High temperature electrical resistivity of solid solution LaSr(Cu,M)O₄ ceramics

The electrical resistivity of ceramics with compositions LaSrMO₄, where M refers to first row transition metals, decreases progressively in the order of Fe, Mn, Cr, Cu, Ni and Co, over the temperature range from 20 to 90O°C. The relatively low resistivity of LaSrCrO₄ and LaSrCoO₄, compared to the other compounds containing aliovalent or divalent metals, respectively, is related to the formation of (La,Sr)MO₃ perovskite phases, rather than true K-phase structures with the composition LaSrMO₄. All of the transition metals investigated dissolve in LaSrCuO₄, to form K-phase solid solutions of the type LaSrCu_0.5M_0.5O₄. An increase in resistivity, compared to that of LaSrCuO₄, is observed when aliovalent Cr, Mn, and Fe are substituted for Cu, but equivalent substitutions of normally divalent Co or Ni result in a reduction in electrical resistivity. All of the LaSrMO₄ compounds and LaSrCu_0.5,M_0.5O₄ solid solutions exhibit semiconducting properties, and the associated activation energy, as derived from Arrhenius plots of log conductivity versus reciprocal temperature, increases in the order CO, Ni, Cu, Cr, Fe and Mn.