Equiatomic Compounds Research Articles

Multifunctional behavior of Fe-doped MnNiGe magnetic equiatomic compound

The exchange bias (HE=∼90 Oe for Hcool=5kOe at 5K) and magnetocaloric effect (1.55J/kg-K for 0–50kOe at 5K) of the new class of ferromagnetic shape memory alloy of nominal composition Mn0.75Fe0.25NiGe have been investigated. The sample can be thought of being derived from the parent MnNiGe alloy, where Fe was doped at the expense of Mn atom. Fe doping at Mn site brings down the martensitic transition temperature below room temperature and induces ferromagnetism in it. The presence of antiferromagnetic (AFM) clusters, due to doping disorder, in otherwise ferromagnetic (FM) compound, plays pivotal role towards the observation of multifunctionality of the studied alloy.

Magnetic and Related Properties of Ternary TmTX Intermetallics

Since many years, rare earth intermetallics R T X, where R = rare earth, T = d-electron and X = p-electron elements, have been a subject of extensive studies due to their intriguing magnetic and electrical properties [1, 2]. Amidst plentitude of such phases with various chemical compositions and stoichiometries, a series of equiatomic compounds RTX received special attention due to simplicity of their crystal structure and large span in their physical behaviors [3]. While much information is available in the literature for the RTX intermetallics with R = Ce Er, relatively little is known on their counterparts with R = Tm. Most recently, we reported on the magnetic properties of TmRhGe and TmRhGa, which were found to order antiferromagnetically below 6.0 K [4] and 3.9 K [5], respectively. Similarly, we established before antiferromagnetic ordering in TmNiIn, TmPtIn and TmAgGe to set at TN = 2.5 [6], 3.4 [7] and 4.2 K [8], respectively. Here, we give the rst account on our on-going studies on a few other Tm-based equiatomic materials, namely TmPdIn, TmAgSn, TmAuGe and TmRuGe. The experimental results are compared with the data previously obtained for the compounds TmNiIn, TmPtIn and TmAgGe.

Electrons per atom ratio determination and Hume-Rothery electron concentration rule for P-based polar compounds studied by FLAPW-fourier calculations.

The extent to which reliable electrons per atom ratio, e/a, are determined and the validity of the Hume-Rothery stabilization mechanism are ensured upon increasing ionicity are studied by applying first-principles full potential linearized augmented plane wave (FLAPW)-Fourier band calculations to as many as 59 binary compounds formed by adding elements from periods 2-6 to phosphorus in group 15 of the Periodic Table. Van Arkel-Ketelaar triangle maps were constructed both by using the Allen electronegativity data and by using an energy difference between the center-of-gravity energies of FLAPW-derived s and p partial densities of states (DOSs) for the equiatomic compounds studied. The determination of e/a and the test of the interference condition, both of which play a key role in the Hume-Rothery stabilization mechanism, were reliably made for all intermetallic compounds, as long as the ionicity is less than 50%. In the A-P (A = Li, Na, K, Rb, and Cs) compounds with ionicity exceeding 50%, however, e/a determination becomes unstable, as reflected in its P concentration dependence. New Hume-Rothery electron concentration rules were theoretically found in two families of polar compounds: skutterudite compounds TMP(3), TMAs(3), and TMSb(3) (TM = Co, Ni, Rh, and Ir; cI32) with e/a = 4.34 and TM(3)P (TM = Cr, Mn, Fe, and Ni; tI32) with e/a = 2.20.

New Intermetallic Zinc Compounds with Ordering Variants of the KHg2 and LT-SrZn5 Type

The intermetallic zinc compounds CaAuZn, SrPdZn, SrPtZn, SrAuZn, BaPd1.57 Zn3.43, and BaAu1.41Zn3.59 were synthesized from the elements in sealed niobium ampoules in an induction furnace. The equiatomic compounds crystallize with the orthorhombic TiNiSi-type structure, space group Pnma. Single-crystal X-ray data exhibited small degrees of Au=Zn mixing within the three-dimensional [AuZn] networks and resulted in the compositions CaAu1.02Zn0.98 and SrAu1.03Zn0.97 for two investigated single crystals. BaPd1.57 Zn3.43 and BaAu1.41 Zn3.59 adopt partially ordered versions of the LT-SrZn5 type, space group Pnma. Both structures were refined on the basis of X-ray single-crystal diffractometer data. a=1331.13(6), b=531.45(3), c=682.20(4) pm, wR=0.0245, 1138 F2 values, 39 variables for BaPd1.57Zn3.43 and a=1344.35(2), b=537.47(2), c=691.22(4) pm, wR=0.0441, 931 F2 values, 37 refined variables for BaAu1.41Zn3.59. The transition metal and zinc atoms form a complex three-dimensional network of (T, Zn)4 tetrahedra which are condensed via common corners and T/Zn-T/Zn bonds. Large cavities within these networks are filled by the barium atoms which have coordination number 19, i. e. Ba@(T, Zn)17Ba2.

Semiempirical Investigation of the Indirect Exchange Interaction in a rem–IN System

The Ruderman–Kittel–Kasuya–Yosida (RKKY) exchange interaction is investigated for the first time in compounds of binary REM (rare-earth metal) – In systems (REМ = Gd, Tb, Dy, Ho, Er, or Тm) using experimental values of the paramagnetic Curie temperature (θp ) of these compounds. The prediction of the RKKY theory on the direct proportionality between θp and the de Gennes factor for equiatomic compounds of heavy REM with indium, similarly to pure REM, is confirmed. Values of the indirect exchange interaction parameter are estimated semiempirically for the examined compounds. As a whole, it is established that for the compounds of REM with indium, as for pure REM, the exchange interaction of RKKY type is characteristic.

A systematic solid state NMR spectroscopic study of the equiatomic lithium half-Heusler phases LiTX (T = Mg, Zn, Cd; X = P, As, Sb, Bi)

The equiatomic intermetallic lithium compounds Li TX ( T = Mg, Zn, Cd; X = P, As, Sb, Bi) were synthesized by reacting the elements in sealed niobium tubes in muffle furnaces. The compounds crystallize with the cubic MgAgAs type structure, space group F 4 ¯ 3 m . The T and X atoms build up blende-type tetrahedral substructures in which the lithium atoms fill octahedral voids formed by the X atoms. Basic structural characterization of the samples was performed by powder X-ray diffraction. The charge distribution in these intermetallic compounds was investigated using metal ion ( 7 Li, 25 Mg and 113 Cd) as well as pnictogen ( 31 P, 75 As, 121 Sb) static and MAS-NMR. The metal ion chemical shifts are uniformly correlated with the pnictogen Pauling electronegativities, reflecting a systematic trend in the bonding characteristics in these phases. Furthermore, static temperature dependent 7 Li wideline NMR spectra show motional narrowing effects on the NMR timescale, indicating lithium ionic mobility. Activation energies estimated from these data decrease systematically with decreasing difference of the electronegativities between the elements Li and X and between the elements T and X . These result can be rationalized in terms of shallower Coulomb potential wells in those compounds with lower ionic character.

High Temperature Thermomechanical Properties of Titanium-Rhodium-based Alloys Containing Scandium

At high temperatures, the equiatomic binary compounds formed by Groups 4 and 8 transition metals are known to undergo martensitic transformation, which may be accompanied by a shape memory effect. Among these compounds, titanium-rhodium (TiRh) is of special interest not only because it undergoes two martensitic transformations at high temperature, for one of which the shape memory effect has been observed, but also because it demonstrates unusual shape recovery behaviour at temperatures higher than 400°C. The present work focuses upon the thermomechanical and mechanical properties of 50 at% rhodium-scandium-titanium ternary alloys where Ti is substituted by Sc. These alloys were investigated for the first time using electrical resistance, dilatometry and three-point bending techniques in the temperature range 20°C to 850°C. It was found that the sample with 0.1 at% Sc exhibited full shape restoration in the ranges of both martensitic transformations at ~340°C and ~750°C. Two-way shape recovery was also observed. A small temperature hysteresis, desirableforalloysused inactuator applications, is present in TiRh and Rh-Sc-Ti alloys. Both TiRh and Sc-containing alloys exhibit continuity of the deformation process on cooling and shape restoration on heating in a wide range of temperatures. This feature of both TiRh and Rh-Sc-Ti alloys implies the possibility of their application in different heat-regulating elements at temperature ranges from room temperature to 850°C.

Systematics and anomalies in formation and crystal structures of RScSb and R3Sc2Sb3 rare earth compounds

• New equiatomic RScSb compounds identified for R = La–Nd, Sm, Gd–Tm, Lu, and Y. • The RScSb compounds crystallize in two different crystal structures. • Lighter R (R = La–Nd, Sm) crystallize with the CeScSi-type (tetragonal tI 12, I 4/ mmm ). • Heavier R (R = Gd–Tm, Lu, Y) adopt the CeFeSi-type (tetragonal tP 6, P 4/ nmm ). • New R 3 Sc 2 Sb 3 phases identified for R = Gd–Tm, Lu, Y; β-Yb 5 Sb 3 -type (orth. oP 32, Pnma ). A systematic study of RScSb (R = rare earth) ternary alloys has been carried out by X-ray diffraction, optical and electron microscopy and microprobe analysis. As a result, the new equiatomic RScSb (R = La–Nd, Sm, Gd–Tm, Lu, Y) compounds have been identified. No formation of equiatomic 1:1:1 phases has been observed for Eu and Yb. It has been found the RScSb compounds crystallize in two different crystal structures. The phases formed by the lighter R (La–Nd, Sm) adopt the CeScSi-type (tetragonal tI 12, I 4/ mmm , an ordered variant of the La 2 Sb-type), while the ones containing the heavier R (R = Gd–Tm, Lu, Y) crystallize with the CeFeSi-type (tetragonal tP 6, P 4/ nmm , an ordered derivative of the Cu 2 Sb-type). The latter phases were expected to be dimorphic, thus suggesting they might be polymorphic having the CeScSi-type as the low-temperature form; however, no proof of this was found in the course of the present study. Besides the equiatomic compounds, the R 3 Sc 2 Sb 3 phases have also been identified. They form from Gd-Tm, Lu, included Y, and crystallize in the β-Yb 5 Sb 3 -type (orthorhombic oP 32, Pnma ). The observed lattice parameters , unit cell volume and volume contraction, for both the series of compounds, decrease on going from La to Lu following the lanthanide contraction trend. First principles calculations pinpoint that the differences in the electronic structure are directly related to the differences in the crystal structures of these compounds.

Prediction of the crystal structure types of equiatomic ternary silicides and germanides

New unsynthesized equiatomic ABX (A and B are various metals; X = Si or Ge) compounds are predicted, and their types of crystal structure are forecasted under standard conditions. Only the data on the properties of the elements—components of compounds are used for their prediction. The calculations are performed using a special-purpose software package of computer analysis of information intended for searching for regularities in databases on the properties of inorganic compounds, and this package is based on the methods of precedent pattern recognition. Computer analysis of the data on the well-known compounds shows that the functions that are most important for the classification of systems in the sign of formation or absence of equiatomic compounds are M(A) × M(B) and I(A) × I(X), where M is the Mendeleev-Pettifor number of element A or B and I is the thermal conductivity of element A or X. The parameters that most strongly separate compounds for crystal chemical classification are functions T(A) + T(B) (where T is the melting temperature of element A or B), I(A), M(A) × M(B), and I(A) × I(X).

Review on cerium intermetallic compounds: A bird's eye outlook through DFT

Cerium based intermetallic compounds exhibit a wealth of physical properties originating from the electronic states of Ce, i.e. diamagnetic Ce4+ ([Xe] 4f0), paramagnetic Ce3+ ([Xe] 4f1). Switching between the electronic states can be induced either chemically such as by inserting hydrogen, by substitutions (size effects) or physically by applying external pressure. The review exposes different classes of Ce intermetallic compounds whose properties are interpreted and/or predicted thanks to quantum computations in the framework of the density functional theoretical (DFT). Focus is broadly made on the family of the equiatomic cerium intermetallic compounds, namely ternary CeTX where T is a transition metal and X a p-element where the hydrogenation effects take a considerable place in changing the electronic configuration of Ce. Other stoichiometries of cerium intermetallic compounds with their physical properties are discussed subsequently in the later part of the review. Rather than presenting an exhaustive enumeration of stoichiometries, illustrative case studies are selected for each class of materials to provide, after presenting the experimental context, insights into original outcome from methods targeted at selective physical and chemical properties.

High Temperature Martensitic Transformation and Shape Memory Behavior in Hfir Intermetallic Compound

The present paper is dedicated to the first observation of the martensitic transformation (MT) and associated shape memory effect (SME) in HfIr equiatomic intermetallic compound. Differential scanning calorimetry allowed determining MT temperatures, which are above 700 K. It was also shown that MT taking place at such high temperatures is associated with SME measured in 3 point bending. MT temperatures and crystal structure changes in the homogeneity range of HfIr compound were also studied. SME behavior changes in the homogeneity range of HfIr compound are discussed

Unexpected Constrained Twin Hierarchy in Equiatomic Ru-Based High Temperature Shape Memory Alloy Martensite

Among the different systems for high temperature shape memory alloys (SMA’s), equiatomic RuNb and RuTa alloys demonstrate both shape memory effect (SME) and MT temperatures above 800°C. Equiatomic compounds undergo two successive martensitic transformations, β (B2) → β’ (tetragonal) → β’’ (monoclinic), whereas out of stoechiometry alloys exhibit a single transition from cubic to tetragonal. In the case of two successive martensitic transformations, we expect to have a finer microstructure of the second martensite because it is supposed to develop inside the smallest twin elements of the former one. In equiatomic Ru-based alloys, if the first martensitic transformation is “normal”, the second one gives different unexpected microstructures with, for instance, twins with a thickness which is larger than the smallest spacing between twin variants of the first martensite. In fact, the reason for this unexpected hierarchy of the twins size is that the second martensitic transformation takes place in special conditions: geometrically, elastically and crystallographically constrained.

Hydrogen storage nanocrystalline TiFe intermetallic compound: Synthesis by mechanical alloying and compacting

Abstract Equiatomic nanocrystalline TiFe intermetallic compound was synthesized from elementary metals by mechanical alloying in a planetary ball mill. Then the powder produced was compacted by cold pressing into bulk samples keeping the nanocrystalline structure. The hydrogen capacity of TiFe bulk samples was found to be of 1.4 wt.%. The absorption isotherm had a long plateau corresponding to pressures of 0.3–0.4 MPa at room temperature. The bulk samples demonstrated high durability after 20 absorption–desorption cycles.

Mechanochemical synthesis and hydrogen sorption properties of nanocrystalline TiFe

The equiatomic intermetallic compound TiFe has been prepared by elemental mechanochemical synthesis in a planetary ball mill from Fe and Ti powders. The structural and phase transformations during synthesis were followed using X-ray diffraction. The reaction of the synthesized compound with hydrogen was studied volumetrically. The results demonstrate that the hydrogen capacity of the mechanochemical TiFe is 1.2 wt % at 2.5 MPa. Its absorption isotherm has an extended plateau in the range 1.6–1.7 MPa at room temperature.

Magnetron Sputtering Applied in Shape Memory Alloys Preparation

Shape memory alloys (SMAs) thin films have attracted much attention in recent years as intelligent and functional materials because of their unique characteristics. The sputtering thin films have been attracted great interest as powerful actuators in microelectromechanical systems (MEMS) such as microvalves, microfluid pumps, and microgrippers. Amongst SMAs, the equiatomic TiNi compound is the most widely used. In this paper, TiNi films prepared by magnetron sputtering are reviewed. The influence of parameters including thickness, target, substrate temperature and work pressure on the microstructure and properties of TiNi films are analysised. In additionally, several TiNi based ternary alloys films such as TiNiCu films, TiNiPd films and TiNiPt films are introduced. At last, the research direction of SMAs thin films is presented.

Intermetallic REPtZn Compounds with TiNiSi-type Structure

The equiatomic rare earth compounds REPtZn (RE = Y, Pr, Nd, Gd-Tm) were synthesized from the elements in sealed tantalum tubes by high-frequency melting at 1500 K followed by annealing at 1120 K and quenching. The samples were characterized by powder X-ray diffraction. The structures of four crystals were refined from single-crystal diffractometer data: TiNiSi type, Pnma, a = 707.1(1), b = 430.0(1), c = 812.4(1) pm, wR2 = 0.066, 602 F2, 21 variables for PrPt1.056Zn0.944; a = 695.2(1), b = 419.9(1), c = 804.8(1) pm, wR2 = 0.041, 522 F2, 21 variables for GdPt0.941Zn1.059; a = 688.2(1), b = 408.1(1), c = 812.5(1) pm, wR2 = 0.041, 497 F2, 22 variables for HoPt1.055Zn0.945; a = 686.9(1), b = 407.8(1), c = 810.4(1) pm, wR2 = 0.061, 779 F2, 20 variables for ErPtZn. The single-crystal data indicate small homogeneity ranges REPt1±xZn1±x. The platinum and zinc atoms build up three-dimensional [PtZn] networks (265 - 269 pm Pt-Zn in ErPtZn) in which the erbium atoms fill cages with coordination number 16 (6 Pt + 6 Zn + 4 Er). Bonding of the erbium atoms to the [PtZn] network proceeds via shorter RE-Pt distances, i. e. 288 - 293 pm in ErPtZn.

Effects of deposition temperature and elemental layer thickness on the properties of Fe/Co multilayers grown by molecular beam epitaxy

Fe/Co multilayers were grown at different temperatures up to 200 °C onto MgO-(1 0 0) monocrystalline substrates, varying both the Co and Fe elemental layer thicknesses. All samples show a multilayered structure where the elemental layers are separated by a thin interfacial region which, for high-temperature growths, is constituted by an equiatomic FeCo compound. The multilayers grown at room temperature show an in-plane uniaxial magnetic anisotropy. The increase in the growing temperature determines an improvement of the sample smoothness and the appearance of two preferred in-plane orientations of the easy magnetization axis having different strengths. By increasing the Co layer thickness, the in-plane magnetic behaviour becomes isotropic, while by increasing the Fe layer thickness, an out-of-plane contribution to the magnetization vector is established, which is responsible for the appearance of a well-defined magnetic morphology constituted by stripe-like domains.

Magnetic properties of the ternary RMgSn (R = Pr, Nd, Sm, Gd–Tm): First series of antiferromagnetic CeScSi-type structure compounds

The equiatomic ternary RMgSn compounds crystallize in the CeScSi (Pr, Nd, Sm, Gd–Tm), TiNiSi (Ce, Pr) or ZrNiAl (Yb) type structures. Macroscopic magnetic measurements, performed in the 5–300 K range, show that all the CeScSi-type compounds behave antiferromagnetically (8 < T N < 79 K). They also evidence metamagnetic-like behavior ( H crit < 7 T). The TiNiSi-type compounds are antiferromagnetic and ferromagnetic below 12 K and 52 K for CeMgSn and PrMgSn, respectively.

ChemInform Abstract: The Crystal Structure of YPdSi, the Isotypic Compounds LnPdSi (Ln: Gd-Lu), and Their Structural Relation to Some Other Equiatomic Compounds of the Rare Earth and Transition Metals with Main Group Elements.

ChemInform Abstract: The Crystal Structure of YPdSi, the Isotypic Compounds LnPdSi (Ln: Gd-Lu), and Their Structural Relation to Some Other Equiatomic Compounds of the Rare Earth and Transition Metals with Main Group Elements.

Structural and elastic properties of typical equiatomic ternary intermetallic compound TiNiSi under pressure

The structural, elastic, and electronic properties of typical equiatomic ternary intermetallic compound orthorhombic TiNiSi are investigated using the pseudopotential plane wave method within the generalized gradient approximation (GGA). The calculated structural parameters are in good agreement with the available experimental data. The elastic constants and their pressure dependences are calculated using the static finite strain technique. From the analysis of the mechanical stability, the good stabilization of the orthorhombic TiNiSi is supported. Band structures show that the orthorhombic structure TiNiSi is a semimetal, even under pressure up to 100 GPa.