A Rutherford backscattering spectrometry (RBS) study has found that concentrations up to 7at.% of Rb and Cs can be introduced to a depth of ∼700 in MgB2 thin films by annealing in quartz ampoules containing the elemental alkali metals at <350 °C. No significant change in transition temperature (Tc) (determined resistively) was observed, in contrast to an earlier report of very high Tcs (>50K) from susceptibility measurements on MgB2 powders. The lack of a significant change in Tc and intra-granular carrier scattering suggests that Rb and Cs diffuse into the film, but do not enter the grains. Instead, the observed changes in the electrical properties, including a significant drop in J c and an increase in Δρ(ρ300- ρ40), arise from a decrease in inter-granular connectivity due to segregation of the heavy alkaline metals and other impurities (i.e.C and O) introduced into the grain boundary regions during the anneals.
ASJC Scopus subject areas
- Physics and Astronomy (miscellaneous)
- Condensed Matter Physics
- Electronic, Optical and Magnetic Materials