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The synthesis of quality single crystals is central to materials chemistry for optical, magnetic, and electronic device applications. The present work reports on the synthesis of single crystals of iron-triazole coordination polymer [Fe(Htrz)2(trz)](BF4) where (Htrz) = 1H-1,2,4-triazole. Crystals of size as long as 80 μm can be achived by controlling the temperature, precursor concentration, and solvent type. It is found that its thermal spin crossover depends largely on the crystal size. Fine crystals are ideal for depositing a thin film that exhibits redox activity. The largest crystals allow reliable electrical conductance measurements that reveal two different activation energies at the low spin state and the high spin state, which are one order of magnitude smaller than the electronic gaps calculated based on density functional theory. The synthetic route sought in the present study can be applied to other coordination polymers and related materials and provides the basis for their applications. [ABSTRACT FROM AUTHOR]

Fully amorphous Zr57Ti5Cu20Al10Ni8 bulk metallic glass specimens were subjected to deformation by high pressure torsion at room temperature. Consecutive high resolution synchrotron x-ray diffraction mapping has revealed the variation of the average atomic bond length and shown no evidence of crystallization in this excellent glass former. Difference in the sign of the atomic distortion obtained in direction parallel to the sample surface and along the cross section indicates strong structural anisotropy. [ABSTRACT FROM AUTHOR]

Ultrafine and nanocrystalline states of equiatomic face‐centered cubic (fcc) high‐entropy alloy (HEA) CoCrFeNiMn ("Cantor" alloy) are achieved by high‐pressure torsion (HPT) at 300 K (room temperature, RT) and 77 K (cryo). Although the hardness after RT‐HPT reaches exceptionally high values, those from cryo‐HPT are distinctly lower, at least when the torsional strain lies beyond γ = 25. The values are stable even during long‐time storage at ambient temperature. A similar paradoxal result is reflected by torque data measured in situ during HPT processing. The reasons for this paradox are attributed to the enhanced hydrostatic pressure, cryogenic temperature, and especially large shear strains achieved by the cryo‐HPT. At these conditions, selected area electron diffraction (SAD) patterns indicate that a partial local phase change from fcc to hexagonal close‐packed (hcp) structure occurs, which results in a highly heterogeneous structure. This heterogeneity is accompanied by both an increase in average grain size and especially a strong decrease in average dislocation density, which is estimated to mainly cause the paradox low strength. [ABSTRACT FROM AUTHOR]

Al85Gd8Ni5Co2 metallic glass was subjected to partial devitrification by high-pressure torsion, continuous heat treatment, and isothermal annealing. The fully amorphous alloy exhibits a well-defined transition in its first devitrification product during isothermal heat treatments from tm + a-Al phase mixture to primary a-Al by increasing the annealing temperature above 555 K. This thermal sensitivity predestinates the composition to identify the controversial thermal contribution of the plastic deformation in metallic glasses. Thermal stability and structure of the partially devitrified samples were systematically analyzed and compared by calorimetry, x-ray diffraction, and electron microscopy. It seems that the effect of severe deformation cannot be singled out by a simple isothermal heat treatment; i.e., high-pressure torsion acts as a spectrum of heat treatments performed at different annealing temperatures. [ABSTRACT FROM AUTHOR]

Abstract: N-type skutterudite Sr0.07Ba0.07Yb0.07Co4Sb12 with ZT =1.4 at 800K was processed by high pressure torsion (HPT), a technique of severe plastic deformation (SPD) to produce a nanocrystalline material with many deformation induced lattice defects like dislocations and vacancies. As already shown previously, after HPT processing ZT ∼1.8 was reached mainly due to a significantly reduced thermal conductivity (the lattice thermal conductivity reached almost the theoretical calculated minimum) although the electrical resistivity was higher. In this paper, the microstructural changes after HPT leading to such high ZT values were investigated. X-ray line profile analysis (XPA) before and after HPT was used to detect a smaller crystallite size and a high number of defects (dislocations and vacancies) resulting in an increase of the electrical resistivity but a significant decrease of the thermal conductivity after HPT processing. The decrease of the crystallite size could also be identified as the reason for enhanced microhardness, which means that Hall–Petch strengthening applies. In addition, for the first time, energy filtered transmission electron microscopy (TEM) was employed for the investigation of HPT processed skutterudites. Dislocations as well as grain boundaries of two types (polarised dipole walls and polarised tilt walls) could be directly observed, confirming what so far was assumed. Also for the first time thermal expansion was measured below and above room temperature and compared with the results before HPT revealing a slightly lower thermal expansion coefficient, the same Debye temperature but an Einstein temperature only half of that before HPT, the latter indicating lower frequencies of the filler atoms after HPT processing. Furthermore it could be shown that the decrease of the electrical resistivity after reaching a maximum runs parallel with a shrinking of the sample during thermal expansion measurements, proving that annealing out and closing of microcracks are responsible for this behaviour. [Copyright &y& Elsevier]

By analyzing the deformation of α-isotactic polypropylene through cyclic uniaxial compression at different temperatures-conclusions are drawn on the contribution of the crystalline phase and the amorphous phase to the hardening curve. The deformation of the crystalline phase, which deforms mainly by simple shear of the crystallites, strongly depends on the properties of the amorphous phase. A separation of strain in a relaxing and a quasipermanent part, as introduced by the work of Hiss et al. (1999, Network Stretching, Slip Processes and Fragmentation of Crystallites During Uniaxial Drawing of Polyethylene and Related Copolymers," Macromolecules, 32, pp. 4390-4403), is undertaken. By this experimental procedure it is possible to characterize the deformation dependence of several physical quantities such as Young's modulus or the stored energy associated to each loading-unloading cycle. Furthermore specific transition strains, A, B, C, and D, can be determined where the recovery properties change. it is demonstrated that beyond point C the strain hardening can be described by the simple rubber hardening model of Haward (1987, "The Application of a Simplified Model for the Stress-Strain Curve of Polymers," Polymer, 28, pp. 1485-1488). [ABSTRACT FROM AUTHOR]

Abstract: High-pressure torsion (HPT), a severe plastic deformation technique, can effectively improve the thermoelectric performance of skutterudites, resulting in ZT values higher than for ball-milled and hot-pressed (BMHP) samples. In this paper the influence of the HPT parameters, i.e. the number of revolutions (equivalent to the applied strain), the processing temperature and the hydrostatic pressure on the microstructural and thermoelectric properties of the skutterudite DD0.60Fe3CoSb12 are evaluated and compared with the BMHP samples before HPT processing. Whilst the three parameters have specific effects on (i) the crystallite size, (ii) the density of lattice defects and (ii) the density of cracks, a suitable combination thereof allows for an increase of the figure of merit by at least 20%. [Copyright &y& Elsevier]

High energy ball milling and subsequent high-pressure torsion method was carried out on nanocrystalline Mg powders catalyzed by 5 wt.% Nb₂O 5 and 5 wt.% carbon nanotubes. In the present research two distinct milling routes were performed in order to reveal the influence of the processing conditions on the hydrogenation behavior of the investigated alloys. The hydrogen sorption behavior of the milled powders and the bulk disks was examined in a Sieverts'-type apparatus. Structural characterization of the catalyzed Mg powders and disks has been carried out by high-resolution transmission electron microscopy and X-ray diffraction.