Thomas B. Shiell's research while affiliated with Carnegie Institution for Science and other places

Publications (18)

Article
Full-text available
Manipulation by external pressure of the optical response of 2D Metal Halide Perovskite (MHPs) is a fascinating route to tune their properties and promote the emergence of novel features. We investigate here DA2PbI4 and DA2GeI4 (DA=decylammonium) perovskites in the pressure range up to ∼12 GPa by x-ray powder diffraction, absorption, and photolumin...
Preprint
Full-text available
The application of an external pressure on Metal Halide Perovskite (MHPs) has become a fascinating way of tuning their optical properties, achieving also novel features. Here, the pressure response of 2D MHPs including a long alkyl chain made of ten carbon atoms, namely decylammonium (DA), has been investigated as a function of the central atom in...
Article
We report the synthesis of bulk, highly oriented, crystalline 4H hexagonal silicon (4H−Si), through a metastable phase transformation upon heating the single-crystalline Si24 allotrope. Remarkably, the resulting 4H−Si crystallites exhibit an orientation relationship with the Si24 crystals, indicating a structural relationship between the two phases...
Article
Glassy carbon is a chemically inert, biocompatible, disordered material with the graphene sheet as its basic building block. Structural characterisation techniques have so far been unable to provide definitive distinction between the many proposed models for its structure. Computer based simulation methods have made a step forward by predicting str...
Article
In article number 2004695, Dougal McCulloch and co‐workers report the synthesis of nanocrystalline diamond from a compressed graphitic precursor at room temperature in a diamond anvil cell. Diamond is one of the most important materials for 21st century technology, but there is much that is still not understood about how it forms. This article show...
Article
Diamond is an attractive material due to its extreme hardness, high thermal conductivity, quantum optical, and biomedical applications. There is still much that is not understood about how diamonds form, particularly at room temperature and without catalysts. In this work, a new route for the formation of nanocrystalline diamond and the diamond-lik...
Article
Full-text available
Structural and optical high-pressure study of FASnBr3 (FA=formamidinium) revealed a cubic to orthorhombic phase transition near 1.4 GPa accompanied by a huge band gap red-shift from 2.4 to 1.6 eV, which is followed by a blue-shift of ~0.2 eV upon further pressure increase. DFT calculations indicate that the variation in band gap is related to chang...
Article
Isothermal equations of state were determined for the open-framework silicon allotrope Si24 and its sodium-filled precursor (Na4Si24) using different pressure media including hydrogen and argon, and with no pressure medium. Si24 does not transform into diamond-cubic silicon under compression, and the low-density phase possesses a bulk modulus of 91...
Article
Glassy carbon (GC) is usually considered the prototypical super-elastic material, which can almost fully recover its shape after compression of several gigapascals (GPa). In this work, nanoindentation is used to study the mechanical response of GC, which was subjected to a range of high pressures using a diamond anvil cell (DAC). We show that GC st...
Article
Glassy carbon (GC) is a class of disordered carbon materials that is known to be superelastic and non-graphitizing up to 3000 °C. The maximum heat treatment temperature is often used as a proxy to denote structure and physical properties. GC synthesised at low temperatures (~1000 °C) is often classified as Type I GC which has advantages of higher e...
Article
Room temperature compression of graphitic materials leads to interesting superhard sp3 rich phases which are sometimes transparent. In the case of graphite itself, the sp3 rich phase is proposed to be monoclinic M-carbon; however, for disordered materials such as glassy carbon the nature of the transformation is unknown. We compress glassy carbon a...
Article
Hexagonal diamond, a potentially superhard material, forms from a glassy carbon precursor at pressures of ∼100 GPa at the relatively low temperature of 400 °C. The formation mechanism of the hexagonal diamond phase was investigated by performing microstructural analysis on cross-sections of the recovered samples. Three distinct structures have been...
Article
Glassy carbon is a technologically important material with isotropic properties that is nongraphitizing up to ∼3000 °C and displays complete or “superelastic” recovery from large compression. The pressure limit of these properties is not yet known. Here we use experiments and modeling to show permanent densification, and preferred orientation occur...
Article
Full-text available
Strong anisotropic compression with pressure on the remarkable non-linear optical material KBe2BO3F2 has been observed with the linear compression coefficient along the c axis found to be about 40 times larger than that along the a axis. An unusual non-monotonic pressure response was observed for the a lattice parameter. The derived bulk modulus of...
Article
Full-text available
Carbon exhibits a large number of allotropes and its phase behaviour is still subject to significant uncertainty and intensive research. The hexagonal form of diamond, also known as lonsdaleite, was discovered in the Canyon Diablo meteorite where its formation was attributed to the extreme conditions experienced during the impact. However, it has r...

Citations

... MA 3 Bi 2 Br 9 is another Bi-based 2D perovskite in which pressure dependent structural and optical properties were observed [88]. At ambient pressure DA 2 PbI 4 and DA 2 GeI 4 (DA = decylammonium) 2D perovskites [90] were recently investigated by applying pressure till 12 GPa. At 11.5 GPa red shift was observed for DA 2 PbI 4 . ...
... In this work, we probe the possibility of stabilizing silicon-doped carbon clathrate frameworks under pressure. Although no pure C clathrate has been made to date, several metastable Si clathrates and tetrahedral frameworks have been created [10,[31][32][33][34], which opens the possibility of using high-energy Si phases as alternative precursors for mixed C-Si clathrates, similar to precursor-based synthesis in other systems [35][36][37][38]. Our calculations indicate that carbon incorporation within silicon clathrate frameworks can improve the overall stability, moving a step towards the realization of additional carbon-based clathrate materials. ...
... [The reduced RDF G(r) commonly used in experiment is related to the RDF g(r) most often reported in simulation work by G(r) = 4πrρ at (g(r) − 1), where ρ at is the atomic density in, e.g., atoms/Å 3 .] For the sake of a robust comparison, the experimental GC sample HTW2500 reported in ref 49 and a NP carbon sample reported in ref 50 are chosen. Figure 8 presents (a) the intensity of X-ray diffraction (XRD) and (b) the G(r) of the reference experimental samples and our simulated NP samples. ...
... Previous efforts have demonstrated conversion of organic polymers like anthracene along with hexamethylenetetramine to graphite, and iron-doped anthracene along with paraffin wax to diamond by equilibrium-based high-pressure high-temperature techniques [22]. Recently, the formation of diamond at very high pressure ~80 GPa in compression at room temperature was demonstrated [23]. However, this pressure is too high for practical applications due to limited yield in the form of grits. ...
... The exploration of the effect of external pressure application on metal halide perovskites (MHPs) is a topic of continuous interest because of the relevant and in some cases impressive modulation of the optical and electronic properties that can be induced on the MHP soft lattice at relatively low-pressure regimes Li et al., 2019;Postorino and Malavasi, 2017;Shi et al., 2020;Szafra nski and Katrusiak, 2017). The rich set of experimental and computational data as a function of pressure collected on 3D perovskites of general formula ABX 3 (A= methylammonium, formamidinium, cesium, etc.; B=Pb, Sn, and Ge; X= Cl, Br, and I) allowed to highlight and define several common trends in the pressure-response of, for example, band gap and carrier lifetime, providing a solid basis to anticipate and predict the phase stability and electronic properties changes in these phases (Coduri et al., 2019(Coduri et al., , 2020Jaffe et al., 2017;Li et al., 2019;Morana and Malavasi, 2021;Postorino and Malavasi, 2017;Seo et al., 1998;Shi et al., 2020;Szafra nski and Katrusiak, 2017). In addition to the fundamental research interest of pressure-induced phenomena, the information collected in situ during pressure application may be possibly used at ambient conditions in devices by a proper modulation of stress/strain phenomena (Jiao et al., 2021;Zhu et al., 2019). ...
... All three of these pre-solar materials have high melting points and therefore are suitable for our Arrhenius-based approach. While we are unware of any study of noble gas incorporation in these pre-solar materials, there are a number of successful atomistic simulation studies of high-temperature effects in silicon-carbide [55], graphite and carbide-derived-carbons [30,31] and glassy carbon [26,27,56]. These structures provide a natural starting point for further atomistic simulations to reveal the astrophysical secrets of noble gases in pre-solar grains. ...
... This software was also used to render the structural images and calculate the coordination numbers of the sp, sp 2 , and sp 3 structural motifs using a cutoff distance of 1.8 Å, which fully encloses the first-neighbors shell for NP carbon. We used a single frame to calculate the RDF and ADF, which is sufficient 15,37 for systems with a large number of atoms. ...
... The XRD patterns for the glassy carbon (GC) electrode and for (Pt/Ani/Ar) are shown in Figure 1b. 35 The two patterns match well. In particular, the pattern for (Pt/Ani/Ar) lacks the intense peaks at about 39.8°, 46.2°, and 68.5°expected for the (111), (200), and (220) reflections in crystalline platinum (PDF# 04-0802). ...
... [8][9][10][11] Recently, attention has been drawn to the shear sensitivity of carbon materials. [12][13][14] The transformation to diamond from glassy carbon 12 and graphite 13,14 was found to be thermodynamically favored with the application of shear. As to graphene, the occurrence of shear-induced diamonization has been predicted by molecular dynamics simulations, 15 while the effect of high shear stress on graphene has not been sufficiently studied by experimental work. ...
... Other forms of carbon, such as glass-like carbon, can be also employed as a proxy for disordered carbonaceous material (e.g., Tumiati et al., 2020). Glass-like carbon, also known as glassy carbon, is a non-crystalline and nongraphitizing carbon, which will not develop graphite crystals up to 3000 • C at room pressure and up to 45 GPa at room temperature (Shiell et al., 2018). This form of amorphous carbon is considered an inert phase which will not react with the experimental assemblages and therefore can also serve as fluid/melt trap (e.g., Van Den Bleeken et al., 2010;Borghini et al., 2018;Dasgupta et al., 2005;Falloon et al., 2008;Robinson et al., 1998;Spandler et al., 2008;Wasylenki et al., 2003). ...