Formation of complex radiation defects in irradiated materials

The principles of formation of the complex vacancy defects (V-clusters), their ensembles and patterns of formation of superlattices of the V-clusters are determined. The inclusion of the drift component of the elementary defects into the field of elastic stresses of the V-cluster in the analysis allowed describing its genesis and development adequately. The mechanisms of motion of the V-clusters in the material are described in detail, considering their interaction with each other. The authors have developed the original physical and mathematical formalism within which it has become possible to describe the order-disorder phase transition when an ensemble of clusters chaotically distributed in the irradiated solid transforms into an ordered coherent superlattice. The critical point of the phase transition and the parameters of the defect lattice itself are determined. They are confirmed by the experimental results. The ordering process in this system is understood as the motion of the undamped wave of order parameter through the material, while other configuration states of the V-cluster ensemble constitute rapidly damping fluctuations. The article also shows the mechanism of linking the symmetry of the V-cluster superlattice to the symmetry of the initial crystal.

Heat Capacities of l-Histidine, l-Phenylalanine, l-Proline, l-Tryptophan and l-Tyrosine

In an effort to establish reliable thermodynamic data for proteinogenic amino acids, heat capacities for l-histidine (CAS RN: 71-00-1), l‑phenylalanine (CAS RN: 63-91-2), l‑proline (CAS RN: 147-85-3), l‑tryptophan (CAS RN: 73-22-3), and l-tyrosine (CAS RN: 60-18-4) were measured over a wide temperature range. Prior to heat capacity measurements, thermogravimetric analysis was performed to determine the decomposition temperatures while X-ray powder diffraction (XRPD) and heat-flux differential scanning calorimetry (DSC) were used to identify the initial crystal structures and their possible transformations. Crystal heat capacities of all five amino acids were measured by Tian–Calvet calorimetry in the temperature interval from 262 to 358 K and by power compensation DSC in the temperature interval from 307 to 437 K. Experimental values determined in this work were then combined with the literature data obtained by adiabatic calorimetry. Low temperature heat capacities of l‑histidine, for which no literature data were available, were determined in this work using the relaxation (heat pulse) calorimetry from 2 K. As a result, isobaric crystal heat capacities and standard thermodynamic functions up to 430 K for all five crystalline amino acids were developed.

In Situ Observation of Electron-Beam-Induced Formation of Nano-Structures in PbTe

Nano-scaled thermoelectric materials attract significant interest due to their improved physical properties as compared to bulk materials. Well-shaped nanoparticles such as nano-bars and nano-cubes were observed in the known thermoelectric material PbTe. Their extended two-dimensional nano-layer arrangements form directly in situ through electron-beam treatment in the transmission electron microscope. The experiments show the atomistic depletion mechanism of the initial crystal and the recrystallization of PbTe nanoparticles out of the microparticles due to the local atomic-scale transport via the gas phase beyond a threshold current density of the beam.

On models for estimating the post-radiation defect state of the -phase

Processes that take place in the precipitates of -phase under irradiation with fast neutrons are topical and draw attention when one searches for ways of improving radiation resistance of structural reactor steels. A special feature of these processes is that the formation of vacancies and interstices proceeds at the background of a disordering of the initial crystal lattice, which mani-fests itself in the formation of antisite defects. X-ray and neutron diffraction techniques are efficient tools of studying changes that occur in the post-radiation structural state of such systems. However, interpretation of the experimental results calls for more complicated models for the description of structural effects exerted by accumulation of radiation defects in the material than those developed before for elementary metals. Several models are proposed in this paper.

Влияние термообработки на деформационные свойства кристаллов сплава Ni-=SUB=-49-=/SUB=-Fe-=SUB=-18-=/SUB=-Ga-=SUB=-27-=/SUB=-Co-=SUB=-6-=/SUB=- при их сжатии вдоль оси [011]

Stress–strain diagrams (σ–ε curves) have been studied during uniaxial compression of Ni_49Fe_18Ga_27Co_6 alloy single crystals in the [011] axis direction for the initial samples and those after 15-min annealing at 1373 K with subsequent quenching in water. It was established that the σ–ε curves of initial crystals exhibited a one-stage character and showed a single stress decay, whereas the curves of heat-treated and quenched crystals displayed two stress decays. The shape-memory (SM) strain recovery on heating the compression-strained crystals showed an anomalous (burstlike) character. Investigation of the reproducibility of burstlike recovery of SM strain in a series of thermomechanical treatment cycles showed that the recovery took place in quenched crystals, whereas the temperature interval of SM recovery in the initial crystal grew from 1 to 12 K with increasing number of thermomechanical treatment cycles.

THE EFFECT OF THE EXTERNAL MEDIUM ON THE STRUCTURAL-PHASE TRANSFORMATIONS OF QUARTZITE UPON HIGH-ENERGY ELECTRON IRRADIATION

The structural transformations of the natural quartzite under the electron irradiation in doses range of 107…108 Gy in various medium were studied using IR-spectroscopy, X-ray diffraction, and crystal-optical analyzes. It was established that under the irradiation, both in air and in a water stream, intense crystallization of the amorphous component occurs, which is siliceous cement. The initial crystal structure of quartzite is also improved as a result of radiation annealing of defects and impurities present in the initial quartz. It was found that the water medium significantly accelerates these processes, however, in the studied doses range for both types of irradiation, degradation of the quartzite crystal structure is not observed.