Effects of pressure on the electrical resistivity of Pr1Ba2(Cu1-xMx)(4)O-8with M = Zn, Ni and x=0, 0.01, 0.02

We have measured the effect of pressure on the electrical resistivity of Pr 1Ba2(Cu1-xMx)(4)O-8 with M = Zn, Ni and x - 0, 0.01, 0.02. At ambient the t emperature coefficient of electrical resistivity was positive below 190 K a nd was negative above 190 K in non-doped Pr1Ba2Cu4O8; the resistivity attai ns a maximum at 190 K (T-m). The resistivity below T-m was insensitive to p ressure, whereas that above T-m rapidly increased with pressure. The substi tution of Zn for Cu increased the residual resistivity but did not seem to have a distinct effect on the behavior above T-m. On the other hand, the su bstitution of Ni changed the metallic temperature dependence below T-m to a semiconducting one. The pressure dependence in these doped compounds was b asically the same as that of non-doped sample; the resistivity was still in sensitive to pressure at low temperatures even after it changed the sign of temperature coefficient of resistivity with the substitution of Ni, We dis cuss the cause of the difference in pressure effects between below and abov e T-m. (C) 2000 Elsevier Science B.V. All rights reserved.