COMPRESSIBILITY AND PRESSURE-DEPENDENCE OF CHARGE-TRANSFER AND T-C INPRISTINE AND IODINE-INTERCALATED SINGLE-CRYSTALS OF BI2.2SR1.8CACU2O8+DELTA

Compressibility measurements for Bi2.2Sr1.8CaCu2O8+delta (Bi-2.2:1.8:1 :2) and IBi2.2Sr1.8CaCu2O8+delta (IBi-2.2:1.8:1:2) single crystals wer e carried out in a diamond-anvil pressure cell up to 9 GPa. The values of bulk modulus are 68.56 and 48.21 Gpa for Bi-2.2:1.8:1:2 and for IB i-2.2:1.8:1:2 single crystals, respectively. Hall coefficients and res istivities for oxygen annealed Bi-2.2:1.8:1:2 and I0.7Bi-2.2:1.8:1:2 s ingle crystals were measured under high pressure up to 1.5 GPa. The va lue of dR(H)/dP for the oxygen annealed crystal is -0.06 x 10(-3) cm(3 ) C-1 GPa(-1), which is one third of the as-grown crystal. The decreas e of dR(H)/dP after oxygen annealing is considered to be due to the in crease of homogeneity of oxygen during high temperature annealing, The dR(H)/dP of I0.7Bi-2.2:1.8:1:2 is -0.39 x 10(-3) cm(3) C-1 GPa(-1), w hich is nearly the same as that of IBi-2.2:1.8:1:2. That the negative dR(H)/dP of intercalated crystals is nearly twice as large as that of pristine crystals is concerned with the deposition of the iodine molec ular state under pressure. The T-c of oxygen-annealed Bi-2.2:1.8:1:2 i ncreases with increasing pressure at a parabolic curve below 1.5 Cpa. By using the Gupta model, we simulated T-c(P) up to 6 GPa, and found t hat the maximum value of T-c(P) is 88 K at P = 4.1 GPa. This is in goo d agreement with the experimental result measured by Klotz et al. [Phy sica C 209 (1993) 499]. The T-c of the I0.7Bi-2.2:1.8:1:2 crystal incr eased linearly at a rate of dT(c)/dP = 3.5 K/GPa. This is the opposite of the behaviour of IBi-2.2:1.8:1:2 which decreased linearly at a rat e of dT(c)/dP = -3.6 K/GPa, although both intercalated crystals are ov erdoped compounds. (C) 1997 Elsevier Science B.V.