The structure and microplasticity of high-purity fullerite C-60 have b
een investigated comprehensively. The crystalline structure, lattice p
arameters, and phase transitions have been studied by x-ray diffractom
etry in the temperature range 30-293 K. It is found that the temperatu
re corresponding to the orientational order-disorder phase transition
is T-c = 260 K. A considerable number of regions with stacking faults
discovered in the samples leads to blurring of the fcc-->sc phase tran
sition in the temperature interval T-c+/-3 K. The a(T) dependences of
the lattice parameter display peculiarities at the following character
istic temperatures: T-c at which the lattice parameter jump Delta a/a
= 3.3 x 10(-3) is observed, and the temperatures T-0 similar or equal
to 155 K, and T-g similar or equal to 95 K which are associated with t
he beginning and end of molecular orientation freezing. It is shown th
at the formation of orientational glass is accompanied by a considerab
le increase in the width of x-ray reflections. The slip geometry and t
he temperature dependence of microhardness H-V are studied in the temp
erature interval 81-293 K. It is shown that a system of the {111}[110]
type is the only slip system in the fee and sc phases, The value of H
-V depends on the indentation plane: H-V(111)>H-V(100). Below T-c, the
microhardness increases abruptly (by approximately 30%). The temperat
ure interval of this anomaly decreases after annealing of the crystal
in vacuum. At T<T-0, the H-V(T) dependence becomes much stronger. It i
s shown that the hardness of C-60 normalized to the elastic shear modu
lus is higher than the hardness of typical molecular crystals at compa
rable homologic temperatures. (C) 1997 American Institute of Physics.