Isolation of the new cubic phases RE4FeGa(12-x)Ge(x) (RE = Sm,Tb; x = 2.5) from molten gallium: single-crystal neutron diffraction study of the Ga/Ge distribution

The compounds RE4FeGa(12-x)Ge(x) (RE = Sm, Tb) were discovered in reactions employing molten Ga as a solvent at 850 degrees C. However, the isostructural Y4FeGa(12-x)Ge(x) was prepared from a direct combination reaction. The crystal structure is cubic with space group Imm, Z = 2, and a = 8.657(4) A and 8.5620(9) A for the Sm and Tb analogues, respectively. Structure refinement based on full-matrix least squares on F(o)2 resulted in R1 = 1.47% and wR2 = 4.13% [I > 2(I)] for RE = Sm and R1 = 2.29% and wR2 = 7.12% [I > 2(I)] for RE = Tb. The compounds crystallize in the U4Re7Si6 structure type, where the RE atoms are located on 8c (1/4, 1/4, 1/4) sites and the Fe atoms on 2a (0, 0, 0) sites. The distribution of Ga and Ge in the structure, investigated with single-crystal neutron diffraction on the Tb analogue, revealed that these atoms are disordered over the 12d (1/4, 0, 1/2) and 12e (x, 0, 0) sites. The amount of Ga/Ge occupying the 12d and 12e sites refined to 89(4)/11 and 70(4)/30%, respectively. Transport property measurements indicate that these compounds are metallic conductors. Magnetic susceptibility measurements and M?ssbauer spectroscopy performed on the Tb analogue show a nonmagnetic state for Fe, while the Tb atoms carry a magnetic moment corresponding to a mu(eff) of 9.25 mu(B).     

Structurally complex cobalt intermetallics grown from liquid aluminum: Co19Al45Si(10-x) (x = 0.13) and Co5Al14Si2

The cobalt aluminum silicides Co19Al45Si(10-x) (x = 0.13) and Co5Al14Si2 were synthesized in liquid aluminum and characterized by single-crystal X-ray diffraction. Co19Al45Si(10-x) (x = 0.13) crystallizes in the monoclinic space group C2/c with lattice parameters a = 19.991(2) A, b = 19.143(2) A, c = 12.8137(15) A, beta = 123.583(2) degrees. Co5Al14Si2 adopts the orthorhombic space group Pnma with cell parameters a = 13.8948(19) A, b = 23.039(3) A, c = 7.3397(10) A. Both structures are exceptionally complex with the Co2Si2 rhombus being a common building motif. The coordination environments of cobalt atoms resemble those of the transition metals in typical quasi-crystal approximants. Co5Al14Si2 shows oxidation resistance in air up to 1000 degrees C by forming a dense-packed Al2O3 layer on the surface of the crystal.     

RE(AuAl2)nAl2(AuxSi1-x)2: a new homologous series of quaternary intermetallics grown from aluminum flux

The combination of early rare earth metals (La- to Gd and Yb), gold, and silicon in molten aluminum results in the formation of intermetallic compounds with four related structures, forming a new homologous series: RE[AuAl2]nAl2(AuxSi(1-x))2, with x approximately 0.5 for most of the compound and n = 0, 1, 2, and 3. Because of the highly reducing nature of the Al flux, rare earth oxides instead of metals can also be used in these reactions. These compounds grow as large plate-like crystals and have tetragonal structure types that can be viewed as intergrowths of the BaAl4 structure and antifluorite-type AuAl2 layers. REAuAl2Si materials form with the BaAl4 structure type in space group I4/mmm (cell parameters for the La analogue are a = 4.322(2) A, c = 10.750(4) A, and Z = 2). REAu2Al4Si forms in a new ordered superstructure of the KCu4S3 structure type, with space group P4/nmm and cell parameters of the La analogue of a = 6.0973(6) A, c = 8.206(1) A, and Z = 2. REAu3Al6Si forms in a new I4/mmm symmetry structure type with cell parameters of a = 4.2733(7) A, c = 22.582(5) A, and Z = 2 for RE = Eu. The end member of the series, REAu4Al8Si, forms in space group P4/mmm with cell parameters for the Yb analogue of a = 4.2294(4) A, c = 14.422(2) A, and Z = 1. New intergrowth structures containing two different kinds of AuAl2 layers were also observed. The magnetic behavior of all these compounds is derived from the RE ions. Comparison of the susceptibility data for the europium compounds indicates a switch from 3-D magnetic interactions to 2-D interactions as the size of the AuAl2 layer increases. The Yb ions in YbAu(2.91)Al(6)Si(1.09) and YbAu(3.86)Al(8)Si(1.14) are divalent at high temperatures.     

Structural studies on single crystals of Chevrel phase selenides REMo6Se8 (RE = La,Ce, Pr,Nd, or Sm) at 298 K

We report on structural studies at room temperature of rare-earth based Chevrel phase selenides of the formula RExMo6Se8, where RE stands for a light rare-earth La (1), Ce (2), Pr (3), Nd (4), or Sm (5). The single crystals were grown at 1650 degrees C < T < 1690 degrees C from off-stoichiometric starting compositions, with the exception of 3, which was grown at 1710 degrees C from a stoichiometric charge (congruently melting material). The crystal structures were solved in space group R3 (No. 148; Z = 1) and found to be isostructural with the well-known Chevrel phases having large cations (e.g., PbMo6S8, REMo6S8). The structures are based on Mo6Se8 metallic clusters that are slightly rotated inside a pseudocubic rare-earth sublattice. Structural refinements revealed that the origin site, occupied by the RE atoms, exhibits slight deficiencies, leading to a RExMo6Se8 composition, with x ranging between approximately 0.82 and approximately 0.92: 1 La0.88Mo6Se8, arh = 6.7577(9) A, alpha rh = 88.62(2) degrees; 2a Ce0.82Mo6Se8, arh = 6.7407(6) A, alpha rh = 88.83(2) degrees; 2b Ce0.92Mo6Se8, arh = 6.7473(9) A, alpha rh = 88.69(2) degrees; 3 Pr0.86Mo6Se8, arh = 6.7385(6) A, alpha rh = 88.81(2) degrees; 4 Nd0.85Mo6Se8, arh = 6.7286(5) A, alpha rh = 88.85(1) degrees; and 5 Sm0.87Mo6Se8, arh = 6.7182(2) A, alpha rh = 88.956(3) degrees. All of the structural data presented in this work (lattice constants, positional parameters and interatomic distances) concern an average RE content of x approximately 0.87. In this way, any influence due to electronic effects (VEC number) can be discarded, and exact correlations between these parameters and the ionic radius of the rare-earth atoms can then be established.     

Polygallide RE2MGa9Ge2 (RE = Ce, Sm; M = Ni, Co) phases grown in molten gallium

The quaternary intermetallics Ce2CoGa9Ge2, Ce2NiGa9Ge2, and Sm2NiGa9Ge2 were prepared by reacting elemental metals in excess of gallium at 850 degrees C. The title compounds crystallize in the tetragonal space group P4/nmm in the Sm2Ni(Si(1-x)Ni(x))Al4Si6 structure type with cell parameters a = 5.9582(5) A, c = 15.0137(18) A, and a = 5.9082(17) A, c = 14.919(6) A, Z = 2, for Ce2CoGa9Ge2 and Sm2NiGa9Ge2, respectively. The structures are composed of covalently bonded three-dimensional networks of [CoGa9Ge2] in which the rare-earth metals fill the voids forming a 2D square net. The structures of RE2MGa9Ge2 are Ga-rich and possess extensive Ga-Ga bonding even though the Ga atoms do not form a network on their own. Magnetic susceptibility measurements for Ce2CoGa9Ge2 and Ce2NiGa9Ge2 show Curie-Weiss paramagnetism, consistent with presence of Ce(3+) ions. Magnetocrystalline anisotropy was observed for Ce2NiGa9Ge2, with the magnetically easy axis lying along the [001] crystallographic direction. A transition to an antiferromagnetic state was observed below 4 K in the easy direction of magnetization. In the magnetically hard direction of the basal plane, paramagnetic behavior was observed down to 1.8 K.     

Ternary rare earth osmium aluminides R(7+)(x)Os(12)Al(61+)(y) belonging to a structural family with layered topology

The 10 intermetallic compounds R(7+)(x)Os(12)Al(61+)(y) (R = Y, Nd, Sm, Gd-Tm) were prepared by arc-melting of the elemental components. They crystallize with a hexagonal structure very similar to that of Y(7.28)Re(12)Al(61.38). The structure was determined from four-circle diffractometer data of Y(7+)(x)Os(12)Al(61+)(y): P6(3)/mcm, a = 1301.5(2) pm, c = 903.0(2) pm, Z =1. Four atomic sites, all located on the 6(3) axis, show fractional occupancy, resulting in the composition Y(7.86(1))Os(12)Al(61.51(4)), corresponding to the Pearson symbol hP90-8.63. The structure may be viewed as consisting of alternating atomic layers of two kinds, although chemical bonding within and between the layers is of similar character as can be judged from the near-neighbor environments, where all of the 11 atomic sites have high coordination numbers. One kind of layers (A). is relatively loosely packed and contains the yttrium and some aluminum atoms. The other kind (B). consists of the osmium and the remaining aluminum atoms in a nearly hexagonal close-packed arrangement. These layers are stacked in the sequence ABAB. A similar building principle has recently been recognized for several other structures of ternary intermetallic compounds of rare earth and transition metals with a high content of aluminum or gallium, where the structures of CeOsGa(4), Ho(3)Ru(4)Ga(15), and Y(2)Pt(6)Al(15) are the most recent examples. This structural family is briefly reviewed. The cell volume of Yb(7+)(x)Os(12)Al(61+)(y) indicates a mixed or intermediate valence character +2/+3 for the ytterbium atoms of this compound.     

Structures and physical properties of rare-earth zinc antimonides Pr6Zn(1+x)Sb(14+y) and RE6Zn(1+x)Sb14 (RE = Sm, Gd-Ho)

A new series of isostructural ternary rare-earth zinc antimonides RE(6)Zn(1+x)Sb(14+y) (RE = Pr, Sm, Gd-Ho) has been obtained by direct reaction of the elements at 1050-1100 degrees C. Single-crystal X-ray diffraction studies revealed that these compounds adopt an orthorhombic structure type (space group Immm (no. 71), Z = 2, a = 4.28-4.11 A, b = 15.15-14.73 A, c = 19.13-18.56 A in the progression from RE = Pr to Ho) that may be regarded as stuffed variants of a (U(0.5)Ho(0.5))(3)Sb(7)-type host structure. Columns of face-sharing RE(6) trigonal prisms, centered by Sb atoms, occupy channels defined by an extensive polyanionic Sb network. This network is constructed from three-atom-wide and four-atom-wide Sb strips, the latter being linked together by single Sb atoms in RE(6)Zn(1+x)Sb(14) (RE = Sm, Gd-Ho; y = 0), but also by additional Sb-Sb pairs in a disordered fashion in Pr(6)Zn(1+x)Sb(14+y) (y = approximately 0.6). Interstitial Zn atoms then partially fill tetrahedral sites (occupancy of 0.5-0.7) and, to a lesser extent, square pyramidal sites (occupancy of 0.04-0.12), accounting for the observed nonstoichiometry with variable x. Except for the Gd member, these compounds undergo antiferromagnetic ordering below T(N) < 9 K, with the magnetic susceptibilities of the Tb, Dy, and Ho members following the Curie-Weiss law above T(N). For the Ho member, the thermal conductivities are low and the Seebeck coefficients are small and positive, implying p-type character consistent with the occurrence of partial Zn occupancies. At low temperatures (down to 5 K), electrical resistivity measurements for the Tb, Dy, and Ho members indicated metallic behavior, which persists at high temperatures (up to 560 K) for the Ho member. Band structure calculations on an idealized "Gd(6)Zn(2)Sb(14)" model revealed the existence of a pseudogap near the Fermi level.     

Neutron diffraction study of the type I clathrate Ba8Al(x)Si(46-x): site occupancies, cage volumes, and the interaction between the guest and the host framework

Samples with the type I clathrate structure and composition Ba(8)Al(x)Si(46-x), where x = 8, 10, 12, 14, and 15, were examined by neutron powder diffraction at 35 K. The clathrate type I structure contains Ba cations as guests in a framework derived from tetrahedrally coordinated Al/Si atoms. The framework is made up of five- and six-membered rings that form dodecahedral and tetrakaidecahedral cages. The change in distances between tetrahedral sites across the series is used to develop a model for the mixed Al/Si occupancy observed in the framework. The calculated volumes of the cages that contain the Ba atoms display a linear increase with increasing Al composition. In the smaller dodecahedral cages, the Ba atomic displacement parameter is symmetry constrained to be isotropic for all compositions. In the larger tetrakaidecahedral cages, the anisotropic atomic displacement of the Ba atom depends upon the composition: the displacement is perpendicular (x = 8) and parallel (x = 15) to the six-membered ring. This difference in direction of the displacement parameter is attributed to interaction with the Al in the framework and not to the size of the cage volume as x increases from 8 to 15. The influence of the site occupation of Al in the framework on displacement of the cation at the 6d site is demonstrated.     

Ternary rare-earth manganese bismuthides: structures and physical properties of RE(3)MnBi(5) (RE = La-Nd) and Sm(2)Mn(3)Bi(6)

Investigations in the ternary RE-Mn-Bi systems where RE is an early rare earth element have revealed the existence of the polybismuthides RE3MnBi5 (RE = La-Nd), previously known only for the Ce member, and the new compound Sm2Mn3Bi6. Their structures were determined from single-crystal X-ray diffraction data. The RE3MnBi5 compounds adopt the hexagonal inverse Hf5Cu3Sn-type structure (Pearson symbol hP18, space group P63/mcm, a = 9.7139(11)-9.5438(16) A, c = 6.4883(7)-6.4089(11) A for RE = La-Nd), containing chains of face-sharing Mn-centered octahedra. Sm2Mn3Bi6 adopts a new monoclinic structure type (Pearson symbol mP22, space group P21/m, a = 10.3917(8) A, b = 4.4557(3) A, c = 13.2793(10) A, beta = 108.0100(10) degrees ) in which the Mn centers are coordinated by Bi atoms in diverse geometries (distorted octahedral, trigonal bipyramidal, and distorted tetrahedral (seesaw)) and participate in extensive metal-metal bonding in the form of chains of Mn3 clusters. Homoatomic bonding interactions involving nominally anionic Bi atoms are manifested as one-dimensional Bi chains in RE3MnBi5 and as four-atom-wide Bi ribbons in Sm2Mn3Bi6. Electrical resistivity measurements on single crystals revealed metallic behavior with prominent transitions near 40 K for RE3MnBi5 and 50 K for Sm2Mn3Bi6. Magnetic susceptibility measurements showed that Pr3MnBi5 undergoes magnetic ordering near 25 K.     

RE2MAl6Si4 (RE = Gd, Tb, Dy; M = Au, Pt): layered quaternary intermetallics featuring CaAl2Si2-type and YNiAl4Ge2-type slabs grown from aluminum flux

Six new intermetallic aluminum silicides--Gd(2)PtAl(6)Si(4), Gd(2)AuAl(6)Si(4), Tb(2)PtAl(6)Si(4), Tb(2)AuAl(6)Si(4), Dy(2)PtAl(6)Si(4), and Dy(2)AuAl(6)Si(4)--have been obtained from reactions carried out in aluminum flux. The structure of these compounds was determined by single-crystal X-ray diffraction. They form in space group Rthremacr;m with cell constants of a = 4.1623(3) A and c = 51.048(5) A for the Gd(2)PtAl(6)Si(4) compound. The crystal structure is comprised of hexagonal nets of rare earth atoms alternating with two kinds of layers that have been observed in other multinary aluminide intermetallic compounds (CaAl(2)Si(2) and YNiAl(4)Ge(2)). All six RE(2)MAl(6)Si(4) compounds show antiferromagnetic transitions at low temperatures (T(N) < 20 K); magnetization studies of the Dy compounds show metamagnetic behavior with reorientation of spins at 6000 G. Band structure calculations indicate that the AlSi puckered hexagonal sheets in this structure are electronically distinct from the other surrounding structural motifs.     

Phase range of the type-I clathrate Sr8Al(x)Si(46-x) and crystal structure of Sr8Al10Si36

Samples of the type-I clathrate Sr(8)Al(x)Si(46-x) have been prepared by direct reaction of the elements. The type-I clathrate structure (cubic space group Pm3n) which has an Al-Si framework with Sr(2+) guest atoms forms with a narrow composition range of 9.54(6) ≤ x ≤ 10.30(8). Single crystals with composition A(8)Al(10)Si(36) (A = Sr, Ba) have been synthesized. Differential scanning calorimetry (DSC) measurements provide evidence for a peritectic reaction and melting point at ～1268 and ～1421 K for Sr(8)Al(10)Si(36) and Ba(8)Al(10)Si(36), respectively. Comparison of the structures reveals a strong correlation between the 24k-24k framework sites distances and the size of the guest cation. Electronic structure calculation and bonding analysis were carried out for the ordered models with the compositions A(8)Al(6)Si(40) (6c site occupied completely by Al) and A(8)Al(16)Si(30) (16i site occupied completely with Al). Analysis of the distribution of the electron localizability indicator (ELI) confirms that the Si-Si bonds are covalent, the Al-Si bonds are polar covalent, and the guest and the framework bonds are ionic in nature. The Sr(8)Al(6)Si(40) phase has a very small band gap that is closed upon additional Al, as observed in Sr(8)Al(16)Si(30). An explanation for the absence of a semiconducting "Sr(8)Al(16)Si(30)" phase is suggested in light of these findings.     

Orthonitridoborate ions [BN3]6- in oxonitridosilicate cages: synthesis, crystal structure, and magnetic properties of Ba4Pr7[Si12N23O][BN3], Ba4Nd7[Si12N23O][BN3], and Ba4Sm7[Si12N23O][BN3

The isotypic title compounds Ba4Pr7[Si12N23O][BN3], Ba4Nd7[Si12N23O][BN3], and Ba4Sm7[Si12N23O][BN3] were prepared by reaction of Pr, Nd, or Sm, with barium, BaCO3, Si(NH)2, and poly(boron amide imide) in nitrogen atmosphere in tungsten crucibles using a radiofrequency furnace at temperatures up to 1650 C. They were obtained as main products (approximately 70%) embedded in a very hard glass matrix in the form of intense dark green (Pr), orange-brown (Sm), or dark red (Nd) large single crystals, respectively. The stoichiometric composition of Ba4Sm7[Si12N23O][BN3] was verified by a quantitative elemental analysis. According to the single-crystal X-ray structure determinations (Ba4Ln7[Si12N23][BN3], Z= , P6 with Ln = Pr: a = 1225.7(1), c = 544.83(9) pm, R1 = 0.013, wR2 = 0.030; Ln = Nd: a = 1222.6(1), c = 544.6(1) pm, R1 = 0.017, wR2 = .039; Ln = Sm: a = 1215.97(5), c = 542.80(5) pm, R1 = 0.047, wR2 = 0.099) all three compounds are built up by a framework structure [Si12N23O]23- of corner-sharing SiX4 tetrahedrons (X = O, N). The oxygen atoms are randomly distributed over the X positions. The trigonal-planar orthonitridoborate ions [BN3]6- and also the Ln(3)3+ are situated in hexagonal cages of the framework (bond lengths Si-(N/O) 169-179 pm for Ln=Pr). The remaining Ba2+ and Ln3- ions are positioned in channels of the large-pored network. The trigonal-planar [BN3]6- ions have a B-N distance of 147.1(6) pm (for Ln = Pr). Temperature-dependent susceptibility measurements for Ba4Nd7[Si12N23O][BN3] revealed Curie-Weiss behavior above 60 K with an experimental magnetic moment of muexp = 3.36(5) microB/Nd. The deviation from Curie-Weiss behavior below 60 K may be attributed to crystal field splitting of the J = 9/2 ground state of the Nd3+ ions. No magnetic ordering is evident down to 4.2 K.     

Ternary rare-earth titanium antimonides RE2Ti(11-x)Sb(14+x) (RE = Sm, Gd, Tb, Yb)

The isostructural rare-earth titanium antimonides RE 2Ti 11 - x Sb 14 + x ( RE = Sm, Gd, Tb, Yb) have been synthesized by arc-melting reactions of the elements. Single-crystal X-ray diffraction revealed that they adopt a new structure type (Pearson symbol oP54, space group Pnma, Z = 2; a = 15.8865(6)-15.9529(9) A, b = 5.7164(2)-5.7135(3) A, c = 12.9244(5)-12.9442(7) A for RE = Sm-Yb). The structure consists of titanium-centered octahedra (CN6) and pentagonal bipyramids (CN7) connected to form a 3D framework whose cavities are filled with RE atoms. 1D linear skewers of titanium atoms, within face-sharing octahedral chains, and similar skewers of antimony atoms, associated with the titanium-centered pentagonal bipyramids, extend along the b direction. On proceeding from Sm 2Ti 11Sb 14 to Tb 2Ti 10.41(1)Sb 14.59(1) and Yb 2Ti 10.58(1)Sb 14.42(1), antimony atoms are disordered within some of the titanium sites. Resistivity measurements on the samarium and ytterbium members indicated metallic behavior.     

Structure and white luminescence of Eu-activated (Ba,Sr)(13-x)Al(22-2x)Si(10+2x)O66 materials

The optical properties of Eu-activated (Ba,Sr)(13-x)Al(22-2x)Si(10+2x)O66 materials have been determined after the structural reinvestigation of the hypothetical Ba 13Al 22Si 10O 66 material on the basis of the Gebert's model. The white fluorescence and phosphorescence of the (Ba,Sr)(13-x)Al(22-2x)Si(10+2x)O66:Eu series result from the existence of two broad emission bands associated with (8)H-4f(6)5d(1)-->(8)S-4f(7) transitions peaking at 534 and 438 nm, the intensities of which may be tuned at room temperature via the control of the europium concentration and the substitution of Sr for Ba. This suggests the possibility to adjust the emission of the material to white LED requisites.     

V2AlC, V4AlC3-x (x approximately 0.31), and V12Al3C8: synthesis, crystal growth, structure, and superstructure

Single crystals of V2AlC and the new carbides V4AlC3-x and V12Al3C8 were synthesized from metallic melts. V2AlC was formed with an excess of Al, while V4AlC3-x (x approximately 0.31) and V12Al3C8 require the addition of cobalt to the melt. All compounds were characterized by XRD, EDX, and WDX measurements. Crystal structures were refined on the basis of single-crystal data. The crystal structures can be explained with a building-block system consisting of two types of partial structures. The intermetallic part with a composition VAl is a two-layer cutting of the hexagonal closest packing. The carbide partial structure is a fragment of the binary carbide VC1-x containing one or three layers. V2AlC is a H-phase (211-phase) with space group P63/mmc, Z=2, and lattice parameters of a=2.9107(6) A, and c=13.101(4) A. V4AlC3-x (x approximately 0.31) represents a 413-phase with space group P63/mmc, Z=2, a=2.9302(4) A, and c=22.745(5) A. The C-deficit is limited to the carbon site of the central layer. V12Al3C8 is obtained at lower temperatures. In the superstructure (P63/mcm, Z=2, a=5.0882(7) A, and c=22.983(5) A) the vacancies on the carbon sites are ordered. The ordering is combined to a small shift of the V atoms. This ordered structure can serve as a structure model for the binary carbides TMC1-x as well. V4AlC3-x (x approximately 0.31) and V12Al3C8 are the first examples of the so-called MAX-phases (MX)nMM' (n=1, 2, 3), where a deficit of X and its ordered distribution in a superstructure is proven, (MX1-x)nMM'.     

Ternary rare-earth arsenides REZn3As3 (RE = La-Nd, Sm) and RECd3As3 (RE = La-Pr)

Ternary rare-earth zinc arsenides REZn(3)As(3) (RE = La-Nd, Sm) with polymorphic modifications different from the previously known defect CaAl(2)Si(2)-type forms, and the corresponding rare-earth cadmium arsenides RECd(3)As(3) (RE = La-Pr), have been prepared by reaction of the elements at 800 °C. LaZn(3)As(3) adopts a new orthorhombic structure type (Pearson symbol oP28, space group Pnma, Z = 4, a = 12.5935(8) ?, b = 4.1054(3) ?, c = 11.5968(7) ?) in which ZnAs(4) tetrahedra share edges to form ribbons that are fragments of other layered arsenide structures; these ribbons are then interconnected in a three-dimensional framework with large channels aligned parallel to the b direction that are occupied by La(3+) cations. All remaining compounds adopt the hexagonal ScAl(3)C(3)-type structure (Pearson symbol hP14, space group P6(3)/mmc, Z = 2; a = 4.1772(7)-4.1501(2) ?, c = 20.477(3)-20.357(1) ? for REZn(3)As(3) (RE = Ce, Pr, Nd, Sm); a = 4.4190(3)-4.3923(2) ?, c = 21.4407(13)-21.3004(8) ? for RECd(3)As(3) (RE = La-Pr)) in which [M(3)As(3)](3-) layers (M = Zn, Cd), formed by a triple stacking of nets of close-packed As atoms with M atoms occupying tetrahedral and trigonal planar sites, are separated by La(3+) cations. Electrical resistivity measurements and band structure calculations revealed that orthorhombic LaZn(3)As(3) is a narrow band gap semiconductor.     

La-Fe-M(M=Al, Si)化合物磁热性能研究进展

介绍了La-Fe-M(M=AI,Si)化合物在磁热性能研究方面的最新进展。具有NaZn13型晶体结构,含高浓度Fe的La-Fe—M(M=AI,Si)化合物为良好的软磁材料;用少量的Co替代化合物中Si,Al元素可以将化合物的居里温度提高至室温;对La(Fe1-yCoy)xSi13-x化合物,适量的Si,Co组合可使化合物在室温产生可与Gd5Si2Ge2比拟的磁热效应;加入适量的间隙原子H,也可使La(FexSi1-x)13在室温的磁热性能远远大于金属Gd;对含Si量低及含Si量高的La(FexSi1-x)13化合物在相转变点附近由温度和磁场诱导相变的本质做了详细阐述。     

A New Family of Nonstoichiometric Layered Rare-Earth Tin Antimonides, RESn(x)()Sb(2) (RE = La, Ce, Pr, Nd, Sm): Crystal Structure of LaSn(0.75)Sb(2)

A new class of nonstoichiometric layered ternary rare-earth tin antimonides, RESn(x)()Sb(2) (RE = La, Ce, Pr, Nd, Sm), has been synthesized through reaction of the elements at 950 degrees C. In the lanthanum series LaSn(x)()Sb(2), tin can be incorporated from a maximum content of x approximately 0.7 or 0.8 to as low as x approximately 0.10. The structure of lanthanum tin diantimonide with the maximum tin content, LaSn(0.75)Sb(2), has been determined by single-crystal X-ray diffraction methods. It crystallizes in the orthorhombic space group -Cmcm with a = 4.2425(5) ?, b = 23.121(2) ?, c = 4.5053(6) ?, and Z = 4. The isostructural rare-earth analogues were characterized by powder X-ray diffraction. The structure of LaSn(0.75)Sb(2) comprises layers of composition "LaSb(2)" in which La atoms are coordinated by Sb atoms in a square-antiprismatic geometry. Between these layers reside chains of Sn atoms distributed over three crystallographically independent sites, each partially occupied at about 20%. The structure of LaSn(0.75)Sb(2) can be regarded as resulting from the excision of RE-Sb and Sb-Sb bonds in the related structures of binary rare-earth diantimonides, RESb(2), and then intercalation of Sn atoms between layers.     

Crystal structure of the new FeSe(1-x) superconductor

The newly discovered superconductor FeSe(1-x) (x approximately 0.08, T(c)(onset) approximately 13.5 K at ambient pressure rising to 27 K at 1.48 GPa) exhibits a structural phase transition from tetragonal to orthorhombic below 70 K at ambient pressure-the crystal structure in the superconducting state shows remarkable similarities to that of the REFeAsO(1-x)F(x) (RE = rare earth) superconductors.