Refinement of edge-to-edge matching model and its application in the Mg17Al12/alpha-Mg and alpha-Y/alpha-Mg systems

A refined version of the edge-to-edge matching model is described here. In the original model, the matching directions were obtained from the planes with all the atomic centers that were exactly in the plane, or the distance from the atomic center to the plane which was less than the atomic radius. The direction-matching pairs were the match of straight rows-straight rows and zigzag rows-zigzag rows. In the refined model, the matching directions were obtained from the planes with all the atomic centers that were exactly in the plane.

Valences of Cu in Y1-xCaxBa2Cu3O6+y

The valences of Cu in Y1-xGaxBa2Cu3O6+y have been investigated by using complex chemical bond theory The results for the valences of Cu(1) and Cu(2) in the calculation suggest that the holes introduced by calcium substitution only reside in CuO2 planes, and there is a competition mechanism for the hole density in CuO2 planes between Ca doping and oxygen depletion. These conclusions are satisfactorily in agreement with experiments.

Semiempirical study on the valences of Cu and bond covalency in Y1-xCaxBa2Cu3O6+y

The valences of Cu and bond covalencies in Y1-xCaxBa2Cu3O6+y, have been investigated using complex chemical bond theory, This theory is the generalization of Phillips, Van Vechten, Levine, and Tanaka's scheme. The results indicate that the valences of Cu(1) and Cu(2) in our calculation agree well with those obtained by the bond valence sum method. The valences of Cu(1) and Cu(2) in our calculation also suggest that the holes introduced by Ca substitution only reside in CuO2 planes and there is a competing mechanism for the hole density in CuO2 planes between,Ca doping and oxygen depletion. These conclusions are in satisfactory agreement with experiments. The calculated ordering of covalencies is Cu(1)-O(4)>Cu(1)-O(1)>Cu(2)-O(2,3)>Cu(2)-O(1)>Ca-O>Y-O similar to Ba-O, regardless of the Ca doping level and oxygen content. [S0163-1829(98)03325-6].

THERMAL-ANALYSIS OF Y1-XCAXBA2CU3O7-Y

TG and DTA analysis of Y1-xCaxBa2Cu3O7-y suggests that the stability of the 123 phase increases with increasing Ca contents. The O(1) in the Cu(1)-O chain is unstable but O(2) and O(3) in Cu(2)-O planes are very stable. There are hardly any oxygen vacanci

THE EFFECT OF DOPING WITH TANTALUM ON THE PROPERTIES OF YBA2CU3O7-Y

YBa2Cu3-xTaxO7-y (x = 0, 0.1, 0.2, 0.3, 0.4, 0.5 and 0.6) superconductors have been prepared, X-ray diffraction shows that the system remains orthorhombic for all compositions studied but. for x > 0.2, Ta2O5 was detected as an impurity phase. Substitution of Ta5+ for Cu2+ occurs in the Cu(2) sites on the Cu(2)O planes. The introduction of the high-valence element tantalum produces extra free electrons. These electrons recombine with the positive carrier of the system, which causes the mobility and the Hall number of YBa2Cu3-xTaxO7-y to decrease and also results in a depression in T(c).