The techniques used in the Tc measurements on the CsBi-GIC's
were nearly the same as those used for the KHg-GIC's, described in
Section . There were several differences, however. One
was that the CsBi samples were routinely cleaved before the Tc
measurement so that any transition observed would be due to the bulk of the
sample, and not a spurious effect arising from alloy adsorbed on the
surface. Lagrange and coworkers do not report whether they cleaved their
samples or not. KHg-GIC's very rarely had any adsorbed alloy since their
intercalation is accomplished through a vapor-phase reaction, in contrast
to the contact reaction necessary to intercalate the MBi-GIC's. Therefore,
KHg samples were not generally cleaved before Tc measurements.
Because cleaving is a difficult operation to perform in the
glovebox on small samples, the CsBi-GIC's were cleaved in air. Handling in
air was also necessary to perform the weight-uptake measurements described
in Section . Because of the compounds' excellent
stability in air,[145] the brief exposures to air were not
thought to influence the superconductivity experiments. The work of the
Nancy group does not state whether their samples were exposed to air before
the low-temperature experiments.
The CsBi-GIC's were place in glass ampoules for the low-temperature
experiments. They were not fixed in metal sample-holders as the KHg-GIC's
were [See Section ], though, because no critical field
measurements were performed on them. The inductive Tc measurements
were performed on the CsBi-GIC's in the same manner as on the KHg-GIC's
[See Section
]. The temperature range of the inductive
measurements was from 4.2 K to about 0.4 K, just as for the KHg
experiments.
The air stability of the CsBi compounds allowed resistive Tc measurements to be performed easily on them. Contacts were made with silver paint on the edges of the GIC in a standard four-probe geometry. The samples were then encapsulated in a cell filled with helium gas for good thermal contact at low temperatures. Both zero-field temperature sweeps and fixed-temperature field sweeps were performed on CsBi alpha- and alpha + beta-phase samples. The temperature range of the resistive measurements was from liquid helium temperature (4.2 K) to about 1.1 K. Current densities used were on the order of 10-1-10-2 A/cm2. The results did not depend on the current density employed. The values of the normal-state resistivity obtained from the temperature sweeps were estimated to be uncertain by about 25% due to remanent fields in the Bitter magnets used for the Shubnikov-de Haas measurements.