Narrow Results

Polymer Nanocomposites (PNC) comprising polyvinylidene fluoride (PVDF)/Multi-walled Carbon Nanotubes (MWCNT) were studied. The structural composition and thermal stability were confirmed from XRD and DSC/TGA data, respectively. The extent of distribution of MWCNT in the PNC increases and the clustering of MWCNT also increases with an increase in the volume fraction of MWCNT ($f_{\mathrm{\text{MWCNT}}})$, as confirmed by FESEM. The PNC shows an insulator-to-metal transition (IMT), with both non-universal percolation threshold $(f_c)$ of $f_{\mathrm{\text{MWCNT}}}=0.006$ and scaling exponents $[s=0.36\pm 0.03,s^{\prime }=1.26\pm 0.1]$, respectively, attributed to adhesiveness/cold pressing and the higher aspect ratio/conductivity of MWCNT. Modulus spectroscopy confirms a non-Debye type universal relaxation behavior $(\beta =0.54)$ only for the percolative sample due to Maxwell–Wagner–Sillars/interfacial polarization, while only dipolar relaxation was probed or the samples below $f_c$. The $f_c$ with static effective dielectric constant $\sim 211$ and low tan $\delta$ may be suitable for charge storage applications.

The effect of high pressure on the superconducting properties of BiPbSrCaCuO ceramic was investigated. We applied cold pressing method on the powder of the prepared samples as well as on the as-prepared samples directly. The former showed a serious destruction of superconductivity, and the latter, however, showed only broadening of the superconducting transitions. It was believed that the structural deformation of the superconducting phases was the main reason for the drastic changes in the electric and magnetic properties of the superconductors.