scholarly journals Semiconducting phase of hafnium dioxide under high pressure: a theoretical studied by quasi-particle GW calculations

2021 ◽  
Author(s):  
Thipok Bovornratanaraks ◽  
Rajeev Ahuja ◽  
Prutthipong Tsuppayakorn-aek
Keyword(s):  
High Pressure ◽  
Hafnium Dioxide ◽  
Semiconducting Materials ◽  
Generalized Gradient ◽  
Gw Approximation ◽  
Quasi Particle ◽  
Wide Range ◽  
Evolutionary Technique ◽  
The Stability ◽  
Pressure Phase

Abstract The phase stability of the hafnium dioxide compounds HfO2, a novelmaterial with a wide range of application due to its versatility and biocompatibility,is predicted to be achievable by using evolutionary technique, based on first-principlescalculations. Herein, the candidate structure of HfO2 is revealed to adopt a tetragonalstructure under high-pressure phase with P4/nmm space group. This evidentlyconfirms the stability of the HfO2 structures, since the decomposition into thecomponent elements under pressure does not occur until the pressure is at least200GPa. Moreover, phonon calculations can confirm that the P4/nmm structure isdynamically stable. The P4/nmm structure is mainly attributed to the semiconductingproperty within using the Perdew{Burke{Ernzerhof, the modified Becke-Johnsonexchange potential in combination with the generalized gradient approximations, andthe quasi-particle GW approximation, respectively. Our calculation manifests that theP4/nmm structure likely to be metal above 200GPa, arising particularly from GWapproximation. The remarkable results of this work provide more understanding ofthe high-pressure structure for designing metal-oxide-based semiconducting materials.

scholarly journals Semiconducting phase of hafnium dioxide under high pressure: a theoretical study by quasi-particle GW calculations

2021 ◽  
Vol 8 (10) ◽  
pp. 105901
Author(s):  
Thipok Bovornratanaraks ◽  
Rajeev Ahuja ◽  
Prutthipong Tsuppayakorn-aek
Keyword(s):  
High Pressure ◽  
Theoretical Study ◽  
Hafnium Dioxide ◽  
Quasi Particle

High-pressure phase transformation of BeGa2O4

1993 ◽  
Vol 8 (7) ◽  
pp. 1721-1727 ◽  
Author(s):  
K. Nakamura ◽  
M. Machida ◽  
M.E. Brito ◽  
H. Tabata
Keyword(s):  
High Pressure ◽  
Phase Transformation ◽  
Elevated Temperatures ◽  
High Pressure Phase ◽  
Type Structure ◽  
Temperature Phase ◽  
Temperature Ranges ◽  
The Stability ◽  
New Phase ◽  
Pressure Phase

High-pressure phase transformation of beryllium gallium oxide (BeGa2O4) has been studied. Applying high pressure at elevated temperatures to the original hexagonal BeGa2O4 (β–Si3N4-type structure), a high-pressure modification with orthorhombic structure (olivine-type structure) was obtained, i.e., o-BeGa2O4. Lattice parameters of the new phase were determined to be a = 0.5698, b = 0.9759, and c = 0.4551 nm. The pressure and temperature ranges where the high-pressure phase was observed are 3.5 to 7.5 GPa and 800 to 1600 °C, respectively. A tentative pressure-temperature phase diagram for BeGa2O4 was proposed. Transformation is not straightforward; decomposition of the original phase into single oxides and their recombination to form o-BeGa2O4 are necessary. This process seems to apply in both ways, formation and decomposition of the high-pressure phase. The stability of the high-pressure phase is explained in terms of the total molar volume for the phase, the result of summing up molar volumes of constituent compounds. This is the first known report on transformation of β–Si3N4-type structure into a denser structure.

Use of Hardness Indentation Coupled with Micro-Raman Spectroscopy in High-Pressure Materials Research

1997 ◽  
Vol 499 ◽  
Author(s):  
A. Kailer ◽  
Y. G. Gogotsi ◽  
K. G. Nickel
Keyword(s):  
Raman Spectroscopy ◽  
High Pressure ◽  
Phase Transformations ◽  
Materials Science ◽  
High Pressure Phase ◽  
Shear Stresses ◽  
Micro Raman Spectroscopy ◽  
Wide Range ◽  
Mechanical Contacts ◽  
Pressure Phase

ABSTRACTHigh-pressure phase transformations occurring in materials are important for a wide range of problems in materials science and engineering. Most of the results in this field have been obtained using high-pressure cells.In this work, we demonstrate that high-pressure phase transformations also take place during mechanical contact of hard solid materials. These solid-state transformations can be studied by simply combining hardness indentation tests with micro-Raman spectroscopy. In contrast to diamond anvil cell (DAC) experiments, the stress conditions during mechanical contacts are highly non-hydrostatic, i.e. very high shear stresses affect the transformation behavior. Nevertheless, the obtained results can be discussed in the light of the phase transformations as known from DAC experiments. The examples of our research presented here include Si, Ge, SiO2 and ZrO2, and show that phase transformations and amorphization at mechanical contacts are a quite common phenomenon, which has important implications.

scholarly journals First Principles Calculation of the Stability of Iron Bearing Carbonates at High Pressure Conditions

Minerals ◽  
2020 ◽  
Vol 10 (1) ◽  
pp. 54
Author(s):  
Jun Tsuchiya ◽  
Risa Nishida ◽  
Taku Tsuchiya
Keyword(s):  
High Pressure ◽  
High Spin ◽  
First Principles ◽  
Lower Mantle ◽  
Local Density ◽  
First Principles Calculation ◽  
Generalized Gradient ◽  
Carbonate Minerals ◽  
Pressure Stability ◽  
The Stability

Carbonate minerals such as ferromagnesite (Mg,Fe)CO 3 are suggested to be a possible major deep-carbon host in the lower mantle, because ferromagnesite is possibly stabilized by Fe spin crossover under pressure. However, the behavior of Fe-bearing carbonates under lower mantle pressure conditions has not been suitably examined thus far. Thus, in this study, we investigate the high-pressure stability of ferromagnesite and possible high-pressure structures with the chemical composition of (Mg 0.833 Fe 0.167 )CO 3 via first principles calculation using internally consistent local density approximation with Hubbard parameter (LDA+U) method, which can more accurately account for the electronic state of Fe than the LDA and generalized gradient approximation (GGA) approaches. The enthalpy values obtained via our calculations suggest that (Mg 0.833 Fe 0.167 )CO 3 undergoes phase transition from the R 3 ¯ c structure (high spin) to the P 1 ¯ (high spin) at 50 GPa, and to C2/m (high-spin) structure above 80 GPa, under static 0 K conditions. Therefore, no spin transitions in these carbonate minerals is expected under the lower mantle pressure conditions.

Performance of Electronic Structure Methods for the Description of Hückel-Möbius Interconversions in Extended π-Systems

2019 ◽  
Author(s):  
Tatiana Woller ◽  
Ambar Banerjee ◽  
Nitai Sylvetsky ◽  
Xavier Deraet ◽  
Frank De Proft ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Basis Set ◽  
Dft Methods ◽  
Molecular Switching ◽  
Wide Range ◽  
Electronic Structure Methods ◽  
Explicitly Correlated ◽  
Relative Errors ◽  
The Stability ◽  
Basis Set Expansion

<p>Expanded porphyrins provide a versatile route to molecular switching devices due to their ability to shift between several π-conjugation topologies encoding distinct properties. Taking into account its size and huge conformational flexibility, DFT remains the workhorse for modeling such extended macrocycles. Nevertheless, the stability of Hückel and Möbius conformers depends on a complex interplay of different factors, such as hydrogen bonding, p···p stacking, steric effects, ring strain and electron delocalization. As a consequence, the selection of an exchange-correlation functional for describing the energy profile of topological switches is very difficult. For these reasons, we have examined the performance of a variety of wavefunction methods and density functionals for describing the thermochemistry and kinetics of topology interconversions across a wide range of macrocycles. Especially for hexa- and heptaphyrins, the Möbius structures have a pronouncedly stronger degree of static correlation than the Hückel and figure-eight structures, and as a result the relative energies of singly-twisted structures are a challenging test for electronic structure methods. Comparison of limited orbital space full CI calculations with CCSD(T) calculations within the same active spaces shows that post-CCSD(T) correlation contributions to relative energies are very minor. At the same time, relative energies are weakly sensitive to further basis set expansion, as proven by the minor energy differences between MP2/cc-pVDZ and explicitly correlated MP2-F12/cc-pVDZ-F12 calculations. Hence, our CCSD(T) reference values are reasonably well-converged in both 1-particle and n-particle spaces. While conventional MP2 and MP3 yield very poor results, SCS-MP2 and particularly SOS-MP2 and SCS-MP3 agree to better than 1 kcal mol<sup>-1</sup> with the CCSD(T) relative energies. Regarding DFT methods, only M06-2X provides relative errors close to chemical accuracy with a RMSD of 1.2 kcal mol<sup>-1</sup>. While the original DSD-PBEP86 double hybrid performs fairly poorly for these extended p-systems, the errors drop down to 2 kcal mol<sup>-1</sup> for the revised revDSD-PBEP86-NL, again showing that same-spin MP2-like correlation has a detrimental impact on performance like the SOS-MP2 results. </p>

Ab initio calculation on the Optical Properties of AA- Stacked two dimensional Graphene, Silicene, Germanene, and Stanene

2018 ◽  
Vol 1 (1) ◽  
pp. 46-50
Author(s):  
Rita John ◽  
Benita Merlin
Keyword(s):  
Optical Properties ◽  
Band Structure ◽  
Density Functional ◽  
Electronic Band Structure ◽  
Complex Refractive Index ◽  
Single Layer ◽  
Generalized Gradient ◽  
Electronic Band ◽  
Wide Range ◽  
Optical Region

In this study, we have analyzed the electronic band structure and optical properties of AA-stacked bilayer graphene and its 2D analogues and compared the results with single layers. The calculations have been done using Density Functional Theory with Generalized Gradient Approximation as exchange correlation potential as in CASTEP. The study on electronic band structure shows the splitting of valence and conduction bands. A band gap of 0.342eV in graphene and an infinitesimally small gap in other 2D materials are generated. Similar to a single layer, AA-stacked bilayer materials also exhibit excellent optical properties throughout the optical region from infrared to ultraviolet. Optical properties are studied along both parallel (||) and perpendicular ( ) polarization directions. The complex dielectric function (ε) and the complex refractive index (N) are calculated. The calculated values of ε and N enable us to analyze optical absorption, reflectivity, conductivity, and the electron loss function. Inferences from the study of optical properties are presented. In general the optical properties are found to be enhanced compared to its corresponding single layer. The further study brings out greater inferences towards their direct application in the optical industry through a wide range of the optical spectrum.

Insights into Potent Therapeutical Antileukemic Agent L-glutaminase Enzyme Under Solid-state Fermentation: A Review

2020 ◽  
Vol 21 (3) ◽  
pp. 211-220 ◽  
Author(s):  
Chandrasai Potla Durthi ◽  
Madhuri Pola ◽  
Satish Babu Rajulapati ◽  
Anand Kishore Kola
Keyword(s):  
Solid State ◽  
Solid State Fermentation ◽  
Food Industry ◽  
Energy Requirement ◽  
Production Studies ◽  
Wide Range ◽  
Hybridoma Technology ◽  
Bacteria And Fungi ◽  
The Stability ◽  
Glutaminase Activity

Aim & objective: To review the applications and production studies of reported antileukemic drug L-glutaminase under Solid-state Fermentation (SSF). Overview: An amidohydrolase that gained economic importance because of its wide range of applications in the pharmaceutical industry, as well as the food industry, is L-glutaminase. The medical applications utilized it as an anti-tumor agent as well as an antiretroviral agent. L-glutaminase is employed in the food industry as an acrylamide degradation agent, as a flavor enhancer and for the synthesis of theanine. Another application includes its use in hybridoma technology as a biosensing agent. Because of its diverse applications, scientists are now focusing on enhancing the production and optimization of L-glutaminase from various sources by both Solid-state Fermentation (SSF) and submerged fermentation studies. Of both types of fermentation processes, SSF has gained importance because of its minimal cost and energy requirement. L-glutaminase can be produced by SSF from both bacteria and fungi. Single-factor studies, as well as multi-level optimization studies, were employed to enhance L-glutaminase production. It was concluded that L-glutaminase activity achieved by SSF was 1690 U/g using wheat bran and Bengal gram husk by applying feed-forward artificial neural network and genetic algorithm. The highest L-glutaminase activity achieved under SSF was 3300 U/gds from Bacillus sp., by mixture design. Purification and kinetics studies were also reported to find the molecular weight as well as the stability of L-glutaminase. Conclusion: The current review is focused on the production of L-glutaminase by SSF from both bacteria and fungi. It was concluded from reported literature that optimization studies enhanced L-glutaminase production. Researchers have also confirmed antileukemic and anti-tumor properties of the purified L-glutaminase on various cell lines.

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.

scholarly journals Effect of food processing on the antioxidant activity of flavones from Polygonatum odoratum (Mill.) Druce

2021 ◽  
Vol 16 (1) ◽  
pp. 92-101
Author(s):  
Guanghui Xia ◽  
Xinhua Li ◽  
Zhen Zhang ◽  
Yuhang Jiang
Keyword(s):  
Antioxidant Activity ◽  
High Pressure ◽  
Food Processing ◽  
Yeast Fermentation ◽  
Pressure Treatment ◽  
Processing Methods ◽  
High Pressure Treatment ◽  
Effect Of Food ◽  
The Stability

Abstract Polygonatum odoratum (Mill.) Druce (POD) is a natural plant widely used for food and medicine, thanks to its rich content of a strong antioxidant agent called homoisoflavones. However, food processing methods could affect the stability of POD flavones, resulting in changes to their antioxidant activity. This study attempts to evaluate the antioxidant activity of POD flavones subject to different processing methods and determines which method could preserve the antioxidant activity of POD flavones. Therefore, flavones were extracted from POD samples, which had been treated separately with one of the four processing methods: extrusion, baking, high-pressure treatment, and yeast fermentation. After that, the antioxidant activity of the flavones was subject to in vivo tests in zebrafish embryos. The results show that yeast fermentation had the least disruption to the antioxidant activity of POD flavones, making it the most suitable food processing method for POD. By contrast, extrusion and high-pressure treatment both slightly weakened the antioxidant activity of the flavones and should be avoided in food processing. The research results provide a reference for the development and utilization of POD and the protection of its biological activity.

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