Phosphides with Zr2Fe12P7-type structure

Twenty-six ternary phosphides Ln₂T₁₂P₇ (Ln = lanthanoid, T = Fe, Co, Ni) were prepared for the first time by reaction of the elemental components in liquid tin or by reaction of the components in evacuated silica tubes. The analysis of their powder patterns indicates their isotypism with Zr₂Fe₁₂P₇. Their lattice constants are reported. Gd₂Ni₁₂As₇ also crystallizes with that structure.     

Crystal structure and electronic properties of the new compounds U3Co12−xX4 with X=Si, Ge

The new compounds U₃Co_12−xX₄ with X=Si, Ge were prepared by direct solidification of the corresponding liquid phase, followed by subsequent annealing at 1173 K. Single crystal X-ray diffraction carried out at room temperature showed that they crystallize with the hexagonal space group P6₃/mmc (no.194) and the unit-cell parameters a=8.130(5), c=8.537(5) Å and a=8.256(1), c=8.608(1) Å for the silicide and germanide, respectively. Their crystal structure derives from the EuMg_5.2 structure type, and is closely related to the Sc₃Ni₁₁Si₄ and Gd₃Ru_4−xAl_12+x types. For the present compounds, no substitution mechanisms have been observed, the partial occupancy of one Co site results from the presence of vacancies, only. The homogeneity ranges, evaluated by energy dispersive spectroscopy analysis, extend from x=0.0(2) to 0.3(2) and from x=0.0(2) to 1.0(2) for U₃Co_12−xSi₄ and U₃Co_12−xGe₄, respectively. The electronic properties of both compounds were investigated by means of DC magnetic susceptibility and DC electrical resistivity measurements. The U₃Co_12−xX₄ compounds are both Pauli paramagnets with their electrical resistivity best described as poor metallic or dirty metallic behavior.     

Ln2BaZnO5 and Ln2BaZn1−xCuxO5: A series of zinc oxides with zinc in a pyramidal coordination

A series of zinc oxides Ln₂BaZnO₅ has been synthesized for Ln = Sm, Eu, Gd, Dy, Ho, and Y. Theses phases are orthorhombic and isostructural with the copper compounds Ln₂BaCuO₅ previously described, as shown from the structural study of one member Y₂BaZnO₅. In this structure, whose framework is built up from edge- and face-sharing LnO₇ polyhedra, the Zn²⁺ ions exhibit an unusual pyramidal coordination ZnO₅. The solid solution Y₂BaZn_1?xCu_xO₅ has been studied by infrared spectroscopy and electron spin resonance (ESR). The distorted square-based pyramidal configuration of Zn²⁺ and Cu²⁺ is confirmed. The ESR spectra of diluted samples exhibit a hyperfine structure and are typical of individual Cu(II) ions. For higher Cu(II) contents, they exhibit an anisotropic broad signal which is interpreted in terms of CuCu interactions.     

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.     

Crystal growth of Ln2NiO4 (Ln = La,Pr, Nd) by skull melting

Growth of large single crystals of quasi-two-dimensional Ln₂NiO₄ (Ln = La, Pr, Nd) has been accomplished using the radio frequency technique of skull melting under controlled oxygen partial pressures. No evidence of intergrowth of other phases such as Ln₃Ni₂O₇ or higher homologs was observed. Determination of the Ni³⁺ content indicates that the crystals are cation deficient.     

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.     

Synthesis, structure and physical properties of LnNi(Sn,Sb)3 (Ln=Pr, Nd, Sm, Gd, Tb)

Five new analogues of the β-CeNiSb₃ family have been synthesized and found to be LnNi(Sn,Sb)₃ and isostructural to the previously reported β-CeNiSb₃. LnNi(Sn,Sb)₃ (Ln=Pr, Nd, Sm, Gd, or Tb) crystallizes in the orthorhombic space group, Pbcm, with lattice parameters of a∼12.9 Å, b∼6.1 Å, c∼12.0 Å. The structure consists of layers of nearly square nets of X (X=Sn/Sb) atoms and highly distorted NiX₆ octahedra. Lanthanide atoms are located between layers of X and NiX₆ octahedra. All analogues are metallic and experimental effective magnetic moments are in agreement with the respective Ln³⁺ calculated moments.     

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).     

The new ternary pnictides Er12Ni30P21 and Er13Ni25As19: Crystal structures and magnetic properties

The new ternary pnictides Er₁₂Ni₃₀P₂₁ and Er₁₃Ni₂₅As₁₉ have been synthesized from the elements. They crystallize with hexagonal structures determined from single-crystal X-ray data for Er₁₂Ni₃₀P₂₁ (space group P6₃/m, a=1.63900(3) nm, c=0.37573(1) nm, Z=1, R_F=0.062 for 1574 F-values and 74 variable parameters), and for Er₁₃Ni₂₅As₁₉ (Tm₁₃Ni₂₅As₁₉-type structure, space group P6?, a=1.6208(1) nm, c=0.38847(2) nm, Z=1, R_F=0.026 for 1549 F-values and 116 variable parameters). These compounds belong to a large family of hexagonal structures with a metal-metalloid ratio of 2:1. HRTEM investigations were conducted to probe for local ordering of the disordered structure at the nanoscale. The magnetic properties of the phosphide Er₁₂Ni₃₀P₂₁ have been studied in the temperature of range 2<T<300 K and with applied fields up to 5 T. The magnetic susceptibility follows the Curie-Weiss law from 4 to 300 K. The measured value of μ_eff=9.59 μ_B corresponds to the theoretical value of Er³⁺.     

Seven new rare-earth transition-metal oxychalcogenides: Syntheses and characterization of Ln4MnOSe6 (Ln=La, Ce, Nd), Ln4FeOSe6 (Ln=La, Ce, Sm), and La4MnOS6

The quaternary oxychalcogenides Ln₄MnOSe₆ (Ln=La, Ce, Nd), Ln₄FeOSe₆ (Ln=La, Ce, Sm), and La₄MnOS₆ have been synthesized by the reactions of Ln (Ln=La, Ce, Nd, Sm), M (M=Mn, Fe), Se, and SeO₂ at 1173 K for the selenides or by the reaction of La₂S₃ and MnO at 1173 K for the sulfide. Warning: These reactions frequently end in explosions. These isostructural compounds crystallize with two formula units in space group of the hexagonal system. The cell constants (a, c in Å) at 153 K are: La₄MnOSe₆, 9.7596(3), 7.0722(4); La₄FeOSe₆, 9.7388(4), 7.0512(5); Ce₄MnOSe₆, 9.6795(4), 7.0235(5); Ce₄FeOSe₆, 9.6405(6), 6.9888(4); Nd₄MnOSe₆, 9.5553(5), 6.9516(5); Sm₄FeOSe₆, 9.4489(5), 6.8784(5); and La₄MnOS₆, 9.4766(6), 6.8246(6). The structure of these Ln₄MOQ₆ compounds comprises a three-dimensional framework of interconnected LnOQ₇ bicapped trigonal prisms, MQ₆ octahedra, and the unusual LnOQ₆ tricapped tetrahedra.     

Magnetic and Calorimetric Studies on One-Dimensional Ln3RuO7(Ln=Pr, Gd)

Magnetic and calorimetric properties of Ln₃RuO₇ (Ln=Pr, Gd) have been investigated. Magnetic susceptibility and specific heat measurements indicate that both Pr₃RuO₇ and Gd₃RuO₇ compounds show magnetic transitions at 55 K and 15 K, respectively. In addition, a clear structural phase transition has been found at 382 K for Gd₃RuO₇ from the specific heat measurements. From the temperature dependence of the magnetic specific heat, the magnetic entropy change is estimated and the magnetic ground states of each ion are determined.     

A structural study of the perovskite series Na0.75Ln0.25Ti0.5Nb0.5O3

The ternary stoichiometric perovskite compounds, Na_0.75Ln_0.25Ti_0.5Nb_0.5O₃ (Ln=La, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm) are intermediate members of the NaNbO₃-Na_0.5Ln_0.5TiO₃ solid solution series. The compounds were synthesized by standard ceramic methods at 1300 °C followed by annealing at 800 °C and quenching to ambient conditions. Rietveld analysis of the powder X-ray diffraction patterns shows that the compounds with Ln ranging from Pr to Tm adopt the orthorhombic space group Pbnm (a≈b≈√2a_p; c≈2a_p; Z=4) and the GdFeO₃ structure. In contrast, Na_0.75La_0.25Ti_0.5Nb_0.5O₃ adopts the orthorhombic space group Cmcm (a≈b≈c≈2a_p; Z=4). All cations located at the A- and B-sites are disordered in these compounds. The unit cell parameters and cell volumes of the compounds decrease regularly with increasing atomic number of the Ln cation. The Pbnm compounds with Ln from Sm to Tm have A-site cations in eight-fold coordination. A-site cations in the Pr and Nd compounds are considered to be in ten-fold coordination. Analysis of the crystal chemistry of the Pbnm compounds shows that B-site cations enter the second coordination sphere of the A-site cations for compounds with Ln from Tb to Tm as the A-B intercation distances are less than the maximum A-^IIO(2) bond lengths. The [111] tilt angles of the (Ti,Nb)O₆ polyhedra in the Pbnm compounds increase with increasing atomic number from 11.1° to 15.8° and are less than those observed in lanthanide orthoferrite and orthoscandate perovskites. These data are considered as relevant to the sequestration of lanthanide fission products in perovskite and the structure of lanthanide-bearing perovskite-structured minerals.     

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.     

Electrical conductivity of Th3P4-type EnLn2S4

Electrical conductivity measurements of Th₃P₄-type EuLn₂S₄ (Ln = LaGd) compounds have been made as functions of temperature and sulfur vapor pressure. These compounds are all p-type semiconductors, and their conductivities at room temperature have almost the same values for the specimens from EuLa₂S₄ to EuNd₂S₄ but increase on going from EnNd₂S₄ to EuGd₂S₄. In addition, the conductivity of EuGd₂S₄ is sensitive to sulfur vapor pressure and obeys the relationship . The mechanism of electrical transport in these compounds is discussed.     

Crystal structures, magnetic and thermal properties of Ln3IrO7 (Ln=Pr, Nd, Sm, and Eu)

Ternary iridium oxides Ln₃IrO₇ (Ln=Pr, Nd, Sm, and Eu) were prepared and their crystal structures, magnetic and thermal properties were investigated. Powder X-ray diffractions (XRDs) were measured for all samples and neutron diffraction (ND) measurements were performed for Pr₃IrO₇. All the profiles were refined with space group Cmcm (No. 63). The lattice parameters for Pr₃IrO₇ refined by using ND data are a=10.9782(13) Å, b=7.4389(9) Å, and c=7.5361(9) Å. From specific heat and differential thermal analysis (DTA) measurements, Ln₃IrO₇ (Ln=Pr, Nd, Sm, and Eu) show thermal anomalies at 261, 342, 420, and 485 K, respectively. The results of powder high-temperature XRD and ND measurements indicate that these anomalies are due to the structural phase transition. Magnetic susceptibilities of these compounds were measured in the temperature range between 1.8 and 400 K. Nd₃IrO₇ shows an antiferromagnetic transition at 2.6 K. A specific heat anomaly has also been observed at the same temperature. For Ln₃IrO₇ (Ln=Pr, Sm, and Eu), no magnetic anomalies have been found in the experimental temperature range.     

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.     

Crystal structures and magnetic properties of fluorite-related oxides Ln3NbO7 (Ln=lanthanides)

Crystal structures and magnetic properties of the ternary oxides Ln₃NbO₇ (Ln=La, Pr, Nd, Sm-Lu) are reported. Their powder X-ray diffraction measurements and Rietveld analyzes show that they have the fluorite-related structures with space group Pnma (Ln=La, Pr, Nd), C222₁ (Ln=Sm-Tb), or Fm-3m (Ln=Dy-Lu). Magnetic susceptibility measurements were carried out from 1.8 to 400 K. The Ln₃NbO₇ compounds for Ln=Pr, Gd, Dy-Yb show Curie-Weiss paramagnetic behavior, and Sm₃NbO₇ and Eu₃NbO₇ show van Vleck paramagnetism. On the other hand, two magnetic anomalies were observed for both Nd₃NbO₇ (0.6 and 2.7 K) and Tb₃NbO₇ (2.0 and 3.2 K). From the results of specific heat measurements, it was found that these anomalies are due to the antiferromagnetic ordering of Ln ions in two different crystallographic sites (the 8-coordinated and 7-coordinated sites).     

Magnetic properties of orthorhombic fluorite-related oxides Ln3SbO7 (Ln=rare earths)

Ternary rare earth antimonates Ln₃SbO₇ (Ln=rare earths) 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=La, Pr, Nd; C222₁ for Ln=Nd-Lu), in which Ln³⁺ ions occupy two different crystallographic sites (the 8-coordinated and 7-coordinated sites). Their magnetic properties were characterized by magnetic susceptibility and specific heat measurements from 1.8 to 400 K. The Ln₃SbO₇ (Ln=Nd, Gd-Ho) compounds show an antiferromagnetic transition at 2.2-3.2 K. Sm₃SbO₇ and Eu₃SbO₇ show van Vleck paramagnetism. Measurements of the specific heat down to 0.4 K for Gd₃SbO₇ and the analysis of the magnetic specific heat indicate that the antiferromagnetic ordering of the 8-coordinated Gd ions occur at 2.6 K, and the 7-coordinated Gd ions order at a furthermore low temperature.     

Magnetic and electrical properties of quadruple perovskites with 12 layer structures Ba4LnM3O12 (Ln=rare earths; M=Ru, Ir): The role of metal-metal bonding in perovskite-related oxides

Structures and magnetic and electrical properties of quadruple perovskites containing rare earths Ba₄LnM₃O₁₂ (Ln=rare earths; M=Ru, Ir) were investigated. They crystallize in the 12L-perovskite-type structure. Three MO₆ octahedra are connected to each other by face-sharing and form a M₃O₁₂ trimer. The M₃O₁₂ trimers and LnO₆ octahedra are alternately linked by corner-sharing, forming the perovskite-type structure with 12 layers. For Ln=Ce, Pr, and Tb, both the Ln and M ions are in the tetravalent state (Ba₄Ln⁴⁺M⁴⁺₃O₁₂), and for other Ln ions, Ln ions are in the trivalent state and the mean oxidation state of M ions is +4.33 (Ba₄Ln³⁺M^4.33+₃O₁₂). All the Ba₄Ln³⁺Ru^4.33+₃O₁₂ compounds show magnetic ordering at low temperatures, while any of the corresponding iridium-containing compounds Ba₄Ln³⁺Ir^4.33+₃O₁₂ is paramagnetic down to 1.8 K. Ba₄Ce⁴⁺Ir⁴⁺₃O₁₂ orders antiferromagnetically at 10.5 K, while the corresponding ruthenium-containing compound Ba₄Ce⁴⁺Ru⁴⁺₃O₁₂ is paramagnetic. These magnetic results were well understood by the magnetic behavior of M₃O₁₂. The effective magnetic moments and the entropy change for the magnetic ordering show that the trimers Ru^4.33+₃O₁₂ and Ir⁴⁺₃O₁₂ have the S= ground state, and in other cases there is no magnetic contribution from the trimers Ru⁴⁺₃O₁₂ or Ir^4.33+₃O₁₂.Measurements of the electrical resistivity of Ba₄LnM₃O₁₂ and its analysis show that these compounds demonstrate two-dimensional Mott-variable range hopping behavior.