The thermally activated deformation of tellurium single crystals

Abstract

Low temperature prismatic glides of tellurium are strongly thermally activated. A meaningful macroelastic‐limit criterion has been found to be most convenient in this situation where extensive parabolic stage occurs to the passage from microplasticity to macroplasticity. This definition is discussed from the point of view of the dislocation substructure and of the experimental results. For a‐glide, the stability of a‐edge dislocations accounts for the strong temperature variation of elastic‐limit, small activation volumes, and a maximum activation energy U0 = (0.50 ± 0.05) eV which can be attributed to the double‐kink nucleation energy. For c‐glide, the stability of c‐screw dislocations leads to a strong lattice friction up to 150°K. Above 150°K, the lattice friction is annihilated; due to an extensive glide polygonisation, c‐edge dislocations form tilt walls, and c‐ and a‐screw dislocations form twist walls.

Influence of non-glide stresses on plastic flow: from atomistic to continuum modeling

“…These stresses are usually shear stresses acting either in the direction of the Burgers vector in a plane other than the slip plane, or perpendicular to the Burgers vector; the latter cannot induce dislocation motion but can alter the dislocation core. The most prominent example of materials in this category are body-centered-cubic (bcc) metals [8,9,[12][13][14][15], but the class of such materials is much broader and includes intermetallic compounds [7,9,10,[16][17][18], oxides and semiconductors [11,[19][20][21][22][23][24] and even organic and geological materials [25][26][27].…”

The asymmetry and orientation dependence ofc-slip in tellurium

“…130 K . From such plots, a value of the elastic limit can be obtained by taking the stress a t which the plateau in activation volume is achieved [4]. This is based on the view that, while the preplastic stage is due to the slip of the more mobile dislocation species (here, the c-edges), 'the yield is mainly due to dislocation multiplication, which is controlled by the slip of the less mobile species, i.e.…”

“…slip directions) a = + (1120) or c = (OOO1) [2]. a-dislocations, which distort the pseudo-covalent bonds within the chains, experience the same kind of (thermally activated) lattice friction as observed in silicon or germanium, but weaker because the bonds are weaker; in particular, they obey the well-known Schmid law [3,4]. In contrast, c-dislocations, which distort only the interchain bonds made from weakly overlapping electron orbitals, experience a lattice friction similar to the one recently studied in b.c.c.…”

“….However, the uniaxial compression tests failed to provide more specific support to this model. This is because the Schmid factor of a-glide can never be made zero in these tests (since the stress axis would then lie along c in the prismatic plane); localized a-slip is then triggered off, a t least in some temperature ranges, resulting in a local glide polygonization with twist walls of c-screws and a-screws [4]. This makes both the direct observation of isolated straight c-screws and the measurement of all the glide parameters in large enough orientation and temperature ranges very difficult.…”

Influence of Dislocations on the Cyclotron Resonance Absorption in Tellurium

“…This isotropy is destroyed when a uniaxial stress is applied acting perpendicularly to the c-axis. I n fact, it is rather difficult to investigate anisotropic reversible properties in tellurium introduced by uniaxial stress of this type since plastic deformation starts already a t very low stresses [ 2 ] of the order of 1 N mm-2 < lO-3E ( E Young's modulus) It is, however, possible to introduce into the crystal a large dislocation density by plastic deformation, i.e. an internal elastic strain field which destroys the basal isotropy.…”