Ceramic coating systems, in particular for gas sensors

The invention relates to a ceramic layer system of at least two layers of considerably different conductivity, containing a ceramic substrate layer (10) of low conductivity and at least one other adjacent ceramic layer of considerable conductivity as the conductive layer (11), in which the conductive layer (11) contains ceramic particles (12) themselves having a slight degree of conductivity but are coated with a material (13) with a high conductivity and hence brings about the considerable conductivity of the conductive layer (11). The material of the ceramic substrate layer (10) and that of the ceramic particles (12) of the conductive layer (11) are selected so that the coefficient of thermal expansion of the conductive layer (11) is close to or the same as that of the ceramic substrate layer (10). The invention also relates to a process for producing gas sensors containing said ceramic layer systems, with the conductivity relating to the conduction of oxygen ions.