evaluate the connectivity in polycrystalline MgB 2 based on a percolation method. On the other hand, since in the superconducting state, the superconducting transition broadening, as found in resistivity measurements in the presence of magnetic fields, contains important information related to the basic vortex-pinning mechanisms governing the critical current density.…”