Structure and physical properties of Na4C60 under ambient and high pressures - art. no. 045418

The structure and physical properties of two-dimensional polymeric Na4C60 ( body-centered monoclinic, space group I2/m) are studied in a wide temperatu re region from 12 to 300 K at 1 bar, and in a pressure region up to 53 kbar at 300 K. The temperature dependence of lattice constants suggests a struc tural anomaly below 100 K where the variation of spin susceptibility is obs erved from electron spin resonance. The thermal expansion of the unit-cell volume V is smaller than that of monomeric Rb3C60 and K3C60. The compressib ility of c is larger than that of a and b, which can be well explained by t he repulsion between Na ions. The compressibility of the center-to-center d istance in the (10(1) over bar) plane is similar to1/3 times smaller that t hat in the (101) plane, which can be well explained by the formation of the polymer chains. Further, a possibility of a three-dimensional polymerizati on is discussed on the basis of the pressure dependence of C-60. . .C-60 di stances.