Crystallographic specific features of the martensitic structure of Ni<Subscript>47</Subscript>Mn<Subscript>42</Subscript>In<Subscript>11</Subscript> alloy

The structure of Ni₄₇Mn₄₂In₁₁ alloy after annealing has been investigated. It is shown that the martensitic transformation in Ni₄₇Mn₄₂In₁₁ alloy upon cooling is accompanied by the formation of 14M modulated martensite. Crystallographic analysis of the martensite structure has been performed. The orientation relationships between the high-temperature austenitic phase and martensite and habit planes of the martensite plates have been determined.     

Electron acoustic imaging of Mn<Subscript>50</Subscript>Ni<Subscript>28</Subscript>Ga<Subscript>22</Subscript> ferromagnetic shape memory alloy

The novel ferromagnetic shape memory alloy Mn₅₀Ni₂₈Ga₂₂ exhibits a single martensite phase with tetragonal structure at room temperature. Its martensite structure was investigated by scanning electron acoustic microscopy. Stripe twin variants exist in every grain and exhibit the configurations of the typical self-accommodation arrangement. The interfaces between twin variants are straight and clear. However, the magnetic domain walls obtained by the Bitter method coincide well with the twin variant boundaries. The first direct evidence of the coincidence between micron-scale magnetic domains and martensite variants is presented. These results will be beneficial for the development of ferromagnetic shape memory alloys and for the understanding of the correlation between magnetic domains and crystallographic twin variant domains as well. PACS  68.37.Hk; 75.70.Kw; 75.60.Ch; 73.50.Rb; 43.58.+z     

Fine structure and mechanical properties of the shape-memory Ni<Subscript>50</Subscript>Ti<Subscript>32</Subscript>Hf<Subscript>18</Subscript> alloy rapidly quenched by spinning

We have reported the results of investigations of the structure and chemical and phase compositions of the amorphous Ni₅₀Ti₃₂Hf₁₈ alloy prepared by rapid quenching from melt by spinning and subjected to heat treatments. The specific features of the fine polycrystalline alloy structure formation depending on the heat-treatment mode have been studied by transmission and scanning electron microscopy, chemical microanalysis, electron diffraction, and X-ray diffraction analysis. According to the data on the temperature behavior of electrical resistivity, critical temperatures of devitrification and subsequent thermoelastic martensitic transformation B2 → B19′ have been determined. The mechanical properties in different heat-treatment modes have been investigated.     

Dependence of electronic structure on the grain size in Mn<Subscript>2</Subscript>O<Subscript>3</Subscript> nanocrystals

. The dependence of electron structure on the grain size in Mn₂O₃ nanocrystals has been investigated using X-ray photoelectron spectroscopy. It is found that the electron structure is sensitively dependent on the average grain size. The experimental results indicate that the O–1s core-level spectra are hardly shifted with decreasing average grain size; however, for a sample with a small grain size (e.g. a 9-nm sample), the shoulder peak evidently appears on the higher-binding-energy side. The main peak width of the Mn–2p core-level spectra becomes wide for samples with decreasing average grain size. The remarkable aspect of the Mn–3s core-level spectra is that the peak is multiply split, with a complex peak structure. The exchange interaction of the 3s and 3d electrons in the Mn³⁺ ion can be used to explain this behavior. PACS 71.23.-k; 73.22.-f     

Fine-grained structure and properties of a Ni<Subscript>2</Subscript>MnIn alloy after a settling plastic deformation

The structure and properties of a polycrystalline Ni–Mn–In Heusler alloy have been studied after a plastic deformation by upsetting. An analysis of points of a martensitic and magnetic phase transformations shows that the martensite transformation takes place at temperatures lower than the Curie point. At high temperatures in the range 930–1110 K the alloy undergoes the phase transformation of ordered phase L2₁ to disordered phase B2, and the melting temperature of the alloy is 1245 K. The flow curves of the alloy cylindrical samples at temperatures 773, 873, and 973 K have been built. An analysis of the alloy microstructure after upsetting at a temperature of 773 K leads to the conclusion that many macrocracks are initiated in the sample. The treatment at 873 and 973 K causes a fragmentation of the grains with grain sizes from several to several dozen micrometers. However, the upsetting at 873 K leads to insignificant scatter in the grain sizes, and the microstructure is more homogeneous and worked out.     

Formation of boride phases from individual powder components during the mechanical synthesis of Ni<Subscript>80</Subscript>Mo<Subscript>7</Subscript>B<Subscript>13</Subscript> alloy

Ni₈₀Mo₇B₁₃ nanocrystalline alloy containing a Ni(Mo,B) face-centered cubic (FCC) solid solution of the substitutional-interstitial type was obtained by high-energy ball milling of the component mixtures. In the temperature range 400–700°C, the metastable solid solution Ni(Mo,B) decomposes, leading to the formation of metastable FCC Ni(Mo) and HCP MoB₄ phases. Upon isothermal annealing at 1000°C for1 h, the alloy transforms into the stable state and contains the equilibrium phases FCC Ni(Mo), cubic Ni₂₁Mo₂B₆, and orthorhombic Ni₃B.     

Structural transformations in the Al<Subscript>85</Subscript>Ni<Subscript>6.1</Subscript>Co<Subscript>2</Subscript>Gd<Subscript>6</Subscript>Si<Subscript>0.9</Subscript> amorphous alloy during multiple rolling

The effect of multiple rolling at room temperature on the structure and crystallization of the Al₈₅Ni_6.1Co₂Gd₆Si_0.9 amorphous alloy has been studied using transmission electron microscopy, differential scanning calorimetry, and X-ray diffraction. The total plastic strain is 33%. It has been shown that the deformation results in the formation of aluminum nanocrystals with the average size that does not exceed 10–15 nm. The nanocrystals are formed in regions of localization of plastic deformation. The deformation decreases the thermal effect of nanocrystallization (∼15%) as compared to the heat release at the first stage of crystallization of the unstrained sample. The morphology, structure, and distribution of precipitates have been investigated. Possible mechanisms of the formation of nanocrystals during the deformation have been discussed.     

Magnetic and structural anomalies of Na<Subscript><Emphasis Type="Italic">n</Emphasis></Subscript>C<Subscript>60</Subscript> (n = 2, 3)

Sodium fullerides Na _n C60 (n = 2, 3) have been synthesized by a liquid phase reaction and investigated with X-ray diffraction (XRD), nuclear magnetic resonance (NMR), electron paramagnetic resonance, and differential thermal analysis. XRD data indicate that the crystal structure of Na₂C₆₀ at 300 K is face centered cubic (FCC). A phase transition from primitive cubic to FCC crystal structure has been observed in this work in Na₂C₆₀ fulleride at 290 K. The transition is accompanied by the step-like change of paramagnetic susceptibility. The crystal structure of Na₃C₆₀ is more complicated than, and different from, what has been reported in the literature. A nearly seven-fold increase of paramagnetic susceptibility with increasing temperature has been observed in the Na₃C₆₀ fulleride at 240–260 K. In the same temperature range, a new line at about 255 ppm appears in the ²³Na NMR spectrum, indicating a significant increase of electron density near the Na nucleus. The observed effect can be explained by a metal-insulator transition caused by a structural transition.     

Thermal sensors based on Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript> and (Sb<Subscript>2</Subscript>Te<Subscript>3</Subscript>)<Subscript>70</Subscript>(Bi<Subscript>2</Subscript>Te<Subscript>3</Subscript>)<Subscript>30</Subscript> thin films

Thin films of Sb₂Te₃ and (Sb₂Te₃)₇₀(Bi₂Te₃)₃₀ alloy and have been deposited on precleaned glass substrate by thermal evaporation technique in a vacuum of 2?×?10^?6 Torr. The structural study was carried out by X-ray diffractometer, which shows that the films are polycrystalline in nature. The grain size, microstrain and dislocation density were determined. The Seebeck coefficient was determined as the ratio of the potential difference across the films to the temperature difference. The power factor for the (Sb₂Te₃)₇₀ (Bi₂Te₃)₃₀ and (Sb₂Te₃) is found to be 19.602 and 1.066 of the film of thickness 1,500 Å, respectively. The Van der-Pauw technique was used to measure the Hall coefficient at room temperature. The carrier concentration was calculated and the results were discussed.     

Formation and structure of nanocrystals in bulk Zr<Subscript>50</Subscript>Ti<Subscript>16</Subscript>Cu<Subscript>15</Subscript>Ni<Subscript>19</Subscript> metallic glass

The possible formation of a nanocrystalline structure in controlled crystallization of a bulk Zr₅₀Ti₁₆Cu₁₅Ni₁₉ amorphous alloy has been studied using differential scanning calorimetry, transmission and high-resolution electron microscopy, and x-ray diffraction. It was established that crystallization of the alloy at temperatures above the glass formation point occurs in two stages and brings about the formation of a nanocrystalline structure consisting of three phases. Local spectral x-ray analysis identified the composition and structure of the phases formed.     

Magnetically controlled thermoelastic martensite transformations and properties of a fine-grained Ni<Subscript>54</Subscript>Mn<Subscript>21</Subscript>Ga<Subscript>25</Subscript> alloy

Comparative studies of physical characteristics (the electrical resistivity, the magnetic susceptibility, the magnetization, the bending deformation, and the degree of shape recovery during subsequent heating) of the Ni₅₄Mn₂₁Ga₂₅ ferromagnetic alloy as-cast and rapidly quenched from melt have been performed in the temperature range 2–400 K. The results are compared to the results of studying the structural–phase transformations by transmission and scanning electron microscopy and X-ray diffraction. It is found that the rapid quenching influences the microstructure, the magnetic state, the critical temperatures, and the specific features of thermoelastic martensite transformations in the alloy. It is found that the resource of the alloy plasticity and thermomechanical bending cyclic stability demonstrates a record-breaking increase in the intercritical temperature range and during subsequent heating.     

Shape memory effect in nanosized Ti<Subscript>2</Subscript>NiCu alloy-based composites

The shape memory effect (SME) in alloys with a thermoelastic martensite transition opens unique opportunities for the creation of miniature mechanical devices. The SME has been studied in layered composite microstructures consisting of a Ti₂NiCu alloy and platinum. It occurs upon a decrease in the active layer thickness at least to 80 nm. Some physical and technological restrictions on the minimum size of a material with SME are discussed.     

Magnetic,thermal, and electrical properties of an Ni<Subscript>45.37</Subscript>Mn<Subscript>40.91</Subscript>In<Subscript>13.72</Subscript> Heusler alloy

The magnetization, the electrical resistivity, the specific heat, the thermal conductivity, and the thermal diffusion of a polycrystalline Heusler alloy Ni_45.37Mn_40.91In_13.72 sample are studied. Anomalies, which are related to the coexistence of martensite and austenite phases and the change in their ratio induced by a magnetic field and temperature, are revealed and interpreted. The behavior of the properties of the alloy near Curie temperature T_C also demonstrates signs of a structural transition, which suggests that the detected transition is a first-order magnetostructural phase transition. The nontrivial behavior of specific heat detected near the martensite transformation temperatures is partly related to a change in the electron density of states near the Fermi level. The peculiar peak of phonon thermal conductivity near the martensitic transformation is interpreted as a consequence of the appearance of additional soft phonon modes, which contribute to the specific heat and the thermal conductivity.     

The effect of antiphase domains on the energy spectra of special boundaries in alloys with the <Emphasis Type="Italic">L</Emphasis>1<Subscript>2</Subscript> superstructure

The special grain boundaries in ordering alloys with the L1₂ superstructure have been investigated by optical metallography and transmission diffraction electron microscopy. The relative energy of the boundaries Σ3 and Σ9 in Ni₃Fe alloy with a short-range order is determined. The energy of these boundaries in an alloy with long-range order is estimated. The energy of twin grain boundaries increases at the phase transitions A1 → L1₂ due to the formation of antiphase grain boundaries in those boundaries. The spectra of special boundaries over Σ and their distributions, depending on the relative energy, change as well. The average relative energy of special grain boundaries in alloys with the L1₂ superstructure increases with increasing the energy of antiphase boundaries.     

Influence of deformation on the structural transformation of the Pd<Subscript>40</Subscript>Ni<Subscript>40</Subscript>P<Subscript>20</Subscript> 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.     

Dipole ordering and ionic conductivity in NASICON-Type Na<Subscript>3</Subscript>Cr<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> structures

The aspects of structure, dipole ordering, and ionic conductivity of the Na₃Cr₂(PO₄)₃ crystal with the four polymorphic phases (α, α', β, and γ) have been investigated. The features of the α-Na₃Cr₂(PO₄)₃ crystal structure and its dipole ordering and relaxation polarization in the low-temperature α and α' phases have been refined. The occurrence of Na₃Cr₂(PO₄)₃ dipole ordering in the α and α' phases and high ionic conductivity in the β and γ phases is attributed to the structural changes in the rhombohedral [Me₂(PO₄)₃]^–3_3∞ crystal frame upon phase transformations α → α', α' → β, and β → γ. A model for explaining the dipole ordering and ionic conductivity phenomena in Na₃Cr₂(PO₄)₃ is proposed.     

Grain size effects on dynamics of Li-ions in Li<Subscript>3</Subscript>V<Subscript>2</Subscript>(PO<Subscript>4</Subscript>)<Subscript>3</Subscript> glass-ceramic nanocomposites

Li₃V₂(PO₄)₃ glass-ceramic nanocomposites, based on 37.5Li₂O-25V₂O₅-37.5P₂O₅ mol% glass, were successfully prepared via heat treatment (HT) process. The structure and morphology were investigated by X-ray diffraction (XRD) and scanning electron microscope (SEM). XRD patterns exhibit the formation of Li₃V₂(PO₄)₃ NASICON type with monoclinic structure. The grain sizes were found to be in the range 32–56 nm. The effect of grain size on the dynamics of Li⁺ ions in these glass-ceramic nanocomposites has been studied in the frequency range of 20 Hz–1 MHz and in the temperature range of 333–373 K and analyzed by using both the conductivity and modulus formalisms. The frequency exponent obtained from the power law decreases with the increase of temperature, suggesting a weaker correlation among the Li⁺ ions. Scaling of the conductivity spectra has also been performed in order to obtain insight into the relaxation mechanisms. The imaginary modulus spectra are broader than the Debye peak-width, but are asymmetric and distorted toward the high frequency region of the maxima. The electric modulus data have been fitted to the non-exponential Kohlrausch–Williams–Watts (KWW) function and the value of the stretched exponent β is fairly low, suggesting a higher ionic conductivity in the glass and its glass-ceramic nanocomposites. The advantages of these glass-ceramic nanocomposites as cathode materials in Li-ion batteries are shortened diffusion paths for Li⁺ ions/electrons and higher surface area of contact between cathode and electrolyte.     

Martensitic transformation and electrical properties of a Ni<Subscript>2.14</Subscript>Mn<Subscript>0.81</Subscript>Fe<Subscript>0.05</Subscript>Ga alloy in its different structural states

Phase transformations in a Ni_2.14Mn_0.81Fe_0.05Ga alloy in different structural states are studied from the temperature dependences of its electrical resistivity. The dependences obtained indicate that, in the coarse-grained state, this alloy undergoes two structural phase transformations: intermartensitic modulation transformation and martensite-austenite transformation. In the nanocrystalline state, these transformations are absent. The recrystallization of a nanocrystalline sample at 773 K for 30 min results in the martensite-austenite transformation; however, the phase transformation related to a change in the martensite modulation period does not occur in this state. The resistivity is shown to depend on the structural state of the alloy.     

Effect of a constant magnetic field on the structure and physical-mechanical properties of Cu<Subscript>57</Subscript>Be<Subscript>43</Subscript> alloy

The work presents data on the microhardness, average grain size, lattice parameters, and phase composition of Cu₅₇Be₄₃ metal alloy, annealed at a temperature of ~350°С for 1 h in a constant magnetic field with the intensity ranging from 80.0 to 557.0 kA/m. The main observed regularities of changes in the structure and properties of the material during annealing in a constant magnetic field and without it are formulated.