Peculiarities of component interaction in {Gd, Er}-V-Sn Ternary systems at 870 K and crystal structure of RV6Sn6 stannides

The phase equilibria in the Gd-V-Sn and Er-V-Sn ternary systems were studied at 870 K by means of X-ray and metallographic analyses in the whole concentration range. Both Gd-V-Sn and Er-V-Sn systems are characterized by formation of one ternary compound at investigated temperature, with stoichiometry RV₆Sn₆ (SmMn₆Sn₆-type, space group P6/mmm, a = 0.55322(3) nm, c = 0.91949(7) nm for Gd, a = 0.55191(2) nm, c = 0.91869(8) nm for Er). Solubility of the third component in the binary compounds was not observed. Compounds with the SmMn₆Sn₆-type were also found with Dy, Ho, Tm, and Lu, while YV₆Sn₆ compound crystallizes in HfFe₆Ge₆ structure type. All investigated compounds are the first ternary stannides with rare earth elements and vanadium.     

The influence of chemical disorder enhancement on the martensitic transformation of the Ni50Mn36Sn14 Heusler-type alloy

The effect of chemical disorder over the martensitic phase transformation of the Ni₅₀Mn₃₆Sn₁₄ Heusler-type alloy was systematically investigated by performing X-ray diffractometry (DRX), DC magnetization and ⁵⁷Fe-doping and ¹¹⁹Sn-Mössbauer spectroscopy measurements. DRX patterns are characteristics of a L2₁-type chemically disordered structure, where the presence of this disorder was first evaluated by analyzing the relative intensity of the (1 1 1) DRX reflection, which varies in the case of Fe-doped and practically disappears for the milled samples. In consequence, the magnetic properties of Fe-doped well-milled samples related to the martensitic phase transformation change substantially. 300 K ⁵⁷Fe-Mössbauer spectroscopy data suggest that the changes in the magnetic properties related to the martensitic transformation are intrinsically correlated to the ferromagnetic and paramagnetic fractions, which are respectively associated with Fe atoms replacing Mn- and Sn-sites. In the case of milled samples, the drastic reduction of alloy magnetization was explained by the increase of the number of Mn atoms in the shell regions, which have a reduced magnetic moment comparatively to those in the grain cores. The magnetization change and the temperature transition in the martensitic transformation are governed by the grain core. The initial magnetic properties and martensitic transformation can be recovered by a subsequent annealing on the milled sample.     

Substitution effect on metal-insulator transition in Cu(Ir1−xMx)2S4 (M = Sn, Hf)

A spinel CuIr₂S₄ exhibits a temperature-induced metal-insulator (M-I) transition at around 226 K. Non-magnetic substitution effect on the M-I transition, T_M-I, in Cu(Ir_1−xM_x)₂S₄ (M = Sn, Hf) has been studied on the focus of the rather low composition region of x. Magnetic property of Cu(Ir_1−xM_x)₂S₄ (M = Sn, Hf) has been examined experimentally. The T_M-I decreases with increasing x and the temperature hysteresis becomes unclear within the experimental errors. The step anomaly in the magnetic susceptibility smears out and the T_M-I becomes ill defined around x = 0.20 in Cu(Ir_1−xSn_x)₂S₄, and x = 0.10 in Cu(Ir_1−xHf_x)₂S₄, respectively. These substitutions play an important role in decoupling the spin-dimerization of Ir⁴⁺-Ir⁴⁺ in CuIr₂S₄, and lead the destruction of the metal-insulator transition.     

Nanocrystalline Fe1−xCoxSn2 solid solutions prepared by reduction of salts in tetraethylene glycol

In an effort to improve the electrochemical performance of tin intermetallic phases as electrode active material for lithium-ion batteries, Fe_1−xCo_xSn₂ solid solutions with x = 0.0, 0.25, 0.3, 0.5, 0.6 and 0.8 were prepared by chemical reduction in tetraethylene glycol. Precise control of the synthesis conditions allowed single-phase nanocrystalline materials to be prepared, with particle diameters of about 20 nm and cubic, nanorods, and U-shaped morphologies. The substitution of iron by cobalt induced a contraction of the unit cell volume. The hyperfine parameters of the ⁵⁷Fe Mössbauer spectra were sensitive to the Co/Fe substitution and revealed a superparamagnetic behaviour. In lithium cells nanocrystalline Fe_1−xCo_xSn₂ active materials delivered reversible capacities above 500 mAh g⁻¹ that depended on the composition and cycling conditions. The intermediate compositions exhibit better electrochemical performance than the end compositions CoSn₂ and FeSn₂.     

Sequential interfacial intermetallic compound formation of Cu6Sn5 and Ni3Sn4 between Sn-Ag-Cu solder and ENEPIG substrate during a reflow process

The interfacial reactions between Sn-3.0 wt.% Ag-0.5 wt.% Cu solder and an electroless nickel-electroless palladium-immersion gold (ENEPIG) substrate were investigated. After initial reflowing, discontinuous polygonal-shape (Cu,Ni)₆Sn₅ intermetallic compounds (IMCs) formed at the interface. During reflowing for up to 60 min, the interfacial IMCs were sequentially changed in the following order: discontinuous (Cu,Ni)₆Sn₅, (Cu,Ni)₆Sn₅ and (Ni,Cu)₃Sn₄, and embedded (Cu,Ni)₆Sn₅ in (Ni,Cu)₃Sn₄. The interfacial product variation resulted from the preferential consumption of Cu atoms within the solder and continuous Ni diffusion from the Ni(P) layer.     

The studies of phase relation, microstructure, magnetic transition, magnetocaloric effect in (Gd1−xErx)5Si1.7Ge2.3 compounds

The phase relation, microstructure, Curie temperatures (T_C), magnetic transition, and magnetocaloric effect of (Gd_1−xEr_x)₅Si_1.7Ge_2.3 (x = 0, 0.05, 0.1, 0.15, and 0.2) compounds prepared by arc-melting and then annealing at 1523 K (3 h) using purity Gd (99.9 wt.%) are investigated. The results of XRD patterns and SEM show that the main phases in those samples are mono-clinic Gd₅Si₂Ge₂ type structure. With increase of Er content from x = 0 to 0.2, the values of magnetic transition temperatures (T_C) decrease linearly from 228.7 K to 135.3 K. But the (Gd_1−xEr_x)₅Si_1.7Ge_2.3 compounds display large magnetic entropy near their transition temperatures in a magnetic field of 0-2 T. The maximum magnetic entropy change in (Gd_1−xEr_x)₅Si_1.7Ge_2.3 compounds are 24.56, 14.56, 16.84, 14.20, and 13.22 J/kg K⁻¹ with x = 0, 0.05, 0.1, 0.15, and 0.2, respectively.     

Synthesis, structure, and high temperature Mössbauer and Raman spectroscopy studies of Ba1.6Sr1.4Fe2WO9 double perovskite

Ba_1.6Sr_1.4Fe₂WO₉ has been prepared in polycrystalline form by solid-state reaction method in air, and has been studied by X-ray powder diffraction method (XRPD), and high temperature Mössbauer and Raman spectroscopies. The crystal structure was resolved at room temperature by the Rietveld refinement method, and revealed that Ba_1.6Sr_1.4Fe₂WO₉ crystallizes in a tetragonal system, space group I4/m, with a = b = 5.6489(10)Å, c = 7.9833(2)Å and adopts a double perovskite-type A₃B′₂B″O₉ (A = Ba, Sr; B′ = Fe/W, and B″ = Fe/W) structure described by the crystallographic formula (Ba_1.07Sr_0.93)_4d(Fe_0.744W_0.256)_2a(Fe_0.585W_0.415)_2bO₆. The structure contains alternating [(Fe/W)_2aO₆] and [(Fe/W)_2bO₆] octahedra. Mössbauer studies reveal the presence of iron in the 3+ oxidation state. The high temperature Mössbauer measurements showed a magnetic to paramagnetic transition around 405 ± 10 K. The transition is gradual over the temperature interval. The decrease in isomer shift is in line with the general temperature dependence. While the isomer shift is rather linear over the whole temperature range, the quadratic dipolar ΔE temperature dependence shows an abrupt change at 405 K. The latter results allow concluding that a temperature-induced phase transition had occurred. The high temperature Raman study confirms the Mössbauer results on the magnetic to paramagnetic transition.     

Magnetic properties of the 1/1 approximant Ag42In42Gd16 to the icosahedral quasicrystal Ag-In-Gd

The structural, magnetic, and ¹⁵⁵Gd Mössbauer spectral properties of the 1/1 approximant Ag₄₂In₄₂Gd₁₆ to an icosahedral quasicrystal Ag-In-Gd are reported. Based on dc magnetic susceptibility measurements, it is shown that the studied compound develops no long-range magnetic order in the temperature range 1.8-300 K. The dc zero-field-cooled and field-cooled susceptibility data indicate that the 1/1 approximant Ag₄₂In₄₂Gd₁₆ is a spin glasss with freezing temperature T_f = 3.6(1) K. This is further confirmed by the analysis of the frequency dependence of T_f using the Vogel-Fulcher law and the dynamic scaling behavior near T_f. It is argued that the spin freezing process is a true equilibrium phase transition rather than a nonequilibrium phenomenon. The large frustration parameter of the studied compound indicates that it belongs to a category of strongly geometrically frustrated magnets. The ¹⁵⁵Gd Mössbauer spectra of the 1/1 approximant Ag₄₂In₄₂Gd₁₆ confirm that the Gd spins are frozen at 1.5 K and are fluctuating at 4.6 K. The Debye temperature of the 1/1 approximant Ag₄₂In₄₂Gd₁₆ is 200(1) K.     

A neutron diffraction study of the hexagonal pseudo-ternary compounds ErMn6−xFexSn6 (x = 0.2, 0.4, 0.6, 0.8, 1.0, 2.0, 3.0, 4.0)

The hexagonal ErMn_6−xFe_xSn₆ solid solution (0.2 < x < 4) has been studied by magnetisation measurements and neutron diffraction. The ordering temperature of the T = (Mn,Fe) sublattice almost continuously increases from T = 386 K for x = 0.2 to T = 498 K for x = 4. The T sublattice orders in the successive magnetic structures helimagnetic H1, antiferromagnetic AF2, helimagnetic H2 and antiferromagnetic AF1 with increasing iron content. While structures AF2 and H1 were already observed in ternary Mn compounds and AF1 in ternary iron compounds, the structure H2 is of a new kind characterized by an AF slab around the Er(1a) site. At low temperature, a change of the easy direction of the Er moment from easy plane to easy axis is observed. The iron-rich compounds display a ferromagnetic order of the Er sublattice. A new kind of magnetic structure characterized by a sine-wave modulated arrangement with a propagating vector Q = (0, 0, q_z) is also observed. The evolution of the magnetic properties (enhancement of the AF character of the (Mn,Fe) sublattice and magnetocrystalline anisotropy of erbium) is discussed.     

Magnetic entropy changes at early stages of nanocrystallization in amorphous Fe90Zr7B3 ribbons

Microstructure, revealed by transmission electron microscopy and conventional Mössbauer spectroscopy, magnetization versus magnetizing field induction and temperature and isothermal magnetic entropy changes in the as-quenched and subjected to annealing at T_a1 = 723 K for 2 or 3 h and at T_a2 = 743 K for 2.5 h of Fe₉₀Zr₇B₃ amorphous alloy are studied. In the as-quenched state the medium range ordered regions are observed. The annealing at T_a1 leads to early stages of crystallization and nanograins with different diameter embedded in amorphous matrix are formed. At the Curie point of the amorphous phase they are magnetically decoupled and behave like superparamagnetic particles. The Curie point of the residual amorphous phase shifts towards higher temperature as compared to the as-quenched state due to the Invar like effect. The peak of the isothermal magnetic entropy changes appears at the Curie temperature of the main amorphous phase. Their values at the maximum applied field of 0.75 T equals to 0.32 J/kg K⁻¹ in the as-quenched alloy and remain almost unchanged after early stages of nanocrystallization. After the annealing at T_a2 the peak of the entropy changes distinctly decreases. Such behavior is ascribed to the biphasic character of the sample. The main amorphous phase and ordered one, which in some circumstances can be treated as an assembly of superparamagnetic particles, contribute to the total magnetic entropy changes.     

Cu6Sn5和Ni3Sn4结构性能的第一原理计算

基于密度泛函理论的第一原理,计算了锡基无铅焊点界面常见的金属间化合物Cu6Sn5和Ni3Sn4的平衡晶格常数、合金形成焓以及弹性常数,分析了结构稳定的电子机制.结果表明,Cu6Sn5较Ni3Sn4合金形成能负,因此Cu6Sn5在热力学上更稳定,其合金化能力也较强.在力学性能方面,两相均属脆性相,表现出弹性各向异性,而Ni3Sn4的键合作用较强,弹性模量、剪切模量均大于Cu6Sn5,但Cu6Sn5表现出更好的塑性.从电子结构的角度,Cu6Sn5的成键主要来自于Cu原子d,p轨道与Sn原子p杂化,而Ni原子d轨道与Sn原子p轨道的强烈杂化作用是Ni3Sn4成键的主要原因.     

Physical properties of Gd7NiPd2 single crystal

Investigations of X-ray diffraction, electronic structure, dc-magnetization M(T), ac-magnetic susceptibility χ_ac(T) and magnetocaloric properties for the Gd₇NiPd₂ single crystal were performed. A single crystal of Gd₇NiPd₂ was grown by the Czochralski method from a levitating melt. Anomalies in χ_ac(T) and M(T)-curves establish that Gd₇NiPd₂ undergoes a long-range ferromagnetic-type ordering at T_C = 298 K, followed by a spin-reorientation below 135 K. The magnetization data indicate that there is an excess magnetic moment calculated per Gd³⁺ ions. The measured XPS valence band indicates the hybridization effect between Gd 5d, Ni 3d and Pd 4d states. The calculated values of entropy change ΔSm for the examined compound amount to −6.85 J/K kg for the a-axis and −6.49 for the c-axis at 7 T.     

Room temperature crystallization kinetics of amorphous Cu6Sn5 + C alloys

Thin film combinatorial sputter deposited Cu₆Sn₅ + C alloys were prepared and found to be amorphous and/or nanostructured upon removal from the sample preparation chamber. Samples having approximate compositions (Cu₆Sn₅)_1−xC_x with 0.16 < x < 0.26 have been stored at room temperature and investigated over the course of about one year using X-ray diffraction (XRD). Simple models were employed to analyze the observed changes in the XRD patterns. Relatively sharp (nanocrystalline) components having Bragg angles corresponding to hexagonal Cu₆Sn₅ grew in intensity at the expense of broader (amorphous) components as a function of time. The grain size of the nanocrystalline components was approximately time independent, but depended on the amount of carbon present. The logarithm of the recrystallization time and the activation energy for crystallization appeared to be linearly dependent on the carbon content for the composition range that has been studied, as inferred from the Avrami-Johnson-Mehl equation. XRD patterns of samples with x > 0.26 appear to be relatively unchanged after a period of storage at room temperature for one year.     

Large magnetocaloric effect in re-entrant ferromagnet PrMn1.4Fe0.6Ge2

Magnetocaloric effects (MCE) at multiple magnetic phase transition temperatures in PrMn_1.4Fe_0.6Ge₂ were investigated by heat capacity and magnetization measurements. PrMn_1.4Fe_0.6Ge₂ is of a re-entrant ferromagnet and performs multiple magnetic phase transitions in the temperature range from 5 to 340 K. A large magnetic entropy change (−ΔS_M) 8.2 J/kg K and adiabatic temperature change (ΔT_ad) 4.8 K are observed for a field change of 0-1.5 T around 25.5 K, associated with the field-induced first order magnetic phase transition (FOMT) from the antiferromagnetic to the ferromagnetic state with an additional Pr magnetic contribution. These results suggest that a re-entrant ferromagnet is probably promising candidate as working material in the hydrogen and nature gas liquefaction temperature range magnetic refrigeration technology.     

Enhancement microwave dielectric properties of La(Mg0.5Sn0.5)O3 ceramics by substituting Mg with Ni

The microwave dielectric properties of La(Mg_0.5−xNi_xSn_0.5)O₃ ceramics were examined with a view to their exploitation for mobile communication. The La(Mg_0.5−xNi_xSn_0.5)O₃ ceramics were prepared by the conventional solid-state method at various sintering temperatures. The X-ray diffraction patterns of the La(Mg_0.4Ni_0.1Sn_0.5)O₃ ceramics revealed no significant variation of phase with sintering temperatures. Apparent density of 6.71 g/cm³, dielectric constant (?_r) of 20.19, quality factor (Q × f) of 74,600 GHz, and temperature coefficient of resonant frequency (τ_f) of −85 ppm/°C were obtained for La(Mg_0.4Ni_0.1Sn_0.5)O₃ ceramics that were sintered at 1550 °C for 4 h.     

Crystal structures and magnetic properties of iron (III)-based phosphates: Na4NiFe(PO4)3 and Na2Ni2Fe(PO4)3

Crystal structures from two new phosphates Na₄NiFe(PO₄)₃ (I) and Na₂Ni₂Fe(PO₄)₃ (II) have been determined by single crystal X-ray diffraction analysis. Compound (I) crystallizes in a rhombohedral system (S. G: R-3c, Z = 6, a = 8.7350(9) Å, c = 21.643(4) Å, R₁ = 0.041, wR₂=0.120). Compound (II) crystallizes in a monoclinic system (S. G: C2/c, Z = 4, a = 11.729(7) Å, b = 12.433(5) Å, c = 6.431(2) Å, β = 113.66(4)°, R₁ = 0.043, wR₂=0.111). The three-dimensional structure of (I) is closely related to the Nasicon structural type, consisting of corner sharing [(Ni/Fe)O₆] octahedra and [PO₄] tetrahedra forming [NiFe(PO₄)₃]⁴⁺ units which align in chains along the c-axis. The Na⁺ cations fill up trigonal antiprismatic sites within these chains. The crystal structure of (II) belongs to the alluaudite type. Its open framework results from [Ni₂O₁₀] units of edge-sharing [NiO₆] octahedra, which alternate with [FeO₆] octahedra that form infinite chains. Coordination of these chains yields two distinct tunnels in which site Na⁺.The magnetization data of compound (I) reveal antiferromagnetic (AFM) interactions by the onset of deviations from a Curie-Weiss behaviour at low temperature as confirmed by Mössbauer measurements performed at 4.2 K. The corresponding temperature dependence of the reciprocal susceptibility χ⁻¹ follows a typical Curie-Weiss behaviour for T > 105 K. A canted AFM state is proposed for compound (II) below 46 K with a field-induced magnetic transition at H ≈ 19 kOe, revealed in the hysteresis loop measured at 5 K. This transition is most probably associated with a spin-flop transition.     

Hydrothermal synthesis and photoluminescence of Ce and Tb doped La2Sn2O7 nanocrystals

Phase-pure Ce-/Tb-doped and co-doped lanthanum stannates (La₂Sn₂O₇) nanocrystals were synthesized by a co-precipitation process combined with hydrothermal techniques without any further heat treatment. The crystal structure, particle size, morphologies, and photoluminescence properties of the as-synthesized products were investigated by X-ray powder diffraction (XRD), transmission electron microscopy (TEM), and photoluminescence spectroscopy (PL). The as-prepared samples were single-phase cubic pyrochlore-type nanocrystals with a typical size of 10-20 nm. PL spectra showed a dominating green-emitting line around 544 nm attributing to ⁵D₄-⁷F₅ magnetic dipole transition for Tb³⁺ doped and Ce³⁺/Tb³⁺ co-doped La₂Sn₂O₇ nanocrystals. Meanwhile, the concentration quenching phenomenon was observed in both La_2−xTb_xSn₂O₇ and La_1.82−xCe_xTb_0.18Sn₂O₇ nanocrystals. Furthermore, an interesting enhancement of the energy transfer induced green emission was observed in the as-synthesized La_1.82−xCe_xTb_0.18Sn₂O₇ nanocrystals.     

Organoheterobimetallic cyanodithioimidocarbonates and their I2-doped products: Synthesis,characterization and conducting properties

Complexes of the type [PhHg]₂[M(cdc)₂], [Me₂Sn][M(cdc)₂], [n-Bu₂Sn][M(cdc)₂], [n-Bu₃Sn]₂[M(cdc)₂] and [Ph₃Sn]₂[M(cdc)₂] (M = Ni(II) and Cu(II); cdc²⁻ = cyanodithioimidocarbonate) and their I₂-doped products have been prepared and characterized by microanalysis, magnetic and solution as well as solid phase conductivity measurements, IR, Raman, electronic, ¹H and ¹³C NMR and ESR spectroscopic techniques. ESR silent diamagnetic compounds [PhHg]₂[Cu(cdc)₂], [Me₂Sn][Cu(cdc)₂], [n-Bu₂Sn][Cu(cdc)₂], [n-Bu₃Sn]₂[Cu(cdc)₂] and [Ph₃Sn]₂[Cu(cdc)₂] are strongly antiferromagnetically coupled. [PhHg]₂[Ni(cdc)₂] is weakly paramagnetic because of the weak axial interactions of sulfur atoms of the ligand cdc²⁻ with some of the Ni(II) centers. Sharp ¹H NMR signals suggest that [PhHg]₂[Cu(cdc)₂], [n-Bu₂Sn][Cu(cdc)₂], [n-Bu₃Sn]₂[Cu(cdc)₂] and [Ph₃Sn]₂[Cu(cdc)₂] remained diamagnetic in solution as well. Majority of the complexes exhibited σ_rt in the range of 10⁻¹¹ to 10⁻¹⁰ S cm⁻¹ while the I₂-doped products show enhanced conductivity in the 10⁻¹⁰ to 10⁻⁶ S cm⁻¹ range and exhibit semiconducting behaviour.     

Effect of CaTiO3 addition on microwave dielectric properties of Mg2(Ti0.95Sn0.05)O4 ceramics

The microwave dielectric properties of CaTiO₃-added Mg₂(Ti_0.95Sn_0.05)O₄ ceramics prepared by the mixed oxide route have been investigated. The combination of spinel-structured Mg₂(Ti_0.95Sn_0.05)O₄ and perovskite-structured CaTiO₃ forms a two-phase system (1 − x)Mg₂(Ti_0.95Sn_0.05)O₄-xCaTiO₃, which was confirmed by the XRD patterns and the EDX analysis and it also leads to a zero τ_f. The microwave dielectric properties of the ceramics can be effectively controlled by varying the x value. For practical applications, a new microwave dielectric material 0.91Mg₂(Ti_0.95Sn_0.05)O₄-0.09CaTiO₃ is suggested and it possesses a good combination of dielectric properties with an ?_r of ∼18.01, a Q × f of ∼92,000 GHz, and a τ_f of ∼0 ppm/°C, which makes it is a very promising candidate material for high frequency applications.