Highlights from Research Conducted at POWDER

Candidate Elastic Quantum Critical Point in LaCu6-xAux

Candidate Elastic Quantum Critical Point in LaCu6-xAuxA combination of neutron diffraction, x-ray diffraction, and heat capacity measurements in conjunction with first principles calculations were used to show that the LaCu6-xAux system hosts the first known example of an elastic quantum critical point. Neutron and x-ray diffraction measurements were performed to study the structural properties as a function of temperature and Au-composition. First principle calculations confirm that the phase transition is driven by an elastic instability and is independent of electronic properties. Heat capacity measurements indicate the presence of quantum fluctuations at the critical composition.

View the full presentation.

Slater Insulator discovered in a new Iridate Perovskite

Slater Insulator discovered in a new Iridate PerovskiteThe magnetism, structural behavior and resistivity change in SrIr1−xSnxO3 indicated this material was a Slater insulator. This is a rare insulator where the magnetism controls the conduction of electrons. The behavior can be controlled by altering the Sn content.

View the full presentation.

Melting of unexpected charge glassy state leads to a pressure induced metal-insulator transition

Melting of unexpected charge glassy state leads to a pressure induced metal-insulator transition PbCrO3 shown to have Pb4+ and Pb2+ ions that form an unexpected charge glassy state, explaining a large volume collapse and metal-insulator transition.

View the full presentation.

Rare magnetic order and insulating behavior in a 4d oxide

Rare magnetic order and insulating behavior in a 4d oxideA rare case of magnetic insulating behavior driven by spin-orbit coupling is revealed in the 4d oxide Sr4RhO6.

View the full presentation.

Melting of unexpected charge glassy state leads to a pressure induced metal-insulator transition

Melting of unexpected charge glassy state leads to a pressure induced metal-insulator transition Applying pressure causes a dramatic volume collapse accompanied by a insulator to metal transition. This is revealed as being due to a melting of a charge glassy state that results in an intermetallic charge transfer. This change was found to alter the valence in the material from Pb2+0.5Pb4+Cr3+O3 to Pb2+Cr4+O3. This valence change occurs since Pb is a so-called valence skipper, i.e. it goes directly from 2+ to 4+ and cannot form a 3+ state. This characteristic is utilized in lead batteries.

View the full presentation.

New multiferroic material with a surprisingly highly symmetric crystal structure

New multiferroic material with a surprisingly highly symmetric crystal structureNeutron diffraction reveals cubic nuclear structure of LaMn3Cr4O12 hosting the G-type AFM structure of the Cr and Mn sublattice with spin orientation along the [111] direction that lacks an inversion center. The magnetism occurs concurrently with the onset of ferroelectric polarization and is enhanced by the application of a magnetic field.

View the full presentation.

Correlation of anisotropy and directional conduction in β-Li3PS4 fast Li+ conductor

Correlation of anisotropy and directional conduction in β-Li3PS4 fast Li+ conductorNeutron and X-ray diffrac3ons determine the stability of β-Li3PS4 and the anisotropic thermal expansion with its structural origin from Li+ channels.

View the full presentation.

Neutrons Provide Insight into a New Approach to Tune Magnetic and Electronic Properties with Chemical Doping

Neutrons Provide Insight into a New Approach to Tune Magnetic and Electronic Properties with Chemical DopingNeutron studies were used to reveal a complex magnetic phase diagram of Cr2(Te1−xWx)O6 systems. While compounds with different x values possess the same crystal structure, they display different magnetic structures below and above xc = 0.7, where both the transition temperature TN and sublattice magnetization (Ms) reach a minimum.

View the full presentation.

Neutrons Provide Insights into Magnetic Structures of New Frustrated Compounds

Neutrons Provide Insights into Magnetic Structures of New Frustrated CompoundsNeutron diffraction studies under applied fields were used to reveal the complex magnetic phase diagram of two new members of the frustrated triangular lattice type with XY-anisotropy.

View the full presentation.

Biennial Magnetic Structure Determination from Neutron Diffraction Data Workshop

Biennial Magnetic Structure Determination from Neutron Diffraction Data WorkshopThe workshop's aim was to enhance the community studying magnetism in materials by learning from experts, the essential theoretical foundations to magnetic representation analysis and work through real examples to gain experience in solving and refining magnetic structures from neutron powder and single crystal diffraction measured from both reactor and spallation sources.

View the full presentation.

Instrumentation Upgrades

The HFIR HB-2A powder diffractometer has undergone two important upgrades that enhance its efficiency, boost its performance, and further improve the ALARA practice.

View the full presentation.

New collimators and improved efficiency of HB-2A Powder Diffractometer

During the HFIR outage engineers, technicians and instrument staff worked to replace the 44 pre-detector collimators on HB-2A. Commissioning measurements have confirmed an intensity increase of 2.6 with a signal to noise efficiency increase of 1.5.

View the full presentation.

Synthesis and Structure of Novel Battery Materials

Lithium transition metal fluorophosphates with a tavorite structure have been recognized as promising electrode materials for lithium-ion batteries because of their good energy storage capacity combined with electrochemical and thermal stability.

View the full presentation.

Magnetically driven metal to insulator transition

Experimental demonstration of a novel pathway to transform a materials conducting properties first predicted 60 years ago, with the unique insulting state existing at room temperature.

View the full presentation.

Neutron Powder Diffraction of Piezoelectric Ceramics at HB2A

Piezoelectrics are a huge industry and their uses will expand if solutions can be found for a few limiting issues. Jennifer Forrester, a researcher at the University of Florida, and Krishna Nittala, a Ph.D. candidate at the university, used the Neutron Powder Diffractometer (NPD, at HB-2A) at HFIR to explore the structure and characteristics of piezoelectric ceramics that might lead to improved applications. Forrester used the NPD to examine crystal structures of lead-free piezoelectric ceramics with the aim of creating materials that can take more deformation and demonstrate improved properties. A limitation of currently used piezoelectrics is that at high temperatures they shift to a cubic structure, losing their piezoelectric properties. Nittala examined samples of piezoelectric materials at gradually increasing temperatures as part of an effort to develop materials with higher transition temperatures. The current temperature limit for piezoelectrics is around 400°C. He examined samples at temperatures ranging from room temperature to 600°C using the ILL vacuum furnace on HB2a. Their results have been published in APL and JACS.

View the full presentation.

Tuning thermoelectric materials at the atomic level, guest-host interactions are important

The clathrate-type semiconductor, Ba8AlxSi46-x, provides a controlled system to explore the role of the interactions between the guest atoms, barium in this case, and the host atoms, Al and Si, because the Al-content can be varied over a large range. We have used neutron diffraction to explore the detailed structural changes of the crystal structure of Ba8AlxSi46-x as a function of Al content using the HB-2A Neutron Powder Diffractometer at the High Flux Isotope Reactor, Oak Ridge National Laboratory.

View the full presentation.

Neutron Study Reveals New Magnetic Structure in NaMnGe2O6 Pyroxene

This work completes the study of the evolutionof magnetic properties of the alkali-metal pyroxenes as a function of the d-orbital occupancy from d1 to d5 and reveals a new magnetic structure in NaMnGe2O6.

View the full presentation.

Polarized neutron diffraction experiments now possible at the HB2A Powder diffractometer

Polarized neutrons were further used to precisely measure the magnitude of the ordered magnetic moment in an itinerant ferromagnet. The difference scattering from neutron beam polarized parallel and antiparallel to the applied magnetic field gives an improvement of nearly one order of magnitude in detection sensitivity.

View the full presentation.

Magnetic order and ice rules in the multiferroic spinel FeV2O4

Neutron diffraction study done at HB2A of FeV2O4, which is rare in exhibiting spin and orbital degrees of freedom on both cation sublattices of the spinel structure. Showing that the direction of ordered vanadium spins at low temperature obey "ice rules" more commonly associated with the frustrated rare-earth pyrochlore systems.

View the full presentation.

Phase stability of Li(Fe1-xMnx)BO3 battery materials

In situ determination of temperatures of melting and phase change in the Li(Mn/Fe)BO3 class of emerging high-capacity (220 mAh/g) Li-ion battery cathode materials.

View the full presentation.

Successive Magnetic Phase Transitions and Multiferroicity in S = 1 Triangular-Lattice Antiferromagnet Ba3NiNb2O9

Successive Magnetic Phase Transitions and Multiferroicity in S = 1Triangular-Lattice Antiferromagnet Ba<sub>3</sub>NiNb<sub>2</sub>O<sub>9</sub>The studies on Ba3NiNb2O9 reveal that (i) it is a new S = 1TLAF system showing two magnetic phase transitions bracketing an intermediate up-up-down phase; (ii) it is a multiferroic system with ferroelectric ground states stabilized at all three magnetic phases.

View the full presentation.