Structural investigation of ternary RIr3B2 compounds (R=Ce and Pr)

Structural studies were performed for the ternary RIr₃B₂ compounds (R=Ce and Pr) from as cast samples. The crystal structure of the ternary boride CeIr₃B₂ (CeCo₃B₂ structure type, space group P6/mmm, a=5.520(3) Å, c=3.066(2) Å, Z=1, V=80.91 ų, ρ_x=15.154 g cm⁻³) was refined to R₁=0.0470, wR₂=0.1240 from single-crystal X-ray diffraction data. The new ternary boride PrIr₃B₂ was found to be isostructural with the CeIr₃B₂ compound. Its lattice parameters a=5.5105(2) Å, c=3.1031(1) Å were obtained from a Rietveld refinement of X-ray powder diffraction data.     

Crystal structure and physical properties of ternary compounds RPt3B, R=La, Pr, Nd

The crystal structure of a new series of ternary rare-earth platinum borides RPt₃B (R=La, Pr, Nd) has been studied by X-ray powder diffraction analyses from the ‘as-cast’ alloys. The tetragonal CePt₃B structure type, space group P4mm (No. 99), has been confirmed for all compounds. Rietveld refinements for the two compounds, PrPt₃B and NdPt₃B, were performed. LaPt₃B is a temperature-independent Pauli-type paramagnet from room temperature down to 4 K. PrPt₃B orders antiferromagnetically at T_N=15 K followed by a ferromagnetic spin flip at T_C=5 K, whereas NdPt₃B exhibits an antiferromagnetic spin alignment at a Néel temperature T_N=7 K. The temperature dependence of the electrical resistivity, ρ(T), reflects the metallic character of these compounds. Furthermore the characteristic changes of slope of ρ(T) plots prove the magnetic transitions.     

Magnetic structures of R2RhSi3 (R=Ho, Er) compounds

Powder X-ray and neutron diffraction and magnetic measurements have been performed on R₂RhSi₃ (R=Ho and Er) compounds at low temperatures. The compounds crystallize in a derivative of the hexagonal AlB₂-type structure. The crystal structure parameters have been refined on the basis of the X-ray and neutron diffraction patterns collected in the paramagnetic region. These compounds are antiferromagnets with Néel temperatures of 5.2 K for Ho₂RhSi₃ and 5 K for Er₂RhSi₃. Both compounds exhibit collinear magnetic structures, described by the propagation vector k=(1/2,0,0) for Ho₂RhSi₃ and k=(0,0,0) for Er₂RhSi₃. This magnetic order is stable in the temperature range between 1.5 K and the Néel temperature.     

Magnetic ordering in ternary RMn2Ge2 compounds (R = Tb, Ho, Er, Tm, Lu) from neutron diffraction study

The compounds RMn₂Ge₂ (R = Tb, Ho, Er, Tm, Lu) have been investigated by neutron diffraction. TbMn₂Ge₂ is a collinear ferrimagnet with the Mn and Tb moment aligned along the c axis (μ_TB = 8.81(59) μ_B: μ_Mn = 2.21(44) μ_B). HoMn₂Ge₂ exhibits incommensurale ordering below 2.1 K characterized by two wavevectors at 1.3 K: q₁ = (0.1543(4), 0.1543(4), 0) and q₂ = (0.210(1), 0.007(1), 0). The Mn sublattice remains antiferromagnetic down to 1.3 K (μ_Mn = 2.38(6) μ_B). The Er moments order ferromagnetically below 5.5 K in ErMn₂Ge₂ (μ_Mn = 6.81(31) μ_B). The moments are perpendicular to the c axis. The Mn sublattice remains antiferromagnetic down to 1.8 K (μ_Mn = 2.34(18) μ_B). The magnetic structure of TmMn₂Ge₂ is characterized by the propagation vector (0.0.1/2). the Tm moments lying in the basal plane. The ordering of the Tm moments yields a canting of the Mn moments (τ = 21(3)°); μ_Tm = 6.63(18) μ_B; μ_Mn = 2.28(27) μ_B). The antiferromagnetic structure of LuMn₂Ge₂ has been determined (μ_Mn = 2.32(14) μ_B). The evolution of the magnetic properties of the heavy rare earth compounds RMn₂Ge₂ is discussed.     

Magnetism of selected ternary Sm compounds

The effect of In for Sn and Gd for Sm substitution on magnetic properties of the SmPdSn_1−xIn_x and Gd_xSm_1−xPdIn compounds has been studied. The behaviour of the first series differs markedly from the second one. One of the most visible difference in the magnetic properties is the fact, that in the SmPdSn_1−xIn_x series the so called non-Curie-Weiss (NCW) behaviour is observed whereas in the case of the gadolinium series the Curie-Weiss law (CW) is fulfilled. The values of magnetic phase transition temperatures, magnetic moment obtained at 7 T and magnetocaloric effect are much higher for Gd-rich compounds.     

New Zr6CoAs2-type R6MnSb2 and R6MnBi2 compounds (R=Y, Lu, Dy, Ho)

A powder X-ray diffraction investigation of the new ternary compounds Zr₆CoAs₂-type R₆MnSb₂ and R₆MnBi₂ (R=Y, Lu, Dy, Ho) is reported. The compounds Ho₆MnSb₂ (a=0.8070(2) nm, c=0.4230(1) nm), Lu₆MnSb₂ (a=0.7930(1) nm, c=0.4173(1) nm), Y₆MnBi₂ (a=0.8242(1) nm, c=0.4292(1) nm), Dy₆MnBi₂ (a=0.8211(1) nm, c=0.4286(1) nm), Ho₆MnBi₂ (a=0.8164(1) nm, c=0.4250(1) nm) and Lu₆MnBi₂ (a=0.8019(2) nm, c=0.4185(1) nm) crystallize in the hexagonal Zr₆CoAs₂-type structure (space group P6b2m No. 189). The Zr₆CoAs₂-type structure is a superstructure of the Fe₂P-type structure.     

The YbNi2−xSn compound, a new structure type of ternary stannides

The crystal structure of the new ternary stannide YbNi_2−xSn [space group P6₃/mmc (N 194), z=4] was investigated using single crystal X-ray diffraction data (automatic single crystal diffractometers Philips PW1100 and Bruker SMART CCD, Mo K radiation). Three crystals with different composition YbNi_1.695Sn [a=4.424(4) Å, c=15.232(6) Å, V=258.2(4) ų, ρ=10.066 g cm⁻³, μ=57.32 mm⁻¹], YbNi_1.705Sn [a=4.424(5) Å, c=15.179(7) Å, V=257.3(4) ų, ρ=10.116 g cm⁻³, μ=57.59 mm⁻¹] and YbNi_1.745Sn [a=4.303(6) Å, c=16.001(9) Å, V=256.7(5) ų, ρ=10.199 g cm⁻³, μ=58.00 mm⁻¹] were refined to R=0.0494, wR²=0.1330, to R=0.0782, wR²=0.1916 and to R=0.0643, wR²=0.1460, respectively. The compounds belongs to a new structure type of intermetallic compounds and are formed from two hypothetical structures YbNi_1.5Sn (space group P6₃/mmc, z=4) and YbNi₂Sn (space group P6₃/mmc, z=4) containing segments of the MnCu₂Al, ZrBeSi and ZrPt₂Al structures.     

Crystal structure of the Nd(Ru0.6Ge0.4)2 and ErRuGe compounds

Using X-ray powder and single crystal diffraction, the crystal structures of the Nd(Ru_0.6Ge_0.4)₂ and ErRuGe compounds were investigated. The compounds belong to the KHg₂ and TiNiSi type structure, respectively.     

Oxidation resistance of B2 rare earth–magnesium intermetallic compounds

The oxidation behaviors of YMg and CeMg were measured in flowing air using the thermal gravimetric analysis technique. Negligible oxidation is observed at room temperature in both compounds. At elevated temperatures, the rare earth metals oxidize preferentially, while the underlying materials transform into Mg-rich intermetallics before the Mg oxidizes to MgO. The oxidation resistance of YMg is several orders of magnitude greater than that of CeMg. The oxidation of YMg follows parabolic kinetics with an activation energy of 104 kJ/mol while that of CeMg obeys a linear law with an activation energy of 136 kJ/mol.     

The crystal structure of HfZrP

The crystal structure of HfZrP has been determined using single crystal X-ray diffraction data. This compound crystallizes in the orthorhombic space group Cmmm (No.65), with a=19.004(3), b=29.372(4), c=3.565(1) Å and the Zr₂P structure type. The Hf and Zr atoms are disordered on one site with total occupancy of 1.0. X-ray powder patterns indicate that (Hf_xZr_1−x)₂P alloys consist of single phase (Zr₂P-type),two phases and single phase (Hf₂P-type) corresponding to 0≤x≤0.5, 0.5<x<0.8 and 0.8≤x≤1.0, respectively.     

Ce2Ir5B2, a new structure type of ternary borides

The crystal structure of a new ternary boride Ce₂Ir₅B₂, space group , a=5.477(2) Å, c=31.518(5) Å, Z=6, V=818.79 Å, was refined down to R=0.0484, wR₂=0.1211 from single crystal X-ray diffraction data. This is the first representative of a new structure type of intermetallic compounds (an ordered variant of the binary Er₂Co₇ compound). The structure of Ce₂Ir₅B₂ is the stacking variant of the MgCu₂- and CeCo₃B₂-type slabs and belongs to the structural series with the general formula R_2+nM_4+3nX_2n (n=2).     

Crystallographic site of Mn in the icosahedral cluster of LaCo13−xMnx compounds

Studies on the structure and the crystallographic site of Mn in LaCo_13−xMn_x compounds were carried out by using X-ray diffraction and X-ray absorption fine structure (XAFS) of the Mn K-edge. These compounds with x≤3.0 adopt a NaZn₁₃-type structure consisting of icosahedral clusters. The lattice constant increases with the Mn concentration. The calculated XAFS curves of the center and the corner sites in the icosahedral clusters for the Mn K-edge are obtained by using the program . The fitting result for the corner site agrees much better with the observed XAFS spectrum than that for the center site. Therefore, the Mn site is determined to be the corner Co site in the icosahedral clusters of all the compounds. In comparison with the crystallographic parameters of LaCo₁₃, the icosahedral clusters composed of Mn atoms expand and the crystallographic Mn site is slightly more close to the La atom.     

Synthesis and properties of Ba3NaRu2O9−δ and Ba3(Na, R)Ru2O9−δ (R=rare earth) crystals

Crystals of Ba₃NaRu₂O_9−δ (δ≈0.5) and Ba₃(Na, R)Ru₂O_9−δ (R=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm and Yb) were grown by an electrochemical method, and their crystallographic, magnetic, and electric properties were studied. All crystals have a hexagonal structure of space group P6₃mmc. Ba₃NaRu₂O_9−δ and Ba₃(Na, R)Ru₂O_9−δ (except Ce) have a negative asymptotic Curie temperature suggesting the existence of an antiferromagnetic order; however, they are paramagnetic at temperatures above 1.7 K. Ba₃NaRu₂O_9−δ has an effective magnetic moment P_eff of 0.91 μ_B, while P_eff of Ba₃(Na, R)Ru₂O_9−δ (except Ce) reflects the large free-ion moment of the rare earth ions. Ba₃(Na, Ce)Ru₂O_9−δ shows peculiar magnetic behavior that differs from the magnetism of other Ba₃(Na, R)Ru₂O_9−δ crystals. The resistivity of all crystals exhibits an activation-type temperature dependence with an activation energy in the range of 0.10.2 eV.     

Crystal structure of the R3Si1.25Se7 (R = Pr, Nd and Sm) compounds

The crystal structure of new ternary R₃Si_1.25Se₇ (R = Pr, Nd and Sm) compounds (Dy₃Ge_1.25S₇ structure type, Pearson symbol hP22.5, space group P6₃, a = 1.05268 (3) nm, c = 0.60396 (3) nm, R_I = 0.0897 for Pr₃Si_1.25Se₇; a = 1.04760 (3) nm, c = 0.60268 (3) nm, R_I = 0.0891 for Nd₃Si_1.25Se₇; a = 1.04166 (6) nm, c = 0.59828 (6) nm for Sm₃Si_1.25Se₇) was determined using X-ray powder diffraction. The nearest neighbours of the R and Si atoms are exclusively Se atoms. The latter form distorted trigonal prisms around the R atoms, octahedra around the Si1 atoms and tetrahedra around the Si2 atoms. Tetrahedral surrounding exists for Se1 and Se3 atoms. Six neighbours surround every Se2 atom.     

New RRh5Ge3 compounds of the new SmRh5Ge3 structure type and their magnetic properties (R=Sm, Gd, Tb)

Powder X-ray diffraction results and macroscopic magnetic properties of new ternary RRh₅Ge₃ compounds (R=Sm, Gd, Tb) are reported. The compounds SmRh₅Ge₃ (a=2.2744(4) nm, c=0.3888(1) nm), GdRh₅Ge₃ (a=2.2711(5) nm, c=0.3872(1) nm) and TbRh₅Ge₃ (a=2.2628(7) nm, c=0.3851(1) nm) crystallize in the hexagonal SmRh₅Ge₃-type structure (space group P6₃/m; No. 176). The GdRh₅Ge₃ and TbRh₅Ge₃ compounds are Curie–Weiss paramagnets down to 5 K.     

X-ray investigations of ternary R3Pd4Ge4 samples

Ternary R₃Pd₄Ge₄ samples (R=Nd, Eu, Er) were investigated by means of X-ray single crystal (four circle diffractometer Philips PW1100, MoK radiation) and powder diffraction (MX Labo diffractometer, CuK radiation). The Er₃Pd_3.68(1)Ge₄ compound belongs to the Gd₃Cu₄Ge₄ structure type, space group Immm, a=4.220(2) Å, b=6.843(2) Å, c=14.078(3) Å, R₁=0.0484 for 598 reflections with F_o>4σ(F_o) from X-ray single crystal diffraction data. No ternary R₃Pd₄Ge₄ compound when R is Nd or Eu was observed. The Nd and Eu containing samples appeared to be multiphase. Ternary phases observed in the Nd₃Pd₄Ge₄ and Eu₃Pd₄Ge₄ alloys and their crystallographic characteristics are the following: NdPd₂Ge₂, CeGa₂Al₂ structure type, space group I4/mmm, a=4.3010(2) Å, c=10.0633(2) Å (X-ray powder diffraction data); NdPd_0.6Ge_1.4, AlB₂ structure type, space group P6/mmm, a=4.2305(2) Å, c=4.1723(2) Å (X-ray powder diffraction data); Nd(Pd_0.464(1)Ge_0.536(1))₂, KHg₂ structure type, space group Imma, a=4.469(2) Å, b=7.214(2) Å, c=7.651(3) Å, R₁=0.0402 for 189 reflections with F_o>4σ(F_o) (X-ray single crystal diffraction data); Eu(Pd,Ge)₂, AlB₂ structure type, space group P6/mmm, a=4.311(2) Å, c=4.235(2) Å; EuPdGe, EuNiGe structure type, space group P2₁/c, and ternary compound with unknown structure (X-ray powder diffraction data).     

Electronic structure of YbTX compounds

The electronic structure of ternary YbTX compounds (T=Au, Pd, Rh, Pt; X=Sn, Bi) was studied by X-ray photoemission spectroscopy (XPS). XPS valence bands were compared with calculations using the tight-binding linear muffin-tin orbital method. The results showed that the valence bands in these compounds were formed mainly by the 4f orbitals of ytterbium and the 4d (5d) orbitals of the transition elements. Analysis of the Yb 4f valence band and Yb 4d core level states clearly indicated the presence of divalent Yb ions in YbAuSn and YbAuBi, and trivalent ions in YbRhSn and YbPtSn. In turn, the Yb ions in YbPdBi exhibited a mixed valence character.     

Lanthanide(III) halides: Thermodynamic properties and their correlation with crystal structure

Temperatures and enthalpies of phase transitions of 17 lanthanide(III) halides determined experimentally are reported. Correlations were made between temperature of fusion of lanthanide(III) halides, on the one hand, and enthalpy of fusion, on the other, versus atomic number of lanthanide. According to this classification, the lanthanide(III) halides split into groups, as also do the corresponding crystal structures. A correlation between the crystal structure of lanthanide(III) halides and their respective entropy of fusion (or entropy of fusion + entropy of solid–solid phase transition) was inferred from the aforementioned features. Fusion in those halides with hexagonal, UCl₃-type and orthorhombic, PuBr₃-type, structures entails an entropy of fusion change (or entropy of fusion + entropy of solid–solid phase transition change) by 50 ± 4 J mol⁻¹ K⁻¹. The homologous entropy change within the group of halides having the rhomboedric, FeCl₃-type, structure, is smaller and equals 40 ± 4 J mol⁻¹ K⁻¹. Halides with monoclinic, AlCl₃-type, crystal structure constitute a third group associated to an even smaller entropy change upon fusion, only 31 ± 4 J mol⁻¹ K⁻¹. The halides with lower entropies of fusion also have a lower S_1300 K − S_298 K indicating either a higher degree of order in the liquid or a higher entropy in the solid at room temperatures.     

Crystal structure and magnetism of the Y2Pd14B5 compound

The crystal structure of the ternary boride Y₂Pd₁₄B₅, space group I4₁/amd, a=8.484(2) Å, c=16.490(3) Å, V=1186.98 ų, Z=4, was refined down to R=0.0475, wR2=0.1276 from single crystal X-ray diffraction data. Two types of coordination for boron atoms were observed: the coordination sphere for the B1 atom is a trigonal prism with one additional atom; the B2 atom has only four neighboring atoms which form a square. No boron–boron contact was observed. Analysis of the Y₂Pd₁₄B₅ crystal structure shows the existence of a correlation between this structure and the Sc₄Ni₂₉B₁₀ structure type. Magnetization and AC susceptibility measurements indicate that there is no superconducting or magnetic transition in Y₂Pd₁₄B₅ down to 2 K.     

The isothermal section of the Gd–Ni–V ternary system at 773 K

The phase equilibria of the Gd–Ni–V system at 773 K were investigated by means of X-ray diffraction (XRD), scanning electron microscopy (SEM), and electron probe microanalysis (EPMA). The experimental results show no existence of ternary compounds at 773 K. The existence of 14 single-phase regions, 25 two-phase regions and 12 three-phase regions was determined. The maximum solubility of V in (Ni), Gd₂Ni₁₇, GdNi₅ and GdNi₂ was measured to be about 16 at.%, 2 at.%, 3 at.% and 2.5 at.%, respectively, while that of Gd in (Ni), Ni₃V, Ni₂V, Ni₂V₃, NiV₃ and (V) was less than 1 at.%. An isothermal section of the Gd–Ni–V system at 773 K has been presented according to the present work.