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Results for “Short range order”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 73 records · Page 4
All sourcesNASA NTRSDOE OSTI
DOE OSTI2022

Cation Short-Range Ordering of MgAl 2 O 4 and NiAl 2 O 4 Spinel Oxides at High Temperatures via In Situ Neutron Total Scattering

Complex oxides that adopt the isometric spinel structure (AB 2 O 4 ) are important for numerous technological applications and are relevant for certain geological processes, which involve exposure to extreme environments such as high pressures and temperatures. Recent studies have shown that the changes to the spinel structure caused by these environments are complex and depend on the material length scale under consideration. In this study we have expanded this approach to the behavior of spinels under high temperature. In situ neutron total scattering experiments, coupled with pair distribution function analysis, performed on two spinel compositions with various levels of pre-existing disorder (MgAl 2 O 4 and NiAl 2 O 4 ) revealed that both compositions trend to a state of maximum disorder where the A and B cations are randomly distributed amongst the two available sites. Temperature-induced cation inversion, conventionally understood as exchange of cations on the A and B sites, is locally expressed as an atomic rearrangement to a tetragonal symmetry, a correlation that is retained up to the maximum temperature studied (1000 °C). Furthermore, a complex thermal expansion behavior is revealed wherein the oxide materials expand heterogeneously at the level of coordination polyhedral with an apparent dependence on bond strength.

36 MATERIALS SCIENCE↗
DOE OSTI2023

Small angle X-ray studies of short-range order in non-stoichiometric pseudoprotic ionic liquids: the influence of chemical structure

Mixtures of organic acids and amines have been studied extensively owing to their unusual physicochemical properties and applications as solvents for extraction. In equimolar ratios they represent pseudoprotic ionic liquids, and in other, “nonstoichiometric” ratios they display a range of odd physicochemical behaviors. We report the results of small-angle X-ray scattering studies of a series of such systems with a range of chemical structures chosen to explore the link between molecular geometry and the character of the emergent nanoscale local liquid structure. We find that while the details vary, structure can emerge even when the hydrogen-bonding character of the components is changed significantly, and the character of their hydrocarbon substituents is altered. The consistent emergence of local order in the face of varying chemical structures indicates that the process is robust. Furthermore, this implies that the emergence of such structure may in fact be far more common in liquid mixtures than is currently recognized, and a great many structures may be suitable for the synthesis of pseudoprotic ionic liquids.

77 NANOSCIENCE AND NANOTECHNOLOGY↗
DOE OSTI2020

Long-Range Ordered Amorphous Atomic Chains as Building Blocks of a Superconducting Quasi-One-Dimensional Crystal

Crystalline and amorphous structures are two of the most common solid-state phases. Crystals having orientational and periodic translation symmetries are usually both short-range and long-range ordered, while amorphous materials have no long-range order. Short-range ordered but long-range disordered materials are generally categorized into amorphous phases. In contrast to the extensively studied crystalline and amorphous phases, the combination of short-range disordered and long-range ordered structures at the atomic level is extremely rare and so far has only been reported for solvated fullerenes under compression. Here, a report on the creation and investigation of a superconducting quasi-1D material with long-range ordered amorphous building blocks is presented. Using a diamond anvil cell, monocrystalline (TaSe4)(2)I is compressed and a system is created where the TaSe(4)atomic chains are in amorphous state without breaking the orientational and periodic translation symmetries of the chain lattice. Strikingly, along with the amorphization of the atomic chains, the insulating (TaSe4)(2)I becomes a superconductor. The data provide critical insight into a new phase of solid-state materials. The findings demonstrate a first ever case where superconductivity is hosted by a lattice with periodic but amorphous constituent atomic chains.

combination of crystalline and amorphous structure↗
DOE OSTI2023

Evidence of Long-Range and Short-Range Magnetic Ordering in the Honeycomb Na 3 Mn 2 SbO 6 Oxide

We present a comprehensive study of the synthesis, structure, and magnetic properties of the honeycomb oxide Na 3 Mn 2 SbO 6 supported by neutron diffraction, heat capacity, and magnetization measurements. The refinements of the neutron diffraction patterns (150, 50, and 45 K) using the Rietveld method confirm the monoclinic (S. G. C2/m) structure. Temperature-dependent magnetic susceptibilities measured at varying fields along with the heat capacity measurements demonstrate the coexistence of long-range ordering (∼42 K) and short-range ordering (∼65 K). The field-dependent isothermal magnetization measurements at 5 K indicate a spin-flop transition around 5 T. Rietveld refinements of the low-temperature (below 45 K) neutron diffraction data further confirm the long-range magnetic ordering. In addition, the temperature variation of the lattice parameters obtained from the neutron powder diffraction analysis exhibited a distinct anomaly near the antiferromagnetic transition temperature. The appearance of the concomitant broadened backgrounds in the neutron powder diffraction data collected at 80, 50, and 45 K supports the short-range ordering. The resultant magnetic structure consists of spins that are aligned antiparallel with the nearest neighbors and also with the spins of the adjacent honeycomb layers. The occurrence of a fully ordered magnetic ground state (Neel antiferromagnetic (AFM)) in Na3Mn 2 SbO 6 consolidates the significance of fabricating new honeycomb oxides.

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

Formation of short-range magnetic order and avoided ferromagnetic quantum criticality in pressurized LaCrGe 3

LaCrGe 3 has attracted attention as a paradigm example of the avoidance of ferromagnetic (FM) quantum criticality in an itinerant magnet. In this work, we combined thermodynamic (specific heat and thermal expansion), transport, x-ray, and neutron scattering as well as μSR measurements to obtain insights on the temperature-pressure phase diagram of LaCrGe 3 . Consistent with previous studies of the phase diagram by transport measurements, our thermodynamic data shows clearly that the FM transition at T FM changes its character from second order to first order when it is suppressed to low temperatures by pressure. In addition, previous studies demonstrated that for high pressures a new phase occurs below T 2 , which was proposed to be a long-wavelength antiferromagnetic state (AFM q ). In this paper, we provide evidence from our thermodynamic data that this phase transition is preceded by yet another phase transition at T 1 >T 2 . Our μSR data indicate that full magnetic volume fraction is only established below T 2 , but that this magnetism is characterized by a short correlation length. Within the experimental resolution, our neutron-scattering data is not able to identify any magnetic Bragg peaks. Overall, the microscopic magnetic data is therefore consistent with the formation of FM clusters in the proximity of the avoided FM quantum critical point in LaCrGe 3 . This conclusion is at odds with the previous proposal of AFM q order and raises questions on the role of disorder in this stochiometric compound.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
DOE OSTI2021

A medium-range structure motif linking amorphous and crystalline states

Amorphous materials have no long-range order, but there are ordered structures at short range (2–5 Å), medium range (5–20 Å) and even longer length scales. While regular and semiregular polyhedra are often found as short-range ordering in amorphous materials, the nature of medium-range order has remained elusive. Consequently, it is difficult to determine whether there exists any structural link at medium range or longer length scales between the amorphous material and its crystalline counterparts. Moreover, an amorphous material often crystallizes into a phase of different composition, with very different underlying structural building blocks, further compounding the issue. Here, we capture an intermediate crystalline cubic phase in a Pd-Ni-P amorphous alloy and reveal the structure of the medium-range order, a six-membered tricapped trigonal prism cluster (6M-TTP) with a length scale of 12.5 Å. We find that the 6M-TTP can pack periodically to several tens of nanometres to form the cube phase. Our experimental observations provide evidence of a structural link between the amorphous and crystalline phases in a Pd-Ni-P alloy at the medium-range length scale and suggest that it is the connectivity of the 6M-TTP clusters that distinguishes the crystalline and amorphous phases. These findings will shed light on the structure of amorphous materials at extended length scales beyond that of short-range order.

36 MATERIALS SCIENCE↗
DOE OSTI2021

Soil minerals affect taxon-specific bacterial growth

Abstract Secondary minerals (clays and metal oxides) are important components of the soil matrix. Clay minerals affect soil carbon persistence and cycling, and they also select for distinct microbial communities. Here we show that soil mineral assemblages—particularly short-range order minerals—affect both bacterial community composition and taxon-specific growth. Three soils with different parent material and presence of short-range order minerals were collected from ecosystems with similar vegetation and climate. These three soils were provided with 18O-labeled water and incubated with or without artificial root exudates or pine needle litter. Quantitative stable isotope probing was used to determine taxon-specific growth. We found that the growth of bacteria varied among soils of different mineral assemblages but found the trend of growth suppression in the presence of short-range order minerals. Relative growth of bacteria declined with increasing concentration of short-range order minerals between 25–36% of taxa present in all soils. Carbon addition in the form of plant litter or root exudates weakly affected relative growth of taxa (p = 0.09) compared to the soil type (p < 0.01). However, both exudate and litter carbon stimulated growth for at least 34% of families in the soils with the most and least short-range order minerals. In the intermediate short-range order soil, fresh carbon reduced growth for more bacterial families than were stimulated. These results highlight how bacterial-mineral-substrate interactions are critical to soil organic carbon processing, and how growth variation in bacterial taxa in these interactions may contribute to soil carbon persistence and loss.

59 BASIC BIOLOGICAL SCIENCES↗
DOE OSTI2025

Short-range magnetic order and planar anisotropy in the topological ferrimagnet Mn 3 ⁢Si 2 ⁢Te 6

Mn 3 ⁢Si 2 ⁢Te 6 is a ferrimagnetic topological nodal-line semiconductor that exhibits unconventional colossal magnetoresistance behavior, with short-range spin fluctuations being potentially intimately linked to the emergent properties. Here we determine the short-range magnetic order and anisotropy through total neutron scattering and polarized neutron powder diffraction measurements on polycrystalline Mn 3 ⁢Si 2⁢ Te 6 . Strong in-plane anisotropy is quantified on the Mn ions through extraction of the local site susceptibility tensor. Here, the real-space local spin structure is determined through the application of magnetic pair distribution function analysis covering a wide temperature range. Short-range order over a locally frustrated trimer of three nearest neighbors is found to exist well above the long-range ferrimagnetic transition.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗