Ternary lanthanoid iron phosphides with YCo5P3 and Zr2Fe12P7-type structures

The new compounds YFe₅P₃ and LnFe₅P₃ (Ln = Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) were prepared by reaction of the elemental components in a tin flux. They have YCo₅P₃-type structure. A structure refinement of GdFe₅P₃ from single-crystal X-ray data resulted in a conventional residual of R = 0.063 for 29 variable parameters and 693 unique structure factors. Crystals of the new compound Ce₂Fe₁₂P₇ were also prepared by the tin flux technique. Their Zr₂Fe₁₂P₇-type structure was refined to R = 0.029 for 23 variables and 1365 F values. The coordination polyhedra of the two and some other closely related structure types are discussed. The thermal parameters of the transition metal atoms in such structures increase with increasing coordination number.     

Syntheses, crystal structures and vibrational spectra of KLn(SO4)2·H2O (Ln=La, Nd, Sm, Eu, Gd, Dy)

The potassium lanthanide double sulphates KLn(SO₄)₂·H₂O (Ln=La, Nd, Sm, Eu, Gd, Dy) were obtained by evaporation of aqueous reaction mixtures of rare earth (III) sulphates and potassium thiocyanate at 298 K. X-ray single-crystal investigations show that KLn(SO₄)₂·H₂O (Ln=Nd, Sm, Eu, Gd, Dy) crystallise monoclinically (Ln=Sm: P2₁/c, Z=4, a=10.047(1), b=8.4555(1), c=10.349(1) Å, wR2=0.060, R1=0.024, 945 reflections, 125 parameters) while KLa(SO₄)₂·H₂O adopts space group P3₂21 (Z=3, a=7.1490(5), c=13.2439(12) Å, wR2=0.038, R1=0.017, 695 reflections, 65 parameters). The coordination environment of the lanthanide ions in KLn(SO₄)₂·H₂O is different in the case of the Nd/Sm/Gd and the Eu/Dy compounds, respectively. In the first case the Ln atoms are nine-fold coordinated in contrast to the latter where the Ln ions are eight-fold coordinated by oxygen atoms. The vibrational spectra of KLn(SO₄)₂·H₂O and the UV-vis reflection spectra of KEu(SO₄)₂·H₂O and KNd(SO₄)₂·H₂O are also reported.     

Magnetic properties and structural transitions of orthorhombic fluorite-related compounds Ln3MO7 (Ln=rare earths, M=transition metals)

Magnetic properties and structural transitions of ternary rare-earth transition-metal oxides Ln₃MO₇ (Ln=rare earths, M=transition metals) were investigated. In this study, we prepared a series of molybdates Ln₃MoO₇ (Ln=La-Gd). They crystallize in an orthorhombic superstructure of cubic fluorite with space group P2₁2₁2₁, in which Ln³⁺ ions occupy two different crystallographic sites (the 8-coordinated and 7-coordinated sites). All of these compounds show a phase transition from the space group P2₁2₁2₁ to Pnma in the temperature range between 370 and 710 K. Their magnetic properties were characterized by magnetic susceptibility measurements from 1.8 to 400 K and specific heat measurements from 0.4 to 400 K. Gd₃MoO₇ shows an antiferromagnetic transition at 1.9 K. Measurements of the specific heat for Sm₃MoO₇ and the analysis of the magnetic specific heat indicate a “two-step” antiferromagnetic transition due to the ordering of Sm magnetic moments in different crystallographic sites, i.e., with decreasing temperature, the antiferromagnetic ordering of the 7-coordinated Sm ions occur at 2.5 K, and then the 8-coordinated Sm ions order at 0.8 K. The results of Ln₃MoO₇ were compared with the magnetic properties and structural transitions of Ln₃MO₇ (M=Nb, Ru, Sb, Ta, Re, Os, or Ir).     

Lanthanoid-nickel-phosphides with ThCr2Si2-type structure

The new compounds YNi₂P₂ and LnNi₂P₂ (Ln = La, Ce, Pr, Nd, Sm, Tb, Dy, Ho, Er, Tm) were prépared by sintering the elemental components in silica tubes. Well-developed crystals were obtained using tin as a flux. They crystallize with the ThCr₂Si₂ (CeGa₂Al₂)-type structure which was refined from single-crystal X-ray data for EuNi₂P₂ to a conventional R value of 0.049 for 118 unique structure factors. While the P atoms in formally isotypic EuCo₂P₂ are isolated from each other, they form pairs in EuNi₂P₂. This results in a different $\text{c}\text{a}$ ratio and an entirely different bonding situation. A comparison of cell volumes shows that Eu in EuNi₂P₂ has an intermediate valence.     

Multiband orange-red photoluminescence of Eu ions in new “114” LnBaZn3GaO7 and LnBaZn3AlO7 oxides

A new series of gallozincates LnBaZn₃GaO₇ (Ln=La, Nd, Sm, Eu, Gd, Dy, Y) and new aluminozincates LnBaZn₃AlO₇ (Ln=Y, Eu, Dy) have been synthesized. Their structure refinements show that these phases belong to the “114” series, with hexagonal P6₃mc space group previously described for SmBaZn₃AlO₇. The photoluminescence study of these oxides shows that the Eu³⁺ activated LnBaZn₃MO₇ oxides with Ln=Y, La, Gd; and M=Al, Ga exhibit strong magnetic and electric dipole transitions (multiband emission) which is of interest for white light production. These results also confirm that the site occupied by Eu³⁺ is not strictly centrosymmetric. The electric dipole transition intensity is the highest in GdBaZn₃MO₇ [M=Al, Ga]: 0.05Eu³⁺ as compared with other Eu³⁺ activated compositions. This is due to the layer distortion around GdO₆ octahedra when compared with YO₆ and LaO₆ octahedra.     

Synthesis and magnetic properties of rare earth ruthenates, Ln5Ru2O12 (Ln=Pr, Nd, Sm-Tb)

Single crystals of Ln₅Ru₂O₁₂ (Ln=Pr, Nd, Sm-Tb) were grown out of either NaOH or KOH fluxes in sealed silver tubes. The crystals of all the phases were observed to be twinned as confirmed by TEM studies. The series crystallize in the C2/m monoclinic system with lattice parameters, a=12.4049(4)-12.7621(6) Å, b=5.8414(2)-5.9488(3) Å, c=7.3489(2)-7.6424(4) Å, β=107.425(3)-107.432(2)° and Z=2. The crystal structure is isotypic with the defect/disorder model of Ln₅Re₂O₁₂ (Ln = Y, Gd) and consists of one dimensional edge shared RuO₆ octahedral chains separated by a two dimensional LnO_x polyhedral framework. Magnetic measurements indicate paramagnetic and antiferromagnetic behavior for Ln=Nd, Sm-Gd and Ln=Tb, respectively.     

Magnetic properties of lanthanide rhenium oxides Ln3ReO7 (Ln=Sm, Eu, Ho)

Ternary lanthanide rhenium oxides Ln₃ReO₇ (Ln=Sm, Eu, Ho) were prepared and their structures were determined by X-ray diffraction measurements. They crystallize in an orthorhombic superstructure of cubic fluorite (space group Cmcm for Ln=Sm, Eu; C222₁ for Ln=Ho). The magnetic properties were characterized by magnetic susceptibility and specific heat measurements from 1.8 to 400 K. The Sm₃ReO₇ shows an antiferromagnetic transition at 1.9 K. The Eu₃ReO₇ indicates a magnetic anomaly at 12 K. On the other hand, the results of the specific heat measurements indicate that both Sm₃ReO₇ and Eu₃ReO₇ undergo a structure transition at 270 and 350 K, respectively. The Ho₃ReO₇ is paramagnetic down to 1.8 K.     

Systematic high-pressure synthesis of new filled skutterudites with heavy lanthanide, LnFe4P12 (Ln=heavy lanthanide, including Y)

New filled skutterudites with heavy lanthanide, LnFe₄P₁₂ (Ln=Tb, Dy, Ho, Er, Tm, Yb, Lu and Y) have systematically been prepared for the first time by the high-pressure technique. The relationship between lattice constants and atomic numbers of lanthanide (including Y) is established for LnFe₄P₁₂. Electrical and magnetic properties of several new filled skutterudites with heavy lanthanide have been studied at low temperatures; YFe₄P₁₂ shows a superconducting transition at around 7 K, and DyFe₄P₁₂ behaves as a ferromagnet below 10 K. Electrical and magnetic anomalies in DyFe₄P₁₂ and YFe₄P₁₂ are mainly discussed.     

Magnetic properties of quadruple perovskites Ba4LnRu3O12 (Ln=La, Nd, Sm-Gd, Dy-Lu)

Quadruple perovskites Ba₄LnRu₃O₁₂ (Ln=La, Nd, Sm-Gd, Dy-Lu) were prepared and their magnetic properties were investigated. They adopt the 12L-perovskite-type structure consisting of Ru₃O₁₂ trimers and LnO₆ octahedra. All of these compounds show an antiferromagnetic transition at 2.5-30 K. For Ba₄NdRu₃O₁₂, ferrimagnetic ordering has been observed at 11.5 K. The observed magnetic transition is due to the magnetic behavior of the Ru^4.33+₃O₁₂ trimer with S=. Magnetic properties of Ba₄LnRu₃O₁₂ were compared with those of triple perovskites Ba₃LnRu₂O₉ and double perovskites Ba₂LnRuO₆.     

Synthesis and magnetic properties of 12L-perovskites Ba4LnIr3O12 (Ln=lanthanides)

New quadruple perovskite oxides Ba₄LnIr₃O₁₂ (Ln=lanthanides) were prepared and their magnetic properties were investigated. They crystallize in the monoclinic 12L-perovskite-type structure with space group C2/m. The Ir₃O₁₂ trimers and LnO₆ octahedra are alternately linked by corner-sharing and form the perovskite-type structure with 12 layers. The Ln and Ir ions are both in the tetravalent state for Ln=Ce, Pr, and Tb compounds , and for other compounds (Ln=La, Nd, Sm-Gd, Dy-Lu), Ln ions are in the trivalent state and the mean oxidation state of Ir ions is . An antiferromagnetic transition has been observed for Ln=Ce, Pr, and Tb compounds at 10.5, 35, and 16 K, respectively, while the other compounds are paramagnetic down to 1.8 K.     

Nd3+, Eu3+, and Gd3+ ions as local probes in the NaxSr3−2xLnx(PO4)2 and KCaLn(PO4)2 rare earth phosphates

Use of Nd³⁺, Eu³⁺, and Gd³⁺ as local structural probes allows the determination of the rare earth positions in the Na_xSr_3?2xLn_x(PO₄)₂ (Ln = La to Tb) and KCaLn(PO₄)₂ phases (Ln = rare earth). Moreover, a common feature of both series is a particularly high splitting of the excitation ${}^6\text{P}{}_{\mathrm{<mtext>7</mtext><mtext>2</mtext>}}$ and ${}^6\text{P}{}_{\mathrm{<mtext>5</mtext><mtext>2</mtext>}}$ levels of the Gd³⁺ ions.     

Fluorite-related phases Ln3MO7, Ln = rare earth,Y, or Sc, M = Nb,Sb, or Ta. I. Crystal chemistry

Compounds Ln₃MO₇, where Ln = La, Nd, Gd, Ho, Er, Y, or Sc, and M = Nb, Ta, or Sb have been examined by powder X-ray diffraction, electron diffraction, and electron microscopy. For large Ln cations, an orthorhombic fluorite-related superstructure is formed, of probable space group Cmcm for Ln = La and C222₁ for Ln = Nd, Gd, Ho, or Y, while for the smaller Ln cations, Er, and under some conditions, Ho and Y, the structure is defect fluorite containing microdomains of ordered, but undetermined, structure. The composition Sc₃MO₇ was not single phase under the conditions used. Compounds of the type Ln₂ScMO₇ have the pyrochlore structure.     

Preparation, characterization, magnetic susceptibility (Eu, Gd and Sm) and XPS studies of Ln2ZrTiO7 (Ln=La, Eu, Dy and Gd)

Bulk and nanosized pyrochlore materials Ln₂ZrTiO₇ (Ln=La, Eu, Dy, Gd and Sm) have been prepared by the sol-gel method. All the samples were characterized by powder X-ray diffraction, Raman and X-ray photoelectron spectroscopy. Magnetic susceptibility (χ) measurements of Gd₂ZrTiO₇, Sm₂ZrTiO₇ and Eu₂ZrTiO₇ were carried out by vibrating sample magnetometer in the temperature range 2-320 K. The variation of χ⁻¹ (or χ) with temperature of Gd₂ZrTiO₇, Sm₂ZrTiO₇ and Eu₂ZrTiO₇ follows the Curie law, intermediate formula and the Curie-Weiss law, respectively. From the linear portion of χT vs. T⁻¹ plot of Eu₂ZrTiO₇ from 2 to 15 K, the classical nearest neighbor exchange (J^cl) and dipolar interactions (D_nn) are obtained. The XPS of Ln₂ZrTiO₇ (Ln=La, Eu, Dy and Gd) gave characteristic peaks for Ln, Ti, Zr and O. The satellite peaks are observed only for 3d La of La₂ZrTiO₇.     

Structural and magnetic properties of the quaternary oxides Ba6Ln2Fe4O15 (Ln=Pr and Nd)

The crystal structures and magnetic properties of the quaternary lanthanide oxides Ba₆Ln₂Fe₄O₁₅ (Ln=Pr and Nd) are reported. They crystallize in a hexagonal structure with space group P6₃mc and have the “Fe₄O₁₅ cluster” consisting of one FeO₆ octahedron and three FeO₄ tetrahedra. Measurements of the magnetic susceptibility, specific heat, and powder neutron diffraction reveal that this cluster behaves as a spin tetramer with a ferrimagnetic ground state of S_T=5 even at room temperature. The cluster moments show a long-range antiferromagnetic ordering at 23.2 K (Ln=Pr) and 17.8 K (Nd), and the magnetic moments of the Ln³⁺ ions also order cooperatively. By applying the magnetic field (∼2 T), this antiferromagnetic ordering of the clusters changes to a ferromagnetic one. This result indicates that there exists a competition in the magnetic interaction between the clusters.     

Synthesis and electrical properties of perovskite oxides, LnB0.75B′0.25O3

A series of ordered perovskite oxides of the type Ln²⁺_0.75B′⁶⁺_0.25O₃ (Ln = rate earth or Y; B = Mn, Fe, Co, Ni; B′ = Mo, W, Re) has been synthesized and characterized by X-ray analysis and density measurements. Compounds with Ln = La are easily formed in all cases as single-phase materials and have either cubic or orthorhombic symmetry. When Ln = rare earth or Y, single-phase materials are formed only in the case of LnFe_0.75Mo_0.25O₃ and these possess an orthorhombic structure. All the phases tested are extrinsic semiconductors in the range of 25–350°C, with E_a ranging from 0.1 to 0.4 eV. Resistivity of the Ln(Fe, Mo)O₃ series of oxides increases from Ln = La to Ln = Lu. Ni-containing compounds are p type, while those containing Fe or Co in the B sites are n type.     

The extended chain compounds Ln12(C2)3I17 (Ln=Pr, Nd, Gd, Dy): Synthesis, structure and physical properties

The title compounds are obtained in high yield from stoichiometric mixtures of Ln, LnI₃ and graphite, heated at 900-950 °C in welded Ta containers. The crystal structures of new Pr and Nd phases determined by single-crystal X-ray diffraction are related to those of other Ln₁₂(C₂)₃I₁₇-type compounds (C 2/c, a=19.610(1) and 19.574(4) Å, b=12.406(2) and 12.393(3) Å, c=19.062(5) and 19.003(5) Å, β=90.45(3)° and 90.41(3)°, for Pr₁₂(C₂)₃I₁₇ and Nd₁₂(C₂)₃I₁₇, respectively). All compounds contain infinite zigzag chains of C₂-centered metal atom octahedra condensed by edge-sharing into the [tcc]_∞ sequence (c=cis, t=trans) and surrounded by edge-bridging iodine atoms as well as by apical iodine atoms that bridge between chains. The polycrystalline Gd₁₂(C₂)₃I₁₇ sample exhibits semiconducting thermal behavior which is consistent with an ionic formulation (Ln³⁺)₁₂(C₂^6-)₃(I⁻)₁₇(e⁻) under the assumption that one extra electron is localized in metal-metal bonding. The magnetization measurements on Nd₁₂(C₂)₃I₁₇, Gd₁₂(C₂)₃I₁₇ and Dy₁₂(C₂)₃I₁₇ indicate the coexistence of competing magnetic interactions leading to spin freezing at T_f=5 K for the Gd phase. The Nd and Dy compounds order antiferromagnetically at T_N=25 and 29 K, respectively. For Dy₁₂(C₂)₃I₁₇, a metamagnetic transition is observed at a critical magnetic field H≈25 kOe.     

Preparation and structure of the light rare-earth copper selenides LnCuSe2 (Ln=La, Ce, Pr, Nd, Sm)

The ternary selenides LnCuSe₂ (Ln=La, Ce, Pr, Nd, Sm) have been synthesized by the reaction at 1173 K of Ln, Cu, and Se in a KBr or KI flux. The compounds, which are isostructural with LaCuS₂, crystallize with four formula units in the space group P2₁/c of the monoclinic system. The structure may be thought of as consisting of layers of CuSe₄ tetrahedra separated by double layers of LnSe₇ monocapped trigonal prisms along the a-axis. Cell constants (Å or deg) at 153 K are: LaCuSe₂, 6.8142(5), 7.5817(6), 7.2052(6), 97.573(1)°; CeCuSe₂, 6.7630(5), 7.5311(6), 7.1650(6), 97.392(1)°; PrCuSe₂, 6.740(1), 7.481(1), 7.141(1), 97.374(2)°; NdCuSe₂, 6.7149(6), 7.4452(7), 7.1192(6), 97.310(1)°; SmCuSe₂, 6.6655(6), 7.3825(7), 7.0724(6), 97.115(1)°. There are no Se-Se bonds in the structure of LnCuSe₂; the formal oxidation states of Ln/Cu/Se are 3+/1+/2−.     

Synthesis, crystal structure and optical investigation of the new phosphates: Na7Mg13Ln(PO4)12 (Ln=La, Eu)

Two new isostructural rare earth phosphates Na₇Mg₁₃Ln(PO₄)₁₂ (Ln=La, Eu) have been synthesized and investigated by X-ray diffraction and optical measurements. They crystallize in the orthorhombic system with the Cmc2₁ space group (Z=4). The crystal structure exhibits a new type of framework built up from LnO₈ (Ln=La, Eu), MO₆ (M=0.5Mg+0.5Na) and MgO_x (x=5, 6) polyhedra and PO₄ tetrahedra linked by common corner, edge or face. It can be described in terms of [Mg₄MP₄O₂₂]_∞ layers stacked along the a direction. These layers are interconnected by [Mg₄LnP₄O₃₆]_∞ undulating chains spreading along the b direction. This framework delimits 6 distinct cavities occupied by Na⁺ cations. The results of the optical study of Na₇Mg₁₃La_1−xEu_x(PO₄)₁₂ (x=0, 0.02, 0.1, 1) reveal the presence of two different Eu³⁺ ion environments whereas the X-ray study predicts the existence of only one Eu site. This difference can be explained by the possible presence of the europium element in the sodium sites with small occupancies which cannot be detected by the X-ray structural determination.     

The crystal growth and magnetic properties of Ln2LiIrO6 (Ln=La, Pr, Nd, Sm, Eu)

Single crystals of a series of lanthanide lithium iridium oxides, Ln₂LiIrO₆ (Ln=La, Pr, Nd, Sm, Eu) with the double perovskite structure have been grown from molten LiOH/KOH fluxes. The compounds crystallize in a distorted 1:1 rock salt lattice of Li⁺ and Ir⁵⁺ cations in the monoclinic space group P2₁/n. The magnetic susceptibilities of Ln₂LiIrO₆ (Ln=Pr, Nd, Sm, Eu) are presented.