Large successive magnetocaloric effects around room temperature in Ni<Subscript>50</Subscript>Mn<Subscript>34</Subscript>In<Subscript>15</Subscript>Al alloy

Two successive magnetocaloric effects consisting of inverse magnetocaloric effect around martensitic transition and negative magnetocaloric effect around magnetic transition of austenitic phase have been observed in Ni₅₀Mn₃₄In₁₅Al alloy. Large inverse magnetic entropy change ΔS_m ( ~ 21.3 J kg^?1 K^?1), small thermal and magnetic hysteresis of martensitic transition give rise of large net refrigerant capacity ( ~ 152.3 J kg^?1) under a magnetic field of 50 kOe, which is comparable with that ( ~ 157.9 J kg^?1) of second-order transition. The large combined magnetocaloric effects make the Ni₅₀Mn₃₄In₁₅Al alloy as a promising candidate material for room temperature magnetic refrigeration.     

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.     

Structure of tetragonal martensite in the In<Subscript>95.42</Subscript>Cd<Subscript>4.58</Subscript> cast alloy

The structure of martensite in the In_95.42Cd_4.58 alloy has been studied by metallography, X-ray diffraction, dilatometry, and transmission electron microscopy. It has been shown that a massive structure built of colonies of tetragonal lamellar plates divided by a twin boundary {101}FCT is formed in the alloy under cooling below the martensite FCC → FCT transition temperature. The alloy recrystallizes after a cycle of FCT → FCC → FCT transitions with a decrease in the grain size by several times compared with the initial structure such fashion that the size of massifs and individual martensite lamella in the massif correlates with the change in the size of the alloy grain. Using thermal cycling, it has been revealed that the alloy tends to stabilize the high-temperature phase.     

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     

Phase transformations and structure of Ni–Mn–In alloys with varying ratio Ni/Mn

The fine structure of Ni–Mn–In alloys has been studied when manganese atoms are substituted for nickel atoms in an annealing state. The concentration dependence of the critical temperatures and the structures of the alloys have been discussed. It has been found that, as manganese atoms replace nickel atoms, the structure after annealing is changed from a two-phase (L2₁ + martensite) to single-phase L2₁ structure. The martensitic transformation in Ni₄₇Mn₄₂In₁₁ alloy is accompanied by the formation of modulated 14M martensite.     

Magnetocaloric Effect and Magnetostriction in a Ni<Subscript>49.3</Subscript>Mn<Subscript>40.4</Subscript>In<Subscript>10.3</Subscript> Heusler Alloy in AC Magnetic Fields

The magnetocaloric effect (MCE) and the magnetostriction in the Ni_49.3Mn_40.4In_10.3 Heusler alloy have been measured in ac magnetic fields to 8 T. It is shown that the contributions of the magnetic and structural subsystems to MCE have opposite signs; in this case, the contribution of the magnetic subsystem is dominant. The anomalous temperature dependence of the magnetostriction during the magnetostructural phase transition (PT) is explained by competition of the processes of growing austenite phase nuclei and the striction processes in them.     

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.     

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.     

Synthesis and electrochemical properties of Li<Subscript>1.2</Subscript>Mn<Subscript>0.54</Subscript>Ni<Subscript>0.13</Subscript>Co<Subscript>0.13</Subscript>O<Subscript>2</Subscript> cathode material for lithium-ion battery

The layered Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ lithium-rich manganese-based solid solution cathode material has been synthesized by a simple solid-state method. The as-prepared material has a typical layered structure with R-3m and C2/m space group. The synthesized Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ has an irregular shape with the size range from 200 to 500 nm, and the primary particle of Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ has regular sphere morphology with a diameter of 320 nm. Electrochemical performances also have been investigated. The results show that the cathode material Li_1.2Mn_0.54Ni_0.13Co_0.13O₂ prepared at 900 °C for 12 h has a good electrochemical performance, which can deliver a high initial discharge capacity of 233.5, 214.2, 199.3, and 168.1 mAh g^?1 at 0.1, 0.2, 0.5, and 1 C, respectively. After 50 cycles, the capacity retains 178.0, 166.3, 162.1, and 155.9 mAh g^?1 at 0.1, 0.2, 0.5, and 1 C, respectively. The results indicate that the simple method has a great potential in synthesizing manganese-based cathode materials for Li-ion batteries.     

Effects of Sn doping on electrochemical characterizations of Li[Ni<Subscript>1/3</Subscript>Co<Subscript>1/3</Subscript>Mn<Subscript>1/3</Subscript>]O<Subscript>2</Subscript> cathode material

Li[Ni_1/3Co_1/3Mn_1/3]O₂ and Sn-doped Li[Ni_1/3Co_1/3Mn_1/3]O₂ cathode materials for lithium battery are synthesized by a solid-state method. The samples are characterized by X-ray diffraction, scanning electron microscope, electrochemical impedance spectroscopy (EIS), and charge–discharge test. The results show that the Sn-doped Li[Ni_1/3Co_1/3Mn_1/3]O₂ has a typical hexagonal α-NaFeO₂ structure and strawberry-like shape with uniform particle size. It has also been found that the Sn-doped Li[Ni_1/3Co_1/3Mn_1/3]O₂ reveals better electrochemical performances than that without Sn doping. The EIS results suggest that Sn presence decreases the total resistance of Li[Ni_1/3Co_1/3Mn_1/3]O₂, which should be related to the improvement on the electrochemical properties.     

Magnetic properties of LiNi<Subscript>0.5</Subscript>Mn<Subscript>0.47</Subscript>Al<Subscript>0.03</Subscript>O<Subscript>2</Subscript> as positive electrode for Li-ion batteries

The layered LiNi_0.5Mn_0.47Al_0.03O₂ was synthesized by wet chemical method and characterized by X-ray diffraction and analysis of magnetic measurements. The powders adopted the α-NaFeO₂ structure. This substitution of Al for Mn promotes the formation of Li(Ni_0.47²⁺Ni_0.03³⁺Mn_0.47⁴⁺Al_0.03³⁺)O₂ structures and induces an increase in the average oxidation state of Ni, thereby leading to the shrinkage of the lattice unit cell. The concentration of antisite defects in which Ni²⁺ occupies the (3a) Li lattice sites in the Wyckoff notation has been estimated from the ferromagnetic Ni²⁺(3a)–Mn⁴⁺(3b) pairing observed below 140 K. The substitution of 3% Al for Mn reduces the amount of antisite defects from 7% to 6.4–6.5%. The analysis of the magnetic properties in the paramagnetic phase in the framework of the Curie–Weiss law agrees well with the combination of Ni²⁺ (S = 1), Ni³⁺ (S = 1/2) and Mn⁴⁺ (S = 3/2) spin-only values. Delithiation has been made by the use of K₂S₂O₈. According to this process, known to be softer than the electrochemical one, the nickel ions in the (3b) sites are converted into Ni⁴⁺ in the high spin configuration, while Ni²⁺(3a)–Mn⁴⁺(3b) ferromagnetic pairs remain, as the Li⁺(3b) ions linked to the Ni²⁺(3a) ions in the antisite defects are not removed. The results show that the antisite defect is surrounded by Mn⁴⁺ ions, implying the nonuniform distribution of the cations in agreement with previous NMR and neutron experiments.     

Investigation of the structural and electrochemical performance of Li<Subscript>1.2</Subscript>Ni<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>O<Subscript>2</Subscript> with Cr doping

Cr-doped layered oxides Li[Li_0.2Ni_0.2???x Mn_0.6???x Cr_2x ]O₂ (x?=?0, 0.02, 0.04, 0.06) were synthesized by co-precipitation and high-temperature solid-state reaction. The materials were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), high-resolution transmission electron microscopy (TRTEM), X-ray photoelectron spectroscopy (XPS), and electrochemical impedance spectroscopy (EIS). XRD patterns and HRTEM results indicate that the pristine and Cr-doped Li_1.2Ni_0.2Mn_0.6O₂ show the layered phase. The Li_1.2Ni_0.16Mn_0.56Cr_0.08O₂ shows the best electrochemical properties. The first discharge specific capacity of Li_1.2Ni_0.16Mn_0.56Cr_0.08O₂ is 249.6 mA h g^?1 at 0.1 C, while that of Li_1.2Ni_0.2Mn_0.6O₂ is 230.4 mA h g^?1. The capacity retaining ratio of Li_1.2Ni_0.16Mn_0.56Cr_0.08O₂ is 97.9% compared with 93.9% for Li_1.2Ni_0.2Mn_0.6O₂ after 80 cycles at 0.2 C. The discharge capacity of Li_1.2Ni_0.16Mn_0.56Cr_0.08O₂ is 126.2 mA h g^?1 at 5.0 C, while that of the pristine Li_1.2Ni_0.2Mn_0.6O₂ is about 94.5 mA h g^?1. XPS results show that the content of Mn³⁺ in the Li_1.2Ni_0.2Mn_0.6O₂ can be restrained after Cr doping during the cycling, which results in restraining formation of spinel-like structure and better midpoint voltages. The lithium-ion diffusion coefficient and electronic conductivity of Li_1.2Ni_0.2Mn_0.6O₂ are enhanced after Cr doping, which is responsible for the improved rate performance of Li_1.2Ni_0.16Mn_0.56Cr_0.08O₂.     

Electronic properties of strain-disordered Ni<Subscript>2.16</Subscript>Mn<Subscript>0.84</Subscript>Ga alloy

The effect of ultrarapid quenching from the melt and severe plastic torsional deformation under high pressure on the crystalline structure and the electrical, optical, and magnetic properties of a Ni_2.16Mn_0.84Ga alloy was studied. The electrical properties are discussed in terms of the Mott two-band model. The peculiarities of the magnetic properties are associated with the magnetism of itinerant electrons. The optical properties correlate with the variations in the electronic spectrum upon disordering of the alloy that follow from the results of the available energy-band-structure calculations.     

Synthesis of Li(Ni<Subscript>0.6</Subscript>Co<Subscript>0.2</Subscript>Mn<Subscript>0.2</Subscript>)O<Subscript>2</Subscript> with sodium DL-lactate as an eco-friendly chelating agent and its electrochemical performances for lithium-ion batteries

(Ni_0.6Co_0.2Mn_0.2)(OH)₂ precursor has been successfully prepared using hydroxide co-precipitation method. The thermodynamic model of hydroxide co-precipitation with sodium DL-lactate as an eco-friendly chelating agent is proposed. The microstructures of (Ni_0.6Co_0.2Mn_0.2)(OH)₂ precursors and Li(Ni_0.6Co_0.2Mn_0.2)O₂ cathode materials are investigated using X-ray diffractometer and scanning electronic microscopy, while the electrochemical performances of Li(Ni_0.6Co_0.2Mn_0.2)O₂ cathode materials are measured using a charge–discharge test. The influences of pH value on the structure and morphological and electrochemical performances of Li(Ni_0.6Co_0.2Mn_0.2)O₂ cathode materials have been discussed in detail. The results show that the sample at pH?=?11.5 exhibits the best lamellar structure and lowest cation mixing, while the sample at pH?=?11.0 delivers the most uniform and full particles and possesses the highest initial charge–discharge performance of 183.4 mAh/g and the best coulombic efficiency of 77.9% at the voltage range of 3.0–4.3 V. Even after 100 cycles, its discharge capacity still remains 165.2 mAh/g with the best retention rate of 90.1%. Furthermore, the sample at pH?=?11.0 delivers the highest discharge capacity at each current density. Even if discharged at 5C (1000 mA/g), the capacity of 115.6 mAh/g has been achieved. The sample at pH?=?11.0 exhibits the highest Li-ion diffusion coefficients (2.072?×?10^?12 cm²/s).     

Improved electrochemical performance of Li<Subscript>1.2</Subscript>Ni<Subscript>0.2</Subscript>Mn<Subscript>0.6</Subscript>O<Subscript>2</Subscript> cathode material with fast ionic conductor Li<Subscript>3</Subscript>VO<Subscript>4</Subscript> coating

Layered lithium-enriched nickel manganese oxides Li_1.2Ni_0.2Mn_0.6O₂ have been synthesized and coated by fast ionic conductor Li₃VO₄ with varying amounts (1, 3, and 5 wt%) in this paper. The effect of Li₃VO₄ on the physical and electrochemical properties of Li_1.2Ni_0.2Mn_0.6O₂ has been discussed through the characterizations of X-ray diffraction (XRD), scanning electron microscopy (SEM), transmission electron microscope (TEM), discharge, cyclic performance, rate capability, and electrochemical impedance spectroscopy (EIS). The discharge capacity and coulomb efficiency of Li_1.2Ni_0.2Mn_0.6O₂ in the first cycle have been improved after Li₃VO₄ coating. And, the 3 wt% Li₃VO₄-coated Li_1.2Ni_0.2Mn_0.6O₂ shows the best discharge capacity (246.8 mAh g^?1), capacity retention (97.3 % for 50 cycles), and rate capability (90.4 mAh g^?1 at 10 C). Electrochemical impedance spectroscopy (EIS) results show that the R _ct of Li_1.2Ni_0.2Mn_0.6O₂ electrode decreases after Li₃VO₄ coating, which is due to high lithium ion diffusion coefficient of Li₃VO₄, is responsible for superior rate capability.     

Martensitic transformations and magnetic properties of nonstoichiometric alloys of the Ni-Mn-In system

Martensitic transformations and magnetic properties of Ni_89-x Mn _x In₁₁ (42 ≤ x ≤ 44) alloys have been investigated. Critical temperatures of magnetic and structural phase transitions in the studied alloy system have been determined. It has been shown that the martensitic transformation induced by the magnetic field is observed in all alloys. Temperature dependences of the spontaneous magnetization of austenite and martensite as well as the magnitude of the critical field, in which martensitic transformation occurs, have been determined.     

Thermal expansion of a Ni<Subscript>2.14</Subscript>Mn<Subscript>0.81</Subscript>Fe<Subscript>0.05</Subscript>Ga alloy in coarse-grained,submicron, and nanocrystalline states

The physical properties of a Ni_2.14Mn_0.81Fe_0.05Ga shape memory alloy in various structural states were studied using dilatometric data obtained in the region of first-order phase transitions.     

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.     

Magnetic properties of nonstoichiometric Ni<Subscript>2</Subscript>MnIn Heusler alloys

Results from studies of the crystal structure, resistivity, susceptibility, and magnetization of nonstoichiometric Ni₅₀Mn_{50 − x} In _x Heusler alloys are presented. Anomalous effects discovered in temperature dependences can be interpreted as the influence of the frustrated magnetic state exhibited by manganese moments in the martensitic phase. A field-induced phase transition to the austenitic phase was observed for several concentrations around room temperature.     

Improvement of electrochemical performance for AlF<Subscript>3</Subscript>-coated Li<Subscript>1.3</Subscript>Mn<Subscript>4/6</Subscript>Ni<Subscript>1/6</Subscript>Co<Subscript>1/6</Subscript>O<Subscript>2.40</Subscript> cathode materials for Li-ion batteries

Li-rich layered-layered-Spinel structure spherical Li_1.3Mn_4/6Ni_1/6Co_1/6O_2.40 particles was successfully prepared and coated with a uniform layer by a two-step co-precipitation method and evaluated in lithium cells. The structures and electrochemical properties of pristine Li_1.3Mn_4/6Ni_1/6Co_1/6O_2.40 and AlF₃-coated Li_1.3Mn_4/6Ni_1/6Co_1/6O_2.40 were characterized. When the coating amount was 2 wt%, the cathode showed the best cycling performance and rate capability compared to others. The AlF₃-coated Li_1.3Mn_4/6Ni_1/6Co_1/6O_2.40 Li-ion cell cathode had a capacity retention of 90.07 % after 50 cycles at 0.5 C over 2.0–4.8 V, while the pristine Li_1.3Mn_4/6Ni_1/6Co_1/6O_2.40 exhibited capacity retention of only 80.73 %. Moreover, the rate capability and cyclic performance also improved. Electrochemical impedance spectroscopy testing revealed that the improved electrochemical performance might attribute to the AlF₃ coating layer which can suppress the increase of impedance during the charging and discharging process by preventing direct contact between the highly delithiated active material and electrolyte.