Nickel substitution in YBaCo4O7: Effect on the physical properties

Substitutions of Ni2+ cations for Co2+ in Y BaCo4O7 have been studied. Though the Ni2+ solubility is limited to about 5%, corresponding to Y BaCo3.8Ni0.2O7, it is found that the temperature of the structural transition T S decreases significantly as the Ni2+ content, x in Y BaCo4−xNixO7, increases. This is shown by the electrical resistivity change observed at T S = 235 K for Y BaCo3.8Ni0.2O7 against T S = 310 K for the undoped Y BaCo4O7 compound. The similar ionic radii of Ni2+ and Co2+ in the tetrahedral coordination CoO4 strongly support a magnetic origin for the structural transition of the LBaCo4O7 compounds.