The Effects of Transition Metal Substitutions for Copper in the Bi-Sr-Ca-Cu-O Superconducting System
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THE EFFECTS OF TRANSITION METAL SUBSTITUTIONS FOR COPPER IN THE Bi-Sr-Ca-Cu-O SUPERCONDUCTING SYSTEM 1
1
t
J.C. Bennett , F.W. Boswell , J.M. Corbett , S. Kohara and F.S. Razavi 1) Dept. of Physics, University of Waterloo, Waterloo, Ont., Canada N2L 3G1 2) Dept. of Physics, Brock University, Ste. Catharines, Ont., Canada ABSTRACT The effects of transition metal dopants on superconductivity in samples of nominal composition Bi 2 CaSr 2 (Cu 1-x Mx ) 2 0 8+0 with M = Co, Fe, Ni and Zn have been investigated for 0 s x i I. Co and Fe additions progressively suppress the T of the doped material and result in semiconducting behaviour for x a-0.2. In the ranges 0 s x s .07 and near x = 1.0, x-ray diffraction reveals the samples are essentially single phase but are multiphase otherwise. Ni and Zn dopants have only a very slight effect on Tc; however,EDX analysis reveals these elements superconducting phase.
are
not
significantly
A common structural feature in the oxide superconductors is the arrangement of copper and oxygen in two-dimensional sheets [1]. It is now widely believed, based on the high degree of anisotropy observed in electrical and magnetic measurements [2], that superconductivity is largely confined to these CuO2 planes. It is further
incorporated
samples
were
the
a -
7
-
i
i
observed that substitutions for Cu in these planes result in a strong suppression of T for both the 40 K LaBaCuO phase [31 and the 90K YBaCuO phase [4]. Recently, T has also been shown to be suppressed by substitutions for Cu in the 20 K In light of Bi 2Sr2 CuO6 + (2021) phase [5]. above results, we have investigated the the effects of transition metal substitutions in the 85 K Bi 2 CaSr 2 Cu2 0 8 5 (2122) phase. The doped
into
j b
j J." C
prepared as
nominal compositions Bi CaSr (Cu 1M 0
(M = Co, Fe, Ni and Zn; 0 s x s 1) by solid-state reaction in alumina crucibles. mixed in stoichiometric amounts then calcined at 8200C for 12 hours in air. reacted
powders
were
then
. d
The
reground,
pelletized and sintered in air for 48 hrs. to ensure homogeneity. All Fe and Ni doped materials were sintered at 850*C. For Co and Zn dopants, the sintering temperature was varied in the range 850*C (undoped) to 8200C (fully doped) in order to avoid phase I separation. Samples sintered under flowing 2 02 were identical to those sintered in air. The structure of the samples was investigated using x-ray powder diffraction (XRD). Figure 1 shows XRD patterns obtained for various levels of Co dopant. In the dopant range 0 a x .07, only diffraction peaks corresponding to the 2122
2
0(tiegrees)
60
Fig. 1 Diffraction patterns of Biz CaSr2 (Cu,_ COx)20s with (a)X=, ()x =0. wih BI2 CSr2 (u1- C.) 2 0 .5 (b) x = .07, (c) x= .15 and (d) x= 1.0 for Cu K x-rays. Peaks are Indexed In (a) for the C a 2122 phase. Peaks marked with crosses are attributed to the 2021 phase while those with open circles come from unknown inpurity phases.
Mat. Res. Soc. Symp. Proc. Vol. 169. ©1990 Materials Research Society
1050
phase or trace impurity phas
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