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Measurements of the oscillatory magnetoresistance of a high-quality graphite single crystal were made for all angles 0 between the magnetic field and the c axis, for magnetic fields up to 24 kG, and for temperatures from 1.22 to 4.22°K. The results were analyzed by a least-squares fitting to a generalized Landau formula. Oscillations due to electrons were observed for all orientations (including Hj_c, where the amplitude dropped by a factor 10 5 ), proving that the electron Fermi surfaces are closed. Although oscillations due to holes were not observed beyond 02^84°, indirect arguments show that the hole Fermi surfaces are also closed. Both electron and hole surfaces are elongated along the c axis and have anisotropy ratios of 12.1_1.4 and about 17, respectively. The electron surface is approximately ellipsoidal, whereas the hole surface is similar except for extended ends giving it a diamond-like shape. The results are consistent with a moderate degree of trigonal asymmetry about the c axis. Comparison between the electron density found from the volume of the electron Fermi surfaces and that determined previously from the nonoscillatory galvanomagnetic data confirms the theoretical prediction that there are four electron Fermi surfaces in the Brillouin zone. More indirect arguments show that there are two hole surfaces. Consideration of the size and location of these surfaces along the six zone edges parallel to the c axis leads to a new determination of A^-0.12 eV for the band parameter which represents the difference of potential between the two types of atomic sites in the graphite lattice. Analysis of the temperature and magnetic field dependence of the oscillatory amplitude yields effective mass values in the basal plane of (0.039_0.001)ra 0 for electrons and (0.057_0.002)m 0 for holes. These masses show an orientation dependence that is consistent with the derived Fermi surface anisotropics. The large amplitude and asymmetric shape of the oscillations in the magnetoconductivity, measured for H||c at 1.26 and 4.22 °K, are accurately described by the theory of Adams and Holstein. However, there is an unexplained monotonic variation with magnetic field in the total magnetoconductivity. The effective change in temperature due to collision broadening AT is about 5 times greater than that estimated from the conductivity relaxation time. This discrepancy in AT is qualitatively explained and is related directly to the fact, established from the data of Berlincourt and Steele, that the AT found from magnetoresistance oscillations is greater than that found from susceptibility oscillations on the same sample.

The basal-plane shear stress-strain behavior of small, highly anisotropic-annealed natural graphite single crystals was studied at room temperature. A static uniaxial-shear stress was applied directly along the basal plane with a minimum of normal force, incorporating a technique to detect translations down to ∼40 Å. Comparative measurements were also made on compression-annealed pyrolytic graphite. The staticshear modulus G was also corroborated by a modified ultrasonic transit-time method. Basal-plane dislocation systems strongly reduce the measured G, where values of (0.013–0.14)×1011 dyn/cm2 were observed. This reduction is found to be caused primarily by a dislocation concentration of ∼2×106 cm−2. The average critical-resolved shear stress σc was 0.29×106 dyn/cm2, and an analysis of the relation between σc and the critical breakaway stress for dislocation pinning shows that dislocation line segments l≃120–310 μ are operative. Plastic curvature of the stress-strain curves shows the effect of very sensitive creep and glissile slip. Laminar flow in this principal slip direction produces a plastic strain ε* = Aσ4.2 analogous to easy glide in hcp metals along the close-packed direction. Classical Andrade t1/3 creep was observed at higher stresses and approached a logarithmic creep behavior with decreasing stress. A saturation effect seen in the shear-strength σs with shear-fracture cycling leads to a resultant σs of (2.5–7.5)×106 dyn/cm2. Possible contributions to the elastic shear strain, including dislocations, grain boundaries, hard inclusions, delamination voids, and the Fermi-level shift, are considered as they affect the measured shear modulus. Dislocation pinning by boron ions, in the dilute concentration range from 7 ppm B up to 1500 ppm B, was found to produce a large increase in G with eventual saturation. After accounting for all known shear-strain components, this saturation value leads to an intrinsic single-crystal graphite C44 value of (0.45±0.06)×1011 dyn/cm2.

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An analysis has been made of oscillations in the Hall effect and magnetoresistance for graphite single crystals at 4.2°K with the field parallel to the hexagonal axis. Two periods of 2.11 X10 -5 gauss -1 and 1.58X10 -5 gauss -1 are shown to be due to the majority electrons and holes, respectively. These same two values were found in both galvanomagnetic effects and are in reasonable agreement with those observed in the susceptibility. There is a phase difference of T between the two galvanomagnetic properties. An analysis of the magnetic field dependence of the amplitude incorporating both effects in a "galvanomagnetic ratio," p/R, has been made giving effective-mass values of 0.030mo for the electrons and 0.060mo for the holes. These are in substantial agreement with those calculated from cyclotron resonance and from the temperature dependence of the susceptibility de Haas-van Alphen oscillations. Corresponding Fermi energies were found to be 0.018 ev for the electrons and 0.012 ev for the holes, giving a very slight band overlap in graphite of 0.030 ev.