Gas sensor and method of manufacturing a gas sensor

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A gas sensor comprises a gas-sensitive material and means for measuring a change in an electrical property of the material to indicate a change in concentration of a specified gas in the vicinity of the senor, the gas-sensitive material having a monoclinic crystallographic structure and comprising a chemical compound including a first rare earth oxy-carbonate and a second rare earth element and/or a transition and/or alkaline-earth metal. Preferably, the rare earth oxy-carbonate is lanthanum, neodymium or praseodymium. The gas sensor may be used for detecting and measuring changes in CO2 levels, by means of a change in electrical conductivity. The gas-sensing material may belong to a class of materials of the form A2-x BxO2CO2, A2-xCxO2CO2, A2-x-yBxCyO2CO2 (where A may be La, Nd and/or Pr; B may be one or more rare earth elements other than La, Nd, Pr (such as holmium); and C may be a transition metal (such as copper) and/or an alkaline-earth metal (such as calcium), with x and y being integers less than 1, for example 0 < x < 0.8 and 0 < y < 0.1.