SYNTHESIS AND STUDY OF (HG,CR)-BASED 1201-TYPE SUPERCONDUCTING CUPRATE (HG,CR)SR2CUO4+DELTA

We have successfully synthesized 1201-type (Hg,Cr)Sr2CuO4+delta with v ery good quality. Resistivity measurements show that the as-synthesize d samples are slightly O under-doped and have T-c onset's up to 67 K, the highest ever seen with the Ba-free Hg-based 1201-type compounds. T he structure of (Hg,Cr)Sr2CuO4+delta is tetragonal with a space group of P4/mmm and lattice constants of a=3.84120(8) Angstrom and c=8.7009( 2) Angstrom. Refinements of the structure are carried out based on thr ee models, A, B, and C, in which O atoms are introduced into the (Hg,C r) layer at the positions (1/2, 1/2, 0), (1/2, 0, 0), and both (1/2, 1 /2, 0) and (1/2, 0, 0) respectively. The Cr occupancy factor is in the same order in all the three models with a very slight variation from 0.41(1) to 0.45(1) atoms per unit cell. The total amount of oxygen ato ms located in the (Hg,Cr) layer is found to be 0.46(3), 0.70(4),and 0. 88(4), respectively.