Searcharxiv⌕ Search

SEARCH · Searcharxiv

Results for “cond-mat.mtrl-sci”

Search indexed arXiv papers on artificial intelligence, large language models, computer vision and robotics. Read source abstracts and follow links to arXiv.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 325 records · Page 18Linked to original sources
arXiv2013

Evolutionary search for new high-k dielectric materials: methodology and applications to hafnia-based oxides

High-k dielectric materials are important as gate oxides in microelectronics and as potential dielectrics for capacitors. In order to enable computational discovery of novel high-k dielectric materials, we propose a fitness model (energy storage density) that includes the dielectric constant, bandgap, and intrinsic breakdown field. This model, used as fitness function in conjunction with first-principles calculations and global optimization evolutionary algorithm USPEX, efficiently leads to practically important results. We found a number of high-fitness structures of SiO2 and HfO2, some of which correspond to known phases and some are new. The results allow us to propose characteristics (genes) common to high-fitness structures - these are the coordination polyhedra and their degree of distortion. Our variable-composition searches in the HfO2-SiO2 system uncovered several high-fitness states. This hybrid algorithm opens up a new avenue of discovering novel high-k dielectrics with both fixed and variable compositions, and will speed up the process of materials discovery.

cond-mat.mtrl-sci↗
arXiv2013

Rate-dependent morphology of Li2O2 growth in Li-O2 batteries

Compact solid discharge products enable energy storage devices with high gravimetric and volumetric energy densities, but solid deposits on active surfaces can disturb charge transport and induce mechanical stress. In this Letter we develop a nanoscale continuum model for the growth of Li2O2 crystals in lithium-oxygen batteries with organic electrolytes, based on a theory of electrochemical non-equilibrium thermodynamics originally applied to Li-ion batteries. As in the case of lithium insertion in phase-separating LiFePO4 nanoparticles, the theory predicts a transition from complex to uniform morphologies of Li2O2 with increasing current. Discrete particle growth at low discharge rates becomes suppressed at high rates, resulting in a film of electronically insulating Li2O2 that limits cell performance. We predict that the transition between these surface growth modes occurs at current densities close to the exchange current density of the cathode reaction, consistent with experimental observations.

physics.chem-ph↗
arXiv2013

Chemical Diffusion at Mixed Ionic Electronic Semiconductor Interfaces and comparison with La2NiO4+d epitaxial thin films

A simple model to describe Mixed Ionic Electronic Conductors (MIEC) in terms of standard semiconductor physics is described. This model allows to understand defect equilibrium and charge transport at ideal heterojunctions between materials simultaneously conducting electronic and ionic point defects and to explore how rectifying effects on the electronic or ionic currents may affect the chemical diffusion and voltage at the interfaces under polarization. We found qualitatively good agreement with experimental measurements of the electrical conductivity relaxation of La2NiO4+d thin films epitaxially grown on NdGaO3 (110) substrates when the possible oxygen exchange between film and substrate is taken into account. We discuss the implications of this model to understand space charge layer formation and chemical diffusion on oxide thin film heterostructures when exposed to high temperatures and different oxygen partial pressures.

cond-mat.mtrl-sci↗
arXiv2013

Probing surface electric field noise with a single ion

We report room-temperature electric field noise measurements combined with in-situ surface characterization and cleaning of a microfabricated ion trap. We used a single-ion electric field noise sensor in combination with surface cleaning and analysis tools, to investigate the relationship between electric field noise from metal surfaces in vacuum and the composition of the surface. These experiments were performed in a novel setup that integrates ion trapping capabilities with surface analysis tools. We find that surface cleaning of an aluminum-copper surface significantly reduces the level of electric field noise, but the surface does not need to be atomically clean to show noise levels comparable to those of the best cryogenic traps. The post-cleaning noise levels are low enough to allow fault-tolerant trapped-ion quantum information processing on a microfabricated surface trap.

physics.atom-ph↗
arXiv2013

Novel multiferroics with ferromagnetic phase induced in paraelectric antiferromagnets by electric field application

The phase diagram of a quantum paraelectric antiferromagnet EuTiO3 under an external electric field was calculated using Landau-Ginzburg-Devonshire theory. It was shown that the application of an external electric field E leads to the appearance of a ferromagnetic phase due to the magnetoelectric coupling. In particular, electric field application decreases the transition temperature TAFM to antiferromagnetic (AFM) phase and induces ferromagnetic (FM) phase, so that at some E field larger than the critical field (Ecr), TFM becomes higher than TAFM and the FM phase appears. Note that Ecr increases and magnetization decreases as the temperature increases. The value of the critical field Ecr = 0.40*10^6 V/cm we calculated appeared close to the value Ecr = 0.5*10^6 V/cm obtained recently by Ryan et al. with the help of density functional theory for EuTiO3 film under a compressive strain produced by substrate. At the fields E >0.83*10^6 V/cm, AFM disappears for all considered temperatures and so FM becomes the only stable magnetic phase. We find that ferromagnetic phase can be induced by an E-field in other paraelectric antiferromagnet oxides with a positive AFM-type magnetoelectric (ME) coupling coefficient and negative FM-type ME coupling coefficient. In particular, the critical E-field was estimated for another paraelectric antiferromagnet Sr0.7Ba0.3MnO3 as 0.2x10^5V/cm at 0 K. Analysis of the dependence of magnetization and antimagnetization on the external electric field and the polarization induced by the field, which yields the magnetoelectric coupling, is reported. The results show the possibility to control multiferroicity, including the FM and AFM phases, with help of an electric field application.

cond-mat.mtrl-sci↗
arXiv2013

Specific Heat Capacity of TiO2 Nanoparticles

We have calculated heat capacity of TiO2 nanoparticles in three stable polymorphs by applying size and surface effects on heat capacity of the bulk structure. The size and surface corrections were imposed on the acoustic and optical bulk phonons, separately. The model used in the present work is a simple modification of the model proposed by Wang et al. We applied the modified model to obtain the specific heat capacity of 10-100 nm TiO2 nanoparticles. A very good consistency is observed between the computational and experimental data. Based on the modified model, particles with sizes larger than 70 nm behave like bulk structure. In addition, the heat capacity of particles smaller than 15 nm become independent from their structure details while demonstrating a drastic increase.

cond-mat.mtrl-sci↗
arXiv2013

Synthesis of Self-assembled Iron Silicon Oxide Nanowires onto Single-crystalline Si(100)

Iron silicon oxide nanowire has been synthesized by putting single crystalline Si(100) wafer into ammonium iron sulfate, hydrogen peroxide, and triethylamine solution heated to from 70 to 100 degree in the air. The prepared iron silicon oxide nanowires with diameters of about 10nm (onto non etched Si(100) wafer) and about 75nm(onto etched Si(100) wafer) and their self assembles were characterized. The possible mechanism that accounted for the formation of iron silicon oxide nanowire is suggested based on experimental evidence.

cond-mat.mtrl-sci↗
arXiv2013

PAC study of the static and dynamic aspects of metal atom inside C60 cage

30 keV 111mCd and 50 keV 199mHg beams from ISOLDE were used to implant on preformed target of C60 with the thickness of 1 mg/cm2. Endofullerene compounds, viz.,111mCd@C60 and 199mHg@C60 formed during implantation were separated by filtration through micropore filter paper followed by solvent extraction. Dried samples of the endofullerene compounds were counted for the coincidence for the 151-245 keV cascade of 111mCd and 374-158 keV cascade for 199mHg for the TDPAC measurement on a six LaBr3 detector system coupled with digital electronics. The results indicate a single site occupied by the Cd atom in the fullerene cage with fast relaxation component which means that the Cd atom does move inside the cage at room temperature. The quadrupole interaction frequency and asymmetry parameter of the Cd atom occupying the site in C60 are WQ=8.14(42) Mrad/s and eta= 0.42(9) respectively with a site population of 28%. Fast relaxation constant is 0.003 ns-1 with a site contribution of 72%. On the other hand, Hg atom has two static sites of quadrupole frequencies, WQ1=281.60(16.9) Mrad/s and WQ2=202.30(22.7) Mrad/s. Respective asymmetry parameters are eta1=0.1(1) and eta2=0.2(1). The static components have a contribution of 40% with the rest 60% coming from the fast relaxing component.

cond-mat.mtrl-sci↗
arXiv2013

The thermoballistic approach to charge carrier transport in semiconductors

A comprehensive survey is given of the thermoballistic approach to charge carrier transport in semiconductors. This semiclassical approach bridges the gap between the drift-diffusion and ballistic ("thermionic") models of carrier transport, whose validity is limited to the range of very small and very large values, respectively, of the carrier mean free path. The physical concept underlying the thermoballistic approach, while incorporating basic features of the drift-diffusion and ballistic descriptions, constitutes a novel, unifying scheme. It is based on the introduction of "ballistic configurations" defined by a random partitioning of the length of a semiconducting sample into ballistic transport intervals, which are linked by points of local thermodynamic equilibrium at which carriers are emitted or absorbed. By averaging the carrier currents in the ballistic intervals over all ballistic configurations, a position-dependent thermoballistic current is derived for arbitrary magnitude of the carrier mean free path. This current is the key element of the thermoballistic concept and forms the point of departure of the calculation of various transport quantities. The present article starts out with an account of the standard drift-diffusion and ballistic transport models, and of a prototype model which paves the way for the fully developed form of that concept. In the main body of the article, a coherent exposition of the thermoballistic approach is given within a general formulation that takes into account arbitrarily shaped, spin-split potential energy profiles and spin relaxation during the carrier motion across ballistic intervals. The calculational procedures devised for implementing the thermoballistic concept are described. Specific examples relevant to present-day semiconductor and spintronics research are considered.

cond-mat.mtrl-sci↗
arXiv2013

Why Are There So Few Perovskite Ferroelectrics?

We use a combination of symmetry arguments and first-principles calculations to explore the connection between structural distortions and ferroelectricity in the perovskite family of materials. We explain the role of octahedral rotations in suppressing ferroelectricity in these materials and show that, as the tolerance factor decreases, rotations alone cannot fully suppress ferroelectricity. Our results show that it is cation displacements (`hidden' in Glazer notation) that accompany the rotations, rather than the rotations themselves, that play the decisive role in suppressing ferroelectricity in these cases. We use the knowledge gained in our analysis of this problem to explain the origin of ferroelectricity in $R3c$ materials such as FeTiO$_3$ and ZnSnO$_3$ and to suggest strategies for the design and synthesis of new perovskite ferroelectrics. Our results have implications not only for the fundamental crystal chemistry of the perovskites but also for the discovery of new functional materials.

cond-mat.mtrl-sci↗
arXiv2013

Theoretical study of the parity and time reversal violating interaction in solids

A new theoretical approach to study the properties in solids, which are sensitive to a change of densities of the valence electrons in atomic cores (hyperfine structure constants, parameters of space parity (P) and time reversal (T) violation interaction, etc.) is proposed and implemented. It uses the two-step concept of calculation of such properties which was implemented earlier for the case of molecules [Progr.\ Theor.\ Chem.\ Phys. B 15, 253 (2006)]. The approach is applied to evaluate the parameter $X$ describing electronic density gradient on the Pb nucleus that is required to interpret the proposed experiment on PbTiO$_3$ crystal [PRA, 72, 034501 (2005)] to search for the Schiff moment of the $^{207}$Pb nucleus because of its high sensitivity to the corresponding P,T-violating interactions. For comparison the $X$ parameter has also been calculated on the Pb nucleus for the $^1Σ^+$ state of $^{207}$PbO molecule using the same density functionals as those utilized in PbTiO$_3$ studies. The relativistic coupled-clusters approach with single, double and perturbative triple cluster amplitudes, applicable to a few atom systems and providing high accuracy for $X$, is also applied to the PbO case to estimate the accuracy of density functional studies.

physics.chem-ph↗
arXiv2013

Biomimetic method for metallic nanostructured mesoscopic models fabrication

Various metallic structures of complex shape, resembling natural objects such as plants, mushrooms, and seashells, were produced when growing nanowires by means of pulsed current electroplating in porous membranes. These structures occur as the result of nanowires self-assembling (biomimetics) if the electroplating is continued after the nanowires reach the membrane surface. By varying the membrane geometry and the pulsed current parameters, and alternating electroplating from two baths with different electrolytes, various models were fabricated, including a hollow container with wall thickness of 10-30 nm. The possibility of shape regulation for models was demonstrated: in certain conditions, mushroom- and shell-like convex-concave models of the same kind were obtained. The hierarchical structure of models at the nano-, micro- and mesoscopic levels is shown through fragmentation and chemical etching.

cond-mat.mtrl-sci↗
arXiv2013

Control of Spin in La(Mn,Zn)AsO Alloy by Carrier Doping

The control of spin without magnetic field is one of challenges in developing spintronic devices. In an attempt to solve this problem, we proposed a novel hypothetic LaMn0.5Zn0.5AsO alloy from two experimentally synthesized rare earth element transition metal arsenide oxides, i.e. LaMnAsO and LaZnAsO. On the basis of the first-principles calculations with strong-correlated correction, we found that the LaMn0.5Zn0.5AsO alloy is an antiferromagnetic semiconductor at ground state, while bipolar magnetic semiconductor at ferromagnetic state. Both electron and hole doping in the LaMn0.5Zn0.5AsO alloy induces the transition from antiferromagnetic to ferromagnetic, as well as semiconductor to half metal. In particular, the spin-polarization direction is switchable depending on the doped carrier's type. As carrier doping can be realized easily in experiment by applying a gate voltage, the LaMn0.5Zn0.5AsO alloy stands for a promising spintronic material to generate and control the spin-polarized carriers with electric field.

cond-mat.mtrl-sci↗
arXiv2013

Shungite as loosely packed fractal nets of graphene-based quantum dots

The current paper presents the first attempt to recreate the origin of shungite carbon at microscopic level basing on knowledge accumulated by graphene science. The main idea of our approach is that different efficacy of chemical transformation of primarily generated graphene flakes (aromatic lamellae in geological literature), subjected to oxidation/reduction reactions in aqueous environment, lays the foundation of the difference in graphite and shungite derivation under natural conditions. Low-efficient reactions in the case of graphite do not prevent from the formation of large graphite layers while high-efficient oxidation/reduction transforms the initial graphene flakes into those of reduced graphene oxide of ~1nm in size. Multistage aggregation of these basic structural units, attributed to graphene quantum dots of shungite, leads to the fractal structure of shungite carbon thus exhibiting it as a new allotrope of natural carbon. The suggested microscopic view has finds a reliable confirmation when analyzing the available empirical data.

cond-mat.mtrl-sci↗
arXiv2013

Vacancy trapping behaviors of hydrogen atoms in Ti3SiC2: a first-principles study

The behaviors of hydrogen (H) in MAX phase material Ti3SiC2 have been investigated using first-principles method. We show that a single H atom prefers to stay 1.01 Å down of the Si vacancy with solution energy of about -4.07 eV, lowerthan that in bulk Ti3SiC2. Multi H atoms exhibit a repulsive interaction at the Si vacancy. And up to five H atoms can be trapped by a Si vacancy without H2 molecules formation. These results suggest the strong vacancy trapping characteristic of H atoms in Ti3SiC2. Meanwhile, the barrier for H diffusion from an interstitial site to a vacancy is 1.17 eV, which is much larger than that in metals, indicating that to some extent H atoms can not easily migrate or aggregate to form bubble in Ti3SiC.

cond-mat.mtrl-sci↗
arXiv2013

Closure and commutability results for Gamma-limits and the geometric linearization and homogenization of multi-well energy functionals

Under a suitable notion of equivalence of integral densities we prove a $Γ$-closure theorem for integral functionals: The limit of a sequence of $Γ$-convergent families of such functionals is again a $Γ$-convergent family. Its $Γ$-limit is the limit of the $Γ$-limits of the original problems. This result not only provides a common basic principle for a number of linearization and homogenization results in elasticity theory. It also allows for new applications as we exemplify by proving that geometric linearization and homogenization of multi-well energy functionals commute.

math.AP↗
arXiv2013

First principles study of pentacene on Au(111)

We investigate the atomic and electronic structure of a single layer of pentacene on the Au(111) surface using density functional theory. To find the candidate structures we strain match the pentacene crystal geometry with the Au(111) surface, in this way we find pentacene overlayer structures with a low strain. We show that the geometries obtained with this approach has lower energy than previous proposed surface geometries of pentacene on Au(111). We also show that the geometry and workfunction of the obtained structures are in excellent agreement with experimental data.

cond-mat.mtrl-sci↗