Correlation of grain size and ac susceptibility in the Bi2Sr2CaCu2O8 system

The cause of ‘weak-link’ grain boundary behaviour in polycrystalline Bi2Sr2CaCu2O8and Bi2Sr2Ca2Cu3O10superconductors

“…In this paper, we have measured the small signals that occur at high temperature and fields and associated them with isolated (non-coupled) well-ordered grains with very high critical properties. We also note that both the fundamental considerations outlined by Deutscher et al [64] and the empirical measurements in the literature [31,65] suggest that at a grain size of 200 nm, the grains in our nanocrystalline samples are still large enough to have the optimum properties of bulk material.…”

“…B2M30HA750 has an extremely high grain boundary resistivity of ´W -1. 65 2 an order of magnitude below J , DN thus the limiting factor for the suppression of J c is due to the high grain boundary resistivity. Similar to B1M30HA750, there is the large decrease in J c t between 10 and 20 K. We consider the B2M30HA750 sample to be similar to the B1M30HA750 sample and as such to be a highly granular sample.…”

Paramagnetism and conductivity in nanostructured Bi-Sr-Ca-Cu-O

“…For the 50 nm material, in addition to a finite γ = 1.5×10 8 K −1 T, an additional term resulting from the appearance of the superconductivity of the Bi2212 minority phase was considered for temperatures below T c . In fact, the x-ray diffraction data [1] provided evidence for a Bi2212 concentration of about x 12 = 0.07 (3). We made no attempt to describe this screening component, shown in the insert to figure 1, by means of some distributions of grain sizes or of T c 's.…”

“…Let us assume that in the most disordered, i.e. the insulating [3] 2.5 nm material, where χ p may be ignored, a moment of 1 µ B per Bi2212 exists which corresponds to a Curie constant, C a = 38 mK. Defining an afm correlation energy kT af via δχ = C af /T af we obtain with δχ = 7 × 10 −5 , T af = 550 K, which is consistent with a temperature-independent δχ up to our maximum temperature of 300 K. Of course, due to the uncertainty of the size and concentration of the afm coupled moments such a result can serve only as a rough estimate.…”

“…As for the growth of Bi2201 whiskers from a La-doped Bi2212-melt [2], the reason for the formation of the Bi2201 crystals for d c 50 nm from the Bi2212 plates is not yet known, and the same holds for other interesting properties of the Bi2201 nanocrystalline materials, i.e. a fairly strong paramagnetism [3] and a low electrical conductivity [1]. Here we report some more detailed investigations of the magnetic behaviour and the conductivity of this nanocrystalline Bi2201 phase in order to shed some more light onto the physical behaviour characterized by the interplay between paramagnetism and conductivity.…”