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1.
A new quaternary layered carbide, Zr2[Al3.56Si0.44]C5, has been synthesized and characterized by X-ray powder diffraction, transmission electron microscopy and thermopower and electrical conductivity measurements. The crystal structure was successfully determined using direct methods, and further refined by the Rietveld method. The crystal is trigonal (space group R3m, Z=3) with lattice dimensions of a=0.331059(5), c=4.09450(5) nm and V=0.38864(1) nm3. The final reliability indices calculated from the Rietveld refinement were Rwp=6.24%, Rp=4.21% and RB=0.82%. The crystal structure is composed of electroconductive NaCl-type ZrC slabs separated by Al4C3-type [Al3.56Si0.44]C3 layers. This material had thermoelectric properties superior to those of the ternary layered carbides Zr2Al3C4 and Zr3Al3C5, with the power factor reaching 7.6×10−5W m−1 K−2.  相似文献   

2.
Two types of new ternary carbides, Zr2Al4C5 and Zr3Al4C6, have been synthesized and characterized by X-ray powder diffraction. The crystal structures were refined from laboratory X-ray powder diffraction data (CuKα1) using the Rietveld method. These carbides form a homologous series with the general formula (ZrC)mAl4C3 (m=2 and 3). The crystal structures can be regarded as intergrowth structures where the Al4C3-type [Al4C4] layers are the same, while the NaCl-type [ZrmCm+1] layers increase in thickness with increasing m value. The new carbides are most probably the end members of continuous solid-solutions (ZrC)m[Al4−xSix]C3 with 0?x?0.44.  相似文献   

3.
Two new phases, Yb1−xAl3−xSix and Yb1−yAl3−xGex, were found by systematic investigations of the according ternary systems. The crystal structures of Yb1−yAl2.8Si0.2 and Yb1−yAl2.8Ge0.2 (defect HT-PuAl3 type) were studied by X-ray powder methods (CuKα1 radiation, λ=1.54056 Å, hexagonal system, space group P63/mmc (No. 194), a=6.009(1) and 6.015(1) Å, c=14.199(2) and 14.241(5) Å, V=444.0(2) and 446.2(3) Å3, 93 and 92 reflections, and 8200 and 8000 profile points for silicide and germanide, respectively). Full profile refinements with 11 and 13 structural parameters resulted in RI=0.049 and 0.054, and Rp=0.088 and 0.104, respectively. The ternary structures are distorted closest packings in comparison with the binary YbAl3 compound with AuCu3-type structure. They are characterized by the formation of Al3-, Si3-, and Ge3-homoatomic clusters and aluminum networks. Magnetization measurements show that both the silicide and germanide are valence fluctuation compounds with enhanced electronic density of states at the Fermi level similar to the binary YbAl3. The characteristic maximum of the magnetic susceptibility increases from ≈120 K for YbAl3 to ≈140 K for Yb1−yAl2.8Si0.2or Yb1−yAl2.8Ge0.2 and further to ≈150 K for Yb1−yAl2.75Si0.25. The S-shape of the electrical resistivity curves is also characteristic of valence fluctuations.  相似文献   

4.
Phase relations were established in the Sr-poor part of the ternary systems Sr-Ni-Si (900 °C) and Sr-Cu-Si (800 °C) by light optical microscopy, electron probe microanalysis and X-ray diffraction on as cast and annealed alloys. Two new ternary compounds SrNiSi3 (BaNiSn3-type) and SrNi9−xSi4+x (own-type) were found in the Sr-Ni-Si system along with previously reported Sr(NixSi1−x)2 (AlB2-type). The crystal structure of SrNi9−xSi4+x (own-type, x=2.7, a=0.78998(3), c=1.1337(2) nm; space group P4/nbm) was determined from X-ray single crystal counter to be a low symmetry derivative of the cubic, parent NaZn13-type. At higher Si-content X-ray Rietveld refinements reveal the formation of a vacant site (□) corresponding to a formula SrNi5.5Si6.51.0. Phase equilibria in the Sr-Cu-Si system are characterized by the compounds SrCu2−xSi2+x (ThCr2Si2-type), Sr(CuxSi1−x)2 (AlB2-type), SrCu9−xSi4+x (0≤x≤1.0; CeNi8.5Si4.5-type) and SrCu13−xSix (4≤x≤1.8; NaZn13-type). The latter two structure types appear within a continuous solid solution. Neither a type-I nor a type-IX clathrate compound was encountered in the Sr-{Cu,Ni}-Si systems.Structural details are furthermore given for about 14 new ternary compounds from related alloy systems with Ba.  相似文献   

5.
Two novel ternary intermediate phases, namely URuSi3−x (x=0.11) and U3Ru2Si7 were found in the Si-rich part of the U-Ru-Si phase diagram. Single crystal X-ray diffraction measurements, carried out at room temperature, indicated that URuSi3−x crystallizes in its own tetragonal type structure (space group P4/nmm, no. 129; unit cell parameters: a=12.108(1) Å and c=9.810(1) Å), being a derivative of the BaNiSn3-type structure. U3Ru2Si7 adopts in turn a disordered orthorhombic La3Co2Sn7-type structure (space group Cmmm, no. 65; unit cell parameters: a=4.063(1) Å, b=24.972(2) Å and c=4.072(1) Å). As revealed by magnetization, electrical resistivity and specific heat measurements, both compounds order magnetically at low temperatures. Namely URuSi3−x is a ferromagnet with TC=45 K, and U3Ru2Si7 shows ferrimagnetic behavior below TC=29 K.  相似文献   

6.
The crystal structures and phase stability of the ternary alloys R3T4+xAl12−x (R=Y, Ce, Gd, U, Th; T=Fe, Ru) have been investigated using the interatomic potentials obtained by the lattice inversion method. These compounds crystallize in the hexagonal Gd3Ru4Al12-type structure and the calculated lattice constants correspond well with the experiments. Among the four different kinds of Al sites in the structure, the most preferential sites for Fe atoms or Ru atoms are 6h sites. The properties related to lattice vibration, such as the phonon density of states (DOS) and Debye temperature of R3Fe4Al12, have been evaluated. A qualitative analysis is carried out with the relevant potentials for the vibrational modes, which makes it possible to predict some thermodynamic properties.  相似文献   

7.
A new aluminum oxycarbonitride, Al5(OxCyN4−xy) (x∼1.4 and y∼2.1), has been synthesized and characterized by X-ray powder diffraction, transmission electron microscopy and electron energy loss spectroscopy (EELS). The title compound was found to be hexagonal with space group P63/mmc, Z=2, and unit-cell dimensions a=0.328455(6) nm, c=2.15998(3) nm and V=0.201805(6) nm3. The atom ratios O:C:N were determined by EELS. The final structural model, which is isomorphous with that of (Al4.4Si0.6)(O1.0C3.0), showed the positional disordering of one of the three types of Al sites. The maximum-entropy method-based pattern fitting (MPF) method was used to confirm the validity of the split-atom model, in which conventional structure bias caused by assuming intensity partitioning was minimized. The reliability indices calculated from the MPF were Rwp=6.94% (S=1.22), Rp=5.34%, RB=1.35% and RF=0.76%. The crystal was an inversion twin. Each twin-related individual was isostructural with Al5C3N (space group P63mc, Z=2).  相似文献   

8.
Phase relations in the ternary system Ce-Pt-Si have been established for the isothermal section at 800 °C based on X-ray powder diffraction, metallography, scanning electron microscopy (SEM) and electron probe microanalysis (EPMA) techniques on about 120 alloys, which were prepared by various methods employing arc-melting under argon or powder reaction sintering. Nineteen ternary compounds were observed. Atom order in the crystal structures of τ18-Ce5(Pt,Si)4 (Pnma; a=0.77223(3) nm, b=1.53279(8) nm c=0.80054(5) nm), τ3-Ce2Pt7Si4 (Pnma; a=1.96335(8) nm, b=0.40361(4) nm, c=1.12240(6) nm) and τ10-CePtSi2 (Cmcm; a=0.42943(2) nm, b=1.67357(5) nm, c=0.42372(2) nm) was determined by direct methods from X-ray single-crystal CCD data and found to be isotypic with the Sm5Ge4-type, the Ce2Pt7Ge4-type and the CeNiSi2-type, respectively. Rietveld refinements established the atom arrangement in the structures of Pt3Si (Pt3Ge-type, C2/m, a=0.7724(2) nm, b=0.7767(2) nm, c=0.5390(2) nm, β=133.86(2)°), τ16-Ce3Pt5Si (Ce3Pd5Si-type, Imma, a=0.74025(8) nm, b=1.2951(2) nm, c=0.7508(1) nm) and τ17-Ce3PtSi3 (Ba3Al2Ge2-type, Immm, a=0.41065(5) nm, b=0.43221(5) nm, c=1.8375(3) nm). Phase equilibria in Ce-Pt-Si are characterised by the absence of cerium solubility in platinum silicides. Cerium silicides and cerium platinides, however, dissolve significant amounts of the third component, whereby random substitution of the almost equally sized atom species platinum and silicon is reflected in extended homogeneous regions at constant Ce content such as for τ13-Ce(PtxSi1−x)2, τ6-Ce2Pt3+xSi5−x or τ7-CePt2−xSi2+x.  相似文献   

9.
Phase relations have been established in the ternary system Ce-Rh-Si for the isothermal section at 800 °C based on X-ray powder diffraction and EPMA on about 80 alloys, which were prepared by arc melting under argon or by powder reaction sintering. From the 25 ternary compounds observed at 800 °C 13 phases have been reported earlier. Based on XPD Rietveld refinements the crystal structures for 9 new ternary phases were assigned to known structure types. Structural chemistry of these compounds follows the characteristics already outlined for their prototype structures: τ7—Ce3RhSi3, (Ba3Al2Ge2-type), τ8—Ce2Rh3−xSi3+x (Ce2Rh1.35Ge4.65-type), τ10—Ce3Rh4−xSi4+x (U3Ni4Si4-type), τ11—CeRh6Si4 (LiCo6P4-type), τ13—Ce6Rh30Si19.3 (U6Co30Si19-type), τ18—Ce4Rh4Si3 (Sm4Pd4Si3-type), τ21—CeRh2Si (CeIr2Si-type), τ22—Ce2Rh3+xSi1−x (Y2Rh3Ge-type) and τ24—Ce8(Rh1−xSix)24Si (Ce8Pd24Sb-type). For τ25—Ce4(Rh1−xSix)12Si a novel bcc structure was proposed from Rietveld analysis. Detailed crystal structure data were derived for τ3—CeRhSi2 (CeNiSi2-type) and τ6—Ce2Rh3Si5 (U2Co3Si5-type) by X-ray single crystal experiments, confirming the structure types. The crystal structures of τ4—Ce22Rh22Si56, τ5—Ce20Rh27Si53 and τ23—Ce33.3Rh58.2−55.2Si8.5−11.5 are unknown. High temperature compounds with compositions Ce10Rh51Si33 (U10Co51Si33-type) and CeRhSi (LaIrSi-type) have been observed in as-cast alloys but these phases do not participate in the phase equilibria at 800 °C.  相似文献   

10.
We have prepared a new layered oxycarbide, [Al5.25(5)Si0.75(5)][O1.60(7)C3.40(7)], by isothermal heating of (Al4.4Si0.6)(O1.0C3.0) at 2273 K near the carbon-carbon monoxide buffer. The crystal structure was characterized using X-ray powder diffraction, transmission electron microscopy and energy dispersive X-ray spectroscopy (EDX). The title compound is trigonal with space group R3?m (centrosymmetric), Z=3, and hexagonal cell dimensions a=0.32464(2) nm, c=4.00527(14) nm and V=0.36556(3) nm3. The atom ratios Al:Si were determined by EDX, and the initial structural model was derived by the direct methods. The final structural model showed the positional disordering of one of the three types of Al/Si sites. The reliability indices were Rwp=4.45% (S=1.30), Rp=3.48%, RB=2.27% and RF=1.25%. The crystal is composed of three types of domains with nearly the same fraction, one of which has the crystal structure of space group Rm. The crystal structure of the remaining two domains, which are related by pseudo-symmetry inversion, is noncentrosymmetric with space group R3m.  相似文献   

11.
Solid state phase equilibria in the ternary Gd-Si-B phase diagram have been proposed at 1270 K using X-ray diffraction, scanning electron microscopy and electron probe microanalysis. Prior to this work, the binary systems Gd-B, Gd-Si and Si-B have also been reinvestigated. The main characteristic of the ternary diagram is the occurrence of two new ternary compounds Gd5Si2B8 and Gd5Si3B0.64. The former crystallizes in tetragonal symmetry, space group P4/mbm with unit cell parameters a=7.2665(3), c=8.2229(7) Å, the second one presents hexagonal symmetry, space group P63/mcm with unit cell parameters a=8.5080(4),c=6.4141(2) Å. The X-ray structures of the two structurally related phases Gd5Si3B0.64 and host binary Gd5Si3 have been refined from three-dimensional single-crystal intensity data to the final R values of 0.036 (Rw=0.046) and 0.046 (Rw=0.055) for 457 and 401 reflections, respectively with [F>4σ(F)]. Both structures exhibit the Mn5Si3-type structure, with in addition for Gd5Si3B0.64 a partial occupancy by boron of the normally vacant interstitial site at the center of the Gd6 octahedron, which corresponds to the origin of the unit cell. Bonding between the interstitial boron atoms and the gadolinium ones forming the Gd6B polyhedra is indicated by the decrease in the corresponding Gd-Gd distances and consequently in the unit cell volume. Finally, the Gd-Si-B phase diagram is compared with the previously reported Er-Si-B, at 1070 K.  相似文献   

12.
Single crystals of the novel ternary compounds EuZn2Si2 and EuZn2Ge2 were grown from pure gallium, indium, or zinc metal used as a flux solvent. Crystal properties were characterized using X-ray single-crystal analyses via Gandolfi and Weissenberg film techniques and by four-circle X-ray single-crystal diffractometry. The new compounds crystallize with ternary derivative structures of BaAl4, i.e., EuZn2Si2 with ThCr2Si2-type (a=0.42607(2) nm, c=1.03956(5) nm, I4/mmm, R1=0.038) and EuZn2Ge2 with CaBe2Ge2-type (a=0.43095(2) nm, c=1.07926(6) nm, P4/nmm, R1=0.067). XAS and magnetic measurements on EuZn2Si2 and EuZn2Ge2 revealed in both compounds the presence of Eu2+ ions carrying large magnetic moments, which order magnetically at low temperatures. The magnetic phase transition occurs at TN=16 and 7.5 K for the silicide and the germanide, respectively. In EuZn2Si2 there occurs a spin reorientation at 13 K and furthermore some canting of antiferromagnetically ordered moments below about 10 K. In EuZn2Ge2 a canted antiferromagnetic structure is formed just at TN.  相似文献   

13.
The ternary compound UFe7Al5 was synthesized by arc melting, followed by annealing at 850°C. The crystal structure was determined by single-crystal X-ray diffraction and refined to a residual value of R=0.039 (S=1.030), with lattice parameters a=8.581(2) Å and c=4.946(1) Å. This compound is a new extreme composition in the family of intermetallics with general formula UFexAl12−x crystallizing in the tetragonal ThMn12-type structure, space group I4/mmm. In contrast to UFexAl12−x within the composition range 4?x?6, in UFe7Al5 the additional iron atom is found in the 8i equipositions. Magnetization measurements versus temperature show two magnetic transitions at 363 and 275 K, respectively, with a ferromagnetic behavior below the highest temperature transition. 57Fe Mössbauer data indicate that the high-temperature transition is related to the ordering of the iron atoms. The dependence of the isomer shifts and magnetic hyperfine fields on the crystallographic site and on the number of the iron nearest neighbors is similar to that observed in the other UFexAl12−x and rare-earth analogues. The magnetic hyperfine field values of iron atoms on 8i sites is larger than in the other sites, in agreement with previous data obtained for other ThMn12-type compounds.  相似文献   

14.
Phases YbZn1−xAlx, YbZn2−xAlx and YbZn3−xAlx were studied by electron microprobe analysis and X-ray single crystal and powder methods. The compound YbZn0.8Al0.2 crystallizes with the CsCl-type, a=3.635(2) Å. Four phases were investigated by single crystal X-ray diffraction: YbZn0.996(6)Al1.004(6), MgNi2-type, P63/mmc, a=5.573(1), c=18.051(3) Å, Z=8, wR2=0.040 and YbZn0.88(3)Al1.12(3), MgCu2-type, , a=7.860(2) Å, Z=8, wR2=0.060, both showing mixed Zn/Al occupancy; YbZn2.50(1)Al0.50(1), CeNi3-type, P63/mmc, a=5.496(1), c=17.336(2) Å, Z=6, wR2=0.036 and YbZn1.92(2)Al1.08(2), PuNi3- or NbBe3-type, , a=5.499(1), c=26.134(5) Å, Z=9, wR2=0.053, where the zinc atoms are ordered in the CaCu5 segment, while share the sites with aluminium in the Laves phase segment. In the pseudobinary section YbZn2−xAlx four structures occur in sequence with increasing the electron concentration: CeCu2 or KHg2 (x=0–0.3), MgZn2 (x=0.33–0.54), MgNi2 (x=0.68–1.01) and MgCu2 (x=1.12–2). This sequence agrees with the results of first-principles calculations, already reported in the literature for other similar series. In the YbZn3−xAlx section CeNi3-type compounds occur with x=0.40–0.88 followed by PuNi3-type compounds with x=0.92–1.10. The stability ranges of these phases are related to the valence electron concentration.  相似文献   

15.
The new lithium ionic conductors, thio-LISICON (LIthium SuperIonic CONductor), were found in the ternary Li2S-SiS2-Al2S3 and Li2S-SiS2-P2S5 systems. Their structures of new materials, Li4+xSi1−xAlxS4 and Li4−xSi1−xPxS4 were determined by X-ray Rietveld analysis, and the electric and electrochemical properties were studied by electronic conductivity, ac conductivity and cyclic voltammogram measurements. The structure of the host material, Li4SiS4 is related to the γ-Li3PO4-type structure, and when the Li+ interstitials or Li+ vacancies were created by the partial substitutions of Al3+ or P5+ for Si4+, large increases in conductivity occur. The solid solution member x=0.6 in Li4−xSi1−xPxS4 showed high conductivity of 6.4×10-4 S cm−1 at 27°C with negligible electronic conductivity. The new solid solution, Li4−xSi1−xPxS4, also has high electrochemical stability up to ∼5 V vs Li at room temperature. All-solid-state lithium cells were investigated using the Li3.4Si0.4P0.6S4 electrolyte, LiCoO2 cathode and In anode.  相似文献   

16.
The ternary aluminides R2Rh3Al9 (R=Y, La-Nd, Sm, Gd-Tm, Lu), R2Ir3Al9 (R=Y, La-Nd, Sm, Gd-Lu), and R2Pd3Al9 (R=Y, Gd-Tm) have been prepared by arc melting of the elemental components with an excess of aluminum and dissolving the aluminum-rich matrix in hydrochloric acid. They crystallize with Y2Co3Ga9-type structure: Cmcm, Z=4. The crystal structures of Ho2Rh3Al9 and Er2Ir3Al9 have been refined from single-crystal X-ray data; Ho2Rh3Al9: a=1316.8(3) pm, b=760.2(2) pm, c=933.7(2) pm, R=0.044 for 255 structure factors and 27 variables; Er2Ir3Al9: a=1313.8(2) pm, b=758.5(1) pm, c=933.8(2) pm, R=0.057 (392 F values, 27 variables). The structure may be viewed as consisting of atomic layers of the compositions A=R2Al3 and B=T3Al6 which alternate in the sequence ABAB along the z direction. Approximately 33% and 27% of the A layers were found to be misplaced in the crystals investigated for Ho2Rh3Al9 and Er2Ir3Al9, respectively. The magnetic properties of most iridium-containing compounds have been determined with a superconducting quantum interference device magnetometer. The yttrium and the lanthanum compounds show Pauli paramagnetism, others reflect the magnetic behavior of the rare-earth components. The magnetic ordering temperatures are all lower than 20 K.  相似文献   

17.
Eighteen new intermetallic compounds RMn2TrxZn20−x (2<x<7; R=rare-earth metal; Tr=Al, In) were synthesized using low-melting mixtures of (Tr/Zn) as a solvent. Structural refinement using single-crystal X-ray diffraction data shows that the compounds are substituted variants of the cubic CeCr2Al20-type structure (Fd-3m, Z=8; unit cell parameters vary from a=14.1152(3)Å for YbMn2Al5.3Zn14.7 to a=14.8125(4)Å for SmMn2In5.9Zn14.1). The Zn and Tr elements show site preferences in the indium compounds, but not in the aluminum analogs. The substitution of trielide element for zinc modifies the valence electron count of the compounds to allow for the incorporation of Mn into the structure. Magnetic susceptibility data show no evidence of magnetic ordering down to 3 K.  相似文献   

18.
The crystal structures of ternary compounds RPt3−xSi1−y(R=Y, Tb, Dy, Ho, Er, Tm, Yb) have been elucidated from X-ray single crystal CCD data. All compounds are isotypic and crystallize in the tetragonal space group P4/mbm. The general formula RPt3−xSi1−y arises from defects: x≈0.20, y≈0.14. The crystal structure of RPt3−xSi1−y can be considered as a packing of four types of building blocks which derive from the CePt3B-type unit cell by various degrees of distortion and Pt, Si-defects.  相似文献   

19.
Two series of intermetallic alloys, RT2Si and RTSi2, have been synthesized from stoichiometric compositions. The crystal structures of EuPt1+xSi2−x (CeNiSi2-type), CeIr2Si (new structure type), YbPd2Si and YbPt2Si (both YPd2Si-type) have been elucidated from X-ray single crystal CCD data, which were confirmed by XPD experiments. The crystal structures of LaRh2Si and LaIr2Si (CeIr2Si-type), {La,Ce,Pr,Nd}AgSi2 (all TbFeSi2-type), and EuPt2Si (inverse CeNiSi2-type) were characterized by XPD data. RT2Si/RTSi2 compounds were neither detected in as-cast alloys Sc25Pt50Si25, Eu25Os25Si50 and Eu25Rh25Si50 nor after annealing at 900 °C. Instead, X-ray single crystal data prompted Eu2Os3Si5 (Sc2Fe3Si5-type) and EuRh2+xSi2−x (x=0.04, ThCr2Si2-type) as well as a new structure type for Sc2Pt3Si2 (own type).  相似文献   

20.
A series of binary rare-earth metal silicides RE5Si3 and ternary boron-interstitial phases RE5Si3Bx (RE=Gd, Dy, Ho, Lu, and Y) adopting the Mn5Si3-type structure, have been prepared from the elemental components by arc melting. Boron “stuffed” phases were subsequently heated at 1750 K within a high-frequency furnace. Crystal structures were determined for both binary and ternary series of compounds from single-crystal X-ray data: hexagonal symmetry, space group P63/mcm, Z=2. Boron insertion in the host binary silicides results in a very small decrease of the unit cell parameters with respect to those of the binaries. According to X-ray data, partial or nearly full boron occupancy of the interstitial octahedral sites in the range 0.6-1 is found. The magnetic properties of these compounds were characterized by the onset of magnetic ordering below 100 K. Boron insertion induces a modification of the transition temperature and θp values in most of the antiferromagnetic binary silicides, with the exception of the ternary phase Er5Si3Bx which was found to undergo a ferromagnetic transition at 14 K. The electrical resistivities for all binary silicides and ternary boron-interstitial phases resemble the temperature dependence of metals, with characteristic changes of slope in the resistivity curves due to the reduced electron scattering in the magnetically ordered states. Zintl-Klemm concept would predict a limiting composition RE5Si3B0.6 for a valence compound and should then preclude the stoichiometric formula RE5Si3B. Density functional theory calculations carried out on some RE5Si3Zx systems for different interstitial heteroatoms Z and different x contents from 0 to 1 give some support to this statement.  相似文献   

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