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At least 829 records · Page 46
All sourcesNASA NTRSDOE OSTI
DOE OSTI2011

Synthesis, structural characterization and magnetic properties of RE{sub 2}MgGe{sub 2} (RE=rare-earth metal)

A series of rare-earth metal-magnesium-germanides RE{sub 2}MgGe{sub 2} (RE=Y, Nd, Sm, Gd-Tm, Lu) has been synthesized by reactions of the corresponding elements at high temperature. Their structures have been established by single-crystal and powder X-ray diffraction and belong to the Mo{sub 2}FeB{sub 2} structure type (space group P4/mbm (No. 127), Z=2; Pearson symbol tP10). Temperature dependent DC magnetization measurements indicate Curie-Weiss paramagnetism in the high-temperature regime for all members of the family, excluding Y{sub 2}MgGe{sub 2}, Sm{sub 2}MgGe{sub 2}, and Lu{sub 2}MgGe{sub 2}. At cryogenic temperatures (ca. 60 K and below), most RE{sub 2}MgGe{sub 2} phases enter into an antiferromagnetic ground-state, except for Er{sub 2}MgGe{sub 2} and Tm{sub 2}MgGe{sub 2}, which do not undergo magnetic ordering down to 5 K. The structural variations as a function of the decreasing size of the rare-earth metals, following the lanthanide contraction, and the changes in the magnetic properties across the series are discussed as well. - Graphical Abstract: The structure of RE{sub 2}MgGe{sub 2} (RE=Y, Nd, Sm, Gd-Tm, Lu) can be best viewed as 2-dimensional slabs of Mg and Ge atoms (anionic sub-lattice), and layers of rare-earth metal atoms (cationic sub-lattice) between them. Within this description, one should consider the Ge-Ge dumbbells (formally Ge{sup 6-}{sub 2}), interconnected with square-planar Mg atom as forming flat [MgGe{sub 2}] layers (z=0), stacked along the c-axis with the layers at z=1/2, made of rare-earth metal cations (formally RE{sup 3+}). Highlights: > RE{sub 2}MgGe{sub 2} (RE=Y, Nd, Sm, Gd-Tm, Lu) are new ternary germanides. > Their structures can be recognized as a 1:1 intergrowth of CsCl- and AlB{sub 2}-like slabs. > Ge atoms are covalently bound into Ge{sub 2} dumbbells. > Most RE{sub 2}MgGe{sub 2} phases are antiferromagnetically ordered at cryogenic temperatures.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2011

Synthesis, structure and physical properties of reduced barium titanate Ba{sub 2}Ti{sub 13}O{sub 22}

Polycrystalline sample of the reduced barium titanate Ba{sub 2}Ti{sub 13}O{sub 22} was synthesized by solid state reaction at 1523 K in Ar atmosphere for the first time. The Rietveld refinement using the powder X-ray diffraction data confirmed the sample to be main phase of Ba{sub 2}Ti{sub 13}O{sub 22} having the orthorhombic crystal system, space group Bmab and the lattice parameters of a=11.67058(11) A, b=14.12020(13) A and c=10.06121(9) A, and V=1657.995(20) A{sup 3}. The valence state of Ti was evaluated by both the Ti-O bond distance analysis and the Ti K-edge XANES analysis. The magnetic susceptibility was nearly temperature independent in the range of 60-300 K, suggesting the Van Vleck Paramagnetism. The electrical conductivity at 300 K is approximately 320.50 S/cm, and a semiconducting behavior was observed below room temperature. The Seebeck coefficient showed a negative value of -1.25 {mu}V/K at 300 K, indicating n-type behavior. These facts were confirmed by the results of the present theoretical calculations by the FLAPW method. - Graphical abstract: Temperature dependence of the electrical conductivity of Ba{sub 2}Ti{sub 13}O{sub 22}. A plot of ln {sigma} versus T{sup -1} is shown by open circles, and a plot of ln {sigma} versus T{sup -1/4} is shown by open triangles. Highlights: > Polycrystalline samples of Ba{sub 2}Ti{sub 13}O{sub 22} synthesis by solid state reaction. > Theoretical calculation by FLAPW method. > Electrical property measurements.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

New metal-organic frameworks of [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La, Ce) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O

Two novel materials, [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La(1a), Ce(1b)) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O (2), with a metal-organic framework (MOF) were prepared with hydrothermal reactions and characterized with photoluminescence, magnetic susceptibility, thermogravimetric analysis and X-ray powder diffraction in situ. The crystal structures were determined by single-crystal X-ray diffraction. Compound 1 crystallized in triclinic space group P1-bar (No. 2); compound 2 crystallized in monoclinic space group P2{sub 1}/c (No. 14). The structure of 1 is built from a 1D MOF, composed of deprotonated citric ligands of three kinds. Compound 2 contains a 2D MOF structure consisting of citrate and oxalate ligands; the oxalate ligand arose from the decomposition in situ of citric acid in the presence of Cu{sup II} ions. Photoluminescence spectra of compounds 1b and 2 revealed transitions between the 5d{sup 1} excited state and two levels of the 4f{sup 1} ground state ({sup 2}F{sub 5/2} and {sup 2}F{sub 7/2}). Compounds 1b and 2 containing Ce{sup III} ion exhibit a paramagnetic property with weak antiferromagnetic interactions between the two adjacent magnetic centers. - Graphical Abstract: [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La(1a), Ce(1b)) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O (2)-with 1D and 2D structures were synthesized and characterized. Highlights: Black-Right-Pointing-Pointer Two MOF - [M(C{sub 6}H{sub 5}O{sub 7})(C{sub 6}H{sub 6}O{sub 7})(C{sub 6}H{sub 7}O{sub 7})(H{sub 2}O)] . H{sub 2}O (M=La(1a), Ce(1b)) and [Ce{sub 2}(C{sub 2}O{sub 4})(C{sub 6}H{sub 6}O{sub 7}){sub 2}] . 4H{sub 2}O (2) - with 1D and 2D structures. Black-Right-Pointing-Pointer The adjacent chains of the 1D framework were correlated with each other through an oxalate ligand to form a 2D layer structure. Black-Right-Pointing-Pointer The source of the oxalate ligand was the decomposition in situ of citric acid oxidized in the presence of Cu{sup II} ions.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Synthesis and characterization of Sr{sub 2}Ir{sub 1-x}M{sub x}O{sub 4} (M=Ti, Fe, Co) solid solutions

The effects of Ti, Fe and Co substitutions for Ir on the structure and on the physical properties of Sr{sub 2}IrO{sub 4} are investigated. A complete solid solution Sr{sub 2}Ir{sub 1-x}Ti{sub x}O{sub 4} is obtained while both Fe and Co doping are relatively limited. In each case however, the c-axis cell parameter and the initial IrO{sub 6} octahedra tilting decreases with substitution. Doping with Ti, Fe and Co results in a decrease of the magnetic susceptibility and in an increase in the paramagnetic effective moment for Co and Fe doped samples and a suppression of the weak ferromagnetic ordering observed for Sr{sub 2}IrO{sub 4}. - Graphical abstract: Solid solutions of Sr{sub 2}Ir{sub 1-x}M{sub x}O{sub 4} (M=Ti, Fe, Co) have been synthesized and characterized by powder X-ray diffraction, magnetism and electrical measurements. Changes in the a parameter and decreases in both the c-axis cell parameters and the initial IrO{sub 6} octahedra tilting are found to be correlated. Highlights: Black-Right-Pointing-Pointer Solid Solutions of Sr{sub 2}Ir{sub 1-x}M{sub x}O{sub 4} (M=Ti, Fe, Co) are synthesized. Black-Right-Pointing-Pointer The Sr{sub 2}Ir{sub 1-x}Ti{sub x}O{sub 4} solid solution is complete while those of Fe and Co are relatively limited. Black-Right-Pointing-Pointer The change in a cell parameter with substitution is much less than that of the c parameter. Black-Right-Pointing-Pointer Decreased tilting and the smaller size of the M cation contrastingly affect the a parameter. Black-Right-Pointing-Pointer Doping results in a suppression of the weak ferromagnetic ordering in Sr{sub 2}IrO{sub 4}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2012

Magnetic and electrical properties of UCr{sub 2}Al{sub 20} single crystals

Single crystals of UCr{sub 2}Al{sub 20} have been grown by flux method and characterized by means of X-ray diffraction, magnetic, heat capacity and electrical transport measurements. The compound exhibits weakly temperature-dependent, moderately exchange-enhanced Pauli paramagnetism and shows regular metallic conductivity. - Graphical abstract: Pauli-like temperature dependence of the molar magnetic susceptibility of single-crystalline UCr{sub 2}Al{sub 20}. Inset: field variation of the magnetization in UCr{sub 2}Al{sub 20} taken at 1.8 K. Highlights: Black-Right-Pointing-Pointer High quality single crystals of UCr{sub 2}Al{sub 20} have been grown. Black-Right-Pointing-Pointer Crystal structure of UCr{sub 2}Al{sub 20} has been refined from the single crystal X-ray diffraction data. Black-Right-Pointing-Pointer Magnetic, heat capacity and electrical transport data have been collected for single crystalline UCr{sub 2}Al{sub 20}. Black-Right-Pointing-Pointer Previous literature report on UCr{sub 2}Al{sub 20} has been corrected and supplemented with new data.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Factors governing Yb magnetism in Yb{sub 0.95}PtIn{sub 2} and other MgCuAl{sub 2}-type structures

The ternary compound 'YbPtIn{sub 2}' has been synthesized and its crystal structure determined using single crystal X-ray diffraction techniques. The compound crystallizes in the MgCuAl{sub 2} structure, a ternary structure type often formed when rare earth metals, Group 10 transition metals, and indium are present in a 1:1:2 ratio. The unit cell is C-centered orthorhombic, space group Cmcm (no. 63) with lattice parameters of a=4.3410(1) A, b=10.3230(2) A, and c=7.8510(2) A. Evidence is found for a substantial non-stoichiometry on the Yb site, in contrast to the Pt and In sites which behave as expected, and it is believed that the stoichiometry of this compound is more properly described as Yb{sub 0.95}PtIn{sub 2}. Magnetic and resistivity measurements reveal that 'YbPtIn{sub 2}' is a weakly interacting, non-magnetic metal exclusively containing Yb{sup 2+}, and with a resistivity ({rho}) varying from 34 {mu}{Omega} cm at room temperature to a residual resistivity {rho}{sub 0} of 23 {mu}{Omega} cm at 1.8 K. Density functional theory calculations suggest that the observed diamagnetic Yb behavior is expected for this compound, but that certain substitutions on the Pt or In site could help stabilize magnetic Yb{sup 3+} and potentially induce heavy fermion behavior. - Graphical abstract: The crystal structure, magnetic behavior, and temperature-dependent resistivity of the new ternary compound Yb{sub 0.95}PtIn{sub 2.} Highlights: Black-Right-Pointing-Pointer Flux growth method used to produce Yb{sub 0.95}PtIn{sub 2} single crystals. Black-Right-Pointing-Pointer Found rare example of non-stoichiometry in a MgCuAl{sub 2}-type structure. Black-Right-Pointing-Pointer The resistivity and diamagnetic response of Yb{sub 0.95}PtIn{sub 2} were modeled. Black-Right-Pointing-Pointer DFT correctly predicts presence of Yb{sup 2+} in Yb{sub 0.95}PtIn{sub 2}. Black-Right-Pointing-Pointer COHP results suggest other MgCuAl{sub 2}-type indides that may contain paramagnetic Yb{sup 3+}.

36 MATERIALS SCIENCE↗
DOE OSTI2012

Studies on solid solutions based on layered honeycomb-ordered phases P2-Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Ni, Zn)

Three complete solid solutions between the layered phases P2-Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Ni, Zn) have been prepared by conventional solid state method and investigated through X-ray diffraction, magnetism and optical measurements. All compositions are characterized by a M{sup 2+}/X{sup 6+} honeycomb ordering within the slabs and crystallize in a hexagonal unit cell. However, a structural transition based on a different stacking is observed as nickel (space group P6{sub 3}/mcm) is substituted by zinc or cobalt (space group P6{sub 3}22). All compositions exhibit a paramagnetic Curie-Weiss behavior at high temperatures; and the magnetic moment values confirm the presence of Ni{sup 2+} and/or Co{sup 2+} cations. The low-temperature antiferromagnetic order of Na{sub 2}Ni{sub 2}TeO{sub 6} and Na{sub 2}Co{sub 2}TeO{sub 6} is suppressed by zinc substitution. The color of the obtained compositions varies from pink, to light green and white when M=Co, Ni, Zn, respectively. - Graphical abstract: The comparison between the structure of Na{sub 2}Ni{sub 2}TeO{sub 6} (left) and Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Zn) (right) evidences the stacking difference with distinct atom sequences along the hexagonal c-axis. Highlights: Black-Right-Pointing-Pointer Solid solutions between lamellar phases Na{sub 2}M{sub 2}TeO{sub 6} (M=Co, Ni, Zn) are investigated. Black-Right-Pointing-Pointer A M{sup 2+}/X{sup 6+} honeycomb ordering characterized all the compositions. Black-Right-Pointing-Pointer A structural transition is shown when Ni is replaced by Co or Zn. Black-Right-Pointing-Pointer The low-temperature AFM ordering of Na{sub 2}Ni{sub 2}TeO{sub 6} and Na{sub 2}Co{sub 2}TeO{sub 6} is suppressed by zinc substitution. Black-Right-Pointing-Pointer Color changes from pink to light green and white when M=Co, Ni, Zn, respectively.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Mixed metallic Ba(Co,Mn)X{sub 0.2-x}O{sub 3-{delta}} (X=F, Cl) hexagonal perovskites

We show here that the incorporation of Mn in Ba-Co-oxohalide, BaCoX{sub 0.2-x}O{sub 3-{delta}}, hexagonal perovskite stabilizes the 6H-form (stacking sequence (chhhch Prime ); c, h=[BaO{sub 3}] and h Prime =[BaOX] layers), with tetramers of face-sharing octahedra) rather than the trimeric 10H-form. On the contrary to previous results on the Fe incorporation in similar system leading to more reduced 10H-compounds, the Mn effect is to increase the mean (Co/Mn) valence better suited to the 6H form. We experienced a poor Mn/Co miscibility during our syntheses leading to great difficulties to isolate mixed Co/Mn single phase materials and/or weak reproducibility. Powder neutron diffraction data shows a mixed Mn/Co octahedral occupancy, while the tetrahedra are filled by Co{sup 3+} cations. Anionic vacancies were refined in the h Prime -[BaO{sub 1-z}X{sub 1-x}] layer and the next c-[BaO{sub 3-z}] layers, while the h-[BaO{sub 3}] layers are not oxygen deficient. Magnetic properties suggest that a part of Mn cations remain paramagnetic until low temperature, while isolated spin clusters (probably driven by AFM Co tetrahedral dimers) behave as low-dimensional AFM systems. Transport measurements reveal a transition from high-temperature metallic to low-temperature semi-conducting states that could occur from defect shallow donor upon the Mn for Co substitution. - Graphical abstract: The incorporation of Mn in Ba-Co-oxohalide, BaCoX{sub 0.2-x}O{sub 3-{delta}}, hexagonal perovskite stabilizes the 6H-form with tetrameric (Co,Mn){sub 4}O{sub 15} face sharing linear chains. This results from a oxidizing Mn effect and particular Mn/Co distribution. Highlights: Black-Right-Pointing-Pointer The incorporation of Mn in BaCoX{sub 0.2-x}O{sub 3-{delta}} (X=F,Cl) hexagonal perovskites stabilizes the 6H-form. Black-Right-Pointing-Pointer It contains tetrameric (Co,Mn){sub 4}O{sub 15} face sharing linear chains. Black-Right-Pointing-Pointer The preference for such chains better than trimeric ones is due to the Manganese oxidizing effect. Black-Right-Pointing-Pointer A particular Mn/Co distribution was evidenced. Black-Right-Pointing-Pointer Transport and magnetic properties drastically change during the Mn incorporation.

36 MATERIALS SCIENCE↗
DOE OSTI2013

The synthesis and characterisation of LaCa{sub 2}Fe{sub 2}GaO{sub 8}

The synthesis and characterisation of LaCa{sub 2}Fe{sub 2}GaO{sub 8} is described. Neutron powder diffraction data reveal LaCa{sub 2}Fe{sub 2}GaO{sub 8} adopts an anion-vacancy ordered, 'triple layer' structure consisting of an OOT{sub L}OOT{sub R} stacking sequence of layers of (Fe/Ga)O{sub 6} octahedra (O) and (Fe/Ga)O{sub 4} tetrahedra (T), related to that of the 4-layer brownmillerite structures (a=5.4784(1) A, b=22.6780(4) A, c=5.6007(1) A, space group Pbma). The apex-linked chains of tetrahedra within structure of LaCa{sub 2}Fe{sub 2}GaO{sub 8} exhibit a cooperative twisting distortion which alternates in direction between adjacent layers of tetrahedra, the first time such an arrangement has been seen in a triple-layer phase. Magnetisation and neutron diffraction data reveal that LaCa{sub 2}Fe{sub 2}GaO{sub 8} exhibits two magnetic ordering transitions. On cooling below 550 K the phase adopts a state with short range antiferromagnetic coupling within each double layer of (Fe/Ga)O{sub 6} octahedra, but only weak coupling between layers. On cooling below 470 K full three-dimensional, G-type antiferromagnetic order is observed. - Graphical abstract: LaCa{sub 2}Fe{sub 2}GaO{sub 8} adopts an anion-vacancy ordered, 'triple layer' structure consisting of an OOT{sub L}OOT{sub R} stacking sequence of layers of FeO{sub 6} octahedra (O) and GaO{sub 4} tetrahedra (T), in which the chains of apex-linked tetrahedra exhibit a cooperative twisting distortion which alternates in direction between adjacent layers of tetrahedra. On cooling below 550 K, LaCa{sub 2}Fe{sub 2}GaO{sub 8} adopts a state with strong two-dimensional antiferromagnetic order within each double layer of FeO{sub 6} octahedra, but only weak coupling between layers. On cooling below 470 K full three-dimensional antiferromagnetic order is observed. Highlights: Black-Right-Pointing-Pointer LaCa{sub 2}Fe{sub 2}GaO{sub 8} exhibits a novel anion-vacancy ordered triple-layer structure type. Black-Right-Pointing-Pointer New structure variant rationalised on the basis of strucutral parameters. Black-Right-Pointing-Pointer Multiple magnetic transitions: paramagnetic-two-dimensional-three-dimensional.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Structural and magnetic characterisation of the pyrochlores Bi{sub 2-x}Fe{sub x}(FeSb)O{sub 7}, (x=0.1, 0.2, 0.3), Nd{sub 1.8}Fe{sub 0.2}(FeSb)O{sub 7} and Pr{sub 2}(FeSb)O{sub 7}

Four antimony-containing pyrochlores with compositions Bi{sub 2-x}Fe{sub x}(FeSb)O{sub 7}, where x=0.1, 0.2, 0.3, and Nd{sub 1.8}Fe{sub 0.2}(FeSb)O{sub 7} have been synthesised, their structural properties examined, and compared to that of the pyrochlore phase Pr{sub 2}(FeSb)O{sub 7} which we have structurally characterised for the first time. The Fe{sup 3+} ions in Pr{sub 2}(FeSb)O{sub 7} are located only on the B-sites whereas in the bismuth- and neodymium-containing pyrochlore structures the Fe{sup 3+} ions are present on both the A- and B-sites giving rise to static displacive disorder in the A{sub 2}O' chains. The presence of a smaller cation on the A-site in materials of composition Bi{sub 2-x}Fe{sub x}(FeSb)O{sub 7} appears to lower the radius ratio (r{sub A}/r{sub B}) and leads to a stabilisation of the structure. Magnetic susceptibility measurements reveal no long range order, but Bi{sub 1.9}Fe{sub 0.1}(FeSb)O{sub 7} and Bi{sub 1.8}Fe{sub 0.2}(FeSb)O{sub 7} undergo transitions at ca. 12K to a spin-glass state; Nd{sub 1.8}Fe{sub 0.2}(FeSb)O{sub 7} and Pr{sub 2}(FeSb)O{sub 7} are paramagnetic. - graphical abstract: Intersite cation mixing in A{sub 2}(FeSb)O{sub 7} (A=Bi, Pr, Nd) pyrochlores. Highlights: Black-Right-Pointing-Pointer The instability of the pyrochlore composition Bi{sub 2}FeSbO{sub 7} is reported for the first time. Black-Right-Pointing-Pointer Structure analysis confirms the presence of Fe on the Bi-site. Black-Right-Pointing-Pointer The presence of Fe{sup 3+} on two distinct sites is supported by Moessbauer spectroscopy. Black-Right-Pointing-Pointer For Nd{sub 2}FeSbO{sub 7} and Pr{sub 2}FeSbO{sub 7,} Fe can also enter the Nd/Prsite. Black-Right-Pointing-Pointer No magnetic order occurs in these materials.

36 MATERIALS SCIENCE↗
DOE OSTI2013

Unconventional critical magnetic behavior in the Griffiths ferromagnet La₀.₄Ca₀.₆MnO₂.₈□₀.₂ oxide

The effects of oxygen vacancy on the critical magnetic behavior in La₀.₄Ca₀.₆MnO₂.₈□₀.₂ around the paramagnetic-ferromagnetic (PM-FM) phase transition were investigated through various techniques such as modified Arrott plot, Kouvel-Fisher method and critical isotherm analysis via dc magnetization measurements recorded around the Curie temperature T C . The obtained critical exponents values are β~0.8, γ~0.7 and δ~1.882 with T C ~164.5 K. Thus the scaling law γ+β=δβ is fulfilled. The critical exponents obey the single scaling-equation of state M(H,ε)|ε|{sup -β}=f{sub ±}(H|ε|{sup -(β+γ)}) where, f₊ for T>T C and f⁻ for T>T C . The found exponents are inconsistent with any known universality class. These results attributed to the existence of Griffiths Phase (Triki et al. (2012) [1]) seem to actually reflect the unconventional critical scaling of the magnetic susceptibility. - Graphical abstract: Modified Arrott plots: M{sup 1/β} vs. (μ₀H){sup 1/γ} with (a) mean-field model (β=0.5, γ=1), (b) 3D-Heisenberg model (β=0.365, γ=1.336), (c) 3D-Ising model (β=0.325, γ=1.24), (d) tricritical mean-field model (β=0.25, γ=1) and (e) (β=0.79, γ=0.71). Highlights: • Study of the critical behavior for La₀.₄Ca₀.₆MnO₂.₈□₀.₂ compound. • A typical second-order magnetic transition near T C . • Unconventional critical exponents were found.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Temperature-dependent XRD, IR, magnetic, SEM and TEM studies of Jahn–Teller distorted NiCr{sub 2}O{sub 4} powders

In the present work we report detailed structural, magnetic and phonon properties of NiCr{sub 2}O{sub 4} powders synthesized via a simple coprecipitation method. Temperature-dependent XRD as well as temperature-dependent IR studies reveal that cubic to tetragonal phase transition is lowered due to size effects. Observed changes in the IR spectra indicate that the paramagnetic–ferrimagnetic phase transition taking place at 74 K is related to further lowering of symmetry to orthorhombic system. Assignment of modes was proposed and factor group analyses in three possible symmetries were carried out. Our results show strong anomalies due to the Jahn–Teller tetragonal distortion and weak due to the orthorhombic distortion and onset of collinear ferrimagnetic order. Shifts of wavenumbers observed below 31 K, where the onset of antiferromagnetic ordering occurs, were attributed to spin–phonon interactions. - Graphical abstract: XRD pattern of NiCr{sub 2}O{sub 4} sample synthesized via a coprecipitation method followed by calcination at 1000 {sup o}C. - Highlights: • NiCr{sub 2}O{sub 4} starts to crystallize near 750 °C. • Coexistence of cubic and tetragonal phases of NiCr{sub 2}O{sub 4} was revealed. • Temperature of the Jahn–Teller distortion is lowered due to the size effects. • Evidences of tetragonal and orthorhombic distortions were found. • Weak spin–phonon interactions were evidenced.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Syntheses, crystal structures, magnetic and luminescence properties of five novel lanthanide complexes of nitronyl nitroxide radical

Five novel Ln(III) complexes based on a new nitronyl nitroxide radical have been synthesized, characterized structurally and magnetically: [Ln(hfac)₃(NITPh-3-Br-4-OMe)₂] (Ln(III)=Eu(1), Gd(2), Tb(3), Dy(4), Ho(5); hfac=hexafluoroacetylacetonate; and NITPh-3-Br-4-OMe=2-3´-Br-4´-methoxyphenyl-4,4,5,5 -tetramethylimidazoline-1-oxyl-3-oxide). The single-crystal structures analyses show that these complexes have similar mononuclear tri-spin structures, in which central Ln(III) ions are all eight coordinated by three hfac molecules and two NITPh-3-Br-4-OMe radicals. The variable-temperature magnetic susceptibility studies reveal the antiferromagnetic interactions between the paramagnetic ions (Ln(III) and radicals) in complexes 1, 2, 3 and 5 and ferromagnetic interaction in complex 4. The luminescence characterizations of complexes Eu(1), Tb(3) and Dy(4) are also studied in this paper. - Graphical abstract: Using a novel halogen phenyl-substituted nitronyl-nitroxide radical, we obtained and characterized five isostructural lanthanide mononuclear tri-spin compounds. Highlights: • A new halogen phenyl-substituted nitronyl-nitroxide radical was designed. • Five new Ln(III) radical complexes have been synthesized and characterized. • The reasonable evaluation the magnetic interactions between Ln(III) ions and radical is meaningful. • These complexes show good luminescent properties.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Synthesis, crystal structure and electrical properties of A-site cation ordered BaErMn{sub 2}O{sub 5} and BaErMn{sub 2}O{sub 6}

In this paper, we report on a synthesis procedure, structural and electrical properties of BaErMn{sub 2}O{sub 5} and BaErMn{sub 2}O{sub 6}, A-site double perovskites having layered arrangement of Ba and Er cations. These materials belong to a family of BaLnMn{sub 2}O{sub 5+δ} oxides, which up to now were successfully synthesized for Ln=Y and La–Ho lanthanides. Up to our knowledge, this is the first report on the successful synthesis of BaErMn{sub 2}O{sub 5} and BaErMn{sub 2}O{sub 6}, yielding>95 wt% of the considered compounds. Structural characterization of the materials is given at room temperature, together with in situ XRD studies, performed during oxidation of BaErMn{sub 2}O{sub 5} in air, at elevated temperatures up to 500 °C. A complex structural behavior was observed, with oxidation process of BaErMn{sub 2}O{sub 5} occurring at around 300 °C. The oxidized BaErMn{sub 2}O{sub 6} shows a structural phase transition at about 225 °C. Results of structural studies are supported by thermogravimetric measurements of the oxidation process, performed in air, as well as reduction process, preformed in 5 vol% of H{sub 2} in Ar. Additionally, isothermal oxidation/reduction cycles were measured at 500 °C, showing interesting properties of BaErMn{sub 2}O{sub 5+δ}, from a point of view of oxygen storage technology. Electrical conductivity of BaErMn{sub 2}O{sub 5} is of the order of 10{sup −4} S cm{sup −1} at room temperature and shows activated character on temperature with activation energy E{sub a}=0.30(1) eV. Positive sign of Seebeck coefficient for this material indicates holes as dominant charge carriers. Oxidized BaErMn{sub 2}O{sub 6} possesses much higher electrical conductivity, almost 0.2 S cm{sup −1} at room temperature. Additional, about 10-fold increase of electrical conductivity, occurring in the vicinity of 225 °C for this material, can be associated with phase transition from charge/orbital-ordered insulator COI(CE) to paramagnetic metal PM phase. The highest conductivity for BaErMn{sub 2}O{sub 6} was measured near 500 °C and is almost equal to 40 S cm{sup −1}, while negative sign of Seebeck coefficient can be associated with electrons being dominant charge carriers. - Graphical abstract: Structure and oxygen storage properties of BaErMn{sub 2}O{sub 5+δ}. - Highlights: • Synthesis of BaErMn{sub 2}O{sub 5} and BaErMn{sub 2}O{sub 6}. • Structural and transport properties of BaErMn{sub 2}O{sub 5+δ}. • Oxygen storage in BaErMn{sub 2}O{sub 5}–BaErMn{sub 2}O{sub 6} system. • Phase transitions in BaErMn{sub 2}O{sub 6}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2013

Structure and properties of Na{sub x}M{sub 2}SbO{sub 6}·yH{sub 2}O, M=Co(III), Ni(III) honeycomb oxyhydrates

The oxyhydrates Na{sub 0.85}Co{sub 2}SbO{sub 6}·1.7H{sub 2}O and Na{sub 0.95}Ni{sub 2}SbO{sub 6}·1.5H{sub 2}O were prepared by Br{sub 2} oxidation of Na{sub 3}Co{sub 2}SbO{sub 6} and Na{sub 3}Ni{sub 2}SbO{sub 6} and exposure to ambient air. Their composition and structure are characterized by thermogravimetric analysis, elemental analysis and powder X-ray diffraction. Both form monolayer hydrates with metal cations (Co or Ni) near the 3+ oxidation state. In the parent materials, MO{sub 6} octahedra surround SbO{sub 6} units, forming a honeycomb geometry; Rietveld refinement of the hydrate phases indicate that this motif is retained. Magnetic susceptibility plots display paramagnetic behavior and Curie–Weiss fits support the 3+ oxidation state (low spin d{sup 6}s=0 for Co and low spin d{sup 7}s=1/2 for Ni). Close inspection of the Ni hydrate’s susceptibility reveals a feature at 6.2 K and a non-linear magnetization at 2 K with no saturation up to 9 T. Heat capacity measurements show a large amount of excess entropy in the Ni hydrate in the 2–20 K temperature range, while the heat capacity of the Co hydrate can be described by a simple lattice contribution. The Ni hydrate sample is easily dehydrated by heating above 100 °C and forms a new Na-deficient phase, Na{sub 0.95}Ni{sub 2}SbO{sub 6}, which is stable at room temperature. Magnetic susceptibility of this phase is consistent with the Ni atom remaining in the 3+ oxidation state after dehydration. - Graphical abstract: Powder diffraction patterns of Na{sub 3}Ni{sub 2}SbO{sub 6}, Na{sub 0.95}Ni{sub 2}SbO{sub 6}·1.5H{sub 2}O and Na{sub 0.95}Ni{sub 2}SbO{sub 6}. Each pattern has been normalized in intensity. Cartoons depict the change in layer separation with hydration and give the approximate distances between layers and Ni atoms. Highlights: • New oxyhydrate phases with honeycomb lattices are formed. • Curie–Weiss fits indicate Ni{sup 3+} (s=1/2). • Heat capacity shows a large release of entropy for Ni phase, likely due to a complex magneto-structural phase transition.

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DOE OSTI2013

New ternary phosphides and arsenides. Syntheses, crystal structures, physical properties of Eu{sub 2}ZnP{sub 2}, Eu{sub 2}Zn{sub 2}P{sub 3} and Eu{sub 2}Cd{sub 2}As{sub 3}

Three new europium pnictides Eu{sub 2}ZnP{sub 2}, Eu{sub 2}Zn{sub 2}P{sub 3} and Eu{sub 2}Cd{sub 2}As{sub 3} have been synthesized and their structures were determined by single-crystal X-ray diffraction. Eu{sub 2}ZnP{sub 2} is isotypic with Yb{sub 2}CdSb{sub 2} (Cmc2{sub 1} (No. 36); cell parameters a=4.1777(7) Å, b=15.925(3) Å, c=7.3008(12) Å), while the latter two compounds crystallize with the Ba{sub 2}Cd{sub 2}Sb{sub 3} structure type (C2/m (No. 12); cell parameters a=15.653(5)/16.402(1) Å, b=4.127(1)/4.445(4) Å, c=11.552(4)/12.311(1) Å and β=126.647(4)/126.515(7)° for Eu{sub 2}Zn{sub 2}P{sub 3} and Eu{sub 2}Cd{sub 2}As{sub 3}, respectively). Magnetic susceptibility measurements in the interval 5–300 K confirm paramagnetic behavior and effective magnetic moments characteristic of Eu{sup 2+} ([Xe] 4f{sup 7}) ground states. Temperature-dependent electrical conductivity measurements also prove that Eu{sub 2}Cd{sub 2}As{sub 3} is a semiconducting compound with a narrow band gap of 0.059 eV below 100 K. According to TG/DSC analyses, Eu{sub 2}Cd{sub 2}As{sub 3} starts to decompose at about 950 K. - Graphical abstract: A polyhedral view of the crystal structure of new pnictides Eu{sub 2}T{sub 2}Pn{sub 3} (T=Zn or Cd; Pn=P or As). Display Omitted - Highlights: • Three new ternary pnictide Zintl compounds, Eu{sub 2}ZnP{sub 2}, Eu{sub 2}Zn{sub 2}P{sub 3} and Eu{sub 2}Cd{sub 2}As{sub 3}, have been synthesized and characterized. • The europium cations are divalent and ferromagnetically coupled in both Eu{sub 2}Zn{sub 2}P{sub 3} and Eu{sub 2}Cd{sub 2}As{sub 3}. • Eu{sub 2}Cd{sub 2}As{sub 3} has a very small band gap of 0.06 eV and starts to decompose over 950 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

Cationic disorder and Mn{sup 3+}/Mn{sup 4+} charge ordering in the B′ and B″ sites of Ca{sub 3}Mn{sub 2}NbO{sub 9} perovskite: a comparison with Ca{sub 3}Mn{sub 2}WO{sub 9}

We describe the preparation, crystal structure determination, magnetic and transport properties of two novel Mn-containing perovskites, with a different electronic configuration for Mn atoms located in B site. Ca{sub 3}Mn{sup 3+}{sub 2}WO{sub 9} and Ca{sub 3}Mn{sup 3+/4+}{sub 2}NbO{sub 9} were synthesized by standard ceramic procedures; the crystallographic structure was studied from X-ray powder diffraction (XRPD) and neutron powder diffraction (NPD). Both phases exhibit a monoclinic symmetry (S.G.: P2{sub 1}/n); Ca{sub 3}Mn{sub 2}WO{sub 9} presents a long-range ordering over the B sites, whereas Ca{sub 3}Mn{sub 2}NbO{sub 9} is strongly disordered. By “in-situ” NPD, the temperature evolution of the structure study presents an interesting evolution in the octahedral size (〈Mn–O〉) for Ca{sub 3}Mn{sub 2}NbO{sub 9}, driven by a charge ordering effect between Mn{sup 3+} and Mn{sup 4+} atoms, related to the anomaly observed in the transport measurements at T≈160 K. Both materials present a magnetic order below T{sub C}=30 K and 40 K for W and Nb materials, respectively. The magneto-transport measurements display non-negligible magnetoresistance properties in the paramagnetic regime. - Graphical abstract: Comparison between the octahedron size and the magnetic behaviour for Ca{sub 3}Mn{sub 2}NbO{sub 9} in the temperature region where the charge and magnetic order occur. Display Omitted - Highlights: • Two novel Mn-containing double perovskites were obtained by solid-state reactions. • Both double perovskites are monoclinic (P2{sub 1}/n) determined by XRPD and NPD. • Ca{sub 3}Mn{sub 2}WO{sub 9} contains Mn{sup 3+} while Ca{sub 3}Mn{sub 2}NbO{sub 9} includes mixed-valence cations Mn{sup 3+}/Mn{sup 4+}. • Ca{sub 3}Mn{sub 2}NbO{sub 9} presents a charge-ordering effect between Mn{sup 3+} and Mn{sup 4+} evidenced by NPD. • The magnetic and transport studies evidenced the charge ordering in Ca{sub 3}Mn{sub 2}NbO{sub 9}.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2014

The layered antimonides RELi{sub 3}Sb{sub 2} (RE=Ce–Nd, Sm, Gd–Ho). Filled derivatives of the CaAl{sub 2}Si{sub 2} structure type

Reported are the synthesis and the structural characterization of an extended family of rare-earth metal–lithium–antimonides with the formula RELi{sub 3}Sb{sub 2} (RE=Ce–Nd, Sm, Gd–Ho). They crystallize in the trigonal space group P3{sup ¯}m1 (No. 164, Pearson symbol hP6) with a structure, best viewed as a filled derivative of the common CaAl{sub 2}Si{sub 2} structure type (ternary variant of α-La{sub 2}O{sub 3}). Across the series, the lattice parameters monotonically decrease, following the lanthanide contraction. Temperature-dependent magnetic susceptibility measurements for CeLi{sub 3}Sb{sub 2}, PrLi{sub 3}Sb{sub 2} and TbLi{sub 3}Sb{sub 2} reveal paramagnetic behavior in the high temperature range, and the obtained effective moments are consistent with the expected ones for the free-ion RE{sup 3+} ground state. Possible ferromagnetic ordering for PrLi{sub 3}Sb{sub 2} and antiferromagnetic ordering for TbLi{sub 3}Sb{sub 2} are observed in the low temperature range (below 20 K). Tight-binding muffin-tin orbital electronic band structure calculations for LaLi{sub 3}Sb{sub 2} are presented and discussed as well. - Graphical abstract: The large family of rare-earth metal–lithium–antimonides with the formula RELi{sub 3}Sb{sub 2} (RE=Ce–Nd, Sm, Gd–Ho) crystallize in the trigonal space group P3{sup ¯}m1 (No. 164, Pearson symbol hP6) with a structure that is a filled derivative of the CaAl{sub 2}Si{sub 2} structure type (ternary variant of α-La{sub 2}O{sub 3}). Display Omitted - Highlights: • RELi{sub 3}Sb{sub 2} (RE=Ce–Nd, Sm, Gd–Ho) constitute an extended family of rare-earth metal–lithium–antimonides. • The layered structure is a filled derivative of the common CaAl{sub 2}Si{sub 2} structure type. • The valence electron count follows the Zintl–Klemm rules. • Electronic band structure calculations for LaLi{sub 3}Sb{sub 2} indicate small band-gap semiconducting behavior.

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