A5065449815- Boron and Carbon Nanomaterials Research
- Physics of Superconductivity and Magnetism
- Thermal properties of materials
- Magnetic and transport properties of perovskites and related materials
- Advanced Condensed Matter Physics
- Electronic and Structural Properties of Oxides
- Quantum and electron transport phenomena
- Advanced Thermoelectric Materials and Devices
- Phase-change materials and chalcogenides
- Glass properties and applications
- Semiconductor materials and interfaces
- MXene and MAX Phase Materials
- Advanced Chemical Physics Studies
- Quantum, superfluid, helium dynamics
- Boron Compounds in Chemistry
- Organic and Molecular Conductors Research
- Semiconductor Quantum Structures and Devices
- Diamond and Carbon-based Materials Research
- Superconductivity in MgB2 and Alloys
- Molecular Junctions and Nanostructures
- Advanced Physical and Chemical Molecular Interactions
- Perovskite Materials and Applications
- Machine Learning in Materials Science
- Rare-earth and actinide compounds
- Spectroscopy and Quantum Chemical Studies
University of New Mexico
2015-2024
Washington State University
2015
The University of Texas at Austin
2015
Lake Shore Cryotronics (United States)
2015
Northeastern University
2015
Sandia National Laboratories California
1986-2009
Sandia National Laboratories
1987-1997
University of Illinois Urbana-Champaign
1997
École Polytechnique Fédérale de Lausanne
1994
Southern Illinois University Carbondale
1988
Resistivity, thermopower, and Hall-effect measurements on large single crystals of the anatase form TiO2 all indicate high mobility n-type carriers that are produced by thermal excitation from a density ∼1018 cm−3 putatively present shallow donor states. The decrease with increasing temperature is consistent scattering optical phonons TiO2.
A scaling analysis of the adiabatic eigenstates an electron placed in a deformable continuum with and without presence Coulombic defect is set forth. This procedure enables us to obtain exact information about system's for various models electron-lattice interaction.
In systems that are two and three dimensional electronically, a large polaron small distinct types of quasiparticles. The type formed depends on which electron-lattice interaction is primary importance. A forms when the due to long-range Coulombic interactions between an electronic carrier solid's ions paramount Competing effects then determine radius polaron. By contrast, can form short-range interaction, such as deformation-potential dominant. its self-trapped shrinks without limit until...
Abstract An extensive calculation of the optical-phonon-assisted transition rates for non-adiabatic electronic hopping motion in a solid is presented. Holstein's Molecular Crystal Model used as basis study and computation involves no restrictions on either magnitude electron-lattice coupling strength, temperature, or difference between energies initial final sites. In strong-coupling small-polaron régime, jump rates, associated d.c. conductivity, a.c. electric-field dependence crystal are...
An exact calculation of the acoustic-phonon-assisted jump rate has been carried out. It is found that while Miller-Abrahams (single-phonon) approximation adequate for study shallow-impurity conduction at helium temperatures, it typically inappropriate hopping between deep states in noncrystalline solids. In particular, multiphonon will display a nonactivated temperature dependence below Debye which similar to often-seen $\mathrm{exp}[\ensuremath{-}{(\frac{{T}_{0}}{T})}^{\frac{1}{4}}]$ behavior.
Electrical conductivity, Seebeck-coefficient, and Hall-effect measurements have been made on single-phase boron carbides, ${\mathrm{B}}_{1\ensuremath{-}x}{\mathrm{C}}_{x}$, in the compositional range $0.1\ensuremath{\le}x\ensuremath{\le}0.2$ between room temperature 1273 K. The results indicate that predominant conduction mechanism is small-polaron hopping carbon atoms at geometrically inequivalent sites.
Transition-metal oxides are a promising class of semiconductors for the oxidation water, process that underpins both photoelectrochemical water splitting and carbon dioxide reduction. However, these materials limited by very slow charge transport. This is because, unlike conventional semiconductors, material aspects metal favor formation slow-moving, self-trapped carriers: small polarons. In this Perspective, we seek to highlight salient features small-polaron transport in oxides, offer...
We have obtained and analyzed Raman spectra of single-crystal, hot-pressed, chemical-vapor-deposited boron carbide materials over their single-phase region (from \ensuremath{\sim}9 to \ensuremath{\sim}20 at. % carbon). These provide insight into the substitutional disorder that characterizes these structurally ordered solids. In particular, although icosahedra chain structures occupy regular lattice positions, there is local resulting from occupancy certain sites within chains by either or...
The Hall coefficient of Gd-doped ${\mathrm{La}}_{2/3}{\mathrm{Ca}}_{1/3}{\mathrm{MnO}}_{3}$ exhibits Arrhenius behavior over a temperature range from ${2T}_{c}$ to ${4T}_{c}$, with an activation energy very close $\frac{2}{3}$ that the electrical conductivity. Although both doping level and thermoelectric indicate holelike conduction, is electronlike. This unusual result provides strong evidence in favor small-polaronic conduction paramagnetic regime manganites.
Boron-rich molecules and solids hold a special place within chemistry. They do not follow the general bonding rules we are taught in chemistry classes. For example, some boron-rich composed of 12-atom clusters boron atoms which each atom resides on vertex an icosahedron. These very stable refractory materials with melting temperatures up to 2400 °C—a thousand degrees greater than silicon's. Beyond this, they possess numerous novel structural, electronic thermal properties that only...
Abstract A variational calculation of the eigenstates three-dimensional analogue Holstein's Molecular Crystal Model is utilized as a basis for determining conditions under which carrier self-trapping does or not occur in this system. It found that below temperature-dependent critical value electron-lattice coupling strength occur; then correspond to an excess electron being only weakly coupled vibratory motion. Above larger self-trapped (small-polaron) exist. Between these two...
Conducting polymers have recently been suggested as thermoelectric materials for use in large-area thermogenerators. To help assessing the feasibility of this electrical conductivity and Seebeck coefficient a series heavily doped regioregular poly(3-hexylthiophene) films are measured between 220 370 K. $p$-type chemical doping up to 34% is accompanied by introduction negatively charged counterions, ${\text{PF}}_{6}^{\ensuremath{-}}$. The counterions produce disordered environment within...
We variationally determine the conditions for formation of large singlet bipolarons within adiabatic approximation. find that, in two- and three-dimensional electronic systems with only a short-range electron-lattice interaction, are small bipolarons. Furthermore, long-range (Fr\"ohlich) interaction characteristic an ionic solid, we classical result that will not form. However, presence both short- components novel domain which can be formed. In particular, exceptionally ratio static to...
Unlike prior attempts to describe the motion of electronic charge carriers in disordered materials, we suggest that (holelike) may actually be selftrapped, i.e., small polarons. In support our hypothesis, discuss measurements electrical conductivity, thermoelectric power, and Hall mobility on some chalcogenide glasses.
Although small (spatially compact) bipolarons readily localize, large (like polarons) can be mobile. As such, are a suitable basis for bipolaronic superconductivity. However, only form in multidimensional ionic solids if the static dielectric constant greatly exceeds twice optical constant. The formation as well normal-state and superconducting properties of appear consistent with observations high-temperature superconductors.
We usually think of electrons in solids and liquids as behaving like free particles whose motion is impeded by occasional collisions. Evidence now accumulating for charge carriers with qualitatively different behavior. These new carriers, the simplest case, are extra condensed matter that become trapped potential wells their own creation, forming units known small polarons.
The small-polaronic diffusion associated with simple models of light interstitials in bcc metals has been investigated. By transcending the simplifications which are often introduced studying electronic small-polaron transport, we calculate coefficients reasonably consistent available data. In particular, an explanation "anamalous" isotope dependence observed for hydrogen emerges from these studies.
Abstract The absolute sign of the Hall effect is determined for several situations charac teristic hopping in covalent materials. In particular, it shown that an excess electron between antibonding orbitals odd-membered (three-site) ring will yield 'anomalously' signed effect, namely, p-type. addition, holes moving bonding a similar structure n-type effect. However, and hole even-membered (four-site) yields conventional result : p-type effects, respectively. Other physically relevant are...
Previous calculations of the nonadiabatic phonon-assisted jump rate have included electron coupling to either optical or acoustical phonons. Such yielded expressions for which are essentially identical in high-temperature ($T\ensuremath{\gtrsim}{T}_{\mathrm{Debye}}$) regime, lattice motion can be treated classically, but differ qualitatively from one another complementary low-temperature ($T\ensuremath{\ll}{T}_{\mathrm{Debye}}$) regime. In this article we extended include both phonon modes....
The boron carbides are composed of twelve-atom icosahedral clusters which linked by direct covalent bonds and through three-atom intericosahedral chains. known to exist as a single phase with carbon concentrations from about 8 20 at. %. This range is made possible the substitution atoms for one another within both icosahedra most widely accepted structural model ${\mathrm{B}}_{4}$C (the carbide nominally 20% carbon) has ${\mathrm{B}}_{11}$C C-B-C Here, free energy studied function...