High pressure studies of alkali metal doped fullerides A4C60

The electrical resistance R of K4C60 and Li4C60 has been measured between 100 and 300 K under pressures up to 1 and 2 GPa, respectively. For both materials, the temperature coefficient of R is negative at all pressures and temperatures in this range. The transport properties of Li4C60 at low pressure are compatible with a recent observation of high ionic conductivity, but surprisingly, this conductivity term increases strongly with increasing pressure, contradicting an intuitive model. For K4C60 we see no sign of a recently suggested structural phase transformation at low temperature, nor can we find any convincing evidence for a lattice disproportionation as recently observed for Rb4C60.

Research Highlights
► First ever data for resistance vs. T for Li4C60 under high pressure.
► Results contradict a recent observation of ionic conductivity.
► First ever data for resistance vs. T for K4C60 under high pressure.
► No evidence for disproportionation or phase transition in K4C60