THE CRYSTAL-STRUCTURE AND PROPERTY OF TERNARY COMPOUNDS AND PHASE-RELATIONS IN THE SYSTEM YB2O3-BAO-CUO AT 950-DEGREES-C

The subsolidus phase relations of the Yb2O3BaOCuO ternary system sintered in the air at 950°C has been investigated by X-ray powder diffraction and thermal analysis. In this system there exist four ternary compounds: Yb2BaCuO5, YbBa2Cu3O7, (Yb, Ba, Cu) YbBa4Cu2O8.67 and (Yb, Ba)Ba2CuO4.25 and 12 ternary compatabilities. The compounds Yb2BaCuO5, an insulator with space group Pbnm, is isostructural with Y2BaCuO5. Its lattice parameters are a = 7.059, b = 12.097, c = 5.617 A ̊. YbBa2Cu3O7 possesses a critical transition temperature 92 K and a space group of Pmmm, isomorphous with the structure of YBa2Cu3O7. The other two compounds (Yb, Ba, Cu) YbBa4Cu2O8.67 and (Yb, Ba)Ba2CuO4.25 are both semiconductors. The former has a space group of P4/mmm with lattice parameters as a = 5.793, c = 8.002 A ̊. Its positions of the ions in a unit cell are as follows: 1(Yb, Ba, Cu) randomly occupies 1(c) equivalent point position, 1 Yb cation occupies 1(a), 4Ba cations occupy 4(i) with z = 0.255, 2Cu cations occupy 1(b) and 1(d) respectively, 8.67 Oxygen anions occupy 2(f) with occupancy 1 3, 2(g) with z = 0.24, 2(h) with z = 0.26 and 4(k) with x = 0.25 respectively. The compound (Yb, Ba)Ba2CuO4.25 occurs a deoxygen phase transition at 812°C with a change in lattice parameters, with a space group of P4/mmm. The lattice parameters of high temperature phase are a = 4.054 A ̊, c = 2a, while the lower has a = 4.106, c = 8.033 A ̊. The positions of their ionic sites are the same as the following: 1(Yb, Ba) randomly occupies 1(a) equivalent point position, 2 Ba cations occupy 2(h) with z = 0.255, 1Cu cation occupies 1(b) equivalent point position and 4.25 Oxygens occupy 1(c) equivalent point position (occupancy 1 4), 2(1) and 2(g) with z = 0.255, respectively. © 1990.