A novel compound having exponential temperature dependent electrical resistivity comprises an electrically insulating bulk material (11), electrically conductive particles (12) of a first kind, and electrically conductive particles (13) of a second kind covered by a lubricant. The bulk material holds the particles of the first and second kinds in place therein; the particles of the second kind are smaller than the particles of the first kind; the particles of the second kind are more in number than the particles of the first kind; and the particles of the second kind have higher surface roughness than the particles of the first kind, wherein the particles of the second kind comprise tips (13a) and the particles of the first kind comprise even surface portions (12a). The particles of the first and second kinds are arranged to form a plurality of current paths (14) through the compound, wherein each of the current paths comprises galvanically connected particles of the first and second kinds and a gap (14a) between a tip (13a) of one of the particles of the second kind and an even surface portion (12a) of one of the particles of the first kind, which gap is narrow enough to allow electrons to tunnel through the gap via the quantum tunneling effect. The bulk material has a thermal expansion capability such that it expands with temperature, thereby increasing the gap widths (w) of the current paths, which in turn increases the electrical resistivity of the compound exponentially.