A study of structure, electric and magnetic properties of the new layered cobalt oxides Sr2Y1-xCaxCo2O7-z

The crystal structure of Sr2Y0.8Ca0.2Co2O6 is orthorhombic below 270 K (Imm m, a = 3.84029(7) Angstrom, b = 3.80691(6) Angstrom and c = 19.4980(3) Angs trom at 20 K), transformed from tetragonal (I4/mmm, a = 3.82765(6) Angstrom and c = 19.5795(3) Angstrom) at 295 K. The crystal structure distortion is accompanied by an anomalous temperature dependence of the degree of buckli ng of the CoO2 plane and is correlated with the development of anisotropic antiferromagnetic ordering of magnetic moments (2.93(2) mu(B) per Co at 20 K). A magnetically glassy state below about 35 K and variable range hopping conduction below about 64 K for Sr2Y1-xCaxCo23.4+O7-z (0.2 less than or eq ual to x less than or equal to 0.5, 0.21 less than or equal to z less than or equal to 0.38) were found by magnetic susceptibility and electrical resi stivity measurements.