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At least 649 records · Page 36
All sourcesNASA NTRSDOE OSTI
DOE OSTI2014

Magnetic and magnetocaloric properties of La{sub 0.6}Pr{sub 0.1}Sr{sub 0.3}Mn{sub 1−x}Fe{sub x}O{sub 3} (0≤x≤0.3) manganites

The La{sub 0.6}Pr{sub 0.1}Sr{sub 0.3}Mn{sub 1−x}Fe{sub x}O{sub 3} (x=0, 0.1, 0.2 and 0.3) samples have been elaborated by the solid-state reaction method. X-ray powder diffraction shows that all the samples crystallize in a rhombohedric phase with R3{sup ¯}c space group. The variation of magnetization as a function of temperature and applied magnetic field was carried out. The samples for x=0 and 0.1 exhibit a FM–PM transition at the Curie temperature T{sub C}, however, for x=0.2 and 0.3 exhibit an AFM–PM one at the Neel temperature T{sub N}, when the temperature increases. A magneto-caloric effect has been calculated in terms of isothermal magnetic entropy change. A large magneto-caloric effect has been observed, the maximum entropy change, |ΔS{sub M}{sup max}|, reaches the highest value of 3.28 J/kgK under a magnetic field change of 5 T with an RCP value of 220 J/kg for La{sub 0.6}Pr{sub 0.1}Sr{sub 0.3}MnO{sub 3} composition, which will be an interesting compound for application materials working as magnetic refrigerants near room temperature. - Graphical abstract: Magnetic entropy change versus temperature and applied magnetic field for x=0.1 (a) and RCP versus applied magnetic field for x=0, 0.1 (b). - Highlights: • The La{sub 0.6}Pr{sub 0.1}Sr{sub 0.3}Mn{sub 1−x}Fe{sub x}O{sub 3} (0≤x≤0.3) polycrystalline samples were prepared by the solid state reaction method. • Crystalline and magnetic structures were investigated using DRX and magnetization measurements. • The magnetocaloric (MC) effect was estimated versus magnetic field and temperatures. • Compounds with x=0, 0.1 exhibit great potential for magnetic refrigeration at room temperature.

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

Synthesis and thermal stability studies of a series of metastable Dion–Jacobson double-layered neodymium-niobate perovskites

The Dion–Jacobson double-layered perovskite, RbNdNb{sub 2}O{sub 7}, is used as a precursor to synthesize the series ANdNb{sub 2}O{sub 7} (A=H, Li, Na, K, NH{sub 4}, Ag), and (MCl)NdNb{sub 2}O{sub 7} (M=Mn, Fe, Cu) through ion-exchange reactions ≤400 °C. Thermal stability studies indicated that most of these compounds are metastable. A combination of X-ray powder diffraction and differential thermal analysis were used to determine various low temperature decomposition pathways; these pathways were very dependent on the interlayer species. Overall the ANdNb{sub 2}O{sub 7} series was found to be less stable than the corresponding lanthanides, ALaNb{sub 2}O{sub 7}. - Graphical abstract: A new series of topochemically-prepared metastable neodymium-containing layered perovskites are studied. - Highlights: • A series of new layered neodymium containing perovskites were synthesized by ion exchange. • Products were studied by variable temperature X-ray diffraction and thermal analysis. • Most of the series are metastable showing exothermic transitions on decomposition. • The Nd compounds are less stable due to the smaller size of the Nd relative to La.

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

A facile one-pot hydrothermal synthesis of β-MnO{sub 2} nanopincers and their catalytic degradation of methylene blue

Branched β-MnO{sub 2} bipods with novel nanopincer morphology were prepared by a facile one-pot hydrothermal method via a redox reaction between NaClO{sub 3} and MnSO{sub 4} in sulfuric acid solution without using any surfactants or templates. The products were characterized in detail by various techniques including X-ray powder diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy, surface area analyzer, field emission scanning electron microscopy and transmission electron microscopy. Results show that the obtained β-MnO{sub 2} nanopincers consist of two sharp nanorods with a diameter of 100–200 nm and a length of 1–2 μm. The concentration of H{sub 2}SO{sub 4} solution plays an important role in controlling the crystal phase and morphology of the final product. A possible formation mechanism for the β-MnO{sub 2} nanopincers was proposed. Moreover, these β-MnO{sub 2} nanostructures exhibited better catalytic performance than the commercial MnO{sub 2} particles to decompose methyl blue (MB) in the presence of H{sub 2}O{sub 2}. - Graphical abstract: Branched β-MnO{sub 2} bipods with novel nanopincer morphology were prepared by a facile one-pot hydrothermal method through oxidizing MnSO{sub 4} with NaClO{sub 3} in H2SO{sub 4} condition without using any surfactants or templates. - Highlights: {sup •} Branched β-MnO{sub 2} nanopincers were prepared by a facile one-pot hydrothermal method. {sup •} Morphology and crystal phase of MnO{sub 2} were controlled by the H{sub 2}SO{sub 4} concentration. {sup •} A possible formation mechanism for the obtained β-MnO{sub 2} nanopincers was proposed. {sup •} The products showed great catalytic performance in degradation of methylene blue.

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

Magnetic structures of β{sub I}-Li{sub 2}CoSiO{sub 4} and γ{sub 0}-Li{sub 2}MnSiO{sub 4}: Crystal structure type vs. magnetic topology

The magnetic structure and properties of the candidate lithium-ion battery cathode materials Pbn2{sub 1}(≡Pna2{sub 1}) Li{sub 2}CoSiO{sub 4} and P2{sub 1}/n Li{sub 2}MnSiO{sub 4} have been studied experimentally using low-temperature neutron powder diffraction and magnetometry. Both materials undergo long-range antiferromagnetic ordering, at 14 K and 12 K respectively, due to super–super-exchange mediated by bridging silicate groups. Despite having different crystal structures (wurtzite- vs. “dipolar”-type), Li{sub 2}CoSiO{sub 4} and Li{sub 2}MnSiO{sub 4} have the same topology in terms of magnetic interactions, and adopt collinear magnetic structures of the same type with the propagation vectors (0, 1/2, 1/2) and (1/2, 0, 1/2), respectively. The magnetic moments in the two materials are aligned in parallel and obliquely to the distorted closed-packed layers of oxygen atoms. The experimentally observed values of the ordered magnetic moments, 2.9 μ{sub B} and 4.6 μ{sub B}, are close to those expected for d{sup 7} Co{sup 2+} and d{sup 5} Mn{sup 2+}, respectively. - Graphical abstract: Despite the different crystal structures β{sub I}-Li{sub 2}CoSiO{sub 4} and γ{sub 0}-Li{sub 2}MnSiO{sub 4} have similar magnetic topology and as a result adopt magnetic structure of the same type. - Highlights: • Magnetic structures of Li{sub 2}CoSiO{sub 4} and Li{sub 2}MnSiO{sub 4} were studied for the first time. • Both materials antiferromagnetically order around 12–14 K. • Despite different crystal structure magnetic structures are of the same type. • The fact is attributed to similar topology of magnetic interactions.

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

Crystal structure of brownmillerite Ba{sub 2}InGaO{sub 5}

Ba{sub 2}InGaO{sub 5} was prepared by high-temperature solid-state reaction. This compound adopts a brownmillerite structure below 1200 °C, which was not found in past studies of Ba{sub 2}(In{sub 1−x}Ga{sub x}){sub 2}O{sub 5}. Combined structure refinements against neutron and X-ray powder diffraction data show that this material adopts a layered ordering of In and Ga. This is one of a few examples of such an ordering in the brownmillerite structure solely due to size difference between the B cations. This ordering further stabilizes the brownmillerite crystal structure compared to other compositions at smaller Ga contents (x<0.5), for which the transition to a disordered cubic perovskite occurs at a much lower temperature. As could be expected, such stronger ordering is detrimental to ionic conductivity. - Graphical abstract: In/Ga cation ordering occurs only for the x=1/2 composition in brownmillerite Ba{sub 2}(In{sub 1−x}Ga{sub x}){sub 2}O{sub 5}. The increased ordering results in an anomalously higher disordering transition temperature to the cubic perovskite. - Highlights: • Ba{sub 2}InGaO{sub 5} has been synthesized with a brownmillerite structure. • Structure refinements show a layered ordering of In and Ga along the stacking axis. • Ionic conductivity is impeded by the stronger structural ordering. • The temperature required to disorder into a cubic perovskite is higher when such ordering occurs.

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

Gamma ray irradiated AgFeO{sub 2} nanoparticles with enhanced gas sensor properties

AgFeO{sub 2} nanoparticles were synthesized via a facile hydrothermal method and irradiated by various doses of gamma ray. The products were characterized with X-ray powder diffraction, UV–vis absorption spectrum and transmission electron microscope. The results revealed that the crystal structure, morphology and size of the samples remained unchanged after irradiation, while the intensity of UV–Vis spectra increased with irradiation dose increasing. In addition, gamma ray irradiation improved the performance of gas sensor based on the AgFeO{sub 2} nanoparticles including the optimum operating temperature and sensitivity, which might be ascribed to the generation of defects. - Graphical abstract: Gamma ray irradiation improved the performance of gas sensor based on the AgFeO{sub 2} nanoparticles including sensitivity and optimum operating temperature, which might be ascribed to the generation of defects. - Highlights: • AgFeO{sub 2} nanoparticles were synthesized and irradiated with gamma ray. • AgFeO{sub 2} nanoparticles were employed to fabricate gas sensors to detect ethanol. • Gamma ray irradiation improved the sensitivity and optimum operating temperature.

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

Synthesis and characterisation of In-doped MnWO{sub 4}-type solid-solutions: Mn{sub 1−3x}In{sub 2x}□{sub x}WO{sub 4} (x=0–0.11)

Substitution of In{sup 3+} for Mn{sup 2+} in MnWO{sub 4}, which is one of the most studied multiferroics, was conducted systematically by solid-state reactions at 1050 °C to obtain a series of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} solid solutions (x=0–0.11; the box indicates vacancy). The successful In-doping could be proven by electron microprobe, and statically disordered structures of this solid solution series were elucidated by Rietveld analyses with X-Ray powder diffraction (XPD) data. Its average structure maintains the space group P2/c at least up to the replacement of 33 at% Mn. The tendency of their unit cells proportionally enlarging with In-doping is an unexpected observation because In{sup 3+} is smaller than Mn{sup 2+}. This could not be explained alone by average atomic bonding distances and angles evaluated from XPD data analyses. Complimentarily, micro-Raman spectra of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} materials feature a hardening of Raman modes due to stronger atomic bonds in W{sub 2}O{sub 4} and WO{sub 2} units with increasing In-doping. This is considered as an inevitable consequence of broken bonding in directly neighbouring Mn–O bonds as the presence of In{sup 3+} in MnWO{sub 4} accompanies the creation of defects at Mn sites. The current study using XRD and micro-Raman suggests the enlarging local space around the bridging oxygen as the reason for the unexpected cell expansion when smaller In{sup 3+} along with defects replace Mn{sup 2+} in MnWO{sub 4}. - Graphical abstract: Despite of substitution of smaller In{sup 3+} for larger Mn{sup 2+}, the In-rich solid solution Mn{sub 0.71(2)}In{sub 0.19(1)}□{sub 0.10}WO{sub 4} undergoes a volume expansion of 0.4% with respect to MnWO{sub 4}. This could be explained by a local space expansion of 0.13% around bridging oxygen at O2 sites, as illustrated by dashed lines for clarity. - Highlights: • Investigation of Mn{sub (1−3x)}In{sub 2x}□{sub x}WO{sub 4} solid solutions (x=0–0.11). • An unexpected lattice expansion by In-doping. • Strong change in local environment around bridging oxygens. • Enhancement of atomic bonds in W{sub 2}O{sub 4} and WO{sub 2} units with increasing In-doping.

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

Synthesis, crystal structure and properties of alluaudite-like triple molybdate Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24}

A new triple molybdate Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24} was synthesized using solid state reactions and studied with X-ray powder diffraction, second harmonic generation (SHG) technique, differential scanning calorimetry, Mössbauer and dielectric impedance spectroscopy. Single crystals of Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24} were obtained and its structure was solved (the space group P1{sup ¯}, a=12.5814(5), b=13.8989(5), c=28.4386(9) Å, α=90.108(2), β=90.064(2), γ=90.020(2)°, V=4973.0(3) Å{sup 3}, Z=2, R=0.0440). Characteristic features of the structure are polyhedral layers composed of pairs of edge-shared FeO{sub 6} and (Fe, Na)O{sub 6} octahedra, which are connected by bridging MoO{sub 4} tetrahedra. The layers share common vertices with bridging MoO{sub 4} tetrahedra to form an open 3D framework with the cavities occupied by the Cs{sup +} and Na{sup +} cations. The compound undergoes first-order phase transformation at 642 K and above this phase transition, electrical conductivity reaches 10{sup −3}–10{sup −2} S cm{sup −1}. Thus, Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24} may be considered as a promising compound for developing new materials with high ionic conductivity. - Graphical abstract: A new triple molybdate Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24} was synthesized and structurally characterized, its physicochemical properties were studied. - Highlights: • New compound Na{sub 25}Cs{sub 8}Fe{sub 5}(MoO{sub 4}){sub 24} was synthesized. • Physicochemical properties of the compound were studied. • The first-order phase transformation is observed. • Electrical conductivity above 642 K is (10{sup −2}–10{sup −3}) S cm{sup −1}. • New compound may be considered as promising object with high ionic conductivity.

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

Monoclinic distortion and magnetic coupling in the double perovskite Sr{sub 2−x}Ca{sub x}YRuO{sub 6}

Abstracts: This work investigates in the insulating double perovskites Sr{sub 2−x}Ca{sub x}YRuO{sub 6}. We address the angular dependence of the strength of the magnetic coupling due to the deviation from planarity of the basal layers of the monoclinic structure, characterized by the in-plane angle α<180°, in order to probe the impact of the structural distortions in the magnetic properties of the compounds. High resolution x-ray powder diffraction, susceptibility, and specific heat measurements were performed. The deviation from planarity significantly increases (α=144° for x=1) while the bond distances vary in a complex way as a consequence of the strong monoclinic distortion. We found that the magnetic transition temperature, T{sub M}, shows a linear dependence on cos [(π−α)/2]. This result is discussed in terms of t{sub 2g}(π)–e{sub g}(σ) mixing of the magnetic orbitals of the Ru{sup 5+} ions and unbalanced competitive super-exchange interactions. The deleterious effect of Ca doping for the magnetic coupling is confirmed by the reduction in the short-range antiferromagnetic correlations characteristic of the parent compound at T>>T{sub M} and the enhancement of magnetic frustration for T<T{sub M}. - Graphical abstract: Tilting of the oxygen octahedra in Sr{sub 2−x}Ca{sub x}YRuO{sub 6} due to strong monoclinic distortions. - Highlights: • Neel temperatures in SrCaYRuO were correlated quantitatively with lattice distortions. • Bending of Ru–O–Y planes plays a major role in the magnetic properties of SrCaYRuO. • The structural–magnetic correlation is due to π–σ mixing of the magnetic orbitals.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Structural and magnetic properties of the La{sub 2−x}Ca{sub x}CoIrO{sub 6} double perovskite series

Polycrystalline samples of the series La{sub 2−x}Ca{sub x}CoIrO{sub 6} (0≤x≤1.2) have been synthesized and its structural and magnetic properties were investigated using experiments of X-ray powder diffraction, temperature dependent magnetic susceptibility and magnetization as a function of applied magnetic field. All grown polycrystalline compounds form in a monoclinic structure (space group P2{sub 1}/n) with a partially ordered distribution of transition metal cations Co/Ir over the six-coordinate sites. Our results indicate variation of the magnetic interactions between Co and Ir magnetic sublattices possibly due to valence changes of the transition metals, induced by doping. The undoped La{sub 2}CoIrO{sub 6} presents magnetic ordering at ∼97K, while for Ca-doped compounds a decrease of net magnetization and ordering temperatures was observed. For x=0.2 and 0.5 the emergence of a second magnetic interaction, due to the presence of high spin Co{sup 3+}, becomes evident. Interestingly, for x=0.8 the large effective magnetic moment indicates strong orbital contribution and spin-orbit coupling and/or the presence of Co{sup 4+} in high spin state. - Graphical abstract: Field cooling M vs.T curves for La{sub 2−x}Ca{sub x}CoIrO{sub 6} shows the suppression of magnetism with increasing La content. Zero field cooled curves indicate a second magnetic phase induced by the appearance of Co{sup 3+}. - Highlights: • Novel double perovskite series La{sub 2−x}Ca{sub x}CoIrO{sub 6} were synthesized by solid state reaction. • La{sup 3+} to Ca{sup 2+} substitution leads to Co valence and possibly spin state changes. • For some doped compounds, the emergence of a second magnetic phase, due to the presence of high spin Co{sup 3+}, becomes evident. • Physical properties of each compound can be well correlated to the electronic and magnetic evolution of the system.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Structural and magnetic study of Yb{sup 3+} in the perovskites Sr{sub 2}YbMO{sub 6} (M=Nb, Ta, Sb)

The compounds Sr{sub 2}YbNbO{sub 6}, Sr{sub 2}YbTaO{sub 6} and Sr{sub 2}YbSbO{sub 6} have been prepared using solid state methods by heating pelleted reagents in air at temperatures up to 1400 °C. Rietveld refinement against room temperature neutron powder diffraction data show that all three compounds crystallise with a cation-ordered variant of the perovskite structure in the P2{sub 1}/n space group. Complete cation ordering occurs between M{sup 5+} and Yb{sup 3+} over two octahedrally-coordinated sites in the structure and all compounds are stoichiometric in oxygen. The Sb–O bond lengths are similar to related perovskite compounds but differ slightly from those indicated by bond valence sums. Magnetic susceptibility data resemble Curie–Weiss paramagnetic behaviour, but can be better understood as arising from the effect of the octahedral crystal field on the {sup 2}F{sub 5/2} ground state of Yb{sup 3+} leading to a temperature dependent magnetic moment on this ion below 100 K. - Graphical abstract: The magnetic susceptibility of the face-centred cubic Yb{sup 3+} lattice is dominated by the temperature dependent single-ion moment below 100 K. - Highlights: • Cation-ordered perovskites are studied using neutron diffraction and magnetometry. • Yb{sup 3+} cations form a pseudo face centred cubic lattice in a distorted structure. • Sb{sup 5+} cation is slightly overbonded as observed in related perovskites. • Crystal field splitting of 4f{sup 13} Yb{sup 3+} giving a temperature dependent moment. • Magnetic susceptibility reproduces theoretical predictions below 100 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Magnetic order and crystal structure study of YNi{sub 4}Si-type NdNi{sub 4}Si

Magnetic measurements and neutron powder diffraction investigation of the magnetic structure of the orthorhombic YNi{sub 4}Si-type (space group Cmmm) NdNi{sub 4}Si compound are presented. The magnetocaloric effect of NdNi{sub 4}Si is calculated in terms of the isothermal magnetic entropy change and it reaches the maximum value of –3.3 J/kg K for a field change of 50 kOe near T{sub C}=12 K. Below ∼12 K, NdNi{sub 4}Si exhibits a commensurate b-axis collinear ferromagnetic ordering with the Cmm′m magnetic space group in a zero magnetic field. At 1.5 K, the neodymium atoms have the magnetic moment of 2.37(5) μ{sub B}. The orthorhombic crystal structure and its thermal evolution are discussed in comparison with the CaCu{sub 5}-type compound. - Graphical abstract: The NdNi{sub 4}Si supplement the series of the orthorhombic derivative of the CaCu{sub 5}-type, namely the YNi{sub 4}Si-type, RNi{sub 4}Si compounds (R=Y, La, Ce, Sm, Gd–Ho). Below ∼12 K in a zero applied magnetic field, NdNi{sub 4}Si exhibits a commensurate b-axis collinear ferromagnetic ordering with the Cmm′m magnetic space group. Compared to the CaCu{sub 5}-type NdNi{sub 4}Si compound, the YNi{sub 4}Si-type counterpart has the relatively high ferromagnetic ordering temperature (9.2 K vs. 12 K), the small magnetocaloric effect (–7.3 J/kg K vs. –3.3 J/kg K for ∆H=50 kOe), and the large magnetic anisotropy at low temperatures. In contrast with CaCu{sub 5}-type NdNi{sub 4}Si, YNi{sub 4}Si-type NdNi{sub 4}Si shows distinct hysteresis loop at 2 K.We suggest that orthorhombic distortion may be used as a prospective route for optimization of permanent magnetic properties in the family of CaCu{sub 5}-type rare earth materials. - Highlights: • Below ∼12 K the YNi{sub 4}Si-type NdNi{sub 4}Si shows a ferromagnetic ordering. • MCE of NdNi{sub 4}Si reaches value of –3.3 J/kg K in 0–50 kOe near Curie point. • NdNi{sub 4}Si exhibits b-axis ferromagnetic order with the Cmm′m magnetic space group. • Contrary to CaCu{sub 5}-type, YNi{sub 4}Si-type NdNi{sub 4}Si shows hysteresis loop at 2 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Preparation and properties of a new ternary phase Mg{sub 3+x}Ni{sub 7−x}B{sub 2} (0.17≤x≤0.66) and its Cu-doping effect

In recent years, the materials in the B–Mg–Ni system have been intensively studied due to their excellent properties of hydrogen storage and superconductivity. Solving the crystal structure of phases in this system will facilitate an understanding of the mechanism of their physical properties. In this study, we report the preparation, crystal structure and physical properties of a new ternary phase Mg{sub 3+x}Ni{sub 7−x}B{sub 2} in the B–Mg–Ni system. The Mg{sub 3+x}Ni{sub 7−x}B{sub 2} phase was prepared by solid-state reactions at 1073 K and its crystal structure was determined and refined using X-ray powder diffraction data. The Mg{sub 3+x}Ni{sub 7−x}B{sub 2} phase crystallizes in the Ca{sub 3}Ni{sub 7}B{sub 2} structure type (space group R-3m, no. 166) with a=4.9496(3)–5.0105(6) Å, c=20.480(1)–20.581(1) Å depending on the x value, where x varies from 0.17 to 0.66. Two samples with nominal compositions Mg{sub 10}Ni{sub 20}B{sub 6} and Mg{sub 12}Ni{sub 18}B{sub 6} were characterized by magnetization and electric resistivity measurements in the temperature range from 5 K to room temperature. Both samples exhibited metallic behavior and showed spin-glass-like behavior with a spin freezing temperature (T{sub f}) around 33 K. A study of the Cu-doping effect showed that limited Cu content can be doped into the Mg{sub 3+x}Ni{sub 7−x}B{sub 2} compound and T{sub f} decreases as the Cu content increases. - Graphical abstract: The crystal structure of the Mg{sub 3+x}Ni{sub 7−x}B{sub 2} phase. - Highlights: • The crystal structure and solid solution range of Mg{sub 3+x}Ni{sub 7−x}B{sub 2} were revealed. • The magnetization and electrical resistivity of Mg{sub 3+x}Ni{sub 7−x}B{sub 2} were studied. • The Cu-doping effect of Mg{sub 3+x}Ni{sub 7−x}B{sub 2} was investigated.

36 MATERIALS SCIENCE↗
DOE OSTI2015

Structural and magnetic properties of RTiNO{sub 2} (R=Ce, Pr, Nd) perovskite nitride oxides

Neutron powder diffraction indicates that CeTiNO{sub 2} and PrTiNO{sub 2} crystallize with orthorhombic Pnma symmetry (Ce: a=5.5580(5), b=7.8369(7), and c=5.5830(4) Å; Pr: a=5.5468(5), b=7.8142(5), and c=5.5514(5) Å) as a result of a{sup –}b{sup +}a{sup –} tilting of the titanium-centered octahedra. Careful examination of the NPD data, confirms the absence of long range anion order in both compounds, while apparent superstructure reflections seen in electron diffraction patterns provide evidence for short range anion order. Inverse magnetic susceptibility plots reveal that the RTiNO{sub 2} (R=Ce, Pr, Nd) compounds are paramagnetic with Weiss constants that vary from −28 to −42 K. Effective magnetic moments for RTiNO{sub 2} (R=Ce, Pr, Nd) are 2.43 μ{sub B}, 3.63 μ{sub B}, and 3.47 μ{sub B}, respectively, in line with values expected for free rare-earth ions. Deviations from Curie–Weiss behavior that occur below 150 K for CeTiNO{sub 2} and below 30 K for NdTiNO{sub 2} are driven by magnetic anisotropy, spin–orbit coupling, and crystal field effects. - Graphical abstract: The structure and magnetism of the oxide nitride perovskites RTiNO{sub 2} (R=Ce, Pr, Nd) have been explored. The average symmetry is shown to be Pnma with a random distribution of oxide and nitride ions and a{sup −}b{sup +}a{sup −} tilting of the titanium-centered octahedra, but electron diffraction shows evidence for short range anion order. All three compounds are paramagnetic but deviations from the Curie Weiss law are seen below 150 K for R=Ce and below 30 K for R=Nd. - Highlights: • The oxide nitride perovskites RTiNO{sub 2} (R=Ce, Pr) have been prepared and their structures determined. • Diffraction measurements indicate short range cis-order of O and N, but no long range order. • Compounds are paramagnetic with Weiss constants that vary from −28 to −42 K. • CeTiO{sub 2}N and NdTiO{sub 2}N deviate from Curie–Weiss behavior below 150 and 30 K, respectively.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2015

How the guest molecules in nanoporous Zn(II) metal-organic framework can prevent agglomeration of ZnO nanoparticles

The host and the apohost framework of [Zn{sub 2}(BDC){sub 2}(H{sub 2}O){sub 2}·(DMF){sub 2}]{sub n} (1·2H{sub 2}O·2DMF), (BDC{sup 2−}=benzene-1,4-dicarboxylate and DMF=N,N-Dimethylformamide), were synthesized and subsequently used for preparation of ZnO nanomaterials. With calcination of the host framework of 1·2H{sub 2}O·2DMF, ZnO nanoparticles were obtained. By the same process on the apohost framework of 1, agglomerated nanoparticles of ZnO were formed. These nano-structures were characterized by X-ray powder diffraction (XRD) and Scanning electron microscopy (SEM). These results indicate that with removal of the guest DMF and coordinated H{sub 2}O molecules from the one-dimensional channels of 1·2H{sub 2}O·2DMF, the tendency of nanoparticles to agglomerate increases and the role of this MOF in preparation of ZnO nanoparticles from this precursor was reduced. - Graphical abstract: Nano-porous zinc(II) MOF with guest DMF and coordinated H{sub 2}O molecules has been synthesized and characterized. The host and the apohost framework of it were used for preparation of ZnO nanomaterials. The role of these species in preparation of ZnO nanoparticles from the host framework is probably similar to the role of polymeric stabilizers in formation of nanoparticles. - Highlights: • Nanoparticles of ZnO were fabricated from nanoporous metal-organic framework. • The effect of guest DMF and coordinated H{sub 2}O molecules on this process was studied. • The effect of them in formation nanoparticle is similar to polymeric stabilizers.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2015

Crystal chemistry of the orthorhombic Ln{sub 2}TiO{sub 5} compounds with Ln=La, Pr, Nd, Sm, Gd, Tb and Dy

The crystal structures of seven samples of orthorhombic (Pnma) Ln{sub 2}TiO{sub 5} compounds with Ln=La, Pr, Nd, Sm, Gd, Tb and Dy were refined by Rietveld analysis of synchrotron X-ray powder diffraction (S-XRD) data. With increasing size of the lanthanide cation, the lattice parameters increase systematically: c by only ~1.5% whereas both a and b by ~6% from Dy{sub 2}TiO{sub 5} to La{sub 2}TiO{sub 5}. The mean Ti–O bond length only increases by ~1% with increasing radius of the Ln cation from Gd to La, primarily due to expansion of the pair of Ti–O{sub 3} bonds to opposite corners of the Ti–O{sub 5} square based pyramid polyhedra. For Dy{sub 2}TiO{sub 5} and Tb{sub 2}TiO{sub 5}, a significant variation in Ti–O{sub 1} and Ti–O{sub 4} bond lengths results in an increased deformation of the Ti–O{sub 5} base. The particular configuration consists of large rhombic shaped tunnels and smaller triangular tunnels along the b axis, which have implications for defect formation and migration caused by radiation damage or the ionic conductivity. - Graphical abstract: Figure: The crystallographic study of a systematic series of compounds with nominal stoichiometry Ln{sub 2}TiO{sub 5} (with Ln representing La, Pr, Nd, Sm, Gd, Tb and Dy) and orthorhombic, Pnma, symmetry shows changes in cell parameters which fit a linear trend. However, bond lengths are shown to deviate from trend with compounds containing the smaller, heavier lanthanides. - Highlights: • First fabrication and crystallographic refinement of compound Pr{sub 2}TiO{sub 5}. • First systematic study of the crystallography, using S-XRD, for Ln{sub 2}TiO{sub 5} series. • Cation to anion bonding trends and valence states are investigated. • The densities and band-gaps of the series are experimentally determined.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Thermoelectric properties of Fe and Al double substituted MnSi{sub γ} (γ~1.73)

Two series of Fe and Al double substituted MnSi{sub γ} chimney ladders with a nominal valence electron count, VEC=14 per transition metal were prepared (γ=1.75). Simultaneous replacement of Mn with Fe and Si with Al yielded the Mn{sub 1−x}Fe{sub x}Si{sub 1.75−x}Al{sub x} series while the second Mn{sub 1−x}Fe{sub x}Si{sub 1.75–1.75x}Al{sub 2x} series follows the pseudo-binary between MnSi{sub 1.75} and FeAl{sub 2}. Scanning electron microscopy and elemental mapping revealed that ~60% of the nominal Al content ends up in the product with the remainder lost to sublimation, and that up to 7% Al can be substituted in the main group sublattice. Profile analysis of X-ray powder diffraction data revealed gradual changes in the cell metrics, consistent with the simultaneous substitution of Fe and Al in a fixed ratio. All samples are p-type with VEC≈13.95 from the structural data and ~1×10{sup 21} holes cm{sup −3} from variable temperature Seebeck measurements. The substituted samples have lower electrical resistivities (ρ{sub 300} {sub K}=2–5 mΩ cm) due to an improved microstructure. This leads to increased thermoelectric power factors (largest S{sup 2}/ρ=1.95 mW m{sup −1} K{sup −2}) compared to MnSi{sub γ}. The thermal conductivity for the Mn{sub 0.95}Fe{sub 0.05}Si{sub 1.66}Al{sub 0.1} sample is 2.7 W m{sup −1} K{sup −1} between 300 and 800 K, and is comparable to literature data for the parent material. - Graphical abstract: The crystal structure, microstructure and thermoelectric properties of Fe and Al double substituted MnSi{sub γ} (γ~1.73) have been investigated. - Highlights: • Up to 7% Al can be substituted in MnSi{sub γ} when co-doped with Fe. • Improved microstructure and reduced electrical resistivities for Al substituted samples. • Largest power factor 1.95 mW m{sup −1} K{sup −2} and best estimated ZT=0.5.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2015

Crystal structure and high-temperature properties of the Ruddlesden–Popper phases Sr{sub 3−x}Y{sub x}(Fe{sub 1.25}Ni{sub 0.75})O{sub 7−δ} (0≤x≤0.75)

Ruddlesden–Popper n=2 member phases Sr{sub 3−x}Y{sub x}Fe{sub 1.25}Ni{sub 0.75}O{sub 7−δ}, 0≤x≤0.75, have been investigated by X-ray and neutron powder diffraction, thermogravimetry and Mössbauer spectroscopy. Both samples as-prepared at 1300 °C under N{sub 2}(g) flow and samples subsequently air-annealed at 900 °C were studied. The as-prepared x=0.75 phase is highly oxygen deficient with δ=1, the O1 atom site being vacant, and the Fe{sup 3+}/Ni{sup 2+} ions having a square pyramidal coordination. For as-prepared phases with lower x values, the Mössbauer spectral data are in good agreement with the presence of both 5- and 4-coordinated Fe{sup 3+} ions, implying in addition a partial occupancy of the O3 atom sites that form the basal plane of the square pyramid. The air-annealed x=0.75 sample has a δ value of 0.61(1) and the structure has Fe/Ni ions in both square pyramids and octahedra. Mössbauer spectroscopy shows the phase to contain only Fe{sup 3+}, implying that all Ni is present as Ni{sup 3+}. Air-annealed phases with lower x values are found to contain both Fe{sup 3+} and Fe{sup 4+}. For both the as-prepared and the air-annealed samples, the Y{sup 3+} cations are found to be mainly located in the perovskite block. The high-temperature thermal expansion of as-prepared and air-annealed x=0.75 phases were investigated by high-temperature X-ray diffraction and dilatometry and the linear thermal expansion coefficient determined to be 14.4 ppm K{sup −1}. Electrical conductivity measurements showed that the air-annealed samples have higher conductivity than the as-prepared ones. - Highlights: • Ruddlesden–Popper, n=2, Sr{sub 3−x}Y{sub x}Fe{sub 1.25}Ni{sub 0.75}O{sub 7−δ}, 0≤x≤0.75, have been synthesised. • The crystal structures of the phases have been determined. • Sr{sub 2.25}Y{sub 0.75}Fe{sub 1.25}Ni{sub 0.75}O{sub 6}, made in N{sub 2}(g) has Fe{sup 3+}/Ni{sup 2+} in square pyramides. • Sr{sub 2.25}Y{sub 0.75}Fe{sub 1.25}Ni{sub 0.75}O{sub 6.4}, made in air has Fe{sup 3+}/Ni{sup 3+} in square pyramides and octahedra. • Air annealed samples have higher electrical conductivity than N{sub 2}(g) annealed.

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