Atomistic Study of Surface Polarization in Superconducting Perovskites

AbstractWe simulated the surface relaxation of the cubic perovskite paraelectric SrTiO3 crystal. The atomic positions in ten near-surface layers placed into the electrostatic field of the remainder of the crystal were calculated. Two-dimensional, periodic slab model was combined with the pair potentials treated in terms of the shell-model. Our calculations show that Ti+4, Sr+2 and O−2 ions shift differently from their crystal sites. This leads to a creation of a dipole moment near the surface which might give the paraelectric crystal the ferroelectric properties.

Download Full-text

[001] Surface Structure in SrTiO3 — Atomistic Study

Surface Review and Letters ◽

10.1142/s0218625x98000633 ◽

1998 ◽

Vol 05 (01) ◽

pp. 341-345 ◽

Cited By ~ 3

Author(s):

Eugene Heifets ◽

Simon Dorfman ◽

David Fuks ◽

Eugene Kotomin ◽

Alex Gordon

Keyword(s):

Dipole Moment ◽

External Field ◽

Polarization Effect ◽

Surface Region ◽

Superconducting Films ◽

Surface Layers ◽

Near Surface ◽

Atomistic Study ◽

Model Technique ◽

Thin Superconducting Films

Thin superconducting films attract great attention as a promising material for plenty of applications. The surface determines most of the physical properties of these films. We studied the polarization effect for the [001] surface of perovskite ABO 3 superconducting crystals on the example of SrTiO 3. Optimization of the ion positions in several surface layers is provided. These ions are placed in the external field of the rest crystal. The interaction between ions is described by means of the shell model technique. We show that Ti +4, Sr 2+ and O -2 ions displace differently from their crystalline sites, which leads to the creation of a dipole moment in the near-surface region.

Download Full-text

ATOMISTIC CALCULATIONS OF (110) SURFACE RELAXATION FOR PEROVSKITE TITANATES

Surface Review and Letters ◽

10.1142/s0218625x99001360 ◽

1999 ◽

Vol 06 (06) ◽

pp. 1215-1219 ◽

Cited By ~ 5

Author(s):

E. HEIFETS ◽

E. A. KOTOMIN ◽

G. BORSTEL

Keyword(s):

Shell Model ◽

Dipole Moments ◽

Surface Relaxation ◽

Surface Layers ◽

Near Surface ◽

Induced Dipole ◽

Atomistic Calculations ◽

Strong Surface ◽

First Time

Using a shell model, for the first time the (110) surface relaxations are calculated for SrTiO 3 and BaTiO 3 perovskites. The positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are calculated. Strong surface rumpling and surface-induced dipole moments perpendicular to the surface are predicted for both the O-terminated and Ti-terminated surfaces.

Download Full-text

Calculations of Surface Structure for SrTiO3 Perovskite

MRS Proceedings ◽

10.1557/proc-671-q9.1 ◽

2001 ◽

Vol 672 ◽

Author(s):

E. Heifetsa ◽

R.I. Eglitisb ◽

E.A. Kotomin ◽

G. Borstelb

Keyword(s):

Ab Initio ◽

Density Functional ◽

Dipole Moments ◽

Surface Relaxation ◽

Surface Layers ◽

Functional Theory ◽

Near Surface ◽

Hartree Fock ◽

Semi Empirical

ABSTRACTWe present and discuss results of the calculations for SrTiO3 (100) surface relaxation with different terminations (SrO and TiO2) using a semi-empirical shell model (SM) as well as abinitio methods based on Hartree-Fock (HF) and Density Functional Theory (DFT) formalisms. Using the SM, the positions of atoms in 16 near-surface layers placed atop a slab of rigid ions are optimized. This permits us determination of surface rumpling and surfaceinduced dipole moments (polarization) for different terminations. We also compare results of the ab initio calculations based on both HF with the DFT-type electroncorrelation corrections, several DFT with different exchange-correlation functionals, and hybrid exchange techniques. OurSM results for the (100) surfaces are in a good agreement with both our ab initio calculations and LEED experiments.

Download Full-text

Origin of the Larger Values of Total Cross Section for Helium Scattering from Isolated Atomic Steps

Dhaka University Journal of Science ◽

10.3329/dujs.v60i2.11532 ◽

2012 ◽

Vol 60 (2) ◽

pp. 271-275

Author(s):

K.S. Sultana ◽

W. Allison ◽

M.Z. Hafiz

Keyword(s):

Cross Section ◽

Surface Relaxation ◽

Surface Layers ◽

Helium Atoms ◽

Pair Potentials ◽

Surface Electronic Structure ◽

Large Step ◽

Helium Scattering ◽

Large Charge ◽

Effect Of Surface

The effect of surface relaxation and the electronic re-arrangement in the vicinity of a step on the total step cross section for helium scattering is investigated. A realistic helium interaction potential at a Cu(001) step is modeled by summing non-spherical pair potentials which allows for the possibility of varying the smoothing across the surface due to the itinerant aspects of the surface electronic structure. Numerical calculations reveal a significant increase in the magnitude of the total step cross section with large charge re-arrangement in the vicinity of the step. Also, the relaxation of surface layers has no effect whatsoever. The present study clearly shows that the origin of the experimentally observed large step cross section is the hard wall scattering from charge re-arrangement in the proximity of the step. Further, the charge re-arrangements probed by thermal helium atoms must be greater than predicted by pairwise models.DOI: http://dx.doi.org/10.3329/dujs.v60i2.11532 Dhaka Univ. J. Sci. 60(2): 271-275, 2012 (July)

Download Full-text

Investigation of inhomogeneous structures of near-surface-layers in ion-implanted silicon

Thin Solid Films ◽

10.1016/s0040-6090(97)01082-1 ◽

1998 ◽

Vol 319 (1-2) ◽

pp. 39-43 ◽

Cited By ~ 1

Author(s):

Z Swiatek ◽

J.T Bonarski ◽

R Ciach ◽

Z.T Kuznicki ◽

I.M Fodchuk ◽

...

Keyword(s):

Surface Layers ◽

Near Surface ◽

Ion Implanted

Download Full-text

Two-dimensional elastic pseudo-spectral modeling of wide-aperture seismic array data with application to the Wichita Uplift-Anadarko Basin region of southwestern Oklahoma

Bulletin of the Seismological Society of America ◽

10.1785/bssa08006a1677 ◽

1990 ◽

Vol 80 (6A) ◽

pp. 1677-1695 ◽

Cited By ~ 2

Author(s):

Ik Bum Kang ◽

George A. McMechan

Keyword(s):

Large Scale ◽

Deep Structure ◽

Sedimentary Basins ◽

P Wave ◽

Two Dimensional ◽

Anadarko Basin ◽

Near Surface ◽

University Of Texas ◽

Wide Aperture ◽

The University

Abstract Full wave field modeling of wide-aperture data is performed with a pseudospectral implementation of the elastic wave equation. This approach naturally produces three-component stress and two-component particle displacement, velocity, and acceleration seismograms for compressional, shear, and Rayleigh waves. It also has distinct advantages in terms of computational requirements over finite-differencing when data from large-scale structures are to be modeled at high frequencies. The algorithm is applied to iterative two-dimensional modeling of seismograms from a survey performed in 1985 by The University of Texas at El Paso and The University of Texas at Dallas across the Anadarko basin and the Wichita Mountains in southwestern Oklahoma. The results provide an independent look at details of near-surface structure and reflector configurations. Near-surface (<3 km deep) structure and scattering effects account for a large percentage (>70 per cent) of the energy in the observed seismograms. The interpretation of the data is consistent with the results of previous studies of these data, but provides considerably more detail. Overall, the P-wave velocities in the Wichita Uplift are more typical of the middle crust than the upper crust (5.3 to 7.1 km/sec). At the surface, the uplift is either exposed as weathered outcrop (5.0 to 5.3 km/sec) or is overlain with sediments of up to 0.4 km in thickness, ranging in velocity from 2.7 to 3.4 km/sec, generally increasing with depth. The core of the uplift is relatively seismically transparent. A very clear, coherent reflection is observed from the Mountain View fault, which dips at ≈40° to the southwest, to at least 12 km depth. Velocities in the Anadarko Basin are typical of sedimentary basins; there is a general increase from ≈2.7 km/sec at the surface to ≈5.9 km/sec at ≈16 km depth, with discontinuous reflections at depths of ≈8, 10, 12, and 16 km.

Download Full-text

Flow Cell with High-Resolution Spatial and Temporal Degree of Saturation Measurements for Two-Dimensional Near-Surface Phenomena Using Unsaturated Transparent Soil

Geotechnical Testing Journal ◽

10.1520/gtj20200082 ◽

2021 ◽

Vol 44 (6) ◽

pp. 20200082

Author(s):

Greg Siemens ◽

Chris Oldroyd ◽

Ryley Beddoe

Keyword(s):

High Resolution ◽

Flow Cell ◽

Degree Of Saturation ◽

Two Dimensional ◽

Surface Phenomena ◽

Near Surface ◽

Transparent Soil

Download Full-text

Important factors in the tracking of tropical cyclones in operational models

Journal of Applied Meteorology and Climatology ◽

10.1175/jamc-d-20-0175.1 ◽

2021 ◽

Author(s):

Timothy Marchok

Keyword(s):

Geophysical Fluid Dynamics Laboratory ◽

Surface Layers ◽

Individual Parameter ◽

Near Surface ◽

Parameter Configuration ◽

Multiple Variables ◽

The Mean ◽

Tropical Cyclone Center ◽

Multiple Configurations ◽

Better Than

AbstractMultiple configurations of the Geophysical Fluid Dynamics Laboratory vortex tracker are tested to determine a setup that produces the best representation of a model forecast tropical cyclone center fix for the purpose of providing track guidance with the highest degree of accuracy and availability. Details of the tracking algorithms are provided, including descriptions of both the Barnes analysis used for center-fixing most variables and a separate scheme used for center-fixing wind circulation. The tracker is tested by running multiple configurations on all storms from the 2015-2017 hurricane seasons in the Atlantic and eastern Pacific Basins using forecasts from two operational National Weather Service models, the Global Forecast System (GFS) and the Hurricane Weather Research and Forecast (HWRF) model. A configuration that tracks only 850 mb geopotential height has the smallest forecast track errors of any configuration based on an individual parameter. However, a configuration composed of the mean of eleven parameters outperforms any of the configurations that are based on individual parameters. Configurations composed of subsets of the eleven parameters and including both mass and momentum variables provide results comparable to or better than the full 11-parameter configuration. In particular, a subset configuration with thickness variables excluded generally outperforms the 11-parameter mean, while one composed of variables from only the 850 mb and near-surface layers performs nearly as well as the 11-parameter mean. Tracker configurations composed of multiple variables are more reliable in providing guidance through the end of a forecast period than are tracker configurations based on individual parameters.

Download Full-text

Experiments on wind-driven heat exchange processes over melting snow

10.5194/egusphere-egu21-10182 ◽

2021 ◽

Author(s):

Michael Haugeneder ◽

Tobias Jonas ◽

Dylan Reynolds ◽

Michael Lehning ◽

Rebecca Mott

Keyword(s):

Snow Cover ◽

Surface Wind ◽

Infrared Camera ◽

Snow Accumulation ◽

Internal Boundary ◽

Small Scale ◽

Snow Melt ◽

Two Dimensional ◽

Atmospheric Conditions ◽

Near Surface

Snowmelt runoff predictions in alpine catchments are challenging because of the high spatial variability of the snow cover driven by various snow accumulation and ablation processes. In spring, the coexistence of bare and snow-covered ground engages a number of processes such as the enhanced lateral advection of heat over partial snow cover, the development of internal boundary layers, and atmospheric decoupling effects due to increasing stability at the snow cover. The interdependency of atmospheric conditions, topographic settings and snow coverage remains a challenge to accurately account for these processes in snow melt models. In this experimental study, we used an Infrared Camera (VarioCam) pointing at thin synthetic projection screens with negligible heat capacity. Using the surface temperature of the screen as a proxy for the air temperature, we obtained a two-dimensional instantaneous measurement. Screens were installed across the transition between snow-free and snow-covered areas. With IR-measurements taken at 10Hz, we capture the dynamics of turbulent temperature fluctuations over the patchy snow cover at high spatial and temporal resolution. From this data we were able to obtain high-frequency, two-dimensional windfield estimations adjacent to the surface.Preliminary results show the formation of a stable internal boundary layer (SIBL), which was temporally highly variable. Our data suggest that the SIBL height is very shallow and strongly sensitive to the mean near-surface wind speed. Only strong gusts were capable of penetrating through this SIBL leading to an enhanced energy input to the snow surface.With these type of results from our experiments and further measurements this spring we aim to better understand small scale energy transfer processes over patch snow cover and it&#8217;s dependency on the atmospheric conditions, enabling to improve parameterizations of these processes in coarser-resolution snow melt models.

Download Full-text