Certain materials
called superconductors by definition have zero resistivity or infinite
conductivity Earlier, only metals and their alloys at very low temperatures
(0 to 15 K) were known to behave as superconductors, but nowadays a
number of ceramic materials and mixed oxides are also known to show
superconductivity at temperatures as high as 150 K Electrical conductance through metals is called metallic or electronic
conductance and is due to the movement of electrons The electronic
conductance depends on
(i) the nature and structure of the metal
(ii) the number of valence electrons per atom
(iii) temperature (it decreases with increase of temperature)