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.

C60 UNDER PRESSURE

1992 ◽  
Vol 06 (19) ◽  
pp. 1153-1158 ◽  
Author(s):  
MANUEL NÚÑEZ-REGUEIRO
Keyword(s):  
Phase Diagram ◽  
High Pressure ◽  
High Temperatures ◽  
Room Temperature ◽  
Fullerene Cage ◽  
Temperature Phase ◽  
Bonded Phase ◽  
Temperature Phase Diagram

The high pressure experiments done on fullerenes are reviewed. C 60 has found to be stable up to about 20 GPa at room temperature and hydrostatic conditions. Application of stronger, or non-hydrostatic, pressures at room temperature can induce the formation of a partially sp3 bonded phase, that apparently conserves the fullerene cage. Extreme non-hydrostatic compressions above about 15 GPa can, though, break down the cage and produce amorphous or cubic diamond. Destruction of the cage at high temperatures has also been observed, but the resulting product is amorphous sp2 material. A preliminary pressure-temperature phase diagram for C 60 is proposed.

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.

First-Principles-Based Surface Phase Diagram of Fully Relaxed Binary Alloy Surfaces

2004 ◽  
Vol 92 (19) ◽  
Author(s):  
O. Wieckhorst ◽  
S. Müller ◽  
L. Hammer ◽  
K. Heinz
Keyword(s):  
Phase Diagram ◽  
Binary Alloy ◽  
First Principles ◽  
Surface Phase

A first-principles surface phase diagram study for Si-adsorption processes on GaAs(111)A surfaces

2010 ◽  
Vol 604 (2) ◽  
pp. 171-174 ◽  
Author(s):  
Toru Akiyama ◽  
Hiroaki Tatematsu ◽  
Kohji Nakamura ◽  
Tomonori Ito
Keyword(s):  
Phase Diagram ◽  
First Principles ◽  
Surface Phase ◽  
Phase Diagram Study ◽  
Adsorption Processes

Intrinsic doping limit and defect-assisted luminescence in Cs4PbBr6

2019 ◽  
Author(s):  
Young-Kwang Jung ◽  
Joaquin Calbo ◽  
Ji-Sang Park ◽  
Lucy D. Wahlley ◽  
Sunghyun Kim ◽  
...  
Keyword(s):  
First Principles ◽  
Room Temperature ◽  
Stokes Shift ◽  
Green Luminescence ◽  
Counter Ions ◽  
Self Consistent ◽  
Deep Ultraviolet ◽  
Halide Perovskite ◽  
Related Compounds ◽  
Level Analysis

Cs<sub>4</sub>PbBr<sub>6 </sub>is a member of the halide perovskite family that is built from isolated (zero-dimensional) PbBr<sub>6</sub><sup>4-</sup> octahedra with Cs<sup>+</sup> counter ions. The material exhibits anomalous optoelectronic properties: optical absorption and weak emission in the deep ultraviolet (310 - 375 nm) with efficient luminescence in the green region (~ 540 nm). Several hypotheses have been proposed to explain the giant Stokes shift including: (i) phase impurities; (ii) self-trapped exciton; (iii) defect emission. We explore, using first-principles theory and self-consistent Fermi level analysis, the unusual defect chemistry and physics of Cs<sub>4</sub>PbBr<sub>6</sub>. We find a heavily compensated system where the room-temperature carrier concentrations (< 10<sup>9</sup> cm<sup>-3</sup>) are more than one million times lower than the defect concentrations. We show that the low-energy Br-on-Cs antisite results in the formation of a polybromide (Br<sub>3</sub>) species that can exist in a range of charge states. We further demonstrate from excited-state calculations that tribromide moieties are photoresponsive and can contribute to the observed green luminescence. Photoactivity of polyhalide molecules is expected to be present in other halide perovskite-related compounds where they can influence light absorption and emission. <br>

Intrinsic doping limit and defect-assisted luminescence in Cs4PbBr6

2019 ◽  
Author(s):  
Young-Kwang Jung ◽  
Joaquin Calbo ◽  
Ji-Sang Park ◽  
Lucy D. Wahlley ◽  
Sunghyun Kim ◽  
...  
Keyword(s):  
First Principles ◽  
Room Temperature ◽  
Stokes Shift ◽  
Green Luminescence ◽  
Counter Ions ◽  
Self Consistent ◽  
Deep Ultraviolet ◽  
Halide Perovskite ◽  
Related Compounds ◽  
Level Analysis

Cs<sub>4</sub>PbBr<sub>6 </sub>is a member of the halide perovskite family that is built from isolated (zero-dimensional) PbBr<sub>6</sub><sup>4-</sup> octahedra with Cs<sup>+</sup> counter ions. The material exhibits anomalous optoelectronic properties: optical absorption and weak emission in the deep ultraviolet (310 - 375 nm) with efficient luminescence in the green region (~ 540 nm). Several hypotheses have been proposed to explain the giant Stokes shift including: (i) phase impurities; (ii) self-trapped exciton; (iii) defect emission. We explore, using first-principles theory and self-consistent Fermi level analysis, the unusual defect chemistry and physics of Cs<sub>4</sub>PbBr<sub>6</sub>. We find a heavily compensated system where the room-temperature carrier concentrations (< 10<sup>9</sup> cm<sup>-3</sup>) are more than one million times lower than the defect concentrations. We show that the low-energy Br-on-Cs antisite results in the formation of a polybromide (Br<sub>3</sub>) species that can exist in a range of charge states. We further demonstrate from excited-state calculations that tribromide moieties are photoresponsive and can contribute to the observed green luminescence. Photoactivity of polyhalide molecules is expected to be present in other halide perovskite-related compounds where they can influence light absorption and emission. <br>

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