LEAD-CHALCOGENIDES UNDER PRESSURE: AB-INITIO STUDY

2013 ◽  
Vol 22 ◽  
pp. 612-618 ◽  
Author(s):  
DINESH C. GUPTA ◽  
IDRIS HAMID
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Ab Initio ◽  
Band Gap ◽  
Rock Salt ◽  
High Pressures ◽  
Ambient Pressure ◽  
High Pressure Phase ◽  
Lead Chalcogenides ◽  
Pressure Phase

ab-initio calculations using fully relativistic pseudo-potential have been performed to investigate the high pressure phase transition, elastic and electronic properties of lead-chalcogenides including the less known lead polonium. The calculated ground state parameters, for the rock-salt structure show good agreement with the experimental data. The enthalpy calculations show that these materials undergo a first-order phase transition from rock-salt to CsCl structure at 19.4, 15.5, 11.5 and 7.3 GPa for PbS, PbSe, PbTe and PbPo, respectively. Present calculations successfully predicted the location of the band gap at L-point of Brillouin zone as well as the value of the band gap in every case at ambient pressure. It is observed that unlike other lead-chalcogenides, PbPo is semi-metal at ambient pressure. The pressure variation of the energy gap indicates that these materials metalized under high pressures. For this purpose, the electronic structure of these materials has also been computed in parent as well as in high pressure phase.

scholarly journals Crystal and electronic structure engineering of tin monoxide by external pressure

2021 ◽  
Author(s):  
Kun Li ◽  
Junjie Wang ◽  
Vladislav A. Blatov ◽  
Yutong Gong ◽  
Naoto Umezawa ◽  
...  
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Band Gap ◽  
High Pressures ◽  
Low Pressure ◽  
Widespread Application ◽  
Space Group ◽  
Tin Monoxide ◽  
High Possibility ◽  
Pressure Phase

AbstractAlthough tin monoxide (SnO) is an interesting compound due to its p-type conductivity, a widespread application of SnO has been limited by its narrow band gap of 0.7 eV. In this work, we theoretically investigate the structural and electronic properties of several SnO phases under high pressures through employing van der Waals (vdW) functionals. Our calculations reveal that a metastable SnO (β-SnO), which possesses space group P21/c and a wide band gap of 1.9 eV, is more stable than α-SnO at pressures higher than 80 GPa. Moreover, a stable (space group P2/c) and a metastable (space group Pnma) phases of SnO appear at pressures higher than 120 GPa. Energy and topological analyses show that P2/c-SnO has a high possibility to directly transform to β-SnO at around 120 GPa. Our work also reveals that β-SnO is a necessary intermediate state between high-pressure phase Pnma-SnO and low-pressure phase α-SnO for the phase transition path Pnma-SnO →β-SnO → α-SnO. Two phase transition analyses indicate that there is a high possibility to synthesize β-SnO under high-pressure conditions and have it remain stable under normal pressure. Finally, our study reveals that the conductive property of β-SnO can be engineered in a low-pressure range (0–9 GPa) through a semiconductor-to-metal transition, while maintaining transparency in the visible light range.

Ab initio study of high pressure phase transition in GaN

1994 ◽  
Vol 55 (11) ◽  
pp. 1357-1361 ◽  
Author(s):  
Ravindra Pandey ◽  
John E Jaffe ◽  
Nicholas M Harrison
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Ab Initio ◽  
High Pressure Phase ◽  
Ab Initio Study ◽  
High Pressure Phase Transition ◽  
Pressure Phase

High-pressure phase transition and lattice dynamics of rock-salt and FeSi-type phases of MgS

2014 ◽  
Vol 94 (4) ◽  
pp. 198-204
Author(s):  
HaiYing Wu ◽  
YaHong Chen ◽  
XinFang Su ◽  
ChengRong Deng ◽  
Zi-Jiang Liu
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Rock Salt ◽  
Lattice Dynamics ◽  
High Pressure Phase ◽  
High Pressure Phase Transition ◽  
Pressure Phase

scholarly journals Comparison of the effects of pressure on three layered hydrates: a partially successful attempt to predict a high-pressure phase transition

2009 ◽  
Vol 65 (6) ◽  
pp. 731-748 ◽  
Author(s):  
Russell D. L. Johnstone ◽  
Alistair R. Lennie ◽  
Simon Parsons ◽  
Elna Pidcock ◽  
John E. Warren
Keyword(s):  
Phase Transition ◽  
High Pressure ◽  
Single Crystal ◽  
Molecular Conformation ◽  
Ambient Pressure ◽  
High Pressure Phase ◽  
Cysteic Acid ◽  
Water Molecules ◽  
High Pressure Phase Transition ◽  
Pressure Phase

We report the effect of pressure on the crystal structures of betaine monohydrate (BTM), L-cysteic acid monohydrate (CAM) and S-4-sulfo-L-phenylalanine monohydrate (SPM). All three structures are composed of layers of zwitterionic molecules separated by layers of water molecules. In BTM the water molecules make donor interactions with the same layer of betaine molecules, and the structure remains in a compressed form of its ambient-pressure phase up to 7.8 GPa. CAM contains bi-layers of L-cysteic acid molecules separated by water molecules which form donor interactions to the bi-layers above and below. This phase is stable up to 6.8 GPa. SPM also contains layers of zwitterionic molecules with the waters acting as hydrogen-bond donors to the layers above and below. SPM undergoes a single-crystal to single-crystal phase transition above 1 GPa in which half the water molecules reorient so as to form one donor interaction with another water molecule within the same layer. In addition, half of the S-4-sulfo-L-phenylalanine molecules change their conformation. The high-pressure phase is stable up to 6.9 GPa, although modest rearrangements in hydrogen bonding and molecular conformation occur at 6.4 GPa. The three hydrates had been selected on the basis of their topological similarity (CAM and SPM) or dissimilarity (BTM) with serine hydrate, which undergoes a phase transition at 5 GPa in which the water molecules change orientation. The phase transition in SPM shows some common features with that in serine hydrate. The principal directions of compression in all three structures were found to correlate with directions of hydrogen bonds and distributions of interstitial voids.

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