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.     

REAu2In4 (RE = La, Ce, Pr, Nd): polyindides from liquid indium

The series of compounds REAu2In4 (RE = La, Ce, Pr, Nd) crystallize from excess In as rod-shaped single crystals. All members adopt the orthorhombic space group Pnma with a = 18.506(2) A, b = 4.6865(6) A, and c = 7.3414(9) A for LaAu2In4, a = 18.514(3) A, b = 4.6624(8) A, and c = 7.389(1) A for CeAu2In4, a = 18.420(4) A, b = 4.6202(9) A, and c = 7.376(2) A for the Pr analogue, and a = 18.406(2) A, b = 4.6114(5) A, and c = 7.4073(7) A for NdAu2In4. The REAu2In4 series can be regarded as polar intermetallic phases composed of a complex [Au2In4]3- polyanion network in which the rare-earth ions are embedded. The [Au2In4]3- network features In tetramer units, which defines the compounds as polyindides. Magnetic measurements found no magnetic ordering down to 2 K for any of the compounds. In addition, LaAu2In4 was found to be Pauli paramagnetic with a small susceptibility. Ab initio density functional methods were used to carry out electronic structure calculations to explore the bonding, the role of gold, and the contributions of different atoms to the density of states near the Fermi energy. We find that the density of states decreases slowly near Ef and reaches a minimum at about 0.5 eV above Ef.     

Rare-earth metal(III) oxide selenides M4O4Se[Se2] (M=La, Ce, Pr, Nd, Sm) with discrete diselenide units: crystal structures, magnetic frustration, and other properties

The rare-earth metal(III) oxide selenides of the formula La4O4Se[Se2], Ce4O4Se[Se2], Pr4O4Se[Se2], Nd4O4Se[Se2], and Sm4O4Se[Se2] were synthesized from a mixture of the elements with selenium dioxide as the oxygen source at 750 degrees C. Single crystal X-ray diffraction was used to determine their crystal structures. The isostructural compounds M4O4Se[Se2] (M=La, Ce, Pr, Nd, Sm) crystallize in the orthorhombic space group Amm2 with cell dimensions a=857.94(7), b=409.44(4), c=1316.49(8) pm for M=La; a=851.37(6), b=404.82(3), c=1296.83(9) pm for M=Ce; a=849.92(6), b=402.78(3), c=1292.57(9) pm for M=Pr; a=845.68(4), b=398.83(2), c=1282.45(7) pm for M=Nd; and a=840.08(5), b=394.04(3), c=1263.83(6) pm for M=Sm (Z=2). In their crystal structures, Se2- anions as well as [Se-Se]2- dumbbells interconnect {[M4O4]4+} infinity 2 layers. These layers are composed of three crystallographically different, distorted [OM4]10+ tetrahedra, which are linked via four common edges. The compounds exhibit strong Raman active modes at around 215 cm(-1), which can be assigned to the Se-Se stretching vibration. Optical band gaps for La4O4Se[Se2], Ce4O4Se[Se2], Pr4O4Se[Se2], Nd4O4Se[Se2], and Sm4O4Se[Se2] were derived from diffuse reflectance spectra. The energy values at which absorption takes place are typical for semiconducting materials. For the compounds M4O4Se[Se2] (M=La, Pr, Nd, Sm) the fundamental band gaps, caused by transitions from the valence band to the conduction band (VB-CB), lie around 1.9 eV, while for M=Ce an absorption edge occurs at around 1.7 eV, which can be assigned to f-d transitions of Ce3+. Magnetic susceptibility measurements of Ce4O4Se[Se2] and Nd4O4Se[Se2] show Curie-Weiss behavior above 150 K with derived experimental magnetic moments of 2.5 micro B/Ce and 3.7 micro B/Nd and Weiss constants of theta p=-64.9 K and theta p=-27.8 K for the cerium and neodymium compounds, respectively. Down to 1.8 K no long-range magnetic ordering could be detected. Thus, the large negative values for theta p indicate the presence of strong magnetic frustration within the compounds, which is due to the geometric arrangement of the magnetic sublattice in form of [OM4]10+ tetrahedra.     

Closely related rare-earth metal germanides RE2Li2Ge3 and RE3Li4Ge4 (RE = La-Nd, Sm): synthesis, crystal chemistry, and magnetic properties

Reported are the syntheses, crystal structures, and magnetic susceptibilities of two series of closely related rare-earth metal-lithium germanides RE(2)Li(2)Ge(3) and RE(3)Li(4)Ge(4) (RE = La-Nd, Sm). All title compounds have been synthesized by reactions of the corresponding elements at high temperatures, and their structures have been established by single-crystal X-ray diffraction. RE(2)Li(2)Ge(3) phases crystallize in the orthorhombic space group Cmcm (No. 63) with the Ce(2)Li(2)Ge(3) structure type, while the RE(3)Li(4)Ge(4) phases crystallize in the orthorhombic space group Immm (No. 71) with the Zr(3)Cu(4)Si(4) structure type, respectively. Both of their structures can be recognized as the intergrowths of MgAl(2)Cu- and AlB(2)-like slabs, and these traits of the crystal chemistry are discussed. Temperature-dependent direct-current magnetization measurements indicate Curie-Weiss paramagnetism in the high-temperature regime for RE(2)Li(2)Ge(3) and RE(3)Li(4)Ge(4) (RE = Ce, Pr, Nd), while Sm(2)Li(2)Ge(3) and Sm(3)Li(4)Ge(4) exhibit Van Vleck-type paramagnetism. The data are consistent with the local-moment magnetism expected for RE(3+) ground states. At temperatures below ca. 20 K, magnetic ordering transitions have been observed. The experimental results have been complemented by tight-binding linear muffin-tin orbital electronic-band-structure calculations.     

A Comparative Study of Two New Structure Types. Synthesis and Structural and Electronic Characterization of K(RE)P(2)Se(6) (RE = Y, La, Ce, Pr, Gd)

Two polytypes of potassium rare-earth-metal hexaselenodiphosphates(IV), K(RE)P(2)Se(6) (RE = Y, La, Ce, Pr, Gd), have been synthesized from the stoichiometric reaction of RE, P, Se, and K(2)Se(4) at 750 degrees C. Both single-crystal and powder X-ray diffraction analyses showed that the structures of these polytypes vary with the size of the rare earth metals. For the smaller rare-earth metals, Y and Gd, K(RE)P(2)Se(6) crystallized in the orthorhombic space group P2(1)2(1)2(1). The yttrium compound was studied by single-crystal X-ray diffraction with the cell parameters a = 6.7366(5) ?, b = 7.4286(6) ?, c = 21.603(2) ?, and Z = 4. This structure type comprises a layered, square network of yttrium atoms that are bound to four distinct [P(2)Se(6)](4)(-) units through selenium bonding. Each [P(2)Se(6)](4)(-) unit possesses a Se atom that is not bound to any Y atom but is pointing out into the interlayer spacing, into an environment of potassium cations. For larger rare-earth metals, La, Ce, and Pr, K(RE)P(2)Se(6) crystallized in a second, monoclinic polytype, the structure of which has been published. Both of these two different polytypes can be related to each other and several other isoelectronic chalcophosphate structures based on a Parthé valence electron concentration analysis. These structures include Ag(4)P(2)S(6), K(2)FeP(2)S(6), and the hexagonal M(II)PS(3) structure types. The magnetic susceptibilities of the title compounds have been studied, and the behavior can been explained based on a simple set of unpaired f-electrons. The diffuse reflectance spectroscopy also showed that these yellow plates are moderately wide band gap ( approximately 2.75 eV) semiconductors.     

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.     

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.     

两类稀土钒酸盐的合成与结构

通过（１）ＬｎＯＣｌ／Ｖ＿２Ｏ＿５，（２）ＬｎＣｌ３／Ｖ及（３）ＬｎＯＣｌ／ＬｎＣｌ／Ｖ＿２Ｏ＿５／Ｖ的高温固态化学反应，得到两种稀土钒酸盐：Ｌｎ＿６Ｖ＿３Ｃｌ＿（１０）Ｏ＿（１２）（Ｌｎ＝Ｌａ）及Ｌｎ＿４Ｖ＿５Ｓｉ＿４Ｏ＿（２２）（Ｌｎ＝Ｌａ～Ｎｄ）。Ｌａ＿６Ｖ＿３Ｏ＿（１０）Ｏ＿（１２）晶体呈浅色透明片状，其结构可认为是由［Ｌａ＿３（ＶＯ＿４）＿３Ｃｌ］单元插入到ＬａＣｌ３结构单元中而形成的，在结构中沿ｃ轴方向存在一系列截面积为１９．１的空洞。Ｌｎ＿４Ｖ＿５Ｓｉ＿４Ｏ＿（２２）（Ｌｎ＝Ｌａ，Ｃｅ，Ｐｒ，Ｎｄ）晶体呈，黑色针状，其结构可认为是由交替的稀土钒硅酸盐薄层及钒氧金红石层沿ｃ轴堆叠而表现为准二维Ｃｈｅｖｋｉｎｉｔｅ型结构。     

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.     

New layered rubidium rare-earth selenides: syntheses,structures, physical properties,and electronic structures for RbLnSe(2)

The compounds RbLnSe(2) (Ln = La, Ce, Pr, Nd, Sm, Gd, Tb, Ho, Er, Lu) have been synthesized by means of the reactive flux method at 1173 K. These isostructural compounds, which have the alpha-NaFeO(2) structure type, crystallize with three formula units in space group D(3d)(5)-R(-)3m of the trigonal system in cells at T = 153 K of dimensions (a, c in A) La, 4.4313(4), 23.710(3); Ce, 4.3873(3), 23.656(3); Pr, 4.3524(11), 23.655(7); Nd, 4.3231(5), 23.670(4); Sm, 4.2799(4), 23.647(3); Gd, 4.2473(7), 23.689(5); Tb, 4.2197(4), 23.631(3); Ho, 4.1869(6), 23.652(5); Er, 4.1541(8), 23.576(7); Lu, 4.1294(6), 23.614(5). The structure consists of close-packed Se layers in a pseudocubic structure distorted along [111]. The Rb and Ln atoms occupy distorted octahedral sites in alternating layers. The Rb-centered octahedra share edges with the Ln-centered octahedra between layers. Within a given layer, both the Rb-centered and Ln-centered octahedra share edges with themselves. RbTbSe(2) and RbErSe(2) exhibit Curie-Weiss paramagnetism between 5 and 300 K, and RbCeSe(2) exhibits Curie-Weiss paramagnetism between 100 and 300 K. The optical transitions for RbCeSe(2), RbTbSe(2), and RbErSe(2) are in the 2.0-2.2 eV region of the spectrum, both from diffuse reflectance spectra and from first-principles calculations. These calculations also provide insight into the electronic structures and chemical bonding in RbLnSe(2). A quadratic fit for the lanthanide contraction of the Ln-Se distance is superior to the linear one only if the closed-shell atoms La and Lu are included.     

Occupation waves the way you have never seen them: the orthorhombic quasicrystal approximants RE(13)Zn(58+)(delta) (RE = Ho, Er, Tm, and Lu)

A series of binary quasicrystal approximants RE13Zn58+delta (RE = Ho, Er, Tm, and Lu) have been prepared, and structural studies were performed by means of single-crystal X-ray diffraction. All four compounds crystallize in the orthorhombic system, but while the Ho-containing compound crystallizes in space group Pcmn, the rest of the compounds crystallize in Pc21n. This work is a continuation of the structural studies on RE13Zn approximately 58 (RE = Ce, Pr, Nd, Sm, Gd, Tb, and Dy), which all belong to the hexagonal system. The sequence of RE13Zn58+delta compounds exhibits a large variability in local ordering and composition, and therefore the crystal structures are generally rather more complex than those previously reported and exhibit a number of different ordering modes. These four compounds are structurally closely related to each other.     

La0.5>RE0.3Sr0.2FeO3－δ (RE = Nd、Ce、Sm)体系双稀土阴极材料的制备与电性能

采用甘氨酸-硝酸盐法(GNP)合成了La0.5RE0.3Sr0.2FeO3－δ(RE=Nd、Ce、Sm)系列复合氧化物粉体. 用X射线衍射(XRD)和TG-DSC分析了样品钙钛矿物相的形成过程, 用Archimedes排水法测量体积密度并计算烧结样品的相对密度, 用四端子技术测量电导率. 结果显示, 掺Nd的样品1200 ℃烧结2 h成为单一立方钙钛矿结构, 掺Ce样品有明显的CeO2立方相析出, 掺Sm样品主相为钙钛矿结构伴有微弱的杂峰. 1250 ℃烧结2 h的La0.5Nd0.3Sr0.2FeO3－δ在600 ℃时电导率高达100 S•cm-1以上, 明显高于La0.5Ce0.3Sr0.2FeO3－δ及La0.5Sm0.3Sr0.2FeO3－δ样品的电导率, 预示着La0.5Nd0.3Sr0.2FeO3－δ可能是一种良好的中温固体氧化物燃料电池(SOFC)阴极材料.     

稀土-反式-2,3-二甲基丙烯酸-邻菲咯啉混配配合物的合成与表征

合成了一种新的双核稀土配合物[REL₃(phen)]₂(RE=La,Ce,Pr,Nd,Sm,Eu,L=反式CH₃CHC(CH₃)COO^-,phen=phenanthroline),并且用红外光谱、紫外光谱、核磁共振谱和元素分析等进行了表征,其中测定了[LaL₃phen]₂的晶体结构.晶体属单斜晶系,P2₁/n空间群,Z=2,晶胞参数a=1.2962(4)nm,b=1.3283(4)nm,c=1.5485(5)nm,β=95.45(2)°,最终偏差因子R=0.033,R_W=0.040.配合物分子为一个中心对称的双核分子,镧离子由两个双齿羧基和两个μ₂-O羧基桥联,La…La^*距离为0.4094nm.中心离子为九配位,形成畸变的三帽三棱柱配位多面体.La-O和La-N的键长范围分别为0.2460～0.2756nm和0.2718～0.2760nm.     

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.     

Intermetallics as zintl phases: Yb2Ga4Ge6 and RE3Ga4Ge6 (RE=Yb, Eu): structural response of a [Ga4Ge6]4- framework to reduction by two electrons

Two new intermetallic compounds, Yb(2)Ga(4)Ge(6) and Yb(3)Ga(4)Ge(6), were obtained from reactions in molten Ga. A third compound, Eu(3)Ga(4)Ge(6), was produced by direct combination of the elements. The crystal structures of these compounds were studied by single-crystal X-ray diffraction. Yb(2)Ga(4)Ge(6) crystallizes in an orthorhombic cell with a=4.1698(7), b=23.254(4), c=10.7299(18) A in the polar space group Cmc2(1). The structure of RE(3)Ga(4)Ge(6) is monoclinic, space group C2/m, with cell parameters a=23.941(6), b=4.1928(11), c=10.918(3) A, beta=91.426(4) degrees for RE=Yb, and a=24.136(2), b=4.3118(4), c=11.017(1) A, beta=91.683(2) degrees for RE=Eu. The refinement [I>2 sigma(I)] converged to the final residuals R(1)/wR(2)=0.0229/0.0589, 0.0411/0.1114, and 0.0342/0.0786 for Yb(2)Ga(4)Ge(6), Yb(3)Ga(4)Ge(6), and Eu(3)Ga(4)Ge(6), respectively. The structures of these two families of compounds can be described by a Zintl concept of bonding, in which the three-dimensional [Ga(4)Ge(6)](n-) framework serves as a host and electron sink for the electropositive RE atoms. The structural relation of RE(3)Ga(4)Ge(6) to of Yb(2)Ga(4)Ge(6) lies in a monoclinic distortion of the orthorhombic cell of Yb(2)Ga(4)Ge(6) and reduction of the [Ga(4)Ge(6)] network by two electrons per formula unit. The results of theoretical calculations of the electronic structure, electrical transport data, and thermochemical and magnetic measurements are also reported.     

EIS Study on the Electrochemical Properties of RE(Ni,Co,Mn,Ti)s Alloys (RE=La,Ce,Pr,Nd) at Different Depths of Discharge (DOD)

In the present investigation, EIS was employed to study the electrode kinetics of AB₅ typed RE (Ni, Co, Mn, Ti)₅ alloy and compare the difference of rare earth component effects when pure La, Ce, Pr or Nd was used individually for RE in the alloy respectively.     

Syntheses, structures, magnetism, and optical properties of lutetium-based interlanthanide selenides

Ln3LuSe6 (Ln = La, Ce), beta-LnLuSe3 (Ln = Pr, Nd), and LnxLu4-xSe6 (Ln = Sm, Gd; x = 1.82, 1.87) have been synthesized using a Sb2Se3 flux at 1000 degrees C. Ln3LuSe6 (Ln = La, Ce) adopts the U3ScS6-type three-dimensional structure, which is constructed from two-dimensional 2(infinity)[Ln3Se6](3-) slabs with the gaps between these slabs being filled by octahedrally coordinated Lu(3+) ions. The series of beta-LnLuSe3 (Ln = Pr, Nd) are isotypic with UFeS3. Their structures include layers formed from LuSe6 octahedra that are separated by eight-coordinate Ln(3+) (Ln = Pr, Nd) ions in bicapped trigonal prismatic environments. Sm1.82Lu2.18Se6 and Gd1.87Lu2.13Se6 crystallize in the disordered F-Ln2S3 type structure with the eight-coordinate bicapped trigonal prismatic Ln(1) ions residing in the one-dimensional channels formed by three different double chains via edge- and corner-sharing. These double chains are constructed from Ln(2)Se7 monocapped trigonal prisms, Ln(3)Se6 octahedra, and Ln(4)S6 octahedra, respectively. The magnetic susceptibilities of beta-PrLuSe3 and beta-NdLuSe3 follow the Curie-Weiss law. Sm1.82Lu2.18Se6 shows van Vleck paramagnetism. Magnetic susceptibility measurements show that Gd1.87Lu2.13Se6 undergoes an antiferromagnetic transition around 4 K. Ce3LuSe6 exhibits soft ferromagnetism below 5 K. The optical band gaps for La3LuSe6, Ce3LuSe6, beta-PrLuSe3, beta-NdLuSe3, Sm1.82Lu2.18Se6, and Gd1.87Lu2.13Se6 are 1.26, 1.10, 1.56, 1.61, 1.51, and 1.56 eV, respectively.     

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.     

New layered germanide halides RE2GeX2 (RE = Y, Gd; X = Br, I)

The title compounds were synthesized from RE, REX3, and Ge under an Ar atmosphere at 1200-1370 K. Y2GeI2 and Gd2GeI2 crystallize in space group Rm with lattice constants a = 4.2135(3) and 4.2527(1) A and c = 31.480(2) and 31.657(1) A, respectively. Gd2GeBr2 crystallizes in two modifications, the 1T-type (space group Pm1; a = 4.1668(2) A, c = 9.8173(6) A) and the 3R-type (space group Rm; a = 4.1442(9) A, c = 29.487(7) A). The structural motifs of RE2GeX2 compounds are Ge-centered slightly distorted RE6 octahedra connected via their common edges and extending in the a and b directions. The resulting close-packed double layers are separated by halogen atoms. The electrical resistivity measurements revealed semiconductor behavior for Y2GeI2 and Gd2GeI2 and a metal-semiconductor transition for 1T-Gd2GeBr2. Magnetic susceptibility and heat capacity measurements show long-range magnetic ordering for Gd2GeI2 and 1T-Gd2GeBr2 at approximately 15 and approximately 13 K, respectively.     

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.