FORMATION OF INTERFACES AND TEMPLATES IN THE Si(111)-Cr SYSTEM

1995 ◽  
Vol 02 (04) ◽  
pp. 439-449 ◽  
Author(s):  
N.I. PLUSNIN ◽  
N.G. GALKIN ◽  
V.G. LIFSHITS ◽  
S.A. LOBACHEV
Keyword(s):  
Room Temperature ◽  
Structural Phase ◽  
High Mobility ◽  
Epitaxial Films ◽  
Semiconductor Film ◽  
Structural Phase Transitions ◽  
Surface Phase ◽  
Surface Phases ◽  
Formation Conditions ◽  
Cr System

The literature data and new data on investigation of the Si(111)-Cr system were systematized to the diagram of structural phase transitions. The ranges on this diagram give the formation conditions of various phases and reflect the mechanism of the Cr/Si (111) and CrSi 2/ Si (111) interface formation during room-temperature Cr deposition following annealing. The proofs of the multilayer surface phase formation and the data about transitions between the multilayer surface phases and bulk silicides during formation of the Cr/Si (111) and CrSi 2/ Si (111) interfaces were presented. The investigation of A- and B-type CrSi 2 templates formation was carried out. It was discovered that nucleation conditions and, in particular, the type of surface phases determine the azimuthal orientation of the epitaxial CrSi 2 islands relative to Si (111) under their nucleation. The A- and B-type CrSi 2 epitaxial films were grown by means of the template technique. The A-type CrSi 2 semiconductor film with low concentration and high mobility of holes was obtained.

Temperature-induced structural phase transitions in RERhSn (RE = Y, Gd-Tm, Lu)

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Simon Engelbert ◽  
Rolf-Dieter Hoffmann ◽  
Jutta Kösters ◽  
Steffen Klenner ◽  
Rainer Pöttgen
Keyword(s):  
Rare Earth ◽  
Phase Transitions ◽  
Driving Force ◽  
Room Temperature ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Line Broadening ◽  
X Ray Diffraction ◽  
Temperature Dependent ◽  
X Ray

Abstract The structures of the equiatomic stannides RERhSn with the smaller rare earth elements Y, Gd-Tm and Lu were reinvestigated on the basis of temperature-dependent single crystal X-ray diffraction data. GdRhSn crystallizes with the aristotype ZrNiAl at 293 and 90 K. For RE = Y, Tb, Ho and Er the HP-CeRuSn type (approximant with space group R3m) is already formed at room temperature, while DyRhSn adopts the HP-CeRuSn type below 280 K. TmRhSn and LuRhSn show incommensurate modulated variants with superspace groups P31m(1/3; 1/3; γ) 000 (No. 157.1.23.1) (γ = 3/8 for TmRhSn and γ = 2/5 for LuRhSn). The driving force for superstructure formation (modulation) is a strengthening of Rh–Sn bonding. The modulation is expressed in a 119Sn Mössbauer spectrum of DyRhSn at 78 K through line broadening.

Relation between tolerance factor and Tc in Aurivillius compounds

2001 ◽  
Vol 16 (11) ◽  
pp. 3139-3149 ◽  
Author(s):  
Donají Y. Suárez ◽  
Ian M. Reaney ◽  
William E. Lee
Keyword(s):  
Room Temperature ◽  
Ferroelectric Phase ◽  
Structural Phase ◽  
Tolerance Factor ◽  
Structural Phase Transitions ◽  
Aurivillius Phases ◽  
Ferroelectric Phase Transition Temperature ◽  
Transmission Electron ◽  
Octahedral Tilting ◽  
Permittivity Measurements

The structures and microstructures of a range of Aurivillius phases were investigated by transmission electron microscopy. Systematic rows of superlattice reflections arising from tilting of octahedra around the c axis were identified, and their intensities at room temperature were shown to diminish as the tolerance factor (t) of the perovskite blocks increased. For compounds with t's approaching 1, no superlattice reflections were observed. the paraelectric-to-ferroelectric phase transition temperature (Tc) was monitored through permittivity measurements as a function of temperature, and Tc was also shown to decrease as t increased. Consequently, the onset of octahedral tilting and Tc appeared to be strongly related Aurivillius phases. Planar defects arising from the structural phase transitions and from stacking irregularities were also discussed.

Release of Tetrahydrofuran, Structural Phase Transitions and Dynamic Relaxation Processes in Ca (BH4)2

2012 ◽  
Vol 184 ◽  
pp. 24-32 ◽  
Author(s):  
Annalisa Paolone ◽  
O. Palumbo ◽  
P. Rispoli ◽  
Rosario Cantelli ◽  
E. Rönnebro ◽  
...  
Keyword(s):  
Phase Transitions ◽  
Room Temperature ◽  
Structural Phase ◽  
Young Modulus ◽  
Relaxation Processes ◽  
Structural Phase Transitions ◽  
Exponential Factor ◽  
Β Phase ◽  
Α Phase ◽  
Calcium Borohydride

Various calcium borohydride samples were investigated by means of combined measurements of thermogravimetry and mass spectrometry, and anelastic spectroscopy. On heating, the release of 2-5% tetrahydrofuran (THF) is detected in all the samples at temperatures below ~480 K, even in those which were previously thermally treated, according to procedures known from the literature, in order to remove the solvent. Dehydrogenation takes place above 480 K. Above room temperature the temperature dependence of the Young modulus of Ca (BH4)2clearly monitors the release of THF and two irreversible structural phase transitions: from the α to the α’ phase around 460 K and from the α’ to the β phase, nearly completely evolved around 590 K. Moreover, the coefficient of elastic energy dissipation presents two dynamic processes below room temperature; a peak around 120 K characterized by an activation energy of 0.20 eV and a pre-exponential factor typical of atom-cluster relaxations, that we attributed to the dynamics of THF molecules retained in the borohydride lattice, and a peak around 200 K, possibly due to the relaxation of H vacancies.

Thermodynamics of Oxygen Chemistry on PbTiO3 and LaMnO3 (001) Surfaces

2011 ◽  
Vol 1309 ◽  
Author(s):  
Ghanshyam Pilania ◽  
R. Ramprasad
Keyword(s):  
Phase Diagram ◽  
High Temperatures ◽  
First Principles ◽  
Room Temperature ◽  
Oxidation Catalysis ◽  
Vacancy Formation ◽  
Surface Phase ◽  
Surface Phases ◽  
O Vacancy ◽  
Low Pressures

ABSTRACTWe present a first principles thermodynamic study of O ad-atom and vacancy formation on the AO- and BO2-terminated (001) surfaces of the PbTiO3 (PTO) and LaMnO3 (LMO) cubic perovskites. Our results show that, owing to the highly energetically unfavorable nature of O vacancy formation on these surfaces, O vacancies appear only at high temperatures and practically irrelevant low pressures on the (T, p) surface phase diagram. In contrast, effortless formation of O ad-atoms on the surfaces is encountered at practically achievable pressures and temperatures. Above room temperature and close to atmospheric pressures, we predict clean PbO and TiO2-terminated (001) PTO surfaces as the stable surface phases while partially or fully O ad-atom covered surfaces are found to be more stable for LMO. These results are consistent with the observation that LMO is far more active towards oxidation catalysis than PTO.

Phase and Structural Behaviour in the NdAlO3-EuAlO3 System

2013 ◽  
Vol 200 ◽  
pp. 93-99 ◽  
Author(s):  
Natalia Ohon ◽  
Leonid Vasylechko ◽  
Yurii Prots ◽  
Marcus Schmidt ◽  
Caroline Curfs
Keyword(s):  
Phase Diagram ◽  
Phase Transitions ◽  
Binary System ◽  
Solid Solutions ◽  
Room Temperature ◽  
Structural Phase ◽  
Structural Phase Transitions ◽  
Structural Behaviour ◽  
First Order

Phase and structural behaviour in the NdAlO3–EuAlO3 system has been studied in the whole concentration range. Depending on x two kinds of solid solutions Nd1‑xEuxAlO3 exist at room temperature: one with rhombohedral (x < 0.15) and one with orthorhombic (x≈ 0.15–0.20, where the co-existence of both phases was observed. First-order structural phase transitions Pbnm↔Rc has been detected in Nd1-xEuxAlO3 with x = 0.3, 0.4, 0.6 at 520 K, 627 K and 988 K, respectively. Based on the experimental and literature data, the phase diagram of the pseudo-binary system NdAlO3–EuAlO3 has been constructed.

IN SITU HALL MEASUREMENTS OF MACROSCOPIC ELECTRICAL PROPERTIES OF CHROMIUM-COVERED Si(111) SURFACES

1999 ◽  
Vol 06 (01) ◽  
pp. 7-12 ◽  
Author(s):  
N. G. GALKIN ◽  
D. L. GOROSHKO ◽  
A. V. KONCHENKO ◽  
V. A. IVANOV ◽  
A. S. GOURALNIK
Keyword(s):  
Electrical Properties ◽  
Hole Concentration ◽  
Hole Mobility ◽  
Epitaxial Films ◽  
Surface Phase ◽  
Sheet Resistivity ◽  
Hall Measurements ◽  
Phase Layers ◽  
Surface Phases

The first in situ Hall measurements of the ordered chromium surface phases on Si(111) substrate and CrSi(111) epitaxial films after their formation are presented. Formation of Si (111)-(1× 1)- Cr (0.1 nm Cr) and Si(111)-[([Formula: see text])/30°]-Cr (0.3 nm Cr) surface phases results in an increase in the sheet resistivity of Si(111)-Cr surface phase samples. The conductivities along the surface phases at these chromium thicknesses are very low. The conductivity decrease is caused by a decrease in the electron mobility in the surface phase layers. Formation of an epitaxial CrSi(111) layer with averaged Hall parameters (hole mobility of 440 cm 2· V -1· s -1, sheet resistivity of 2.2·104 Ω-1 and sheet hole concentration of 0.65·1012 cm -2) has been observed at 1.5–1.8 nm of chromium thickness.

Phase Diagram and Cation Dynamics of Mixed MA1-xFAxPbBr3 Hybrid Perovskites

2021 ◽  
Author(s):  
Mantas Simenas ◽  
Sergejus Balčiūnas ◽  
Sarunas Svirskas ◽  
Martynas Kinka ◽  
Maciej Ptak ◽  
...  
Keyword(s):  
Phase Diagram ◽  
Room Temperature ◽  
Structural Phase ◽  
Cubic Phase ◽  
Structural Phase Transitions ◽  
X Ray Diffraction ◽  
X Ray ◽  
Dielectric Relaxations ◽  
Broadband Dielectric Spectroscopy ◽  
Molecular Cation

<p>We use a multi-technique approach to determine the phase diagram and molecular cation dynamics of mixed methylammonium-formamidinium MA1-xFAxPbBr3 (0 ≤ x ≤ 1) hybrid perovskites. The calorimetric, ultrasonic and X-ray diffraction experiments show a substantial suppression of the structural phase transitions and stabilization of the cubic phase upon mixing. We use the broadband dielectric and Raman spectroscopies to study the MA and FA cations dynamics in these compounds. The broadband dielectric spectroscopy indicates absence of the MA cation ordering and a gradual increase of the rotation barrier upon mixing. The room-temperature dielectric permittivity substantially decreases as the fraction of the FA cations is increased. No significant changes of the permittivity are detected at temperatures where the dielectric relaxations are absent. We also observe weak signatures of a dipolar glass phase for the highest mixing level (x = 0.5). The Raman spectroscopy supports the dielectric results and reveals additional subtle information about the FA cation dynamics.</p><br>

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