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All sourcesNASA NTRSDOE OSTI
DOE OSTI2025

Tuning the structure and superconductivity of SrNi 2⁢ P 2 by Rh substitution

The compound SrNi 2⁢ P 2 is unique among the ThCr 2 ⁢Si 2 class since it exhibits a temperature-induced transition upon cooling from an uncollapsed tetragonal (ucT) state to a one-third-collapsed orthorhombic (tcO) state where one out of every three P-rows bond across the Sr layers. This compound is also known for exhibiting bulk superconductivity below 1.4 K at ambient pressure. Here, in this paper, we report on the effects of Rh substitution in Sr⁢(Ni 1-x ⁢Rh x ) 2 ⁢P 2 on the structural and superconducting properties. We studied the variation of the nearest P-P distances as a function of the Rh fraction at room temperature, as well as its temperature dependence for selected compositions. We find that increasing the Rh fraction leads to a decrease in the transition temperature between the ucT and tcO states, until a full suppression of the tcO state for x ≥ 0.166. The superconducting transition first remains nearly insensitive to the Rh fraction, and then it increases to 2.3 K after the tcO state is fully suppressed. These results are summarized in a phase diagram, built upon the characterization by energy dispersive x-ray spectroscopy, x-ray diffraction, resistance, magnetization, and specific heat measurements done on crystalline samples with varying Rh content. The relationship between band structure, crystal structure, and superconductivity is discussed based on previously reported band structure calculations on SrRh 2 ⁢P 2 . Moreover, the effect of Rh fraction on the stress-induced structural transitions is also addressed by means of strain-stress studies done by uniaxial compression of single-crystalline micropillars of Sr⁢(Ni 1-x ⁢Rh x ) 2 ⁢P 2 .

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2019

Neutron Diffraction and Neutron Radiography Investigation into Powder Sintering of Ti/Al and TiH{sub 2}/Al Compacts

Sintering behaviors of two types of powder compact, i.e., Ti/Al and TiH{sub 2}/Al, under vacuum were studied using in situ neutron diffraction, in situ thermal dilatometric measurement, and ex situ neutron radiography. Their densification, microstructure, hydrogen concentration, and phase transformation features were compared. The results indicate that the predominant phase identified in the samples sintered from both compacts is γ-TiAl phase with minor Ti{sub 3}Al phase. Dehydrogenation of TiH{sub 2} plays a decisive role in the sintering behavior and the resultant microstructure. In comparison with the Ti/Al compact, dehydrogenation occurring in the TiH{sub 2}/Al compact leads to a higher level of densification and faster sintering kinetics.

36 MATERIALS SCIENCE↗
DOE OSTI2016

Structural and Crystal Chemical Properties of Alkali Rare-earth Double Phosphates

When appropriately activated, alkali rare-earth double phosphates of the form: M 3 RE(PO 4 ) 2 (where M denotes an alkali metal and RE represents either a rare-earth element or Y or Sc) are of interest for use as inorganic scintillators for radiation detection at relatively long optical emission wavelengths. These compounds exhibit layered crystal structures whose symmetry properties depend on the relative sizes of the rare-earth and alkali-metal cations. Single-crystal X-ray and powder neutron diffraction methods were used here to refine the structures of the series of rare-earth double phosphate compounds: K 3 RE(PO 4 ) 2 with RE = Lu, Er, Ho, Dy, Gd, Nd, Ce, plus Y and Sc - as well as the compounds: A 3 Lu(PO 4 ) 2 , with A = Rb, and Cs. The double phosphate K 3 Lu(PO 4 ) 2 was reported and structurally refined previously. This material had a hexagonal unit cell at room temperature with the Lu ion six-fold coordinated with oxygen atoms of the surrounding phosphate groups. Additionally two lower-temperature phases were observed for K 3 Lu(PO 4 ) 2 . The first phase transition to a monoclinic P21/m phase occurred at ~230 K, and the Lu ion retained its six-fold coordination. The second K 3 Lu(PO 4 ) 2 phase transition occurred at ~130 K. The P21/m space group symmetry was retained, however, one of the phosphate groups rotated to increase the oxygen coordination number of Lu from six to seven. This structure then became isostructural with the room-temperature form of the compound K 3 Yb(PO 4 ) 2 reported here that also exhibits an additional high-temperature phase which occurs at T = 120 °C with a transformation to hexagonal P-3 space group symmetry and a Yb-ion coordination number reduction from seven to six. This latter result was confirmed using EXAFS. The single-crystal growth methods structural systematics, and thermal expansion properties of the present series of alkali rare-earth double phosphates, as determined by X-ray and neutron diffraction methods, are treated here.

36 MATERIALS SCIENCE↗
DOE OSTI2024

Magnetic ordering in Eu 2 In and Eu 2 Sn

Eu 2 In and Eu 2 Sn crystallize in the orthorhombic Co 2 Si-type structure (oP12, Pnma, No. 62) with In and Sn atoms occupying one 4c site and the Eu atoms filling two other 4c sites. Eu 2 In has a nearly ideal first-order magnetostructural transition (FOMT) at 55 K with a hysteresis of less than 0.1 K, a large entropy change and an adiabatic temperature change of 5.0 K in a field of 2 T. The anhysteretic nature of the FOMT is likely due to there being no change in cell symmetry and relatively small changes in the lattice parameters. There is no magnetostructural transition in Eu2Sn. In this work we present the results of powder neutron diffraction, magnetization, and Eu Mössbauer spectroscopy aimed to investigate the nature of magnetic order for both Eu 2 In and Eu 2 Sn. The Eu Mössbauer spectrum of Eu 2 In at 5 K shows two equal area components, consistent with Eu occupying two equal multiplicity crystallographic sites. However, the different hyperfine fields (B) of 27 T and 17 T suggest that the magnetic environments of the Eu moments on the two 4c sites are different. Neutron diffraction data at 2.5 K show that in Eu 2 In the order is ferromagnetic, with Eu moments on both Eu sites oriented parallel to the a-axis; moment values of 6.8 μB and 6.5 μB were found. For Eu 2 Sn measurements find two antiferromagnetic transitions, which are corroborated by neutron diffraction. Analysis of density-functional theory calculations shows negligible energy difference between differing magnetic configurations, indirectly supporting stability of multiple magnetic structures observed experimentally. While the transition at T N1 = 30 K corresponds to the formation of a simple k 1 = 0 antiferromagnetic structure with Eu-moments pointing along the b-axis, at T N2 = 13 K a coexisting second magnetic order with k 2 = [0, ½, ½] appears.

36 MATERIALS SCIENCE↗
DOE OSTI2020

Effects of charging rates on LiNi 0.6 Mn 0.2 Co 0.2 O 2 (NMC622)/graphite Li-ion cells

Enabling fast charging capability of lithium-ion battery is of great importance to widespread adoption of electric vehicles. Increasing the charging rates from state-of-the-art 2C (30 min) to 6C (10 min) requires deep understanding on the cell aging mechanism. Here, 400 mAh pouch cells are cycled at 1C, 4C and 6C charging rates with 1C discharging rate. Capacity fading, cathode structural changes, Li inventory loss, electrolyte composition changes and Li plating on graphite electrodes are thoroughly studied by various characterization techniques. The rapid capacity fading in cells at 6C charging rate is mainly due to Li inventory loss from cathode structure and metallic Li plating on graphite electrode at higher charging rate. Post-mortem analysis also revealed changes in electrolyte such as increased salt molarity and transesterification during fast charging.

25 ENERGY STORAGE↗
DOE OSTI2013

Synthesis, structural and magnetic characterisation of the fluorinated compound 15R-BaFeO{sub 2}F

The compounds 15R-BaFeO{sub 2}F and 15R-BaFeO{sub 2.27}F{sub 0.5} have been synthesised by the low temperature fluorination of 15R-BaFeO{sub 3−d}F{sub 0.2} using polyvinylidenedifluoride (PVDF) as a fluorination agent. The materials have been structurally characterised by Rietveld analysis of the X-ray- and HRPD-powder neutron diffraction data. A detailed analysis of bond valence sums suggests that the oxide and fluoride ions order on the different anion sites. A reinvestigation of our recently published structure (Clemens et al., 2013) [34] of 6H-BaFeO{sub 2}F is also reported and incorporation of fluoride in h-type layers is also confirmed in this compound. The magnetic moments for 15R-BaFeO{sub 2}F and 15R-BaFeO{sub 2.25}F{sub 0.5} align in the a/b-plane with antiferromagnetic alignment of the moments between adjacent layers, and are flipped by 90° as compared to the precursor compound. 15R-BaFeO{sub 2}F exhibits very robust antiferromagnetism with a Néel temperature between 300 and 400 °C. - Graphical abstract: The crystal and magnetic structure of the perovskite phase 15R-BaFeO{sub 2}F. - Highlights: • 15R-BaFeO{sub 2}F and 15R-BaFeO{sub 2.27}F{sub 0.5}were prepared via low temperature fluorination using PVDF. • A structural investigation of the compounds BaFeO{sub 2}F is presented in detail. • This analysis suggests ordering of O{sup 2−} and F{sup −} anions between different layers. • 15R-BaFeO{sub 2}F shows antiferromagnetic ordering at 300 K with T{sub N} ∼300–400 °C. • The magnetic moments align in the a/b-plane.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2017

Synthesis and magnetic structure of the layered manganese oxide selenide Sr{sub 2}MnO{sub 2}Ag{sub 1.5}Se{sub 2}

The synthesis of a high-purity sample of the layered oxide selenide Sr{sub 2}MnO{sub 2}Ag{sub 1.5}Se{sub 2} is reported. At ambient temperature it crystallises in the space group I4/mmm with two formula units in the unit cell and lattice parameters a=4.08771(1) Å, c=19.13087(8) Å. The compound displays mixed-valent manganese in a formal oxidation state close to +2.5 and powder neutron diffraction measurements reveal that below the Néel temperature of 63(1) K this results in an antiferromagnetic structure which may be described as A-type, modelled in the magnetic space group P{sub I}4/mnc (128.410 in the Belov, Neronova and Smirnova (BNS) scheme) in which localised Mn moments of 3.99(2) μ{sub B} are arranged in ferromagnetic layers which are coupled antiferromagnetically. In contrast to the isostructural compound Sr{sub 2}MnO{sub 2}Cu{sub 1.5}S{sub 2}, Sr{sub 2}MnO{sub 2}Ag{sub 1.5}Se{sub 2} does not display long range ordering of coinage metal ions and vacancies, nor may significant amounts of the coinage metal readily be deintercalated using soft chemical methods. - Graphical abstract: Sr{sub 2}MnO{sub 2}Ag{sub 1.5}Se{sub 2} containing mixed valent Mn ions undergoes magnetic ordering with ferromagnetic coupling within MnO{sub 2} sheets and antiferromagnetic coupling between MnO{sub 2} sheets. - Highlights: • High purity sample of Sr{sub 2}MnO{sub 2}Ag{sub 1.5}Se{sub 2} obtained. • Magnetic structure determined. • Compared with related mixed-valent manganite oxide chalcogenides.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Cluster mediated conversion of amorphous Al(OH) 3 to γ-AlOOH

In this work, we report a synthetic pathway by which amorphous Al(OH) 3 is converted to γ-AlOOH through hydrothermal reaction in the presence of water at temperature T = 473 K. X-ray pair distribution function measurements reveal that the initially amorphous Al(OH) 3 possesses a locally γ-Al(OH) 3 -like structure, while nanocrystalline γ-AlOOH precipitates within 1 h of continuous hydrothermal exposure. Solid state nuclear magnetic resonance measurements show that resonant features associated with four- and five-member Al clusters persist through 20 min of hydrothermal treatment, and ultraviolet (UV) spectra mark the onset of UV-induced photoluminescent features characteristic to γ-AlOOH with 10 min of exposure, indicating a coexistence region of γ-Al(OH) 3 -like and γ-AlOOH-like amorphous species. Furthermore, powder x-ray diffraction measurements of desiccated powders reveal that the conversion process takes place in distinct, power law-defined stages with initial γ-AlOOH nucleation occurring within the first 20 min, followed by a ~ 1 h period of rapid grain coarsening and the subsequent onset of Lifshitz-Slyozov-Wagner-like coalescence.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Characterization of shielding materials used in neutron scattering instrumentation

The nuclear cross-sections of certain isotopes make some materials excellent candidates for neutron shielding. We have performed a series of measurements examining the transmission, reflection, and nuclear Bragg scattering of a series of common materials used for neutron shielding. Here, we concentrate on characterizing the materials most likely to be used in neutron scattering instrumentation.

46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
DOE OSTI2018

Magnetic and thermal behavior of a family of compositionally related zero-dimensional fluorides

The mild hydrothermal crystal growth technique has been leveraged to synthesize four new zero-dimensional transition metal fluorides. Their structures were determined by single crystal X-ray diffraction and confirmed by powder X-ray diffraction. The thermal, optical, and magnetic properties were investigated and the presence of thermal polymorphism and antiferromagnetism were observed. In addition, the potential application of these materials as precursors for advanced functional materials was explored.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2022

Li-Rich and Halide-Deficient Argyrodite Fast Ion Conductors

Here, we report on a new family of halide-deficient and Li-rich argyrodite fast-ion conductors, Li 6+x PS 5+x (Cl/Br/I) 1–x (0 ≤ x ≤ 0.85). Exploration of the influence of aliovalent anion substitution in Li 6 PS 5 X (X = Cl, Br, I)–using a combination of high-resolution powder neutron diffraction and electrochemical impedance spectroscopy–reveals that aliovalent anion substitution induces higher Li-ion concentration and Li site disorder, and creates S 2– /I – anion site disorder on the 4a site. In the series Li 6+x PS 5+x I 1–x (0 ≤ x ≤ 0.4), the resulting conductivity for Li 6.4 PS 5.4 I 0.6 (0.13 mS·cm –1 ) represents almost a 100-fold increase over that of the parent phase, Li 6 PS 5 I (0.0033 mS·cm –1 ), and establishes one of the first fast-ion conducting argyrodite thiophosphate iodides. For Cl-argyrodites, the ionic conductivity decreases a little with lower halide-content but ionic conductivity for the Br-argyrodites is almost unchanged. Overall, all Cl/Br-argyrodites Li 6 +xPS 5+x (Cl/Br) 1–x (0 ≤ x ≤ 0.75) with a low halide content exhibit surprisingly high ionic conductivities > 1 mS·cm –1 despite a very low degree of sulfur/halogen anion site disorder. Our findings highlight the importance of attaining a disordered Li-ion sublattice and sulfur/halogen anion site disorder (anionic charge homogeneity) in argyrodites, where Li ions occupy high energy sites and activate concerted ion migration that drives the ionic conductivity.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2024

Noncentrosymmetric Nowotny Chimney Ladder Ferromagnet Cr 4 Ge 7 with a High Curie Temperature of ~207 K

Noncentrosymmetric magnets usually host intriguing magnetic interactions inherent in the crystal structure with broken inversion symmetry, which can give rise to rich magnetic behaviors. Here, we report herein the high-pressure synthesis, crystal structure, magnetizations, and magnetic structure of a so-called Nowotny chimney ladder compound Cr 4 Ge 7 . Our analysis on the powder neutron diffraction data revises the crystal structure as a noncentrosymmetric space group (P4̅c2, No. 116). It exhibits two magnetic orders within the temperature range of 2–400 K. The first order at ~207 K associated with a small magnetic moment of ~0.75 μ B is assigned to a commensurate ferromagnetic structure with a propagation vector k = (0, 0, 0). The weak itinerant ferromagnet nature should be caused by the complex Cr spin orders from different Wyckoff positions. The second order-like behavior at ~18 K is assumed to arise from a competition between the Dzyaloshinskii–Moriya and Heisenberg interactions. The results provide an excellent platform for the study of intricate interactions among various magnetic exchanges as well as for the exploration of high-temperature exotic magnetic properties.

36 MATERIALS SCIENCE↗
DOE OSTI2019

An Entropically Stabilized Fast-Ion Conductor: Li 3.25 [Si 0.25 P 0.75 ]S 4

We report on a family of lithium fast ion conductors, Li 3+x [Si x P 1–x ]S 4 , that exhibit an entropically stabilized structure type in a solid solution regime (0.15 < x < 0.33) with superionic conductivity above 1 mS·cm –1 . Exploration of the influence of aliovalent substitution in the thermodynamically unstable β-Li 3 PS 4 lattice using a combination of single crystal X-ray and powder neutron diffraction, the maximum entropy method, and impedance spectroscopy reveals that substitution induces structural splitting of the localized Li sites, effectively stabilizing bulk β-Li 3 PS 4 at room temperature and delocalizing lithium ion density. The optimal material, Li 3.25 [S i0.25 P 0.75 ]S 4 , exhibits inherent entropic site disorder and a frustrated energy landscape, resulting in a high conductivity of 1.22 mS·cm –1 that represents an increase of three orders of magnitude compared to bulk β-Li 3 PS 4 and one order of magnitude higher than the nanoporous form. The enhanced ion conduction and lowered activation barrier with increasing site disorder as a result of aliovalent “tuning” reveals an important strategy toward the design of fast ion conductors that are vital as solid state electrolytes.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2021

Iridate Li8IrO 6 : An Antiferromagnetic Insulator

In this work, a polycrystalline iridate Li 8 IrO 6 material was prepared via heating Li 2 O and IrO 2 starting materials in a sealed quartz tube at 650 °C for 48 h. The structure was determined from Rietveld refinement of room-temperature powder neutron diffraction data. Li 8 IrO 6 adopts the nonpolar space group $R\bar{3}$ with Li atoms occupying the tetrahedral and octahedral sites, which is supported by the electron diffraction and solid-state 7Li NMR. This results in a crystal structure consisting of LiO 4 tetrahedral layers alternating with mixed IrO 6 and LiO 6 octahedral layers along the crystallographic c -axis. The +4 oxidation state of Ir 4+ was confirmed by near-edge X-ray absorption spectroscopy. An in situ synchrotron X-ray diffraction study of Li 8 IrO 6 indicates that the sample is stable up to 1000 °C and exhibits no structural transitions. Magnetic measurements suggest long-range antiferromagnetic ordering with a Néel temperature (TN) of 4 K, which is corroborated by heat capacity measurements. The localized effective moment $μ_{\text{eff}}$ (Ir) = 1.73 $μ_{\text{B}}$ and insulating character indicate that Li 8 IrO 6 is a correlated insulator. First-principles calculations support the nonpolar crystal structure and reveal the insulating behavior both in paramagnetic and antiferromagnetic states.

36 MATERIALS SCIENCE↗
DOE OSTI2022

LiMo 8 O 10 : Polar Crystal Structure with Infinite Edge-Sharing Molybdenum Octahedra

Here, polycrystalline LiMo 8 O 10 was prepared in a sealed Mo crucible at 1380 °C for 48 h using the conventional high-temperature solid-state method. The polar tetragonal crystal structure (space group I4 1 md) is confirmed based on the Rietveld refinement of powder neutron diffraction and 7 Li/ 6 Li solid-state NMR. The crystal structure features infinite chains of Mo 4 O 5 (i.e., Mo 2 Mo 4/2 O 6/2 O 6/3 ) as a repeat unit containing edge-sharing Mo 6 octahedra with strong Mo–Mo metal bonding along the chain. X-ray absorption near-edge spectroscopy of the Mo-L 3 edge is consistent with the formal Mo valence/configuration. Magnetic measurements reveal that LiMo 8 O 10 is paramagnetic down to 1.8 K. Temperature-dependent resistivity [ρ(T)] measurement indicates a semiconducting behavior that can be fitted with Mott’s variable range hopping conduction mechanism in the temperature range of 215 and 45 K. The ρ(T) curve exhibits an exponential increase below 5 K with a large ratio of ρ 1.8 /ρ 300 = 435. LiMo 8 O 10 shows a negative field-dependent magnetoresistance between 2 and 25 K. Heat capacity measurement fitted with the modified Debye model yields the Debye temperature of 365 K.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗
DOE OSTI2025

Absence of Long-Range Magnetic Ordering in a Trirutile High-Entropy Oxide (Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )Ta 1.92 O 6–δ

Functionalities of solid-state materials are usually considered to be dependent on their crystal structures. The limited structural types observed in the emerging high-entropy oxides put constraints on the exploration of their physical properties and potential applications. Herein, we synthesized the first high-entropy oxide in a trirutile structure, (Mn 0.2 Fe 0.2 Co 0.2 Ni 0.2 Cu 0.2 )Ta 1.92 O 6–δ , and investigated its magnetism. The phase purity and high-entropy nature were confirmed by powder Xray diffraction and energy-dispersive spectroscopy, respectively. X-ray photoelectron spectroscopy indicated divalent Mn, Co, Ni, and Cu along with trivalent Fe. Magnetic property measurements showed antiferromagnetic coupling and potential short-range magnetic ordering below ~4 K. The temperature-dependent heat capacity data measured under zero and high magnetic fields confirmed the lack of long-range magnetic ordering and a possible low-temperature phonon excitation. The discovery of the first trirutile high-entropy oxide opens a new pathway for studying the relationship between the highly disordered atomic arrangement and magnetic interaction. Furthermore, it provides a new direction for exploring the functionalities of highentropy oxides.

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CH↗