Synthesis, crystal structure, electrical, and magnetic properties of the new layered cobalt oxides (Sr, Ca, Ln)(3)Co2O6 +/-delta (Ln = Sm, Eu, Gd, Tb, Dy, Ho, and Y)

New layered Co oxides of nominal formula Sr-2(Ln(0.8)Ca(0.2)) Co2O6 (Ln = S m, Eu, Gd, Tb, Dy, Ho, and Y) are reported. Single-phase polycrystalline sa mples were obtained at compositions Sr2Y1-xCaxCo22.5+O6-delta (0.2 less tha n or equal to x less than or equal to 0.5; 0 less than or equal to delta le ss than or equal to 0.24), Sr2Y1-xCaxCo23.4+O6+delta' (0.2 less than or equ al to x less than or equal to 0.5; 0.62 less than or equal to delta' less t han or equal to 0.79), and Sr2Dy0.8Ca0.2Co2O6.09. Powder X-ray and neutron diffraction, thermogravimetric analysis, magnetic susceptibility, and ac re sistivity measurements were used to characterize the samples. The tetragona l unit cell for Sr2Y0.8Ca0.2Co2O6.00 (I4/mmm; a = 3.82765(6) Angstrom, and c = 19.5795(3) Angstrom) is comparable to that of the double layer supercon ducting copper oxide La2-xSrxCaCu2 O-6. A long-range antiferromagnetic (AF) ordered state below about 300 K is found for Sr2Y1-xCaxCo22.5+O6-delta, an d a magnetically glassy state below about 40 K for the oxidized AF phases. All materials are electrically insulating, (C) 1999 Academic Press.