Jadeite and its relatives: fake news or a real tool to constrain shock conditions?

2021 ◽  
Author(s):  
Ioannis Baziotis ◽  
Stamatios Xydous ◽  
Angeliki Papoutsa ◽  
Jinping Hu ◽  
Chi Ma ◽  
...  
Keyword(s):  
First Principles ◽  
Chemical Space ◽  
Formula Unit ◽  
First Principles Calculations ◽  
Fake News ◽  
State Transformation ◽  
Solid State Transformation ◽  
Crater Diameter ◽  
Grain Sizes ◽  
New Occurrences

Abstract Jadeite is frequently reported in shocked meteorites, displaying a variety of textures and grain sizes that suggest formation by either solid-state transformation or by crystallization from a melt. Sometimes, jadeite has been identified solely on the basis of Raman spectra. Here we argue that additional characterization is needed to confidently identify jadeite and distinguish it from related species. Based on chemical and spectral analysis of three new occurrences, complemented by first-principles calculations, we show that related pyroxenes in the chemical space (Na)M2(Al)M1(Si2)TO6 – (Ca)M2(Al)M1(AlSi)TO6 – (□)M2(Si)M1(Si2)TO6 with up to 2.25 atoms Si per formula unit have spectral features similar to jadeite. However, their distinct stability fields and synthesis pathways, considered together with textural constraints, have specific implications for precursor phases and estimates of impactor size, encounter velocity, and crater diameter. A reassessment of reported jadeite occurrences puts in a new light many previous conclusions about the shock histories preserved in particular meteorites.

scholarly journals A chemical map of NaSICON electrode materials for sodium-ion batteries

2021 ◽  
Vol 9 (1) ◽  
pp. 281-292
Author(s):  
Baltej Singh ◽  
Ziliang Wang ◽  
Sunkyu Park ◽  
Gopalakrishnan Sai Gautam ◽  
Jean-Noël Chotard ◽  
...  
Keyword(s):  
Transition Metal ◽  
First Principles ◽  
Electrode Materials ◽  
Chemical Space ◽  
Sodium Ion ◽  
Sodium Ion Batteries ◽  
First Principles Calculations

Using first-principles calculations, we chart the chemical space of 3d transition metal-based NaSICON phosphates with the formula NaxMM′(PO4)3 (with M and M′ = Ti, V, Cr, Mn, Fe, Co and Ni). Novel NaSICON compositions were revealed.

scholarly journals Active discovery of organic semiconductors

2021 ◽  
Vol 12 (1) ◽  
Author(s):  
Christian Kunkel ◽  
Johannes T. Margraf ◽  
Ke Chen ◽  
Harald Oberhofer ◽  
Karsten Reuter
Keyword(s):  
Organic Semiconductors ◽  
First Principles ◽  
Organic Molecules ◽  
Design Space ◽  
Chemical Space ◽  
Search Space ◽  
First Principles Calculations ◽  
Test Space ◽  
Predictive Quality ◽  
Conduction Properties

AbstractThe versatility of organic molecules generates a rich design space for organic semiconductors (OSCs) considered for electronics applications. Offering unparalleled promise for materials discovery, the vastness of this design space also dictates efficient search strategies. Here, we present an active machine learning (AML) approach that explores an unlimited search space through consecutive application of molecular morphing operations. Evaluating the suitability of OSC candidates on the basis of charge injection and mobility descriptors, the approach successively queries predictive-quality first-principles calculations to build a refining surrogate model. The AML approach is optimized in a truncated test space, providing deep methodological insight by visualizing it as a chemical space network. Significantly outperforming a conventional computational funnel, the optimized AML approach rapidly identifies well-known and hitherto unknown molecular OSC candidates with superior charge conduction properties. Most importantly, it constantly finds further candidates with highest efficiency while continuing its exploration of the endless design space.

scholarly journals Simultaneous tuning of the magnetic anisotropy and thermal stability of $$\alpha ^{''}$$-phase Fe$$_{16}$$N$$_{2}$$

2021 ◽  
Vol 11 (1) ◽  
Author(s):  
D. Odkhuu ◽  
S. C. Hong
Keyword(s):  
Thermal Stability ◽  
Magnetic Anisotropy ◽  
First Principles ◽  
Alpha Phase ◽  
Formula Unit ◽  
First Principles Calculations ◽  
A Value ◽  
Valence Electrons ◽  
Re Elements ◽  
Thermal Stability Of

AbstractSimultaneously enhancing the uniaxial magnetic anisotropy ($$K_u$$ K u ) and thermal stability of $$\alpha ^{''}$$ α ′ ′ -phase Fe$$_{16}$$ 16 N$$_{2}$$ 2 without inclusion of heavy-metal or rare-earth (RE) elements has been a challenge over the years. Herein, through first-principles calculations and rigid-band analysis, significant enhancement of $$K_u$$ K u is proposed to be achievable through excess valence electrons in the Fe$$_{16}$$ 16 N$$_{2}$$ 2 unit cell. We demonstrate a persistent increase in $$K_u$$ K u up to 1.8 MJ m$$^{\text {-}3}$$ - 3 , a value three times that of 0.6 MJ m$$^{\text {-}3}$$ - 3 in $$\alpha ^{''}$$ α ′ ′ -Fe$$_{16}$$ 16 N$$_{2}$$ 2 , by simply replacing Fe with metal elements with more valence electrons (Co to Ga in the periodic table). A similar rigid-band argument is further adopted to reveal an extremely large $$K_u$$ K u up to 2.4 MJ m$$^{\text {-}3}$$ - 3 in (Fe$$_{0.5}$$ 0.5 Co$$_{0.5}$$ 0.5 )$$_{16}$$ 16 N$$_{2}$$ 2 obtained by replacing Co with Ni to Ga. Such a strong $$K_u$$ K u can also be achieved with the replacement by Al, which is isoelectronic to Ga, with simultaneous improvement of the phase stability. These results provide an instructive guideline for simultaneous manipulation of $$K_u$$ K u and the thermal stability in 3d-only metals for RE-free permanent magnet applications.

Electronic Structure and X-ray Absorption Spectra of Rutile TiO2 Using First-Principles Calculations

2014 ◽  
Vol 52 (12) ◽  
pp. 1025-1029
Author(s):  
Min-Wook Oh ◽  
Tae-Gu Kang ◽  
Byungki Ryu ◽  
Ji Eun Lee ◽  
Sung-Jae Joo ◽  
...  
Keyword(s):  
Electronic Structure ◽  
Absorption Spectra ◽  
First Principles ◽  
First Principles Calculations ◽  
Rutile Tio2 ◽  
X Ray ◽  
X Ray Absorption

To Bend or Not to Bend, the Dilemma of Multiple Bonds

2019 ◽  
Author(s):  
Michele Pizzocchero ◽  
Matteo Bonfanti ◽  
Rocco Martinazzo
Keyword(s):  
First Principles ◽  
2D Materials ◽  
Main Group ◽  
First Principles Calculations ◽  
Group 14 ◽  
Multiple Bonds ◽  
Main Group Elements ◽  
Structural Distortions

The manuscript addresses the issue of the structural distortions occurring at multiple bonds between high main group elements, focusing on group 14. These distortions are known as trans-bending in silenes, disilenes and higher group analogues, and buckling in 2D materials likes silicene and germanene. A simple but correlated \sigma + \pi model is developed and validated with first-principles calculations, and used to explain the different behaviour of second- and higher- row elements.

Thermodynamic Stability of Hexagonal and Rhombohedral Bn at Cvd Conditions from Van der Waals Corrected First Principles Calculations

2019 ◽  
Author(s):  
Henrik Pedersen ◽  
Björn Alling ◽  
Hans Högberg ◽  
Annop Ektarawong
Keyword(s):  
Thin Films ◽  
Thermodynamic Stability ◽  
First Principles ◽  
Thermal Equilibrium ◽  
Density Functional ◽  
Van Der Waals ◽  
Chemical Vapor ◽  
First Principles Calculations ◽  
Functional Theory ◽  
The Stability

Thin films of boron nitride (BN), particularly the sp<sup>2</sup>-hybridized polytypes hexagonal BN (h-BN) and rhombohedral BN (r-BN) are interesting for several electronic applications given band gaps in the UV. They are typically deposited close to thermal equilibrium by chemical vapor deposition (CVD) at temperatures and pressures in the regions 1400-1800 K and 1000-10000 Pa, respectively. In this letter, we use van der Waals corrected density functional theory and thermodynamic stability calculations to determine the stability of r-BN and compare it to that of h-BN as well as to cubic BN and wurtzitic BN. We find that r-BN is the stable sp<sup>2</sup>-hybridized phase at CVD conditions, while h-BN is metastable. Thus, our calculations suggest that thin films of h-BN must be deposited far from thermal equilibrium.

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