SYNTHESIS, CRYSTAL STRUCTURE, ELECTRICAL, AND MAGNETIC PROPERTIES OF THE NEW LAYERED COBALT OXIDES (Sr, Ca, Ln)3Co2O6+-delta (Ln=Sm, Eu, Gd, Tb, Dy, Ho, AND Y)

摘要

New layered Co oxides of nominal formula Sr2(Ln0.8Ca0.2) Co2O6 (Ln=Sm, Eu, Gd, Tb, Dy, Ho, and Y) are reported. Single-phase polycrystalline samples were obtained at compositions Sr2Y1-xCaxCo2.5+2O6-delta (0.2 less than or equal to x less than or equal to 0.5; 0 less than or equal to delta less than or equal to 0.24), Sr2Y1-xCaxCo3.4+2O6+delta' (0.2 less than or equal to x less than or equal to 0.5; 0.62 less than or equal to delta' less than or equal to 0.79), and Sr2Dy0.8Ca0.2Co2O6.09. Powder X-ray and neutron diffraction, thermogravimetric analysis, magnetic susceptibility, and ac resistivity measurements were used to characterize the samples. The tetragonal unit cell for Sr2Y0.8Ca0.2Co2O6.00 (I4/mmm; a=3.82765(6) angstroms, and c=19.5795(3) angstroms) is comparable to that of the double layer superconducting copper oxide La2-xSrxCaCu2O6. A long-range antiferromagnetic (AF) ordered state below about 300 K is found for Sr2Y1-xCaxCo2.5+2O6-delta, and a magnetically glassy state below about 40 K for the oxidized AF phases. All materials are electrically insulating.