scholarly journals Infrared Optical Conductivity of Bulk Bi2Te2Se

Crystals ◽  
2020 ◽  
Vol 10 (7) ◽  
pp. 553
Author(s):  
Elena S. Zhukova ◽  
Hongbin Zhang ◽  
Victor P. Martovitskiy ◽  
Yurii G. Selivanov ◽  
Boris P. Gorshunov ◽  
...  
Keyword(s):  
Optical Conductivity ◽  
Near Infrared ◽  
Three Dimensional ◽  
Frequency Increase ◽  
Band Structure Calculations ◽  
Infrared Measurements ◽  
Dirac Materials ◽  
Bulk Carriers ◽  
Structure Calculations ◽  
Complex Dispersion

Mid- and near-infrared measurements reveal that the optical conductivity of the three-dimensional topological insulator, Bi2Te2Se, is dominated by bulk carriers and shows a linear-in-frequency increase at 0.5 to 0.8 eV. This linearity might be interpreted as a signature of three-dimensional (bulk) Dirac bands; however, band-structure calculations show that transitions between bands with complex dispersion contribute instead to the inter-band optical conductivity at these frequencies and, hence, the observed linearity is accidental. These results warn against the oversimplified interpretations of optical-conductivity measurements in different Dirac materials.

Probing Optical Transitions in Porous Silicon by Reflectance Spectroscopy in the Near Infrared, Visible and UV

1994 ◽  
Vol 358 ◽  
Author(s):  
W. Theiβ ◽  
R. Arens-Fischer ◽  
M. Arntzen ◽  
M.G. Berger ◽  
S. Frohnhoff ◽  
...  
Keyword(s):  
Porous Silicon ◽  
Dielectric Function ◽  
Near Infrared ◽  
Solid Phase ◽  
Pore Wall ◽  
Reflectance Spectroscopy ◽  
Wall Material ◽  
Bulk Silicon ◽  
Band Structure Calculations ◽  
Structure Calculations

ABSTRACTReflectance spectroscopy has been used to obtain the dielectric function of the solid phase of porous silicon. The method is based on a fit of a parameterized dielectric function model to measured spectra. A crucial step in the procedure is the 'dielectric averaging' of the microscopic dielectric function of the pore wall material to the macroscopic effective dielectric function which governs the optical properties.Results are given for heavily and moderately p-doped samples of various porosities. For the latter large differences to bulk silicon have been found. The obtained dielectric functions are compared to the results of band structure calculations taken from literature.

Unusual Bonding in Ternary Nitrides: Preparation, Structure and Properties of Ce2MnN3.

1998 ◽  
Vol 53 (1) ◽  
pp. 63-74 ◽  
Author(s):  
Rainer Niewa ◽  
Grigori V. Vajenine ◽  
Francis J. DiSalvo ◽  
Haihua Luob ◽  
William B. Yelon
Keyword(s):  
Electrical Resistivity ◽  
Three Dimensional ◽  
Structure And Properties ◽  
Electronic Effects ◽  
Nitrogen Gas ◽  
Metallic Behavior ◽  
Band Structure Calculations ◽  
Dimensional Network ◽  
Square Planar ◽  
Structure Calculations

Ce2MnN3 was prepared by reaction of cerium nitride and manganese with nitrogen gas at 900 °C. It crystallizes isotypic to AC2MN3 (Ac = U, Th; M = Cr, Mn) and Ce2CrN3, space group Immm (No. 71), a = 3.74994(6) Å, b = 3.44450(6) Å and c = 12.4601(2) Å. The manganese atoms are coordinated in a nearly square planar fashion by four nitrogen atoms. These corner-connected MnN4 units form infinite 1∞[MnN2N2/2] chains, which run parallel to each other along the crystallographic a-axis, forming the motif of hexagonal rod packing. Cerium atoms connect the chains into a three-dimensional network. The results of measurements of the magnetic susceptibility, as well as of the electrical resistivity suggest metallic behavior. Electronic effects leading to shorter bonds between manganese and bridging nitrogen atoms than between manganese and terminal nitrogen atoms in the 1∞[MnN2N2/2] chains were investigated through extended Hückel and LMTO band structure calculations. Issues pertaining to stability of this and some other nitridometallate structures are discussed.

Polygermyne: Germanium sheet polymers with efficient near-infrared luminescence

2001 ◽  
Vol 667 ◽  
Author(s):  
Günther Vogg ◽  
Martin S. Brandt ◽  
Lex J.-P. Meyer ◽  
Martin Stutzmann ◽  
Zoltán Hajnal ◽  
...  
Keyword(s):  
Near Infrared ◽  
Stokes Shift ◽  
Layered Crystal ◽  
Zintl Phase ◽  
Infrared Luminescence ◽  
Band Structure Calculations ◽  
Optical And Electronic Properties ◽  
Direct Band ◽  
Topotactic Transformation ◽  
Structure Calculations

ABSTRACTThe structural, optical and electronic properties of the Ge sheet polymer poylgermyne are summarized. Prepared via topotactic transformation of Zintl-phase CaGe2, (GeH)n forms a layered crystal in a tr6 stacking sequence with a distance of 5.65 Å between adjacent layers. The photoluminescence at 1.3 eV is excited nearly resonantly with a Stokes shift of 0.2 eV. Together with band structure calculations this shows that polygermyne has a direct band gap.

Ternary K2Zn5As4-type pnictides Rb2Cd5As4and Rb2Zn5Sb4, and the solid solution Rb2Cd5(As,Sb)4

2013 ◽  
Vol 69 (5) ◽  
pp. 455-459 ◽  
Author(s):  
Hua He ◽  
Stanislav S. Stoyko ◽  
Arthur Mar ◽  
Svilen Bobev
Keyword(s):  
Solid Solution ◽  
Three Dimensional ◽  
Solid Solution Phase ◽  
Direct Reaction ◽  
Zintl Phases ◽  
Group V ◽  
Band Structure Calculations ◽  
Pearson Symbol ◽  
Small Band ◽  
Structure Calculations

Dirubidium pentacadmium tetraarsenide, Rb2Cd5As4, dirubidium pentazinc tetraantimonide, Rb2Zn5Sb4, and the solid-solution phase dirubidium pentacadmium tetra(arsenide/antimonide), Rb2Cd5(As,Sb)4[or Rb2Cd5As3.00(1)Sb1.00(1)], have been prepared by direct reaction of the component elements at high temperature. These compounds are charge-balanced Zintl phases and adopt the orthorhombic K2Zn5As4-type structure (Pearson symboloC44), featuring a three-dimensional [M5Pn4]2−framework [M= Zn or Cd;Pnis a pnicogen or Group 15 (Group V) element] built of linkedMPn4tetrahedra, and large channels extending along thebaxis which host Rb+cations. The As and Sb atoms in Rb2Cd5(As,Sb)4are randomly disordered over the two available pnicogen sites. Band-structure calculations predict that Rb2Cd5As4is a small-band-gap semiconductor and Rb2Zn5Sb4is a semimetal.

The Stannide LiRh3Sn5 – Synthesis, Structure, and Chemical Bonding

2005 ◽  
Vol 60 (9) ◽  
pp. 933-939 ◽  
Author(s):  
Puravankara Sreeraj ◽  
Dirk Johrendt ◽  
Helen Müller ◽  
Rolf-Dieter Hoffmann ◽  
Zhiyun Wu ◽  
...  
Keyword(s):  
Band Structure ◽  
Electronic Band Structure ◽  
Three Dimensional ◽  
Structure Type ◽  
Lithium Content ◽  
Single Crystal Diffraction ◽  
Electronic Band ◽  
X Ray ◽  
Band Structure Calculations ◽  
Structure Calculations

The lithium rhodium stannide LiRh3Sn5 was synthesized from the elements in a sealed tantalum tube and investigated via X-ray powder and single crystal diffraction: Pbcm, a = 538.9(1), b = 976.6(3), c = 1278.5(3) pm, wR2 = 0.0383, 1454 F2 values, and 44 variables. Refinement of the occupancy parameters revealed a lithium content of 92(6)%. LiRh3Sn5 crystallizes with a new structure type. The structure is built up from a complex three-dimensional [Rh3Sn5] network, in which the lithium atoms fill channels in the b direction. The [Rh3Sn5] network is governed by Rh-Rh (274 - 295 pm), Rh-Sn (262 - 287 pm), and Sn-Sn (289 - 376 pm) interactions. The lithium atoms have CN 13 (4 Rh+9 Sn). Electronic band structure calculations and the COHP bond analysis reveal strong Rh−Sn bonds and also significant Rh−Rh bonding within the Rh3Sn5 network, which is additionally stabilized by weak but frequent Sn−Sn interactions.

scholarly journals Structure, Chemical Bonding and 119Sn Mössbauer Spectroscopy of LaRhSn and CeRhSn

2005 ◽  
Vol 60 (10) ◽  
pp. 1036-1042 ◽  
Author(s):  
Tobias Schmidt ◽  
Dirk Johrendt ◽  
C. Peter Sebastian ◽  
Rainer Pöttgen ◽  
Kazimierz Łątka ◽  
...  
Keyword(s):  
Rare Earth ◽  
High Frequency ◽  
Three Dimensional ◽  
Strong Mixing ◽  
X Ray ◽  
Band Structure Calculations ◽  
Trigonal Prismatic Coordination ◽  
Structure Calculations ◽  
Trigonal Prismatic ◽  
The Rare Earth

The rare earth (RE) stannides LaRhSn and CeRhSn were prepared from the elements by arcmelting or by reactions in sealed tantalum tubes in a high-frequency furnace. The structures have been refined from X-ray single crystal diffractometer data: ZrNiAl type, P6̅2̅m, a = 748.74(5), c = 422.16(3) pm, wR2 = 0.0307, 310 F2 values for LaRhSn and a = 745.8(1), c = 408.62(9) pm, wR2 = 0.0397, 354 F2 values for CeRhSn with 14 variables per refinement. The structures contain two crystallographically different rhodium sites which both have a tricapped trigonal prismatic coordination: [Rh1Sn3RE6] and [Rh2Sn6RE3]. Together the rhodium and tin atoms (280 - 288 pm Rh-Sn distances in LaRhSn and 277 - 285 pm in CeRhSn) build up three-dimensional [RhSn] networks in which the rare earth atoms fill distorted hexagonal channels. DFT band structure calculations reveal a large cerium 4 f contribution at the Fermi level and a strong mixing of cerium 5d/4 f with rhodium 4d orbitals. These results are in agreement with the short Ce-Rh bonds (304 and 309 pm) and also with the electronic and magnetic properties. 119Sn Mössbauer spectra of LaRhSn and CeRhSn show a single tin site at isomer shifts of δ = 1.98(2) (LaRhSn) and 1.79(1) mm/s (CeRhSn) subject to quadrupole splitting of Δ EQ = 0.79(4) (LaRhSn) and 1.12(3) mm/s (CeRhSn). The 1.8 K data show no transferred hyperfine field at the tin site for CeRhSn.

Positron annihilation study for cadmium (electronic structure and enhancement effect)

Open Physics ◽  
2003 ◽  
Vol 1 (4) ◽  
Author(s):  
A. Hamid
Keyword(s):  
Atomic Orbital ◽  
Three Dimensional ◽  
Maximum Deviation ◽  
Enhancement Effect ◽  
Annihilation Radiation ◽  
Augmented Plane Wave ◽  
Band Structure Calculations ◽  
Positron Wave Function ◽  
Positron Annihilation Study ◽  
Structure Calculations

AbstractThe three dimensional electron density in momentum space ρ(p) and in wave vector space n(k) was reconstructed for cadmium (Cd). The measurements were performed using the two dimensional angular correlation of annihilation radiation (2D-ACAR) technique. Enhanced contributions in the spectra were observed around 5.5 mrad, discussed in terms of a Kahana-like enhancement effect. From another viewpoint, Fermi radii were analyzed in the (λM K), (ALM) and (AHK) planes, and they showed a maximum deviation of about 4% from the free electron Fermi radius. Moreover, comparisons to a radio-frequency size effect (RFSE) experiment and theoretical band structure calculations (using augmented plane wave (APW), linear combination of atomic orbital (LCAO) and linear muffin tin orbital (LMTO) methods) were examined. The results showed a qualitative agreement with both APW and LCAO calculations. However, a favorable agreement with the APW method was determined via Fermi surface dimensions. The differences of bands' occupation of n(k) between the current work and the APW method were argued in view of positron wave function in Cd.

Urban energetics applications and Geomatic technologies in a Smart City perspective

2015 ◽  
Vol 6 (1) ◽  
pp. 19-29 ◽  
Author(s):  
G. Bitelli ◽  
P. Conte ◽  
T. Csoknyai ◽  
E. Mandanici
Keyword(s):  
Smart City ◽  
Laser Scanning ◽  
Near Infrared ◽  
Three Dimensional ◽  
Energy Sector ◽  
Primary Objective ◽  
Airborne Lidar ◽  
City Management ◽  
Urban Context ◽  
Research Areas

The management of an urban context in a Smart City perspective requires the development of innovative projects, with new applications in multidisciplinary research areas. They can be related to many aspects of city life and urban management: fuel consumption monitoring, energy efficiency issues, environment, social organization, traffic, urban transformations, etc. Geomatics, the modern discipline of gathering, storing, processing, and delivering digital spatially referenced information, can play a fundamental role in many of these areas, providing new efficient and productive methods for a precise mapping of different phenomena by traditional cartographic representation or by new methods of data visualization and manipulation (e.g. three-dimensional modelling, data fusion, etc.). The technologies involved are based on airborne or satellite remote sensing (in visible, near infrared, thermal bands), laser scanning, digital photogrammetry, satellite positioning and, first of all, appropriate sensor integration (online or offline). The aim of this work is to present and analyse some new opportunities offered by Geomatics technologies for a Smart City management, with a specific interest towards the energy sector related to buildings. Reducing consumption and CO2 emissions is a primary objective to be pursued for a sustainable development and, in this direction, an accurate knowledge of energy consumptions and waste for heating of single houses, blocks or districts is needed. A synoptic information regarding a city or a portion of a city can be acquired through sensors on board of airplanes or satellite platforms, operating in the thermal band. A problem to be investigated at the scale A problem to be investigated at the scale of the whole urban context is the Urban Heat Island (UHI), a phenomenon known and studied in the last decades. UHI is related not only to sensible heat released by anthropic activities, but also to land use variations and evapotranspiration reduction. The availability of thermal satellite sensors is fundamental to carry out multi-temporal studies in order to evaluate the dynamic behaviour of the UHI for a city. Working with a greater detail, districts or single buildings can be analysed by specifically designed airborne surveys. The activity has been recently carried out in the EnergyCity project, developed in the framework of the Central Europe programme established by UE. As demonstrated by the project, such data can be successfully integrated in a GIS storing all relevant data about buildings and energy supply, in order to create a powerful geospatial database for a Decision Support System assisting to reduce energy losses and CO2 emissions. Today, aerial thermal mapping could be furthermore integrated by terrestrial 3D surveys realized with Mobile Mapping Systems through multisensor platforms comprising thermal camera/s, laser scanning, GPS, inertial systems, etc. In this way the product can be a true 3D thermal model with good geometric properties, enlarging the possibilities in respect to conventional qualitative 2D images with simple colour palettes. Finally, some applications in the energy sector could benefit from the availability of a true 3D City Model, where the buildings are carefully described through three-dimensional elements. The processing of airborne LiDAR datasets for automated and semi-automated extraction of 3D buildings can provide such new generation of 3D city models.

scholarly journals Fermi surface of the skutterudite CoSb3 : Quantum oscillations and band-structure calculations

2021 ◽  
Vol 103 (8) ◽  
Author(s):  
M. Naumann ◽  
P. Mokhtari ◽  
Z. Medvecka ◽  
F. Arnold ◽  
M. Pillaca ◽  
...  
Keyword(s):  
Band Structure ◽  
Fermi Surface ◽  
Quantum Oscillations ◽  
Band Structure Calculations ◽  
Structure Calculations
Sign in / Sign up

Export Citation Format

Share Document