A related structure with the general formula Bi2RE2Co1.7–2Ox (RE=CaorSr),which containsan expansion of the rock salt layer present in Co3O4O9, can form.23,74 Although the superlattice structure does lead to relatively low thermal conductivities of ∼0.8 and ∼1.2WK−1 m−1 for Bi2Ca2Co1.7Ox73 and Bi2Sr1.94La0.06Co2O9,74 respectively,