Synthesis, magnetism and electronic structure of YbNi2−xFexAl8 (x=0.91) isolated from Al flux

The combination of ytterbium, nickel, iron in liquid aluminum resulted in the formation of the new intermetallic compound YbNi_2−xFe_xAl₈ (x=0.91) which adopts the CaCo₂Al₈ structure type with a=14.458(3) Å, b=12.455(3) Å, c=3.9818(8) Å and space group Pbam. Its resistivity drops with decreasing temperature, saturating to a constant value at lower temperatures. Above 50 K, the inverse magnetic susceptibility data follows Curie-Weiss Law, with a calculated μ_eff=2.19 μ_B. Although the observed reduced moment in magnetic susceptibility measurement suggests that the Yb ions in this compound are of mixed-valent nature, ab initio electronic structure calculations within density functional theory using LDA+U approximation give an f¹³ configuration in the ground state.     

Crystal structures and phase stability in pseudobinary CaAl2−xZnx

Samples in the pseudobinary system CaAl_2−xZn_x (0?x?2) were synthesised from the elements. Three different structure types, the C15 and C36 Laves phase structures and the KHg₂ (CeCu₂) structure, were observed. The structures and homogeneity ranges of the underlying phases were investigated by electron microscopy and thermal analysis as well as X-ray powder diffraction. The stability ranges for the different structure types were found to be 0?x?0.18, 0.28?x?0.68 and 0.93?x?2 for the C15, C36 and KHg₂ structure types, respectively.     

Exchange interactions in R2Fe17−xGax (R=Y, Sm, Gd, Tb, Ho and Tm) compounds

We calculated the molecular field coefficients, n_FeFe and n_RFe (R=Sm, Gd, Tb, Ho and Tm), for R₂Fe_17−xGa_x and the values of n_FeFe and n_SmFe for R₂Fe_17−xT_x (T=Al and Si) using the experimental values of the Curie temperature. The values of n_FeFe increase in spite of the decrease of μ_Fe for 0?x?5. The values of n_SmFe have large values when the magnetic anisotropy is axial. For 6?x?8, the values of n_FeFe, n_HoFe and n_TmFe increase largely, which is related to the change of the easy magnetization direction. For Y₂Fe_17−xT_x (T=Ga and Al), the values of n_FeFe have a maximum value with increasing those of μ_Fe. With increasing V⁻¹, the values of n_FeFe have a maximum value around the same value of V⁻¹ for Y₂Fe_17−xT_x (T=Ga and Al). For Y₂Fe_17−xSi_x, the values of n_FeFe increase with increasing V⁻¹.     

Structure and thermal conductivity of Na1−xGe3+z

Structural analyses as well as low temperature thermal conductivity is reported for the binary phase Na_1−xGe_3+z. Specimens were characterized by thermal analysis, conventional and synchrotron powder X-ray diffraction, neutron powder diffraction, ²³Na nuclear magnetic resonance spectroscopy, and electrical and thermal transport measurements. With structural characteristics qualitatively analogous to some aluminum-silicate zeolites, the crystal structure of this phase exhibits an unconventional covalently bonded tunnel-like Ge framework, accommodating Na in channels of two different sizes. Observed to be non-stochiometric, Na_1−xGe_3+z concurrently exhibits substantial structural disorder in the large channels and a low lattice thermal conductivity, of interest in the context of identifying novel low thermal conductivity intermetallics for thermoelectric applications.     

The crystal structure of the new ternary antimonide Dy3Cu20+xSb11−x (x≈2)

New ternary antimonide Dy₃Cu_20+xSb_11−x (x≈2) was synthesized and its crystal structure was determined by direct methods from X-ray powder diffraction data (diffractometer DRON-3M, CuKα-radiation, R_I=6.99%,R_p=12.27%,R_wp=11.55%). The compound crystallizes with the own cubic structure type: space group , Pearson code cF272, . The structure of the Dy₃Cu₂₀Sb_11−x (x≈2) can be obtained from the structure type BaHg₁₁ by doubling of the lattice parameter and subtraction of 16 atoms. The studied structure was compared with the structures of known compounds, which crystallize in the same space group with similar cell parameters.     

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.     

Magnetic order and heavy fermion behavior in CePd1+xAl6−x: Synthesis, structure, and physical properties

The physical properties including magnetic susceptibility, specific heat, and electrical resistivity of single crystals are reported for the compound CePd_1+xAl_6−x (x=0.5) which crystallizes in the tetragonal SrAu₂Ga₅-type structure (space group P4/mmm). The compound was grown from an excess of molten Al flux from the respective elements and the crystal structure was established from single-crystal X-ray diffraction. Anomalies in the low temperature specific heat C_p(T) and electrical resistivity ρ(T) show that the compound undergoes ferromagnetic order at T_C=2.8 K. In the ordered state, CePd_1.5Al_5.5 displays heavy fermion behavior with a Sommerfeld coefficient of ca. 500 mJ/mol-K².     

Site preference and vibrational properties of R3T4+xAl12−x (R=Y, Ce, Gd, U, Th; T=Fe, Ru)

The crystal structures and phase stability of the ternary alloys R₃T_4+xAl_12−x (R=Y, Ce, Gd, U, Th; T=Fe, Ru) have been investigated using the interatomic potentials obtained by the lattice inversion method. These compounds crystallize in the hexagonal Gd₃Ru₄Al₁₂-type structure and the calculated lattice constants correspond well with the experiments. Among the four different kinds of Al sites in the structure, the most preferential sites for Fe atoms or Ru atoms are 6h sites. The properties related to lattice vibration, such as the phonon density of states (DOS) and Debye temperature of R₃Fe₄Al_12, have been evaluated. A qualitative analysis is carried out with the relevant potentials for the vibrational modes, which makes it possible to predict some thermodynamic properties.     

Metal-nonmetal transition in the sphalerite-type solid solution [ZnSnSb2]1−x[2(InSb)]x

Samples of the solid solution [ZnSnSb₂]_1−x[2(InSb)]_x have been prepared over the whole range of composition by tin flux synthesis. The lattice parameter of the sphalerite-type average structure varies linearly between that of the end members ZnSnSb₂ and InSb, a=6.2849(2) and 6.4776(15), respectively. Electron diffraction shows different kinds of structured diffuse scattering for Zn and In rich samples, respectively. The former is attributed to compositional short range ordering, the latter to thermally excited phonon modes. A metal-nonmetal transition takes place between the compositions x=0.8 and x=0.9.     

Visible light-sensitive yellow TiO2−xNx and Fe-N co-doped Ti1−yFeyO2−xNx anatase photocatalysts

Nitrogen substituted yellow colored anatase TiO_2−xN_x and Fe-N co-doped Ti_1−yFe_yO_2−xN_x have been easily synthesized by novel hydrazine method. White anatase TiO_2−δ and N/Fe-N-doped samples are semiconducting and the presence of ESR signals at g ∼1.994-2.0025 supports the oxygen vacancy and g∼4.3 indicates Fe³⁺ in the lattice. TiO_2−xN_x has higher conductivity than TiO_2−x and Fe/Fe-N-doped anatase and the UV absorption edge of white TiO_2−x extends in the visible region in N, Fe and Fe-N co-doped TiO₂, which show, respectively, two band gaps at ∼3.25/2.63, ∼3.31/2.44 and 2.8/2.44 eV. An activation energy of ∼1.8 eV is observed in Arrhenius log resistivity vs. 1/T plots for all samples. All TiO₂ and Fe-doped TiO₂ show low 2-propanol photodegradation activity but have significant NO photodestruction capability, both in UV and visible regions, while standard Degussa P-25 is incapable in destroying NO in the visible region The mid-gap levels that these N and Fe-N-doped TiO₂ consist may cause this discrepancy in their photocatalytic activities.     

Crystal structures of RPt3−xSi1−y(R=Y, Tb, Dy, Ho, Er, Tm, Yb) studied by single crystal X-ray diffraction

The crystal structures of ternary compounds RPt_3−xSi_1−y(R=Y, Tb, Dy, Ho, Er, Tm, Yb) have been elucidated from X-ray single crystal CCD data. All compounds are isotypic and crystallize in the tetragonal space group P4/mbm. The general formula RPt_3−xSi_1−y arises from defects: x≈0.20, y≈0.14. The crystal structure of RPt_3−xSi_1−y can be considered as a packing of four types of building blocks which derive from the CePt₃B-type unit cell by various degrees of distortion and Pt, Si-defects.     

Electron charge distribution of CaAl2−xZnx: Maximum entropy method combined with Rietveld analysis of high-resolution-synchrotron X-ray powder diffraction data

Using short wavelength X-rays from synchrotron radiation (SPring-8), high-resolution powder diffraction patterns were collected. In order to study both the structural relationship and the mechanism of stability in the CaAl_2−xZn_x system, among the Laves phases (MgCu₂ and MgNi₂ type) and KHg₂-type structures, the charge density distribution of CaAl_2−xZn_x as a function of x was obtained from the diffraction data by Rietveld analysis combined with the maximum entropy method (MEM). In the MEM charge density maps overlapping electron densities were clearly observed, especially in the Kagomé nets of the Laves phases. In order to clarify the charge redistribution in the system, the deformation charge densities from the densities formed by the constituent free atoms are discussed. In the ternary MgNi₂-type phase, partial ordering of Al and Zn atoms is observed, a finding that is supported by ab-initio total energy calculations.     

Thermochemistry of Li1+xMn2−xO4 (0?x?1/3) spinel

Lithium substituted Li_1+xMn_2−xO₄ spinel samples in the entire solid solution range (0?x?1/3) were synthesized by solid-state reaction. The samples with x<0.25 are stoichiometric and those with x?0.25 are oxygen deficient. High-temperature oxide melt solution calorimetry in molten 3Na₂O·4MoO₃ at 974 K was performed to determine their enthalpies of formation from constituent binary oxides at 298 K. The cubic lattice parameter was determined from least-squares fitting of powder XRD data. The variations of the enthalpy of formation from oxides and the lattice parameter with x follow similar trends. The enthalpy of formation from oxides becomes more exothermic with x for stoichiometric compounds (x<0.25) and deviates endothermically from this trend for oxygen-deficient samples (x?0.25). This energetic trend is related to two competing substitution mechanisms of lithium for manganese (oxidation of Mn³⁺ to Mn⁴⁺ versus formation of oxygen vacancies). For stoichiometric spinels, the oxidation of Mn³⁺ to Mn⁴⁺ is dominant, whereas for oxygen-deficient compounds both mechanisms are operative. The endothermic deviation is ascribed to the large endothermic enthalpy of reduction.     

REAuAl4Ge2 and REAuAl4(AuxGe1−x)2 (RE=rare earth element): Quaternary intermetallics grown in liquid aluminum

The two families of intermetallic phases REAuAl₄Ge₂ (1) (RE=Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Er, Tm and Yb) and REAuAl₄(Au_xGe_1−x)₂ (2) (x=0.4) (RE=Ce and Eu) were obtained by the reactive combination of RE, Au and Ge in liquid aluminum. The structure of (1) adopts the space group R-3m (CeAuAl₄Ge₂, , ; NdAuAl₄Ge₂, , ; GdAuAl₄Ge₂, , ; ErAuAl₄Ge₂, , ). The structure of (2) adopts the tetragonal space group P4/mmm with lattice parameters: , for EuAuAl₄(Au_xGe_1−x)₂ (x=0.4). Both structure types present slabs of “AuAl₄Ge₂” or “AuAl₄(Au_xGe_1−x)₂” stacking along the c-axis with layers of RE atoms in between. Magnetic susceptibility measurements indicate that the RE atoms (except for Ce and Eu) possess magnetic moments consistent with +3 species. The Ce atoms in CeAuAl₄Ge₂ and CeAuAl₄(Au_xGe_1−x)₂ (x=0.4) appear to be in a mixed +3/+4 valence state; DyAuAl₄Ge₂ undergoes an antiferromagnetic transition at 11 K and below this temperature exhibits metamagnetic behavior. The Eu atoms in EuAuAl₄(Au_xGe_1−x)₂ (x=0.4) appear to be in a 2+ oxidation state.     

New rare earth metal-rich indides RE14Ni3In3 (RE=Sc, Y, Gd-Tm, Lu)—synthesis and crystal chemistry

The rare earth-nickel-indides RE₁₄Ni₃In₃ (RE=Sc, Y, Gd-Tm, Lu) were synthesized from the elements by arc-melting and subsequent annealing. The compounds were investigated on the basis of X-ray powder and single crystal data: Lu₁₄Co₂In₃ type, P4₂/nmc, Z=4, a=888.1(1), c=2134.7(4), wR2=0.0653, 1381 F² values, 63 variables for Sc_13.89Ni_3.66In_2.45; a=961.2(1), c=2316.2(5), wR2=0.0633, 1741 F² values, 64 variables for Y_13.84Ni_3.19In_2.97; a=965.3(1), c=2330.5(5), wR2=0.0620, 1765 F² values, 63 variables for Gd₁₄Ni_3.29In_2.71; a=956.8(1), c=2298.4(5), wR2=0.0829, 1707 F² values, 64 variables for Tb_13.82Ni_3.36In_2.82; a=951.7(1), c=2289.0(5), wR2=0.0838, 1794 F² values, 64 variables for Dy_13.60Ni_3.34In_3.06; a=948.53(7), c=2270.6(1), wR2=0.1137, 1191 F² values, 64 variables for Ho_13.35Ni_3.17In_3.48; a=943.5(1), c=2269.1(5), wR2=0.0552, 1646 F² values, 64 variables for Er_13.53Ni_3.14In_3.33; a=938.42(7), c=2250.8(1), wR2=0.1051, 1611 F² values, 64 variables for Tm_13.47Ni_3.28In_3.25; a=937.3(1), c=2249.6(5), wR2=0.0692, 1604 F² values, 64 variables for Tm_13.80Ni_3.49In_2.71; and a=933.4(1), c=2263.0(5), wR2=0.0709, 1603 F² values, 64 variables for Lu_13.94Ni_3.07In_2.99. The RE₁₄Ni₃In₃ indides show significant Ni/In mixing on the 4c In1 site. Except the gadolinium compound, the RE₁₄Ni₃In₃ intermetallics also reveal RE/In mixing on the 4c RE1 site, leading to the refined compositions. Due to the high rare earth metal content, the seven crystallographically independent RE sites have between 9 and 10 nearest RE neighbors. The RE₁₄Ni₃In₃ structures can be described as a complex intergrowth of rare earth-based polyhedra. Both nickel sites have a distorted trigonal-prismatic rare earth coordination. An interesting feature is the In2-In2 dumb-bell at an In2-In2 distance of 304 pm (for Gd₁₄Ni_3.29In_2.71). The crystal chemical peculiarities of the RE₁₄Ni₃In₃ indides are briefly discussed.     

Three-layer Aurivillius phases containing magnetic transition metal cations: Bi2−xSr2+x(Nb,Ta)2+xM1−xO12, M=Ru, Ir, Mn, x≈0.5

We report the synthesis of Aurivillius-type phases incorporating magnetic M⁴⁺ cations (M=Mn, Ru, Ir), based on the substitution of M⁴⁺ for Ti⁴⁺ in Bi₂Sr₂(Nb,Ta)₂TiO₁₂. The key to incorporating these magnetic transition metal cations appears to be the partial substitution of Sr²⁺ for Bi³⁺ in the α-PbO-type layer of the Aurivillius phase, leading to a concomitant decrease in the M⁴⁺ content; i.e., the composition of the prepared compounds was Bi_2−xSr_2+x(Nb,Ta)_2+xM_1−xO₁₂, x≈0.5. These compounds only exist over a narrow range of x, between an apparent minimum (x≈0.4) Sr²⁺ content in the α-PbO-type [Bi₂O₂] layer required for Aurivillius phases to form with magnetic M⁴⁺ cations, and an apparent maximum (x≈0.6) Sr²⁺ substitution in this [Bi₂O₂] layer. Rietveld-refinement of synchrotron X-ray powder diffraction data making use of anomalous dispersion at the Nb and Ru K edges show that the overwhelming majority of the incorporated M cations occupy the central of the three MO₆ octahedral layers in the perovskite-type block. Magnetic susceptibility measurements are presented and discussed in the context of the potential for multiferroic (magnetoelectric) properties in these materials.     

First-principles investigation of R2O3(ZnO)3 (R=Al, Ga, and In) in homologous series of compounds

Atomic and electronic structures of R₂O₃(ZnO)₃ (R=Al, Ga, and In), which are included in homologous series of compounds, are investigated using first-principles calculations based on density functional theory. Three models with different R atom arrangements in the five-fold and four-fold coordination sites are examined. Al and Ga prefer the five-fold coordination sites. The formation energies are much larger than those of the competing phases, ZnR₂O₄, with a normal spinel structure. On the other hand, In₂O₃(ZnO)₃ shows no clear site preference and can be more stable than the spinel at high temperatures when configurational entropy contribution is taken into account. Electronic states near the conduction band bottom are mainly composed of Zn-4s orbital in Al₂O₃(ZnO)₃, while the contributions of Ga-4s and In-5s are comparable to Zn-4s in Ga₂O₃(ZnO)₃ and In₂O₃(ZnO)₃.     

Structure and phase composition of nanocrystalline Ce1−xLuxO2−y

The microstructure and phase stability of nanocrystalline mixed oxide Lu_xCe_1−xO_2−y (x=0-1) are described. Nano-sized (3-4 nm) oxide particles were prepared by the reverse microemulsion method. Morphological and structural changes upon heat treatment in an oxidizing atmosphere were studied by transmission electron microscopy (TEM), X-ray diffraction (XRD), Raman and Yb³⁺ emission spectroscopy, the latter ion being present as an impurity in the Lu₂O₃ starting material. Up to 950 °C, the samples were single phase, with structure changing smoothly with Lu content from fluorite type (F) to bixbyite type (C). For the samples heated at 1100 °C phase separation into coexisting F- and C-type structures was observed for 0.35<x<0.7. It was also found that addition of Lu strongly hinders the crystallite growth of ceria during heat treatment at 800 and 950 °C.     

Magnetic properties of Fe2P-type R6CoTe2 compounds (R=Gd-Er)

The magnetic structure of the Fe₂P-type R₆CoTe₂ phases (R=Gd-Er, space group P6¯2m) has been investigated through magnetization measurement and neutron powder diffraction. All phases demonstrate high-temperature ferromagnetic and low-temperature transitions: T_C=220 K and T_CN=180 K for Gd₆CoTe₂, T_C=174 K and T_CN=52 K for Tb₆CoTe₂, T_C=125 K and T_CN=26 K for Dy₆CoTe₂, T_CN=60 K and T_N=22 K for Ho₆CoTe₂ and T_CN∼30 K and T_N∼14 K for Er₆CoTe₂.Between 174 and 52 K Tb₆CoTe₂ has a collinear magnetic structure with K₀=[0, 0, 0] and with magnetic moments along the c-axis, whereas below 52 K it adopts a non-collinear ferromagnetic one.Below 60 K the magnetic structure of Ho₆CoTe₂ is that of a non-collinear ferromagnet. The holmium magnetic components with a K₀=[0, 0, 0] wave vector are aligned ferromagneticaly along the c-axis, whereas the magnetic component with a K₁=[1/2, 1/2, 0] wave vector are arranged in the ab plane. The low-temperature magnetic transition at ∼22 K coincides with the reorientation of the Ho magnetic component with the K₀ vector from the collinear to the non-collinear state.Below 30 K Er₆CoTe₂ shows an amplitude-modulate magnetic structure with a collinear arrangement of magnetic components with K₀=[0, 0, 0] and K₁=[1/2, 1/2, 0]. The low-temperature magnetic transition at ∼14 K corresponds to the variation in the magnitudes of the M_Er^K0 and M_Er^K1 magnetic components.In these phases, no local moment was detected on the cobalt site.The magnetic entropy of Gd₆CoTe₂ increases from ΔS_mag=−4.5 J/kg K at 220 K up to ΔS_mag=−6.5 J/kg K at 180 K for the field change Δμ₀H=0-5 T.     

Hydrothermal synthesis and magnetic properties of RMn2O5 (R=La, Pr, Nd, Tb, Bi) and LaMn2O5+δ

RMn₂O₅ (R=La, Pr, Nd, Tb, Bi) crystallites were prepared by a mild hydrothermal method and characterized by powder X-ray diffraction, scanning electron microscopy, X-ray photoelectron spectroscopy (XPS) and magnetic measurement. The formation of manganates was sensitive to the alkalinities and Mn-containing precursors of the reaction mixtures. This family of manganates is isostructural and has a space group of Pbam. The magnetic measurements for RMn₂O₅ showed an antiferromagnetic transition. The strong irreversibility between the ZFC and FC curves indicated a helicoidally magnetic structure below 40 K. The max d.c. susceptibilities of LaMn₂O_5+δ (δ=0.01, 0.06, 0.08, 0.16, 0.17) were found to be variable and the excess oxygen (δ) in the compounds was influenced by the alkalinity used in the hydrothermal synthesis.