Synthesis and crystal structure of two new cerium rhodium oxides: Ce2/3−xRh2O4 (x∼0.12) with Ce mixed valency and CeRh2O5

The new compounds Ce_2/3−xRh₂O₄ (x∼0.11-0.14) and CeRh₂O₅ have been prepared. Their structures were determined from single crystal X-ray diffraction data. Electrical and magnetic properties were also evaluated. Based on the structural analysis and physical properties, oxidation states for CeRh₂O₅ can be assigned as Ce⁴⁺Rh³⁺₂O₅. A small variation in x was detected for Ce_2/3−xRh₂O₄ indicating a formula ranging from Ce^3.64+_0.55Rh³⁺₂O₄ to Ce^3.81+_0.525Rh³⁺₂O₄.     

Crystal structure and magnetic properties of Ce7Ni5±xGe3±xIn6 and Pr7Ni5±xGe3±xIn6

The indides Ce₇Ni_5±xGe_3±xIn₆ and Pr₇Ni_5±xGe_3±xIn₆ were synthesized from the elements by arc-melting of the components. Single crystals were grown via special annealing sequences. Both structures were solved from X-ray single crystal diffraction data: new structure type, P6/m, Z=1, a=11.385(2), c=4.212(1) Å, wR₂=0.0640, 634F² values, 25 variables for Ce₇Ni_4.73Ge_3.27In₆ and a=11.355(6), c=4.183(2) Å, wR₂=0.0539, 563F² values, 25 variables for Pr₇Ni_4.96Ge_3.04In₆. Both indides show homogeneity ranges through Ni/Ge mixing (M sites). This new structure type can be derived from the AlB₂ structure type by a substitution of the Al and B atoms by CeM₁₂ and NiIn₆Ce₃ polyhedra (tricapped trigonal prism). Magnetic susceptibility measurements on a polycrystalline sample of Ce₇Ni₅Ge₃In₆ indicated Curie-Weiss like paramagnetic behavior down to 1.71 K with the effective magnetic moment slightly reduced in relation to the value expected for trivalent cerium ions. No magnetic ordering is evident.     

Structure and photoluminescence properties of Ce-doped novel silicon-oxynitride Ba4−zMzSi8O20−3xN2x (M=Mg, Ca, Sr)

Structural and photoluminescence properties of undoped and Ce³⁺-doped novel silicon-oxynitride phosphors of Ba_4−zM_zSi₈O_20−3xN_2x (M=Mg, Sr, Ca) are reported. Single-phase solid solutions of Ba_4−zM_zSi₈O_20−3xN_2x oxynitride were synthesized by partial substitutions of 3O²⁻→2N³⁻ and Ba→M (M=Mg, Ca, Sr) in orthorhombic Ba₂Si₄O₁₀. The influences of the type of alkaline earth ions of M, the Ce³⁺ concentration on the photoluminescence properties and thermal quenching behaviors of Ba₃MSi₈O_20−3xN_2x (M=Mg, Ca, Sr, x=0.5) were investigated. Under excitation at about 330 nm, Ba₃MSi₈O_20−3xN_2x:Ce³⁺ (x=0.5) exhibits efficient blue emission centered at 400-450 nm in the range of 350-650 nm owing to the 5d→4f transition of Ce³⁺. The emission band of Ce³⁺ shifts to long wavelength by increasing the ionic size of M due to the modification of the crystal field, as well as the Ce³⁺ concentrations due to the Stokes shift and energy transfer or reabsorption of Ce³⁺ ions. Among the silicon-oxynitride phosphors of Ba₃MSi₈O_18.5N:Ce³⁺, M=Sr_0.6Ca_0.4 possesses the best thermal stability probably related to its high onset of the absorption edge of Ce³⁺.     

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.     

Crystal structure, thermal expansion and conductivity of anisotropic La1−xSrxGa1−2xMg2xO3−y (x=0.05, 0.1) single crystals

Crystal structure and anisotropy of the thermal expansion of single crystals of La_1−xSr_xGa_1−2xMg_2xO_3−y (x=0.05 and 0.1) were measured in the temperature range 300-1270 K. High-resolution X-ray powder diffraction data obtained by synchrotron experiments have been used to determine the crystal structure and thermal expansion. The room temperature structure of the crystal with x=0.05 was found to be orthorhombic (Imma, Z=4, a=7.79423(3) Å, b=5.49896(2) Å, c=5.53806(2) Å), whereas the symmetry of the x=0.1 crystal is monoclinic (I2/a, Z=4, a=7.82129(5) Å, b=5.54361(3) Å, c=5.51654(4) Å, β=90.040(1)°). The conductivity in two orthogonal directions of the crystals has been studied. Both, the conductivity and the structural data indicate three phase transitions in La_0.95Sr_0.05Ga_0.9Mg_0.1O_2.92 at 520-570 K (Imma-I2/a), 770 K (I2/a-R3c) and at 870 K (R3c-R-3c), respectively. Two transitions at 770 K (I2/a-R3c) and in the range 870-970 K (R3c-R-3c) occur in La_0.9Sr_0.1Ga_0.8Mg_0.2O_2.85.     

Magnetostructural correlations in the antiferromagnetic Co2−x Cux(OH)AsO4 (x=0 and 0.3) phases

The Co_2−xCu_x(OH)AsO₄ (x=0 and 0.3) compounds have been synthesized under mild hydrothermal conditions and characterized by X-ray single-crystal diffraction and spectroscopic data. The hydroxi-arsenate phases crystallize in the Pnnm orthorhombic space group with Z=4 and the unit-cell parameters are a=8.277(2) Å, b=8.559(2) Å, c=6.039(1) Å and a=8.316(1) Å, b=8.523(2) Å, c=6.047(1) Å for x=0 and 0.3, respectively. The crystal structure consists of a three-dimensional framework in which M(1)O₅-trigonal bipyramid dimers and M(2)O₆-octahedral chains (M=Co and Cu) are present. Co₂(OH)AsO₄ shows an anomalous three-dimensional antiferromagnetic ordering influenced by the magnetic field below 21 K within the presence of a ferromagnetic component below the ordering temperature. When Co²⁺ is partially substituted by Cu²⁺ions, Co_1.7Cu_0.3(OH)AsO₄, the ferromagnetic component observed in Co₂(OH)AsO₄ disappears and the antiferromagnetic order is maintained in the entire temperature range. Heat capacity measurements show an unusual magnetic field dependence of the antiferromagnetic transitions. This λ-type anomaly associated to the three-dimensional antiferromagnetic ordering grows with the magnetic field and becomes better defined as observed in the non-substituted phase. These results are attributed to the presence of the unpaired electron in the dx²−y² orbital and the absence of overlap between neighbour ions.     

Crystal structures of the La3AgSnSe7 and R3Ag1−δSnS7 (R=La, Ce; δ=0.18−0.19) compounds

The crystal structures of new quaternary compounds La₃AgSnSe₇ (space group P6₃, Pearson symbol hP24, a=1.0805(4) nm, c=0.6245(1) nm, R1=0.0315), La₃Ag_0.82SnS₇ (space group P6₃, Pearson symbol hP23.64, a=1.0399(1) nm, c=0.6016(1) nm, R1=0.0149) and Ce₃Ag_0.81SnS₇ (space group P6₃, Pearson symbol hP23.62, a=1.0300(1) nm, c=0.6002(1) nm, R1=0.0151) were determined by means of X-ray single crystal diffraction. Structural investigations of the R₃Ag_1−δSnS₇ (R=La, Ce; δ=0.18-0.19(1)) compounds at 450 and 530 K were performed. Low temperature data (12 K) for Ce₃Ag_0.81SnS₇ were also collected. The nearest neighbours of the La(Ce), Ag and Sn atoms are exclusively Se(S) atoms. The latter form distorted trigonal prisms around the La(Ce) atoms, and distorted tetrahedrons around the Sn atoms. The Ag (Ag1) atoms have triangular surroundings: they are located very close to the planes built of three Se(S) atoms. The Ag2 atoms in the structures of the La₃Ag_0.82SnS₇, Ce₃Ag_0.81SnS₇ compounds are located practically in the centres of trigonal antiprisms. The pseudo-potentials determined through the Ag atoms show relatively low barrier between two nearest positions which decreases when temperature rises.     

Crystal structure and physical properties of quaternary clathrates Ba8ZnxGe46−x−ySiy, Ba8(Zn,Cu)xGe46−x and Ba8(Zn,Pd)xGe46−x

Three series of vacancy-free quaternary clathrates of type I, Ba₈Zn_xGe_46−x−ySi_y, Ba₈(Zn,Cu)_xGe_46−x, and Ba₈(Zn,Pd)_xGe_46−x, have been prepared by reactions of elemental ingots in vacuum sealed quartz at 800 °C. In all cases cubic primitive symmetry (space group Pm3?n, a∼1.1 nm) was confirmed for the clathrate phase by X-ray powder diffraction and X-ray single crystal analyses. The lattice parameters show a linear increase with increase in Ge for Ba₈Zn_xGe_46−x−ySi_y. M atoms (Zn, Pd, Cu) preferably occupy the 6d site in random mixtures. No defects were observed for the 6d site. Site preference of Ge and Si in Ba₈Zn_xGe_46−x−ySi_y has been elucidated from X-ray refinement: Ge atoms linearly substitute Si in the 24k site whilst a significant deviation from linearity is observed for occupation of the 16i site. A connectivity scheme for the phase equilibria in the “Ba₈Ge₄₆” corner at 800 °C has been derived and a three-dimensional isothermal section at 800 °C is presented for the Ba-Pd-Zn-Ge system. Studies of transport properties carried out for Ba₈{Cu,Pd,Zn}_xGe_46−x and Ba₈Zn_xSi_yGe_46−x−y evidenced predominantly electrons as charge carriers and the closeness of the systems to a metal-to-insulator transition, fine-tuned by substitution and mechanical processing of starting material Ba₈Ge₄₃. A promising figure of merit, ZT ∼0.45 at 750 K, has been derived for Ba₈Zn_7.4Ge_19.8Si_18.8, where pricey germanium is exchanged by reasonably cheap silicon.     

Une nouvelle famille structurale: Les oxydes Ln4−2xBa2+2xZn2−xO10−2x (Ln = La,Nd)

Two original compounds, Ln_4?2xBa_2+2xZn_2?xO_10?2x, were isolated for Ln = La, Nd and 0 ≤ x ≤ 0.25. These oxides are tetragonal with a and c parameters close to 6.91 and 11.59 Å, respectively, for lanthanum, and 6.75 and 11.54 Å for neodymium. The structure of these phases was determined from X-ray powder patterns in the most symmetric space group, $\text{I}\text{4}\text{mcm}$, using Patterson and Fourier functions for x = 0. The structure should be compared to that of copper oxides La_4?2xBa_2+2xCu_2?xO_10?2x: it is built up of identical Ln₂O₅ layers formed from face- and edge-sharing LnO₈ polyhedra, between which Ba²⁺ and Zn²⁺ ions are inserted. Contrary to the copper compounds, two successive Ln₂O₅ layers are rotated by 90°, involving a doubling of c. The result for Zn²⁺ is tetrahedral coordination, while the coordination of Ba²⁺ becomes a bicapped antiprism.     

A Novel Boron-Rich Scandium Borocarbide; Sc4.5−xB57−y+zC3.5−z(x=0.27, y=1.1, z=0.2)

A novel ternary boron-rich scandium borocarbide Sc_4.5−xB_57−y+zC_3.5−z (x=0.27, y=1.1, z=0.2) was found. Single crystals were obtained by the floating zone method by adding a small amount of Si. Single-crystal structure analysis revealed that the compound has an orthorhombic structure with lattice constants of a=1.73040(6), b=1.60738(6) and c=1.44829(6) nm and space group Pbam (No. 55). The crystal composition ScB_13.3C_0.78Si_0.008 calculated from the structure analysis agreed with the measured composition of ScB_12.9C_0.72Si_0.004. The orthorhombic crystal structure is a new structure type of boron-rich borides and there are six structurally independent B₁₂ icosahedra I1—I6, one B₈/B₉ polyhedron and nine bridging sites all which interconnect each other to form a three-dimensional boron framework. The main structural feature of the boron framework structure can be understood as a layer structure where two kinds of boron icosahedron network layer L1 and L2 stack each other along the c-axis. There are seven structurally independent Sc sites in the open spaces between the boron icosahedron network layers.     

Preparation, crystal structure, and superconductive characteristics of new oxynitrides (Nb1−xMx)(N1−yOy) where M=Mg, Si, and x≈y

New niobium oxynitrides containing either magnesium or silicon were prepared at 1000 °C by ammonia nitridation of oxide precursors obtained via the citrate route. The products had rock-salt type crystal structures. Crystallinity was improved by annealing in 0.5 MPa N₂ and the final compositions were (Nb_0.95Mg_0.05)(N_0.92O_0.08) at 1500 °C and (Nb_0.87Si_0.09□_0.04)(N_0.87O_0.13) at 1200 °C. The magnesium and oxide ions partially co-substitute the niobium and nitride ions in the octahedral sites of the δ-NbN lattice, respectively. Silicon ions were also successfully doped together with oxide ions into the rock-salt type NbN lattice. The Si doped product exhibited relatively large displacement at the octahedral sites and was accompanied by a small amount of cation vacancies. Superconductivity was improved by annealing to obtain critical temperatures/volume fractions of T_c=17.6 K/100% for Mg- and T_c=16.2 K/95% for the Si-doped niobium oxynitrides.     

Structure and physical properties of nonstoichiometric rare-earth cadmium antimonides, RECd1−xSb2 (RE=La, Ce, Pr, Nd, Sm)

The ternary rare-earth cadmium antimonides RECd_1−xSb₂ (RE=La, Ce, Pr, Nd, Sm) were prepared by reaction of the elements at 1000 °C. The presence of Cd defects, previously found for LaCd_0.700(5)Sb₂ and CeCd_0.660(4)Sb₂, has been confirmed by single-crystal X-ray diffraction studies for the isotypic compounds PrCd_0.665(3)Sb₂, ), NdCd_0.659(3)Sb₂, ), and SmCd_0.648(3)Sb₂, ). These compounds adopt the HfCuSi₂-type structure (Pearson symbol tP8, space group P4/nmm, Z=2). The electrical and magnetic properties of samples with nominal composition RECd_0.7Sb₂ were investigated. All exhibit metallic behaviour, but CeCd_0.7Sb₂ undergoes an abrupt drop in its electrical resistivity below 3 K. LaCd_0.7Sb₂ exhibits temperature-independent Pauli paramagnetism and SmCd_0.7Sb₂ displays van Vleck paramagnetism. The remaining compounds obey the modified Curie-Weiss law at high temperatures. CeCd_0.7Sb₂ undergoes ferromagnetic ordering below 3 K, reaching a saturation magnetization of ∼1.0 μ_B, whereas PrCd_0.7Sb₂ and NdCd_0.7Sb₂ remain paramagnetic down to 2 K.     

Magnetic properties of EuLn2O4 (Ln=rare earths)

Ternary rare earth oxides EuLn₂O₄ (Ln=Gd, Dy-Lu) were prepared. They crystallized in an orthorhombic CaFe₂O₄-type structure with space group Pnma. ¹⁵¹Eu Mössbauer spectroscopic measurements show that the Eu ions are in the divalent state. All these compounds show an antiferromagnetic transition at 4.2-6.3 K. From the positive Weiss constant and the saturation of magnetization for EuLu₂O₄, it is considered that ferromagnetic chains of Eu²⁺ are aligned along the b-axis of the orthorhombic unit cell, with neighboring Eu²⁺ chains antiparallel. When Ln=Gd-Tm, ferromagnetically aligned Eu²⁺ ions interact with the Ln³⁺ ions, which would overcome the magnetic frustration of triangularly aligned Ln³⁺ ions and the EuLn₂O₄ compounds show a simple antiferromagnetic behavior.     

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.     

Crystal growth of a series of lithium garnets Ln3Li5Ta2O12 (Ln=La, Pr, Nd): Structural properties, Alexandrite effect and unusual ionic conductivity

We report the single crystal structures of a series of lanthanide containing tantalates, Ln₃Li₅Ta₂O₁₂ (Ln=La, Pr, Nd) that were obtained out of a reactive lithium hydroxide flux. The structures of Ln₃Li₅Ta₂O₁₂ were determined by single crystal X-ray diffraction, where the Li⁺ positions and Li⁺ site occupancies were fixed based on previously reported neutron diffraction data for isostructural compounds. All three oxides crystallize in the cubic space group (No. 230) with lattice parameters a=12.7735(1), 12.6527(1), and 12.5967(1) Å for La₃Li₅Ta₂O₁₂, Pr₃Li₅Ta₂O₁₂, and Nd₃Li₅Ta₂O₁₂, respectively. A UV-Vis diffuse reflectance spectrum of Nd₃Li₅Ta₂O₁₂ was collected to explain its unusual Alexandrite-like optical behavior. To evaluate the transport properties of Nd₃Li₅Ta₂O₁₂, the impedance data were collected in air in the temperature range 300?T(°C)?500.     

R12Pt7In (R=Ce, Pr, Nd, Gd, Ho)—new derivatives of the Gd3Ga2-type

A new compound Ce₁₂Pt₇In was synthesized and its crystal structure at 300 K has been determined from single crystal X-ray data. It is tetragonal, space group I4/mcm, Z=4, with the lattice parameters: a=12.102(1) Å and c=14.542(2) Å, wR2=0.1102, 842 F² values, 33 variable parameters. The structure of Ce₁₂Pt₇In is a fully ordered ternary derivative of the Gd₃Ga₂-type. Isostructural compounds has been found to form with Pr (a=11.976(1) Å, c=14.478(2) Å), Nd (a=11.901(1) Å, c=14.471(2) Å), Gd (a=11.601(3) Å, c=14.472(4) Å), and Ho (a=11.369(1) Å, c=14.462(2) Å). Magnetic properties of Ce₁₂Pt₇In, Pr₁₂Pt₇In and Nd₁₂Pt₇In were studied down to 1.7 K. All three ternaries order magnetically at low temperatures with complex spin arrangements. The electrical resistivity of Ce₁₂Pt₇In and Nd₁₂Pt₇In is characteristic of rare-earth intermetallics.     

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).     

Crystal structures of lanthanide and zirconium phosphates with general formula Ln0.33Zr2(PO4)3, where Ln=Ce, Eu, Yb

Crystal structures of synthetic phosphates Ce_0.33Zr₂(PO₄)₃, Eu_0.33Zr₂(PO₄)₃ and Yb_0.33Zr₂(PO₄)₃ have been refined by Rietveld method using powder diffraction data. Unit cell parameters: a=8.7419 (4), c=23.128 (2) Å; a=8.7659 (1), c=22.822 (1) Å; a=8.8078 (4), c=22.485 (3) Å, respectively; Z=6. Values of final R-factors in isotropic approximation: R_wp=4.00, R_wp=3.33, R_wp=4.12%, respectively. New space group P3¯c has been established for the compounds with general formula Ln_0.33Zr₂(PO₄)₃, where Ln=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu and Y. It has been confirmed that the synthetic phosphates with general formula Ln_0.33Zr₂(PO₄)₃ belong to the NZP (sodium zirconium phosphate) structure type.     

Crystal Structure of Pseudorhombohedral InFe1−xTixO3+x/2 (x=2/3)

The structure of pseudorhombohedral-type InFe_1−xTi_xO_3−x/2 (x=2/3) was refined by Rietveld profile fitting. The crystal is a commensurate member of a series in a solution range on InFeO₃-In₂Ti₂O₇ including incommensurate structures. The structure with the unit cell of a=5.9188(1), b=10.1112(2), and c=6.3896(1) Å, β=108.018(2)°, and a space group P2₁/a is the alternate stacking of an edge-shared InO₆ octahedral layer and an Fe/Ti-O plane along c^*. Metal sites on the Fe/Ti-O plane are surrounded by four oxygen atoms on the Fe/Ti-O plane and two axial ones. Electric conductivities of the order 10⁻⁴ S/cm were observed for the samples at 1000 K, while the oxide ion transport number is almost zero as no electromotive force was detected by an oxygen concentration cell.