Layered Ternary Compound Research Articles

ChemInform Abstract: Synthesis and Structure of Nb3SiTe6, a New Layered Ternary Niobium Telluride Compound.

Abstract Nb3SiTe6, a new type of layered ternary telluride compound, has been synthesized. The structure is determined by single-crystal X-ray diffraction methods. The compound crystallizes in space group Pnma (No. 62) with Z=4, a=6.353(2) A , b=13.938(5) A , c=11.507(4) A , V=1018.9(6) A 3 , R=4.77% and R w =4.88% . The structure contains sheets of mixed niobium and silicon with tellurium atoms capping both sides. The layered framework has an unusual coordination environment.

Polytypism, polymorphism and compositional faults in layered ternary and quaternary compounds

Polytypism, polymorphism and compositional faults in layered ternary and quaternary compounds

Direct diffusion bonding of Ti 3SiC 2 and Ti 3AlC 2

Two typical layered ternary compounds, Ti 3SiC 2 and Ti 3AlC 2, were joined directly by solid-state diffusion bonding method. By various bonding tests at 1100–1300 °C for 30–120 min under 10–30 MPa, and characterizing the microstructure and diffusion reactive phases of the joints by scanning electron microscopy (SEM), energy dispersive X-ray spectrometer (EDS), transmission electron microscopy (TEM) and X-ray diffraction (XRD), the optimal condition for direct joining of Ti 3SiC 2 and Ti 3AlC 2 was obtained. Strong joints of Ti 3SiC 2/Ti 3AlC 2 can be achieved via diffusion bonding, which is attributed to remarkable interdiffusion of Si and Al at the joint interface. The shear strength of the Ti 3SiC 2/Ti 3AlC 2 joints was determined.

X-ray diffraction study of ternary layered compounds in the PbSe-Bi2Se3 system

The pseudobinary system PbSe-Bi2Se3 has been studied by x-ray diffraction using cleaved single-crystal specimens and powders, and the compositions of the layered compounds existing in this system have been refined. The monoclinic cell parameters of the compounds Pb5Bi6Se14 and Pb5Bi12Se23, belonging to the [(PbSe)5] m [(Bi2Se3)3] n homologous series, have been determined.

Effect of cadmium, silver, and tellurium doping on the properties of single crystals of the layered compounds PbBi4Te7 and PbSb2Te4

We have studied the effects of doping and excess Te on the thermoelectric properties of single crystals of the layered ternary compounds PbBi4Te7 and PbSb2Te4. X-ray diffraction characterization has shown that the crystals have highly disordered structures. The nature of the possible point defects in the compounds has been analyzed. The silver atoms in Ag-doped PbBi4Te7 seem to reside in the van der Waals gaps between the slabs. The introduction of excess Te is shown to markedly reduce the lattice thermal conductivity of both compounds.

Anisotropic thermoelectric properties of the layered compounds PbSb2Te4 and PbBi4Te7

Single crystals of the ternary layered compounds PbSb2Te4 (p-type) and PbBi4Te7 (n-type) have been grown by Czochralski pulling with melt supply through a floating crucible. The in-plane and out-of-plane thermoelectric power, electrical conductivity, and thermal conductivity of the PbSb2Te4 and PbBi4Te7 crystals and related alloys have been measured in the temperature range 85–340 K. The results attest to a significant thermoelectric anisotropy in the crystals, especially in the p-type material PbSb2Te4.

Crystal growth and thermoelectric properties of tetradymite-like layered chalcogenides and (Bi2Te3)1−x−y (Sb2Te3) x (Sb2Se3) y solid solutions

Thermoelectric materials for segmented n-and p-legs of thermoelectric generators have been prepared by Czochralski growth with melt supply through a floating crucible. Two-segment ingots have been obtained using melt compositions corresponding to ternary layered compounds in the PbTe-Bi2Te3 and PbTe-Sb2Te3 systems, with (Bi2Te3)1−x−y(Sb2Te3)x(Sb2Se3)y solid solutions as seed materials. Seeded growth of the ternary compounds makes it possible to fabricate legs without joining segments by soldering. Using scanning hot point microprobe measurements, we have studied the thermoelectric power distribution across the seed-crystal interface. The results attest to a steep thermoelectric power gradient across the seed-crystal interface in a narrow region. Quantitative analysis of the distribution of the number of measurements with respect to thermoelectric power has revealed peaks corresponding to individual segments.

Optical constants at and below energy gap of layered ternary Tl compounds

Incoherent reflection mode of spectroscopic phase modulated ellipsometry (SPME) was firstly applied to quasi-two-dimensional TlInS2, TlGaS2 and TlGaSe2 to obtain uniaxial optical anisotropy of these materials at room temperature. Simulation of the measured SPME signal was performed within uniaxial incoherent reflection model, with a result of perfect match to experimental data for all three compounds. Birefringence in a photon energy range from below the energy gap of each material and down to 0.76eV was reliably determined. Obtained birefringence agrees well with optical anisotropy reported earlier from light figure studies of the above materials in the visible spectral range. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Ab initio investigation of the electronic structure and bondingproperties of the layered ternary compound Ti3SiC2at high pressure

The pressure dependences of the lattice parameters, electronic structure,and bonding properties of the layered ternary compound Ti3SiC2were investigated by performing ab initio plane-wave pseudopotential total energycalculations. The material exhibited elastic anisotropy. The lattice constants andaxial ratio were studied for different pressures, and the same trend was obtainedas is measured in experiment. It was found that although the structure was stableat high pressure, the electronic structure and atomic bonding were definitelyaffected. The electrical conductivity was predicted to reduce with pressure, whichwas interpreted by analysing the band dispersion curve and density ofstates at the Fermi level. The strengths of the atomic bonds in Ti3SiC2were considered by analysing the Mulliken population and by examiningthe bond length contraction for various pressures. A redistribution ofcharge density that accompanied high pressures was also revealed.

Electronic and structural properties of the layered ternary carbide Ti3AlC2

The electronic and structural properties of the layered ternary compound Ti3AlC2 have been determined using the ab initio pseudopotential method based on density functional theory. We have obtained the equilibrium lattice parameters, the equilibrium atomic positions in the unit cell, and interatomic distances. The calculated bulk modulus is 190 GPa and is comparable to that of TiC. The band structure, density of states (DOS) and effective charges are presented and compared with those of TiC. The band structure indicates that Ti3AlC2 is an electronic conductor. The electronic structure discloses that the bonding in Ti3AlC2 is anisotropic and metallic–covalent–ionic in nature. Compare to the structure of TiC, the presence of Al changes the Ti–C–Ti–C covalent bond chain into a Ti–C–Ti–C–Ti–Al bond chain through its reaction with Ti, forming the layered structure. Effective charge calculations suggest the ionic formula of Ti3AlC2 to be (Ti1.18+)(Ti0.59+)2(Al0.52−)(C0.92−)2.

Electronic structure and bonding properties of layered machinableTi2AlCandTi2AlNceramics

The electronic structure and chemical bonding of the layered ternary compounds ${\mathrm{Ti}}_{2}\mathrm{AlC}$ and ${\mathrm{Ti}}_{2}\mathrm{AlN}$ have been calculated by the ab initio pseudopotential total-energy method. The results show that ${\mathrm{Ti}}_{2}\mathrm{AlC}$ and ${\mathrm{Ti}}_{2}\mathrm{AlN}$ exhibit metallic electrical conductivity with an anisotropic character and ${\mathrm{Ti}}_{2}\mathrm{AlC}$ should be more conductive than ${\mathrm{Ti}}_{2}\mathrm{AlN}.$ The chemical bonding in ${\mathrm{Ti}}_{2}\mathrm{AlC}$ and ${\mathrm{Ti}}_{2}\mathrm{AlN}$ is also anisotropic and is metallic-covalent-ionic in nature. On the basis of total-energy estimation we conclude that the replacement of C by N will result in a stabilization of the hexagonal structure and decrease in metallic properties.

Fatigue-crack growth and fracture properties of coarse and fine-grained Ti 3SiC 2

The MAX phases are a group of layered ternary, quaternary, or quinary compounds with characteristics of both metals and ceramics. Over recent decades, the synthesis of bulk MAX phase parts for wider engineering applications has gained increasing attention in aerospace, nuclear, and defence industries. The recent adoption of additive manufacturing (AM) technologies in MAX phase fabrication is a step forward in this field. This work overviews the recent progress in additive manufacturing (AM) of bulk MAX phases along with the achieved geometric features, microstructures, and properties after briefing the conventional powder sintering methods of fabricating MAX phase components. Critical challenges associated with these innovative AM-based methods, including, poor AM processability, low MAX phase purity, and insufficient geometric accuracy of the final parts, are also discussed. Accordingly, outlooks for the immediate future in this area are discussed based on the optimization of present fabrication routes and the potential of other AM technologies.

ChemInform Abstract: Structural Study of Ternary Layered Compounds in the (GeTe)n×(Bi2Te3)m and (GeTe)n×(Sb2Te3)m Homologous Series.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Anomalous high field magnetic properties of a third stage CrCl 3 graphite intercalation compound and induced magnetism in the ternary layered compound C 21CrCl 3(MnCl 2) 2

The magnetisation of the third stage graphite intercalation compound (GIC) with CrCl 3 exhibits an anomalous behaviour in high magnetic fields analogous to the first stage CoCl 2 GIC. This anomaly can be explained by magnetostriction. The ternary graphite compound with CrCl 3 and MnCl 2 is a stacking of ferromagnetic CrCl 3 layers alternating with paramagnetic MnCl 2 layers. It is shown that a magnetic polarisation is induced by the ordered ferromagnetic layers on the paramagnetic ones. At low temperatures a long range antiferromagnetic order sets in.

Layered machinable ceramics for high temperature applications

Recently the authors reported on the fabrication and characterization of a layered ternary compound Ti{sub 3}SiC{sub 2}, that was found to combine many of the best attributes of metals and ceramics. Like metals it is an excellent electric and thermal conductor, easily machinable, relatively soft, not susceptible to thermal shock and behaves plastically at higher temperatures. Like ceramics it is oxidation resistant, refractory, and, most importantly, it maintains its strength to temperatures that render the best superalloys available today unusable. Upon realizing the remarkable properties exhibited by Ti{sub 3}SiC{sub 2} the authors carried out a literature search for other compounds with the same chemistry. They found one only, namely: Ti{sub 3}GeC{sub 2} which has properties that are very similar to Ti{sub 3}SiC{sub 2}. The purpose of this paper is two-fold. The first is to demonstrate the similarities between the properties of the H-phases, Ti{sub 3}GeC{sub 2} and Ti{sub 3}SiC{sub 2}. The second is to present some compelling microstructural evidence that indicates that these compounds behave as polycrystalline nanolaminates. To that effect the authors fabricated and characterized the following H-phases: Ti{sub 2}AlC, Ti{sub 2}AlN, Ti{sub 2}GeC and as well as Ti{sub 3}GeC{sub 2}. In addition they fabricated V{sub 2}AlC, Ta{sub 2}AlC,more » and Nb{sub 2}AlC and tested their machinability.« less

ChemInform Abstract: Synthesis, Crystal and Electronic Structure of a New Ternary Layered Compound: Nb2SiTe4.

AbstractChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.

Short Te …︁ Te bonding contacts in a new layered ternary telluride: Synthesis and crystal structure of 2D Nb3GexTe6 (x ≃ 0.9)

AbstractThe new layered ternary compound Nb3GexTe6 (x ≃ 0.90) was prepared by direct combination of the elements taken in the stoichiometric proportions 3 : 1 : 6, heated at 1 000 °C for 10 days in silica tubes and quenched to room temperature. The phase crystallizes in the orthorhombic symmetry, space group Pnma (#62), with the following single crystal refined parameters: a = 643.18(5) pm, b = 1391.98(11)pm and c = 1 154.07(5) pm, with Z = 4. The structure was refined to an R of 3.4% (Rw = 4.6%), with 1969 independent reflexions and 49 parameters. The structure is based on the close stacking of trigonal prismatic (TP) slabs in the AA/BB mode. The slabs can be seen as built up from face sharing biprisms, which are filled either by one or by two niobium cations situated in the middle of the trigonal prisms. The germanium is located in the middle of the common face of two prisms, leading to a rather unusual anionic square coordination. The refinements showed that this latter cation does not fill completely its square site. No cation was found in the van der Waals gap between the slabs. The mean dGeTe distance (276.5 pm) is in agreement with GeII cations, while some Te …︁ Te distances (from 333.84 to 361.65pm) are too short for anions in a simple contact. These bonding distances, already mentionned in some MTe2 compounds, are to be ascribed to charge transfer in the structure, with a partial oxidation state for the tellurium anions. Short NbNb and NbGe distances (292.0 and 281.3 pm, respectively) imply intercationic bonding within the slabs.

Synthesis and structure of Nb 3SiTe 6, a new layered ternary niobium telluride compound

Nb 3SiTe 6, a new type of layered ternary telluride compound, has been synthesized. The structure is determined by single-crystal X-ray diffraction methods. The compound crystallizes in space group Pnma (No. 62) with Z=4, a=6.353(2) A ̊ , b=13.938(5) A ̊ , c=11.507(4) A ̊ , V=1018.9(6) A ̊ 3, R=4.77% and R w=4.88% . The structure contains sheets of mixed niobium and silicon with tellurium atoms capping both sides. The layered framework has an unusual coordination environment.

Preparation and Characterization of “PbVS3” a New Composite Layered Compound

Abstract “PbVS3”, a new ternary layered compound, has been obtained. The structure is composed of two kinds of layers of pseudo-tetragonal PbS and pseudo-orthohexagonal VS2. They are alternately stacked together forming composite crystal of LaCrS3 type. All of the powder X-ray diffraction peaks are well indexed on the basis of only a monoclinic PbS subcell.

Superconductivity in layered ternary chalcogenides A xTaS 2 and A xNbS 2 and influence of topotactic solvation

The superconducting transititon temperatures T c for the layered ternary compounds A o.33TaS 2and A o.5NbS 2 A = Li, Na, K, Rb, Cs) were found to depend strongly on the alkali cation. This cation dependence disappears upon additional uptake of water or other polar solvents into the lattice. Although the general decrease in T c upon intercalation for A o.5NbS 2 can be understood basically in terms of charge transfer within a rigid band approach, it is obvious that additional factors such as charge density wave suppression (in the case of Ta compounds), band structure variations due to coulomb interactions of unsolvated and solvated interlayer cations and cation coordination influence the superconducting properties of the systems investigated.