We demonstrate a nonvolatile, reversible change of infrared reflectance from the thin film of perovskite manganite (Pr1−xCaxMnO3) by applying electric pulse. The result provides a possibility to use the electric-pulse-induced phenomena of this compound in optical devices.
With the aim to reduce the permittivity of a dielectric substrate, closed pores have been introduced into alumina based ceramics by our innovated superplastisically foaming method. Affect of the ambient humidity on the dielectric constant was compared to those for conventional porous ceramics as well as full densified one. In the dry atmosphere, the dielectric constant (k) decreased with the porosity similar to the conventional porous ceramics. Affect of the ambient humidity on the dielectric property was almost identical to that of fully densified one. The degradation of mechanical strength depended on the pore size introduced.
Alumina-graphite composite ceramics were fabricated by normal sintering in a reducing atmosphere, and their bulk resistivity measured. Because the composites consisted of connected clusters of conducting graphite particles within an insulating alumina matrix, the experimental results were discussed in terms of percolation theory. The electrical resistivity increases as the volume fraction of graphite (x) decreases, following a well-accepted power law model. The observed critical exponent was larger than the expected universal value based on a three-dimensional structure, due to a weighted distribution of conductivity throughout the sample. The renormalized pressure coefficient of resistance, d(ln R)/dP, decreased as x decreased and was explained by a strong enhancement of d(ln q)/dx as the percolation threshold was approached.
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