Christina M. Rost- PhD
- Professor (Assistant) at James Madison University
Christina M. Rost
- PhD
- Professor (Assistant) at James Madison University
About
58
Publications
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4,774
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Introduction
Current institution
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August 2016 - present
August 2012 - June 2016
Publications
Publications (58)
High-entropy oxide (HEO) thermodynamics transcend temperature-centric approaches, spanning a multidimensional landscape where oxygen chemical potential plays a decisive role. Here, we experimentally demonstrate how controlling the oxygen chemical potential coerces multivalent cations into divalent states in rock salt HEOs. We construct a preferred...
This manuscript presents a working model linking chemical disorder and transport properties in correlated-electron perovskites with high-entropy formulations and a framework to actively design them. We demonstrate this new learning in epitaxial Sr$x$(Ti,Cr,Nb,Mo,W)O$3$ thin films that exhibit exceptional crystalline fidelity despite a diverse chemi...
Interest in high‐entropy inorganic compounds originates from their ability to stabilize cations and anions in local environments that rarely occur at standard temperature and pressure. This leads to new crystalline phases in many‐cation formulations with structures and properties that depart from conventional trends. The highest‐entropy homogeneous...
High entropy oxides (HEOs) have garnered much interest due to their available high degree of tunability. Here, we study the local structure of (MgNiCuCoZn)0.167(MnCr)0.083O, a composition based on the parent HEO (MgNiCuCoZn)0.2O. We synthesized a series of thin films via pulsed laser deposition at incremental oxygen partial pressures. X‐ray diffrac...
Rare-earth oxides (REOs) are an important class of materials owing to their unique properties, including high ionic conductivities, large dielectric constants, and elevated melting temperatures, making them relevant to several technological applications such as catalysis, ionic conduction, and sensing. The ability to predict these properties at mod...
High-entropy materials shift the traditional materials discovery paradigm to one that leverages disorder, enabling access to unique chemistries unreachable through enthalpy alone. We present a self-consistent approach integrating computation and experiment to understand and explore single-phase rock salt high-entropy oxides. By leveraging a machine...
We unravel the distinct role each cation plays in phase evolution, stability, and properties within Mg1/5Co1/5Ni1/5Cu1/5Zn1/5O high-entropy oxide (HEO) by integrating experimental findings, thermodynamic analyses, and first-principles predictions. Our approach is through sequentially removing one cation at a time from the five-component high-entrop...
High entropy oxides (HEO)s have garnered much interest due to their available high degree of tunability. Here, we study the local structure of (MgNiCuCoZn)0.167(MnCr)0.083O, a composition based on the parent HEO (MgNiCuCoZn)0.2O.We synthesized a series of thin films via pulsed laser deposition at incremental oxygen partial pressures. X-ray diffract...
The prototype high-entropy oxide (HEO) Y0.2La0.2Ce0.2Pr0.2Sm0.2O2−δ represents a particularly complex class of HEOs with significant anion sublattice entropy. The system takes either a fluorite or bixbyite-type crystal structure, depending on synthesis kinetics and thermal history. Here, we synthesize bulk ceramics and epitaxial thin films of Y0.2L...
Entropy-stabilized oxides are single-phase, multicomponent oxides that are stabilized by a large entropy of mixing, ΔS, overcoming a positive enthalpy. Due to the −TΔS term in the Gibbs' free energy, G, it can be hypothesized that entropy-stabilized oxides demonstrate a robust thermal stability. Here, we investigate the high temperature stability (...
The study of high-entropy materials has attracted enormous interest since they could show new functional properties that are not observed in their related parent phases. Here, we report single crystal growth, structure, thermal transport, and magnetic property studies on a novel high-entropy oxide with the spinel structure (MgMnFeCoNi)Al2O4. We hav...
High‐entropy materials defy historical materials design paradigms by leveraging chemical disorder to kinetically stabilize novel crystalline solid solutions comprised of many end‐members. Formulational diversity results in local crystal structures that are seldom found in conventional materials and can strongly influence macroscopic physical proper...
As various property studies continue to emerge on high entropy and entropy-stabilized ceramics, we seek a further understanding of the property changes across the phase boundary between “high-entropy” and “entropy-stabilized” phases. The thermal and mechanical properties of bulk ceramic entropy stabilized oxide composition Mg 0.2 Co 0.2 Ni 0.2 Cu 0...
As various property studies continue to emerge on high entropy and entropy-stabilized ceramics, we seek further understanding of property changes across the phase boundary between \enquote{high-entropy} and \enquote{entropy-stabilized}. The thermal and mechanical properties of bulk ceramic entropy stabilized oxide composition Mg$_{0.2}$Co$_{0.2}$Ni...
Vanadium oxide films are widely employed as thermal detectors in uncooled infrared detection systems due to their high temperature coefficient of resistance near room temperature. One strategy toward maximizing detectivity and reducing the thermal time constant in these systems is to minimize the system platform dimensions. This approach necessitat...
High entropy oxides are emerging as an exciting new avenue to design highly tailored functional behaviors that have no traditional counterparts. Study and application of these materials are bringing together scientists and engineers from physics, chemistry, and materials science. The diversity of each of these disciplines comes with perspectives an...
High entropy oxides are emerging as an exciting new avenue to design highly tailored functional behaviors that have no traditional counterparts. Study and application of these materials are bringing together scientists and engineers from physics, chemistry, and materials science. This diversity of disciplines each come with perspectives and jargon...
Disorder enhances desired properties, as well as creating new avenues for synthesizing materials. For instance, hardness and yield stress are improved by solid-solution strengthening, a result of distortions and atomic-size mismatches. Thermochemical stability is increased by the preference of chemically disordered mixtures for high-symmetry superl...
Topological kagome magnets RMn6Sn6 (R = rare earth element) attract numerous interests due to their non-trivial band topology and room-temperature magnetism. Here, we report a high entropy version of kagome magnet, (Gd0.38Tb0.27Dy0.20Ho0.15)Mn6Sn6. Such a high entropy material exhibits multiple spin reorientation transitions, which is not seen in a...
This work reports on a pump–probe laser-based heating and sensing metrology to study the failure mechanisms of materials during extreme heat fluxes localized near surfaces, the localization of which is controlled by the focus of the laser beam and sensed by the reflection of a secondary probe laser. We focus the demonstration of these power density...
In this work, the high entropy oxide A2CuO4 Ruddlesden–Popper (La0.2Pr0.2Nd0.2Sm0.2Eu0.2)2CuO4 is explored by charge doping with Ce⁺⁴ and Sr⁺² at concentrations known to induce superconductivity in the simple parent compounds, Nd2CuO4 and La2CuO4. Electron doped (La0.185Pr0.185Nd0.185Sm0.185Eu0.185Ce0.075)2CuO4 and hole doped (La0.18Pr0.18Nd0.18Sm0...
Disorder enhances desired properties, as well as creating new avenues for synthesizing materials. For instance, hardness and yield stress are improved by solid-solution strengthening, a result of distortions and atomic size mismatches. Thermo-chemical stability is increased by the preference of chemically disordered mixtures for high-symmetry super...
In this work, the high entropy oxide A2CuO4 Ruddlesden-Popper (La0.2Pr0.2Nd0.2Sm0.2Eu0.2)2CuO4 is explored by charge doping with Ce+4 and Sr+2 at concentrations known to induce superconductivity in the simple parent compounds, Nd2CuO4 and La2CuO4. Electron doped (La0.185Pr0.185Nd0.185Sm0.185Eu0.185Ce0.075)2CuO4 and hole doped (La0.18Pr0.18Nd0.18Sm0...
We present data for epitaxial thin films of the prototypical entropy-stabilized oxide (ESO), Mg0.2Ni0.2Co0.2Cu0.2Zn0.2O, that reveals a systematic trend in lattice parameter and properties as a function of substrate temperature during film growth with negligible changes in microstructure. A larger net Co valence in films grown at substrate temperat...
Due to their diverse bonding character and corresponding property repertoire, carbides are an important class of materials regularly used in modern technologies, including aerospace applications and extreme environments, catalysis, fuel cells, power electronics, and solar cells. The recent push for novel materials has increased interest in high ent...
This work studies the thermal conductivity and phonon scattering processes in a series of n‐type lead telluride‐lead selenide (PbTe–PbSe) nanostructured thin films grown by atomic layer deposition (ALD). The ALD growth of the PbTe–PbSe samples in this work results in nonepitaxial films grown directly on native oxide/Si substrates, where the Volmer–...
Despite the exceptional thermal and mechanical functionalities of diamond, its superlative properties are highly subject to the presence of point defects, dislocations, and interfaces. In this study, polycrystalline diamond is ion implanted with C³⁺, N³⁺, and O³⁺ ions at an energy of 16.5 MeV, producing an amorphous layer at the projected range and...
Visibly transparent and electrically conductive oxides are attractive for a wide array of applications. Indium tin oxide (ITO) and fluorine tin oxide (FTO) are a subset of the larger transparent conducting oxide family, and possess transmittance in the visible spectrum as well as high electrical conductivity. Even though their unique optical and el...
Heterogeneous nanosystems offer a robust potential for manipulating various functional material properties, beyond those possible from their individual constituent materials. We demonstrate the formation of a class of materials with a homogeneous lattice but spatially heterogeneous electrical functionality; specifically, we develop epitaxial modula...
It is shown using classical molecular dynamics simulations that phonon scattering from disorder in the interatomic forces introduced by charge transfer and not from mass disorder is needed to explain the thermal conductivity reduction experimentally measured that accompanies the addition of a sixth cation to the entropy stabilized oxide J14 [(Mg0.1...
Twelve different equiatomic five-metal carbides of group IVB, VB, and VIB refractory transition metals are synthesized via high-energy ball milling and spark plasma sintering. Implementation of a newly developed ab initio entropy descriptor aids in selection of candidate compositions for synthesis of high entropy and entropy stabilized carbides. Ph...
We report on the thermal resistances of thin films (20 nm) of hafnium zirconium oxide (Hf1-xZrxO2) with compositions ranging from 0 ≤ x ≤ 1. Measurements were made via time-domain thermoreflectance and analyzed to determine the effective thermal resistance of the films in addition to their associated thermal boundary resistances. We find effective...
Manipulating a crystalline material's configurational entropy through the introduction of unique atomic species can produce novel materials with desirable mechanical and electrical properties. From a thermal transport perspective, large differences between elemental properties such as mass and interatomic force can reduce the rate at which phonons...
We have measured the growth of the spin glass correlation length through the aging effect. Measurements were made on bulk Cu0.95Mn0.05 and a Cu0.88Mn0.12 thin film multilayer with CuMn layer thicknesses of 4.5 nm separated by 60-nm Cu layers. As the glass temperature Tg is approached (0.9Tg<T<0.96Tg) in the bulk sample, we find that the waiting tim...
Fundamental theories predict that reductions in thermal conductivity from point and extended defects can arise due to phonon scattering with localized strain fields. To experimentally determine how these strain fields impact phonon scattering mechanisms, we employ ion irradiation as a controlled means of introducing strain and assorted defects into...
This paper explores thin films of the entropy-stabilized oxide (ESO) composition MgxNixCoxCuxZnxScxO (x ∼ 0.167) grown by laser ablation in incremental gas pressures and O2/Ar ratios to modulate particle kinetic energy and plume reactivity. Low pressures supporting high kinetic energy adatoms favor the kinetic stabilization of a single rocksalt pha...
Visibly transparent and electrically conductive oxides are attractive for a wide array of applications. Indium tin oxide (ITO) and fluorine tin oxide (FTO) are a subset of the larger transparent conducting oxide family, and possess transmittance in the visible spectrum as well as high electrical conductivity. Even though their unique optical and el...
GaN surface and near-surface chemistry influence on band offsets of oxide overlayers is demonstrated through X-ray photoelectron spectroscopy measurements using epitaxial (111)-oriented MgO films on (0001)-oriented Ga-polar GaN as a case study. For identical cleaning and MgO growth conditions, GaN subsurface oxygen impurities influence the GaN bare...
Time domain thermoreflectance (TDTR) and frequency domain thermoreflectance (FDTR) are common pump-probe techniques that are used to measure the thermal properties of materials. At elevated temperatures, transducers used in these techniques can become limited by melting or other phase transitions. In this work, time domain thermoreflectance is used...
We investigate the effect of mass disorder on the thermal conductivity of Lennard-Jones based multi-component solid solutions via classical molecular dynamics simulations. In agreement with Klemens' perturbation theory, the thermal conductivity reduction due to mass scattering alone is found to reach a critical point, whereby adding more impurity a...
Nanoscale Compositional Analysis of a Thermally Processed Entropy-Stabilized Oxide via Correlative TEM and APT - Volume 23 Issue S1 - David R. Diercks, Geoff Brennecka, Brian P. Gorman, Christina M. Rost, Jon-Paul Maria
Entropy-stabilized oxides (ESOs) provide an alternative route to novel materials discovery and synthesis. It is, however, a challenge to demonstrate that the constituent elements in an entropy-stabilized crystal are homogeneously and randomly dispersed among a particular sublattice, resulting in a true solid solution with no evidence of local order...
Carbon coated aligned multi-walled carbon nanotube (AMWCNT/C) sheets were used for studying the controlled radial growth of MWCNTs. Pyrolytic carbon (PyC) was deposited on the surface of nanotubes using multiple cycles of chemical vapor infiltration. Morphological and structural characterization showed that when graphitization was done in one step,...
The thermal conductivity of n- and p-type doped gallium nitride (GaN) epilayers having thicknesses of 3–4 μm was investigated using time domain thermoreflectance. Despite possessing carrier concentrations ranging across 3 decades (10¹⁵–1018 cm–3), n-type layers exhibit a nearly constant thermal conductivity of 180 W/mK. The thermal conductivity of...
Density functional theory calculations were carried out for three entropic rocksalt oxides,
(Mg0.1Co0.1Ni0.1Cu0.1Zn0.1)O0.5, termed J14, and J14þLi and J14þSc, to understand the role of
charge neutrality and electronic states on their properties, and to probe whether simple expressions
may exist that predict stability. The calculations predict that...
Configurational disorder can be compositionally engineered into mixed oxide by populating a single sublattice with many distinct cations. The formulations promote novel and entropy-stabilized forms of crystalline matter where metal cations are incorporated in new ways. Here, through rigorous experiments, a simple thermodynamic model, and a five-com...
Chemical Homogeneity in Entropy-Stabilized Complex Metal Oxides - Volume 21 Issue S3 - Ali Moballegh, Christina M. Rost, Jon-Paul Maria, Elizabeth C. Dickey
Questions
Question (1)
I'm currently reading through vast amounts of literature on High Entropy Alloys. Many of these compositions create a system with a dendritic microstructure where the dendrite has one composition (equilmolar solid solution, or preferring higher levels of one component vs. another), and the interdendritic region contains a different composition. The system as a whole maintains the same crystal structure. These materials are being classified as single phase.
I was under the impression that a single phase is one where part of a system (or the whole system) is both chemically and structurally homogeneous.
Could anyone provide a bit more clarity, perhaps in the context of HEAs or similar systems?
Thank so much!
