YBa_2Co_3O_yの結晶構造と磁性  [in Japanese] Crystallographic and Magnetic Properties of YBa_2Co_3O_y  [in Japanese]

YBa_2Co_30_y prepared at 1200 K under reduced pressure forms a cubic perovskite type oxide with a superstrcture (a=1.24[nm]:E phase). Heat treatments of the E phase oxide in oxygen of 0.106 [MPa] at 1100 [K], 1200 [K], and 1320 [K] formed a tetragonal oxide (a=1.22[nm], c=1.25[nm]:C phase), an orthorombic oxide (a=0.389[nm], b=0.365[nm], c=1.253[nm]:D phase), and a tetragonal oxide (a=0.39[nm], c=1.13[nm]:A' phase) with a small amount of other oxides, respectively. The magnetic susceptibilities of the E and C phases oxides are expressed as a sum of a temperature-independent term and the Curie-Weiss term. The D phase oxide is a ferromagnet with magnetization σ=0.63μ_B/Co and Curie temperature T_c=57[K]. The A' phase oxide a paramagnet with anomalous susceptibility maximum at 170 [K]. The electrical resistances of the four oxide phases are semiconductive and, in addition, only the E phase oxide shows a remarkable resistance decrease below 200 [K].