The thermal expansion coefficients of pure fullerite are determined on the basis of powder x-ray studies in the temperature range 30–293 K. The obtained results are in good agreement with dilatometric and neutron-scattering data. The data on thermal expansion are used to analyze the heat capacity at constant volume CV. The intramolecular component of CV is analyzed consistently and accurately taking into account the complete set of temperature-dependent intramolecular eigenfrequencies. The rotational component of heat capacity is obtained by subtracting the intramolecular and phonon contributions from the total CV. The phonon component is evaluated on the basis of the Debye model using the Debye temperature (ΘD(0)=55.4 K) calculated from the known sound velocities. The general and partial Grüneisen parameters are calculated as functions of temperature. The results obtained for the high-temperature phase indicate that rotations of C60 molecules are strongly hindered and intercorrelated.

Polycrystalline fullerite Ñ 60 intercalated with Xe atoms at 575 K and a pressure of 200 MPa was studied by powder x-ray diffraction. The integrated intensities of a few brighter reflections have been utilized to evaluate the occupancy of the octahedral interstitial sites in Ñ 60 crystals, which turned out to be (34±4) %, and in good agreement with another independent estimate. It is found that reflections of the (h00) type become observable in Xe-doped Ñ 60 . The presence of xenon in the octahedral sites affects both the orientational phase transition as well as the glassification process, decreasing both characteristic temperatures as well as smearing the phase transition over a greater temperature range. Considerable hysteretic phenomena have been observed close to the phase transition and the glassification temperature. The signs of the two hysteresis loops are opposite. There is reliable evidence that at lowest temperatures studied the thermal expansion of the doped crystal is negative under cool-down.

The structure and microplasticity of high-purity fullerite C60 have been investigated comprehensively. The crystalline structure, lattice parameters, and phase transitions have been studied by x-ray diffractometry in the temperature range 30–293 K. It is found that the temperature corresponding to the orientational order–disorder phase transition is Tc=260 K. A considerable number of regions with stacking faults discovered in the samples leads to blurring of the fcc→sc phase transition in the temperature interval Tc±3 K. The a(T) dependences of the lattice parameter display peculiarities at the following characteristic temperatures: Tc at which the lattice parameter jump Δa/a=3.3×10−3 is observed, and the temperatures T0≃155 K, and Tg≃95 K which are associated with the beginning and end of molecular orientation freezing. It is shown that the formation of orientational glass is accompanied by a considerable increase in the width of x-ray reflections. The slip geometry and the temperature dependence of microhardness HV are studied in the temperature interval 81–293 K. It is shown that a system of the {111}〈110〉 type is the only slip system in the fcc and sc phases. The value of HV depends on the indentation plane: HV111>HV100. Below Tc, the microhardness increases abruptly (by approximately 30%). The temperature interval of this anomaly decreases after annealing of the crystal in vacuum. At T<T0, the HV(T) dependence becomes much stronger. It is shown that the hardness of C60 normalized to the elastic shear modulus is higher than the hardness of typical molecular crystals at comparable homologic temperatures.

The lattice parameters of monoclinic ortho-bromobenzophenone (2-BrBP) were determined using powder X-ray diffraction, in the temperature range of 90–300 K. It is found that ortho-bromobenzophenone has small linear expansion coefficients (about 10−5 K−1) and is characterized by weak anisotropy. There were no phase transitions in the studied temperature range.

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