Series Of Intermetallic Compounds Research Articles

Unusual superconductivity in crystallographically disordered RT2−xSn2 compounds

The discovery of new superconducting materials represents a complementary and crucial tile to shed light on the mechanism controlling the phenomenon of superconductivity. During the search for new superconducting materials, we discovered a new series of intermetallic compounds with the general composition RZn2−xSn2 (R = La, Ce, Pr, Nd). Their formation and crystal structure have been investigated. The Zn content decreases along the series from ≈ 1.50 in LaZn1.50(1)Sn1.98(2) to ≈ 1.32 in NdZn1.321(8)Sn2.01(2), due to the partial occupation of one of the two Zn sites [the Zn1 (2c) site, which from ≈ 50% in the La compound drops to ≈ 42%, ≈ 37% and ≈ 32% in the Ce, Pr and Nd compounds, respectively]. Both the Zn occupation factor and unit cell volume follow the lanthanide contraction. No such compound has been observed with Sm. AC and DC magnetic susceptibility and transport measurements revealed LaZn1.5Sn2 to undergo a sharp superconducting transition at Tc = 5.5 K. In order to search for further possible superconductive homologues, the lanthanum substituted phases La(Zn,T)2–xSn2 (T = Ti, Mn, Fe, Co, Ni, Cu, Pd, Ag, Pt, Au, Cd; x ≈ 0.5) were also prepared. The crystal structure of the ternary compounds is a disordered defective derivative of the tetragonal CaBe2Ge2-type (tP10, P4/nmm), with a partially occupied Zn Wyckoff site and a disordered Sn position. Three related isostructural series, corresponding to three new prototypes, have been identified; they all contain conventional checkered pyramidal layers characteristic of the archetype. The magnetic and transport properties have been measured for some of these substituted quaternary La compounds and we found that superconductivity is preserved in them but in the orthorhombic compounds or when T was a magnetic transition metal (e.g., Ni or Mn). A slight decrease in Tc down to about 4.0 K was detected as a result of the Zn by T atomic substitution.

Effects of different binder systems on the reaction mechanism, microstructure and mechanical properties of PcBN composites

In this paper, PcBN composites were prepared with cBN, Al and Ti micropowders under high temperature and ultra-high pressure. The phase and microstructure of PcBN were analyzed, and the possible reactions in different systems were deduced. The synthesis process of PcBN under high pressure (5.5 GPa) and different temperature (950–1550 °C), and the influence of sintering temperature on the hardness and flexural strength of PcBN were studied. The results show that cBN in cBN-Al and cBN-Ti systems has reacted with Al and Ti respectively at 950 °C. In the cBN-Al-Ti system, cBN does not react with Al and Ti alone, but Al and Ti react to form a series of intermetallic compounds. With the increase of temperature, the type and mass of phase change constantly, and tend to be stable at 1350 °C. The binder has an obvious chemical reaction at the edge of the cBN particle, and the new phase is generated to firmly bond the internal particles together. The mechanical properties of PcBN sintered by cBN-Al-Ti system are the best.

Phase Control of Co-Sn Alloys through Direct Electro-Deoxidation of Co3O4/SnO2 in LiCl-KCl Molten Salt

Co can form a series of intermetallic compounds with Sn which usually exhibit unique physical and chemical properties. However, it is a challenge to control the phase composition of Co-Sn alloys. Here, we attempted to prepare Co3Sn2, CoSn and CoSn2 from the mixture of Co3O4/SnO2 using electro-deoxidation. We investigated the effects of sintering temperature for the mixed oxide plate and electrolysis conditions, such as voltage, electrolysis time, and molten salt temperature on the electro-deoxidation process of Co3O4/SnO2. The electrochemical deoxidation mechanisms of Co3O4, SnO2, and Co3O4/SnO2 composites were also explored by cyclic voltammetry using metallic cavity electrode. The Co-Sn alloys with different phase compositions, such as Co3Sn2, CoSn, and CoSn2, were obtained through controlling the molar ratio between Co and Sn in the initial Co3O4/SnO2 plate and the molten salt temperature. The obtained Co-Sn alloys were used as anode materials for lithium-ion batteries which showed 123.0, 246.5, and 323.4 mAh g−1 for Co3Sn2, CoSn, and CoSn2, respectively.

Mixing Enthalpies of Sr–Sb Melts

The mixing enthalpies of Sr–Sb melts were measured by isoperibolic calorimetry at 1230 K over the entire composition range referred to the liquid components. Large exothermic mixing effects were found (∆Hmin = –70.1 ± 4.8 kJ/mole). They were indicative of very strong interaction between the components and agreed with the Sr–Sb phase diagram. A series of intermetallic compounds, SrSb, SrSb3, Sr3Sb2, and Sr2Sb, was found in the system. Minimum ∆H for the liquid alloys corresponds to the composition range where SrSb and Sr3Sb2 phases exist. The mixing enthalpies were found to be less exothermic than those for the intermetallic phases. This finding agrees with data for the alloys in systems with strong interaction between the components and is indicative of short-range ordering in liquid state. The mixing enthalpies for Mg (Ca, Sr)–Sb melts decrease in the Mg–Sb → Ca–Sb → Sr–Sb series, which agrees with increasing differences in the electronegativity of the components.

A magnetic study of the HoCo12-xFexB6 ferrimagnetic compounds

The effects of Fe substitution on the structural and magnetic properties of the HoCo12-xFexB6 (0 ≤ x ≤ 2) series of intermetallic compounds have been studied. All of the compounds form in the rhombohedral SrNi12B6-type structure, the lattice constants increasing linearly with x. These compounds are ferrimagnets with a small transition metal magnetic moment and exhibit a spin reorientation transition. The Curie temperature decreases from 147 K for x = 0–105 K for x = 2. The Fe for Co substitution leads also to a progressive decrease of the spontaneous magnetization. The spin reorientation transition temperature is significantly reduced upon Fe for Co substitution whereas the compensation temperature is much less sensitive to the Fe composition.

Magnetic structure and magnetoelastic coupling of GdNiSi3 and TbNiSi3

The series of intermetallic compounds $R$NiSi$_3$ ($R$ = rare earth) shows interesting magnetic properties evolving with $R$ and metamagnetic transitions under applied magnetic field for some of the compounds. The microscopic magnetic structures must be determined to rationalize such rich behavior. Here, resonant x-ray magnetic diffraction experiments are performed on single crystals of GdNiSi$_{3}$ and TbNiSi$_{3}$ at zero field. The primitive magnetic unit cell matches the chemical cell below the N\'eel temperatures $T_{N}$ = 22.2 and 33.2 K, respectively. The magnetic structure is determined to be the same for both compounds (magnetic space group $Cmmm'$). It features ferromagnetic {\it ac} planes that are stacked in an antiferromagnetic $+-+-$ pattern, with the rare-earth magnetic moments pointing along the $\vec{a}$ direction, which contrasts with the $+--+$ stacking and moment direction along the $\vec{b}$ axis previously reported for YbNiSi$_3$. This indicates a sign reversal of the coupling constant between second-neighbor $R$ planes as $R$ is varied from Gd and Tb to Yb. The long {\it b} lattice parameter of GdNiSi$_{3}$ and TbNiSi$_{3}$ shows a magnetoelastic expansion upon cooling below $T_N$, pointing to the conclusion that the $+-+-$ stacking is stabilized under lattice expansion. A competition between distinct magnetic stacking patterns with similar exchange energies tuned by the size of $R$ sets the stage for the magnetic ground state instability observed along this series.

Magnetic Properties of the RAuBi2 (R = Ce, Pr, Nd, Gd, Sm) Series of Intermetallic Compounds

In this work we report the physical properties of the series of intermetallic compounds RAuBi2 (R = Ce, Pr, Nd, Gd, Sm) studied by means of x-ray powder diffraction, magnetic susceptibility, heat capacity and electrical resistivity measurements. These compounds were grown using the metallic Bi self-flux technique and they crystallize in a tetragonal ZrCuSi2 (P4/nmm) structure. Our RAuBi2 single crystals show an antiferromagnetic ordering TN ≥ 2.3K for all measured compounds. The values of TN show a dramatic breakdown of the De Gennes factor along this series.

Preparation of hydrides of intermetallic compounds

Interaction of a series of intermetallic compounds with ammonia at 100–250°C and 1.5 MPa in the presence of promoter NH4Cl was studied. The optimal conditions of preparations of hydride phases have been determined. Properties of hydronitrogenation products of intermetallic compounds have been compared with those of direct hydrogenation products.

Evolution of the magnetic properties along the RCuBi2 (R = Ce, Pr, Nd, Gd, Sm) series of intermetallic compounds

In this paper, the evolution of the magnetic properties along the series of intermetallic compounds RCuBi2 (R = Ce, Pr, Nd, Gd, Sm) is discussed. These compounds crystallize in a tetragonal ZrCuSi2 (P4/nmm) structure, and our single crystals of RCuBi2 grown from Bi-flux show no evidence for Cu-deficiency [Ye et al., Acta Crystallogr. C 52, 1325 (1996)] as previously reported for R = Ce. For R = Ce, Pr, Gd, and Sm, we found an antiferromagnetic ordering at TN ∼ 16 K, 4.2 K, 13.6 K, and 4.9 K, respectively. For R = Nd, we saw no evidence for a magnetic phase transition down to T = 2 K. These values of TN clearly show a dramatic breakdown of the De Gennes factor in this series. We discuss our data taken into account the tetragonal crystalline electrical field and the anisotropic Ruderman-Kittel-Kasuya-Yoshida magnetic interaction between the R-ions in this family of compounds.

ChemInform Abstract: Microstructures of Pt-Sn and Rh-Sn Particles on SiO2.

The effect of adding Sn to Pt and Rh particles on SiO{sub 2} is examined by transmission electron microscopy following heat treatments in H{sub 2} and O{sub 2} atmospheres. With both metals, after heating in H{sub 2}, no fcc metal is observed but rather a series of intermetallic compounds with multiple phases coexisting within most 20 to 200-{angstrom} particles. The surfaces of these particles are the Sn-rich MSn{sub 4} phases. When Pt-Sn is oxidized, the only phases observed are Pt metal and SnO{sub 2}. Dark field imaging shows that the SnO{sub 2} forms 10 to 30-{angstrom} crystals which surround the single-crystal Pt particles and are in contact with the SiO{sub 2}. When Rh-Sn is oxidized Rh, Rh{sub 2}O{sub 3}, and SnO{sub 2} are detected, but SnO{sub 2} forms before Rh{sub 2}O{sub 3}, and the presence of Sn retards the oxidation of Rh.

Observation of RKKY-Kondo Competition and Non-Fermi-Liquid Behavior in the Intermetallic Compound Series Ce(Cu1−x Ni x )Si2

We study Kondo-RKKY competition in the intermetallic compound series Ce(Cu1−xNix)Si2 (x=0, 0.2, 0.4, 0.6, 0.8, 1.0) by performing X-ray diffraction, electrical resistivity, magnetic susceptibility measurements and Ce-LIII-edge X-ray absorption spectra. The results reveal that RKKY interaction dominates and leads to spin-glass behavior at the Cu rich end. For the Ni rich end the Kondo effect prevails and drives the system towards an intermediate-valence regime with nearly quenched magnetism. According to the experimental result, we are able to obtain a phase diagram similar to Theumann’s theoretical model. This work also observed non-Fermi-liquid behavior from the ρ(T) and χ(T) measurements at x=0.6, indicating this series to lie in the vicinity of a quantum critical point at this content.

USING NEUTRON DIFFRACTION AND MÖSSBAUER SPECTROSCOPY TO STUDY MAGNETIC ORDERING IN THE R3T4Sn4 FAMILY OF COMPOUNDS

We review the complementary roles that 119Sn Mössbauer spectroscopy and neutron diffraction are playing in developing a complete description of magnetic ordering in the R 3 Cu 4 Sn 4 and R 3 Ag 4 Sn 4 intermetallic compound series. We show that the two techniques yield consistent pictures of the order, and in many cases both are essential to obtaining a complete description. The recent neutron diffraction work on Sm 3 Cu 4 Sn 4, Sm 3 Ag 4 Sn 4 and Gd 3 Ag 4 Sn 4 is highlighted.

Evolution of the magnetic properties and magnetic structures along the RmMIn3m+2 (R=Ce, Nd, Gd, Tb; M=Rh, Ir; and m=1,2) series of intermetallic compounds

We discuss the evolution of the magnetic properties and magnetic structures along the series of intermetallic compounds RmMIn3m+2 (R=Ce, Nd, Gd, Tb; M=Rh, Ir; and m=1,2). The m=1,2 are, respectively, the single layer and bilayer tetragonal derivatives of their cubic RIn3 relatives. Using a mean field model including an isotropic first-neighbors Ruderman-Kittel-Kasuya-Yoshida interaction (K) and the tetragonal crystalline electrical field (CEF), we demonstrated that, for realistic values of K and CEF parameters, one can qualitatively describe the direction of the ordered moments and the behavior of the ordering temperature for these series. The particular case, where the rare-earth ordered moments lie in the ab plane or are tilted from the c axis and TN can be reduced by tuning the CEF parameters, revealed an interesting kind of frustration that may be relevant to the physical properties of complex classes of materials such as the RmMIn3m+2 (M=Rh, Ir, and Co; m=1,2) heavy-fermion superconductors.

Structure and magnetic properties of Gd 4(Co,Ti) 41 alloys

Series of intermetallic compounds are usually obtained by the general formula R m− n T 5 m+2 n , i.e., taking m RT 5 unit cells and replacing n R atoms by T–T pairs. The combination ( m, n) = (7,3) which corresponds to R 4T 41 has not been reported yet. In this work we have investigated the possibility to synthesize the Gd 4Co 41− x Ti x compounds by annealing the stoichiometric as-cast samples in the temperature interval of 1133–1438 K. The Gd 4Co 39Ti 2 alloy annealed at 1133 K crystallizes into the disordered TbCu 7-type structure. The saturation magnetization M s of this sample is 77.3 Am 2/kg at room temperature and the alloy exhibits uniaxial anisotropy. The Gd 4Co 39Ti 2 alloy annealed at 1438 K crystallizes into the disordered Th 2Ni 17-type hexagonal phase (2:17H) with cell parameters a = 8.350(1) and c = 8.224(1) Å.

RZnSn (R: Rare Earth): A Novel Series of Intermetallic Compounds with the YPtAs Structure Type.

AbstractFor Abstract see ChemInform Abstract in Full Text.

4f-Ligand dehybridization in the intermetallic compound series CeNi 2(Sn xSi 1− x) 2

Structural, transport, magnetic, and thermal measurements, as well as Ce–L III spectroscopy were employed in this work in order to examine the 4f-ligand dehybridization in the series CeNi 2(Sn x Si 1− x ) 2 ( x=0, 0.2, 0.4, 0.6, 0.8, and 1.0). The results revealed that CeNi 2Si 2 is a typical intermediate-valence (IV) compound with strong s–f hybridization, while CeNi 2Sn 2 is a Kondo-lattice compound with a low Néel temperature T N∼1.9 K. With increasing x, the decrease of s–f hybridization will drive the series away from an IV regime toward a magnetically ordered state. From the results, the evolution arises from competitions between s–f hybridization, the Kondo scattering, and the RKKY interaction, as well as the crystal-field effect.

Evolution from intermediate-valence to antiferromagnetic Kondo-lattice behavior in CeNi(Ge xSi 1− x) 2

A cerium-based intermetallic compound series CeNi(Ge x Si 1− x ) 2 ( x=0, 0.2, 0.4, 0.5, 0.6, 0.8, 1.0) were synthesized. Among the compounds, CeNiSi 2 is an intermediate-valence compound, while CeNiGe 2 is a Kondo-lattice with a two-step antiferromagnetic phase transition. In this work, X-ray powder diffraction, transport, magnetic and thermal measurements, as well as Ce-L III spectroscopy are presented in order to study the crossover from non-magnetic intermediate-valance regime to antiferromagnetic Kondo-lattice regime in the CeNi(Ge x Si 1− x ) 2 series. Increasing Ge concentration will depress the hybridization between 4f electrons and conducting electrons and enhance the RKKY interaction, which eventually drive the system to a magnetically ordered state.

RZnSn (R = rare earth): a novel series of intermetallic compounds with the YPtAs structure type

We report on the synthesis and crystal structure of the new family of rare earth ternary equiatomic RZnSn compounds. The phases are found to form for R = La to Nd, Sm, Gd to Lu, Y, all belonging to the hexagonal hP12-P6 3/mmc YPtAs structure type. The lattice parameters, as obtained by the Guinier method on polycrystalline samples, vary regularly from La [ a = 4.588(1), c = 17.044(2) Å] to Lu [ a = 4.439(1), c = 15.415(1) Å]. The crystal structure was refined for the Gd and Y compounds using single crystal data, and for the La, Ce, Pr, Nd and Sm compounds by means of the Rietveld method.

Theoretical studies on cerium nickel aluminides: polar intermetallics with heavy fermion behavior

The electronic structures of Ce 4Ni 6Al 23, CeNiAl 4, CeNi 2Al 5, CeNiAl and CeNi 4Al have been calculated using the TB-LMTO-ASA (tight-binding, linear muffin-tin orbital, atomic-spheres approximation) approach to probe relationships between chemical bonding and physical properties in this series of intermetallic compounds. Analysis from crystal orbital Hamilton populations (COHP) reveal that the Al-rich compounds may be considered as “polar intermetallic” because the Fermi level coincides to the separation of bonding and antibonding states of the Ni–Al framework. On the other hand, although the densities of states (DOS) of CeNiAl suggest “polar intermetallic” behavior, the bonding is more complex. Finally, the Ni-rich example, CeNi 4Al, has significant Ni-3 d character at the Fermi level. The results of these calculations are also discussed in connection with heavy fermion or possible valence fluctuation behavior observed for some of these intermetallic compounds: those showing exceptional properties also exhibit significant “lattice covalency” between Ce and the Ni–Al nets.

Magnetic properties of R 3Cu 4X 4 (R=Gd–Er; X=Ge, Sn) compounds

In this work, the results of magnetic and neutron-diffraction studies of a new series of intermetallic compounds R 3Cu 4X 4 (R=Gd–Er; X=Ge, Sn) are presented. The X-ray and neutron-diffraction data indicate that these compounds crystallise in the orthorhombic Gd 3Cu 4Ge 4-type structure (space group Immm). In this structure, the rare-earth atoms occupy two non-equivalent crystallographic positions: 2d and 4e. The magnetometric and neutron diffraction measurements indicate that the R 3Cu 4X 4 (R=Gd–Er; X=Ge, Sn) compounds are antiferromagnets with Néel temperatures between 23 K for Tb 3Cu 4Ge 4 and 5.9 K for Er 3Cu 4Sn 4. For Tb 3Cu 4Ge 4, Er 3Cu 4Ge 4 and Er 3Cu 4Sn 4, additional phase transitions are observed below the Néel temperature. The neutron-diffraction data indicate that the magnetic moments are localised only on the rare earth atoms. The moments located at different crystallographic sites have different values and order at different temperatures.