Search for low-temperature staging transitions in stage-2 potassium-graphite intercalation compounds

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Abstract
We have carefully studied the T-dependent (00L) profiles of ≥95% pure stage-2 potassium-graphite intercalation compounds (K-GIC’s) with different K to C ratios to look for staging transitions predicted by simple thermodynamics models. Hendricks-Teller model fits show that the dens- est sample undergoes a negligible change in stage purity with no identifiable stage-3 peaks at any T, while ∼1%, random stage-3 impurity cells tend to phase separate at low T; the in-plane structure is single phased as reported in earlier studies. The (00L) profile of an intermediate-density sample shows the same tendency towards greater stage-3 impurity phase separation at low T; the in-plane structure is, however, multiphased. The most dilute sample exhibits an appreciable change in stage purity and a similar multiphased in-plane structure at low T. These results are discussed in light of theoretical predictions and recent related experimental studies.