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Register a new userFirst principles studies of SnTiO3 perovskite as a potential ferroelectric material
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In the context of the search for environment-respectful, lead- and bismuth- free chemical compounds for devices such as actuators, SnTiO3 (ST) is investigated from first principles within DFT. Full geometry optimization provides a stable tetragonal structure relative to cubic one. From the equation of state the equilibrium volume of SnTiO3 is found smaller than ferroelectric PbTiO3 (PT) in agreement with a smaller Sn2+ radius. While ionic displacements exhibit similar trends between ST and PT a larger tetragonality (c/a ratio) for ST results in a larger polarization, PST = 1.1 C.m2. The analysis of the electronic band structure detailing the Sn-O and Ti-O interactions points to a differentiated chemical bonding and a reinforcement of the covalent bonding with respect to Pb homologue.
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The structural, elastic and electronic properties of ReN are investigated by first-principles calculations based on density functional theory. Two competing structures, i.e., CsCl-like and NiAs-like structures, are found and the most stable structure, NiAs-like, has a hexagonal symmetry which belongs to space group P63/mmc with a=2.7472 and c=5.8180 AA. ReN with hexagonal symmetry is a metal ultra-incompressible solid and has less elastic anisotropy. The ultra-incompressibility of ReN is attributed to its high valence electron density and strong covalence bondings. Calculations of density of states and charge density distribution, together with Mulliken atomic population analysis, show that the bondings of ReN should be a mixture of metallic, covalent, and ionic bondings. Our results indicate that ReN can be used as a potential ultra-incompressible conductor. In particular, we obtain a superconducting transition temperature T$_c$=4.8 K for ReN.
The band structure, optical and defects properties of Ba_{2}TeO are systematically investigated using density functional theory with a view to understanding its potential as an optoelectronic or trans- parent conducting material. Ba_{2}TeO crystallizes with tetragonal structure (space group P4/nmm) and with a 2.93 eV optical band gap 1 . We find relatively modest band masses for both electrons and holes suggesting applications. Optical properties show a infrared-red absorption when doped. This could potentially be useful for combining wavelength filtering and transparent conducting functions. Furthermore, our defect calculations show that Ba_{2}TeO is intrinsically p-type conducting under Ba-poor condition. However, the spontaneous formation of the donor defects may constrain the p-type transport properties and would need to be addressed to enable applications.
Radiative cooling has recently revived due to its significant potential as an environmentally friendly cooling technology. However, the design of particle-matrix cooling nanocomposites was generally carried out via tedious trial-and-error approaches, and the atomistic physics for efficient radiative cooling was not well understood. In this work, we identify the atomistic metrics of Barium Sulfate (BaSO$_4$) nanocomposite, which is an ultra-efficient radiative cooling material, using a predictive first-principles approach coupled with Monte Carlo simulations. Our results show that BaSO$_4$-acrylic nanocomposites not only attain high total solar reflectance of 92.5% (0.28 - 4.0 um), but also simultaneously demonstrate high normal emittance of 96.0% in the sky window region (8 - 13 um), outperforming the commonly used $alpha$-quartz ($alpha$-SiO$_2$). We identify two pertinent characters of ultra-efficient radiative cooling paints: i) a balanced band gap and refractive index, which enables strong scattering while negating absorption in the solar spectrum, and ii) a sufficient number of infrared-active optical resonance phonon modes resulting in abundant Reststrahlen bands and high emissivity in the sky window. The first principles approach and the resulted physical insights in this work pave the way for further search of ultra-efficient radiative cooling materials.
A novel stable crystallographic structure is discovered in a variety of ABO3, ABF3 and A2O3 compounds (including materials of geological relevance, prototypes of multiferroics, exhibiting strong spin-orbit effects, etc...), via the use of first principles. This novel structure appears under hydrostatic pressure, and is the first post-post-perovskite phase to be found. It provides a successful solution to experimental puzzles in important systems, and is characterized by one-dimensional chains linked by group of two via edge-sharing oxygen/fluorine octahedra. Such unprecedented organization automatically results in anisotropic elastic properties and new magnetic arrangements. Depending on the system of choice, this post-post-perovskite structure also possesses electronic band gaps ranging from zero to ~ 10 eV being direct or indirect in nature, which emphasizes its universality and its potential to have striking, e.g., electrical or transport phenomena.
Following our ab initio nonlinear optical (NLO) materials design guidelines, in this Letter, we discovered a novel type of structure to realize potential deep-ultraviolet (DUV) NLO performance in the classical beryllium borate system. By densely stacking the NLO-active layered frameworks, the key design scheme for the structural evolution from the (Be2BO3F2) layers in KBe2BO3F2 (KBBF) to the novel (Be2BO5H3) layers in berborite is illustrated. Based on available experimental results and systematical theoretical evaluation from first principles, the NLO properties of berborite are further obtained as comparable as the only pratical DUV NLO crystal KBBF. It is demonstrated that berborite can achieve available DUV phase-matched output with strong NLO effect for the practically important 177.3 nm and 193.7 nm lasers. Once obtained with sizable single crystal, it can be applied as a promising DUV NLO crystal.
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