THE GREAT ABILITY OF MERCURY-BASED CUPRATES TO ACCOMMODATE TRANSITION-ELEMENTS - 11 NEW SUPERCONDUCTORS HG(1-X)M(X)BA(2)CA(M-1)CU(M)O(2M+2+DELTA) (M=V, MO, W, TI, CR)

The Hg-Ba-Cu-M-O and Hg-Ba-Ca-Cu-M-O systems have been investigated for M=V, Mo, W, Ti, Cr. Eleven new superconductors Hg(1-x)M(x)Ba(2)Cu(m)O(2m+2+delta) have been synthesized at normal pressure with the 1201 structure for M = Ti, Mo, W and Cr, with the 1212 structure for M = Mo, W, Ti and Cr, and with the 1223 structure with M = V, Mo, Ti and Cr. The XRD and ED investigation of these oxides shows that the a parameter of their tetragonal cell is not strongly influenced by the presence of the transition element, whereas the c parameter is significantly decreased with respect to HBC and HBCC systems, due to the partial replacement of Hg by M. The structural anisotropy in the three series of oxides, represented by the cia ratio varies in the following way: (c/a)(Cr) < (c/a)(V) < (c/a)(Mo) < (c/a)(Ti) < (c/a)(W)< (c/a)(Hg). The investigation of the superconducting properties of these new cuprates shows, in most of the cases, various transitions, with significant superconducting volume fractions (40% to 90%). The chromium phases exhibit the lowest critical temperatures (T-c midpoint from 57 K to 104 K); the best characteristics in the 1201 cuprates are obtained for V (T-c midpoint=89 K), whereas in the 1212 cuprates the highest T-c midpoint = 123-124 K, T-c onset = 127-128 K is obtained for M = V, Mo, Ti, and in the 1223 cuprates the maximum T-c midpoint = 131-132 K, T-c onset = 134 K is reached for M = Mo and Ti.