High Entropy Materials: Concentrated Solid Solution, Intermetallics, Ceramics, Functional Materials and Beyond: High Entropy Ceramics
Sponsored by: ACerS Basic Science Division, TMS Alloy Phases Committee
Program Organizers: Xingbo Liu, West Virginia University; Michael Gao, National Energy Technology Laboratory; Peter Liaw, University of Tennessee; Jian Luo, University of California, San Diego; Yiquan Wu, Alfred University; Yu Zhong, Worcester Polytechnic Institute
Wednesday 8:00 AM
November 4, 2020
Room: Virtual Meeting Room 33
Location: MS&T Virtual
Session Chair: Yiquan Wu, Alfred University; Julie Schoenung, University of California, Irvine
8:00 AM Invited
High-entropy Sesquioxide Transparent Ceramics with Up-conversion Functionality: Iva Milisavljevic1; Guangran Zhang; Yiquan Wu1; 1Alfred University
High-entropy materials are a new field of research involving entropy stabilized single-phase solid solutions with at least five equal molar elements. High-entropy sesquioxide transparent ceramics in equal molar and nearly equal molar were successfully fabricated by vacuum sintering to reach a relative density of 99.98%. Their thermal, optical and luminescence properties were investigated and discussed. The highest in-line transmittance in visible and IR range is nearly 80%. By adding luminescence ions, the high-entropy ceramics show an up-conversion emission. Such a high-entropy transparent ceramics could be realized in multiple sesquioxide composition systems. By incorporating the high-entropy principle with transparent ceramics will largely broaden the family of optical ceramics.
8:20 AM
Chemical Defect Reactivity of A-site High-Entropy LaFeO3 and LaMnO3 Based Perovskite Oxides: Hector De Santiago1; Wei Li1; Wenyuan Li1; Xingbo Liu1; 1West Virginia University
Perovskite oxides have demonstrated fascinating properties. Herein, high-entropy perovskite oxides (HEPOs) of LaMnO3 and LaFeO3 were synthesized, in equimolar A-site composition with tunable rare metal elements of Pr3+, Gd3+, Nd3+, Ba2+ and Sr2+, through a modified Pechini sol-gel method. The effects of high-entropy A-site elements on the kinetic properties of these mixed ionic and electronic conductors were systematically investigated. The XRD corroborated the stabilization of single phase for the synthesized HEPOs which retain stability after being exposed to high temperatures. Furthermore, the electrical conductivity relaxation studies demonstrated that HEPOs changes to new thermodynamic stability isothermally under atmospheric oxygen partial pressure (pO2), indicating Schottky defect reaction controlled p-type conductivity. Furthermore, the conductivity relaxation time for thermodynamic stability at atmospheric and low pO2 require long time, due to the formation of Schottky defects or the stabilization of the high configurational entropy. Further work will focus on exploring the B-site high entropy stabilization.
8:40 AM Invited
Tuning of Lattice Distortion in High-entropy Oxides by High Pressure: Qiaoshi Zeng1; 1Hpstar
As a new class of multi-principal component oxides with high chemical disorder, the structure and properties stability/tunability of high-entropy oxides (HEOs) is of great interest and importance but remains unclear. Here, using in situ synchrotron radiation X-ray diffraction, Raman spectroscopy, ultraviolet-visible absorption spectroscopy, and ex-situ high-resolution transmission electron microscopy, we confirmed the existence of lattice distortion in the crystalline structure of a HEO according to the deviation of bond angles from the ideal values, and discovered an unparalleled pressure-induced continuous tuning of lattice distortion (bond angles) and optical properties. As continuous bending of bond angles, pressure eventually induced breakdown of the long-range connectivity of lattice and caused amorphization. The amorphous state can be partially recovered upon decompression forming glass-nanoceramic composite HEO. These results revealed the unexpected tunability of the structure and properties of HEOs, which could promote the fundamental understanding and also applications of HEOs.
9:00 AM Invited
Controllable Phase Heterogeneity in High Entropy Oxides: Alexander Dupuy1; Julie Schoenung1; 1University of California, Irvine
A unique characteristic of high entropy oxide (HEO) materials is their reversible entropy-driven phase transformation between the single phase and multiphase states. This feature presents an opportunity to produce oxide materials with highly controlled phase states. Here we explore the manifestation, behavior, and consequences of this phase transformation in (CoCuMgNiZn)O. First, we show that solid state synthesis and sintering can be used to consolidate fully dense HEO ceramics with grain sizes spanning several orders of magnitude. We demonstrate that the phase heterogeneity can be controlled through heat treatment, while the as-consolidated grain size significantly influences the secondary phase evolution and morphology. Then, we discuss our efforts to characterize the secondary phases using atom probe tomography (APT), x-ray absorption spectroscopy (XAS), x-ray diffraction (XRD), and electron microscopy. Finally, we explore the ramifications that the controlled phase state has on the electrical and mechanical properties.
9:20 AM Invited
Magnetic Properties of High Entropy Oxides: Abhishek Sarkar1; Ralf Witte2; Robert Kruk2; Richard Brand2; Horst Hahn1; 1Technische Universität Darmstadt; 2Karlsruhe Institute of Technology (KIT)
High entropy oxides (HEOs) are single-phase solid solutions consisting of 5 or more cations in equiatomic amount. Several compositions along with different crystal structures are already reported for HEOs. Each of these systems exhibits distinct phase stabilization mechanism. In addition to the intriguing structural features, the distinct design concept promotes possibilities for fine tailoring of the functional properties. For instance, HEOs exhibit colossal dielectric constant, high room temperature Li-ion conductivity, highly reversible Li-storage capability, low thermal conductivity, etc. The focus of this study is the magnetic properties of HEOs, which are driven by the crystal structure and the synergy stemming from the presence of multiple elements. The magnetic ordering in HEOs despite the chemical disorder is appealing. In addition, exchange bias, non-collinearity, magnetocrystalline anisotropy, etc., can also be observed in single-phase HEOs. The vast research space that the HEOs offer, can result in the discovery of unprecedented physical phenomena.
9:40 AM Invited
Quantification of the Feasible High Entropy Alloy Space via Novel Alloy Search Schemes: Raymundo Arroyave1; 1Texas A&M University
Over the past decades, the concept of "high entropy alloys" has become a source of inspiration for the field of metallurgy as we try to identify yet to be explored regions in the metal alloy space with properties that can potentially surpass those of alloys currently in use in a number of applications. The "high entropy" premise of much of the HEA program in the early years has given way to the argument that the HEA space is vast and therefore there are boundless opportunities for further discovery. While strictly speaking the HEA alloy+process space indeed is infinite, in this work we present some recent investigations that suggest that, while big, the feasible HEA space in any given sub-sector (e.g. FCC HEAs, RHEAs, etc) is severely constrained by typical alloy design considerations. Combining CALPHAD, physics-based models, machine learning, search/optimization algorithms we present a more nuanced view of the HEA space.
10:00 AM Invited
Phase Transformation and Kinetic Behavior of High Entropy Oxide Materials Characterized via Rapid In-situ Non-ambient X-ray Diffraction: Brianna Musico1; Cordell Delzer1; Claudia Rawn1; Veerle Keppens1; David Mandrus1; 1University of Tennessee
Since the first report in 2015, High Entropy Oxides (HEOs) have gained interest from a variety of fields as they provide an expanded compositional space with opportunities for designing novel materials and tuning their properties. In order to compare synthesis methods and gain insight in the kinetics involved, we have employed rapid in-situ non-ambient X-ray diffraction to characterize the phase transformation and evolution of crystallinity in HEO materials synthesized via both the solid-state method and polymeric steric entrapment. From these studies the transformation behavior and kinetic behavior are revealed and discussed as function of composition and processing method.