N. S. Afonikova

Influence of deformation on the structural transformation of the Pd40Ni40P20 amorphous phase

The influence of plastic deformation on the structure of the Pd40Ni40P20 amorphous alloy has been investigated using X-ray diffraction and measurements of the velocity of sound. It has been revealed that the rolling of the sample leads to a change in the structure of the amorphous phase (distortion of the first coordination sphere) and that the structural transformations are more pronounced in the near-surface region of the sample. The rolling also results in a decrease in the transverse velocity of sound. The observed effects decrease with time. It has been demonstrated that the revealed effects are associated with the inelastic deformation of the amorphous alloy.

Anomalous states of the structure of (NH4)2SO4 crystals in the temperature range 4.2–300 K

Crystals of the (NH4)2SO4 ammonium sulfate are studied using x-ray diffractometry. It is revealed that the temperature dependence of the lattice parameters exhibits an anomalous behavior, namely, a global hysteresis, and an anomalous increase in the lattice parameter a and the unit cell volume at temperatures below the ferroelectric phase transition point (Tc=223 K). The series of superstructure reflections observed corresponds to an incommensurate composite structure. Analysis of the temperature behavior of the mismatch parameters for the matrix (host) and superstructure (guest) lattices demonstrates that the (NH4)2SO4 compound undergoes a number of phase transitions, including a transition to a three-dimensionally incommensurate composite phase and transitions to commensurate (along one of the crystallographic directions) composite phases.

Effect of heat treatment on the structure and elastic properties of a bulk Pd40Cu30Ni10P20 metallic glass

The effect of heat treatment over the range from room temperature to 500°C on the elastic properties of a bulk amorphous Pd40Cu30Ni10P20 alloy was studied. It is shown that the increase in the shear modulus under crystallization of the alloy is two-staged and that the most significant increase in the modulus occurs at the second stage. The obtained results are compared to the x-ray structural data. It is also found that the density characteristics of the as-cast material change very slightly during the transformation from the amorphous to the crystal state, with the density decreasing slightly due to crystallization.

The initiating action of continuous heating on structural remodeling in Ag3AsS3 crystals

The effect of continuous heating on the characteristics of phase transformations in proustite (Ag3AsS3) is established. It is shown that continuous heating, like continuous cooling, stimulates structural remodeling, in this case reducing the temperature of the known phase transitions.

Anomalous states of the structure of [Rb0.7(NH4)0.3]2SO4 crystals in the temperature range 4.2–300 K

Crystals of [Rb0.7(NH4)0.3]2SO4 solid solutions are studied using x-ray diffractometry in the temperature range 4.2–300 K. No anomalies are revealed in the temperature dependences of the lattice parameters and the volume of the host unit cell. A series of superstructure reflections observed along the basis axes corresponds to the guest lattice formed in the matrix of the host structure. From analyzing the axial ratio of these structures and their temperature dependences, it is concluded that the structure of the crystal has the form of an incommensurate composite. The guest structure of the composite at room temperature can be considered a set of chains that are not correlated along the b direction. In the plane perpendicular to the chain axes, these chains form a regular framework that is also incommensurate to the host lattice.

Anomalous states of the crystal structure of (Rb0.1(NH4)0.9)2SO4 solid solutions in the temperature range 4.2–300 K

Crystals of (Rb0.1(NH4)0.9)2SO4 solid solutions are studied using x-ray diffractometry. It is revealed that the temperature dependence of the lattice parameter a exhibits an anomalous behavior, namely, the “invar effect” at temperatures above the ferroelectric phase transition point Tc and an anomalous increase in the temperature range from Tc to the liquid-helium temperature. An anomalous increase in the lattice parameter a and an increase in the intensity of Bragg reflections with a decrease in the temperature are interpreted within the model of the coexistence of two sublattices hypothetically responsible for the ferroelectric phase transition. A series of superstructure reflections observed along the basis axes corresponds to a sublattice formed in the matrix of the host structure. Analysis of the ratio between the lattice parameters of these structures allows the inference that, in the temperature range 4.2–300 K, the structure of the crystal under investigation can be considered an incommensurate single-crystal composite.

Phase transitions in silicon single crystals resulting from directional plastic deformation

The formation of polytypic modifications is observed in dislocation-free silicon single crystals under directional plastic deformation. It is shown that the deformation-stimulated phase appears on the surface of the sample in the form of small grains ranging from several hundred to several thousand angstroms in size. A twin structure in the individual grains is observed.

X-ray Diffraction Tests of Near-Surface Layer of Copper Treated by Ball Rolling

The characteristic parameters of the grain-boundary structure and the internal strain values are determined via X-ray diffraction in copper samples exposed to ball rolling. The characteristic coherence length is found to be 75–100 nm and the root-mean-square internal strains are ~1 × 10–3. The found values are close to those obtained after other types of severe plastic deformation, such as equal-channel angular pressing.