Crystal structures and textures in the hot-forged Ni-Mn-Ga shape memory alloys

Three ferromagnetic shape-memory alloys with the chemical compositions of Ni₅₃Mn₂₅Ga₂₂, Ni₄₈Mn₃₀Ga₂₂, and Ni₄₈Mn₂₅Ga₂₂Co₅ were prepared by the induction-melting and hot-forging process. The crystal structures were investigated by the neutron powder diffraction technique, showing that Ni₅₃Mn₂₅Ga₂₂ and Ni₄₈Mn₂₅Ga₂₂Co₅ have a tetragonal, 14/mmm martensitic structure at room temperature, while Ni₄₈Mn₃₀Ga₂₂ has a cubic, L2₁ austenitic structure at room temperature. The development of textures in the hot-forged samples shows the in-plane plastic flow anisotropy from the measured pole figures by means of the neutron diffraction technique. Significant texture changes were observed for the Ni₄₈Mn₂₅Ga₂₂Co₅ alloy after room temperature deformation, which is due to the deformation-induced rearrangements of martensitic variants. An excellent shape-memory effect (SME) with a recovery ratio of 74 pct was reported in this Ni₄₈Mn₂₅Ga₂₂Co₅ polycrystalline alloy after annealing above the martensitic transformation temperature, and the “shape-memory” influence also occurs in the distributions of grain orientations.

Crystal structures and textures of hot forged Ni48Mn30Ga22 alloy investigated by neutron diffraction technique

A ferromagnetic shape memory alloy of Ni48Mn30Ga22 prepared by induction melting was successfully hot forged. Strong textures and a large anisotropy of in plane plastic flow were developed during the hot forging process. The crystal structures, both in austenitic and martensitic states, were investigated by means of neutron powder diffraction technique. The result suggests that Ni48Mn30Ga22 has a cubic L21 Heusler structure at room temperature, the same as that in the stoichiometric Ni2MnGa. When cooled to 243 K, the Ni48Mn30Ga22 alloy changes into a seven layered orthorhombic martensitic structure. No substantial change of the neutron diffraction pattern was observed upon further cooling to 19 K, indicating that there is no intermartensitic transformation in the investigated alloy, which is different from the transformation processes in the Ni–Mn–Ga alloys with higher martensitic transformation temperatures.

Structure and phase stability of NiMnGa ferromagnetic shape memory alloys by experimental and ab-initio techniques

This paper summarizes some of our recent results on crystal structure, microstructure, orientation relationship between martensitic variants and crystallographic features of martensitic transformation in Ni-Mn-Ga FSMAs. It was shown that Ni53Mn25Ga22 has a tetragonal I4/mmm martensitic structure at room temperature. The neighboring martensitic variants in Ni53Mn25Ga22 have a compound twinning relationship with the twinning elements K1={112}, K2={11-2}, η1=<11-1>, η2=<111>, P={1-10} and s=0.379. The ratio of the relative amounts of twins within the same initial austenite grain is ~1.70. The main orientation relationship between austenite and martensite is Kurdjumov-Sachs (K-S) relationship. Based on the crystallographic phenomenological theory, the calculated habit plane is {0.690 -0.102 0.716}A (5.95° from {101}A), and the magnitude, direction and shear angle of the macroscopic transformation shear are 0.121, <-0.709 0.105 0.698>A (6.04° from <-101>A) and 6.88°, respectively.

Insight into local structure and molecular dynamics in organic solid-state ionic conductors

Elucidating the rate and geometry of molecular dynamics is particularly important for unravelling ion-conduction mechanisms in electrochemical materials. The local molecular motions in the plastic crystal 1-ethyl-1-methylpyrrolidinium tetrafluoroborate ([C2 mpyr][BF4 ]) are studied by a combination of quantum chemical calculations and advanced solid-state nuclear magnetic resonance spectroscopy. For the first time, a restricted puckering motion with a small fluctuation angle of 25° in the pyrrolidinium ring has been observed, even in the low-temperature phase (-45 °C). This local molecular motion is deemed to be particularly important for the material to maintain its plasticity, and hence, its ion mobility at low temperatures.

Structure and characteristics of milled silk particles

This study examined the structure, thermal property, and ion adsorption of silk particles. The particles were prepared by attritor-bead mill combination, using alkaline (pH10) charge repulsion and surfactant steric repulsion methods. Both methods produced particles with a dominant β-sheet structure, similar to the silk fibre. There was no significant difference in the decomposition temperatures for either the silk fibre or the micro/nano silk particles. An important finding from this study is clear evidence of reduction of amorphous content during the final stage of powdering using the bead mill. As a result, despite reduction in β-sheet crystallites with the progressive milling, the relative β-sheet content actually increased during this process. However, intermolecular forces between the β-sheets reduced significantly and hence the XRD results showed significant reduction in crystallinity in nano silk particles but crystal forming segments remained with β-sheet conformations after milling. The structural change influenced the ion-adsorption property where particle-size reduction resulted in a significant increase in both the rate and volume of HCrO4- adsorption. © 2014 Elsevier B.V.

Synthesis, structure and spectral properties of dithiocarbamato bridged dirhenium(III,II) complexes: a combined experimental and theoretical study

Sodium salts of dimethyldithiocarbamate, diethyldithiocarbamate and pyrrolidinedithiocarbamate react with the multiply bonded paramagnetic dirhenium(III,II) complex Re₂(μ-O₂CCH₃)Cl₄(μ-dppm)₂, 1 (dppm = Ph₂PCH₂PPh₂) in refluxing ethanol to afford the paramagnetic substitution products of the type Re₂(η²-S,S)₂(μ-S,S)(μ-Cl)₂(μ-dppm), where S,S represents the dithiocarbamato ligands [S,S = S₂CNMe₂, 4(L_Me); S₂CNEt₂, 4(L_Et) and S₂CN(CH₂)₄, 4(L_Pyr)]. These are the first examples of dirhenium complexes that contain bridging dithiocarbamato ligand along with the dppm ligand. These complexes have very similar spectral (UV-Vis, IR, EPR) and electrochemical properties which are also reported. The identity of 4(L_Et) has been established by single-crystal X-ray structure determination (Re-Re distance 2.6385 (9) Å) and is shown to have edge-shared bioctahedral structure. The electronic structure and the absorption spectra of the complexes are scrutinized by the density functional theory (DFT) and time-dependent density functional theory (TD-DFT) analyses.

Organotin(IV) complexes derived from proteinogenic amino acid: Synthesis, structure and evaluation of larvicidal efficacy on Anopheles stephensi mosquito larvae

Five new organotin(IV) complexes of composition [Bz2SnL1]n (1), [Bz3SnL1HH2O] (2), [Me2SnL2H2O] (3), [Me2SnL3] (4) and [Bz3SnL3H]n (5) (where L1 = (2S)-2-([(E)-(4-hydroxypentan-2-ylidene)]amino)-4-methylpentanoate, L2 = (rac)-2-([(E)-1-(2-hydroxyphenyl)methylidene]amino)-4-methylpentanoate and L3 = (2S)- or (rac)-2-([(E)-1-(2-hydroxyphenyl)ethylidene]amino)-4-methylpentanoate) were synthesized and characterized using 1H NMR, 13C NMR, 119Sn NMR and infrared spectroscopic techniques. The crystal structure of 2 reveals a distorted trigonal-bipyramidal geometry around the tin atom where the oxygen atoms of the carboxylate ligand and a water ligand occupy the axial positions, while the three benzyl ligands are located at the equatorial positions. On the other hand, the analogous derivative of enantiopure L3H (5) consists of polymeric chains, in which the ligand-bridged tin atoms adopt the same trans-Bz3SnO2 trigonal-bipyramidal configuration and are now coordinated to a phenolic oxygen atom instead of H2O. In 2, the OH hydrogen of the ketoimine substituent has moved to the nearby nitrogen atom while in the salicylidene derivative 5, the OH is located almost midway between the phenolic oxygen atom and the nitrogen atom of the C=N group. For the dibenzyltin derivative 1, a polymeric chain structure is observed as a result of a long intermolecular SnO bond involving the exocyclic carbonyl oxygen atom from the tridentate ligand of a neighbouring tin-complex unit. The tin atom in this complex has distorted octahedral coordination geometry. In contrast, the racemic dimethyltin(IV) complexes 3 and 4 display discrete monomeric structures with a distorted octahedral- and trigonal-bipyramidal geometry, respectively. The structures show that the coordination mode of the Schiff base ligand depends primarily on the number of bulky benzyl ligands (R) at the tin atom, as indeed found in the structures of related complexes where R = phenyl. With three bulky R groups, the tridentate chelating O,N,O coordination mode is preferred, whereas with fewer or less bulky R ligands, only the carboxylate and hydroxy groups are involved, which leads to polymers. Larvicidal efficacies of two of the new tribenzyltin(IV) complexes (2 and 5) were assessed on the second larval instar of Anopheles stephensi mosquito larvae and compared with two triphenyltin(IV) analogues, [Ph3SnL1H]n and [Ph3SnL3H]n. The results demonstrate that the compounds containing Sn-Ph ligands are more effective than those with Sn-Bz ligands.