We have undertaken first-principles electronic structure calculations to show that the chemical functionalization of two-dimensional hydrogenated silicene (silicane) and germanene (germanane) can become a powerful tool to increase the photocatalytic water-splitting activity. Spin-polarized density functional theory within the GGA-PBE and HSE06 types of exchange correlation functionals has been used to obtain the structural, electronic, and optical properties of silicane and germanane functionalized with a series of nonmetals (N, P, and S), alkali metals (Li, Na, and K) and alkaline-earth metals (Mg and Ca). The surface-adsorbate interaction between the functionalized systems with H2 and O2 molecules that leads to envisaged hydrogen and oxygen evolution reaction activity has been determined.

First principles-based electronic structure calculations of superhard iron tetraboride (FeB 4 ) under high pressure have been undertaken in this study. Starting with a "conventional" superconducting phase of this material under high pressure leads to an unexpected phase transition toward a semiconducting one. This transition occurred at 53.7 GPa, and this pressure acts as a demarcation between two distinct crystal symmetries, metallic orthorhombic and semiconducting tetragonal phases, with Pnnm and I4 1 /acd space groups, respectively. In this work, the electron-phonon coupling-derived superconducting T c has been determined up to 60 GPa and along with optical band gap variation with increasing pressure up to 300 GPa. The dynamic stability has been confirmed by phonon dispersion calculations throughout this study.metal-semiconductor phase transition | superhard material | first principle study | high pressure | superconductivity T he shorter interatomic distances of metal under external pressure consequently increase the valence and conduction band widths, which leads to the enhancement of free electronlike behavior. The development of creating immensely substantial pressure at laboratories enables us to observe the core electrons overlapping under enormous compression and dramatically influences the electronic properties of normally free electron metals such as Li and Na (1-3). The metalto-insulating phase transformation has been contrived both experimentally and theoretically for both the normal metals while exerting pressure on them. This observation propelled us to investigate the electronic and structural phase transformation of the experimentally synthesized superhard material iron tetraboride (FeB 4 ) under high pressure (4-8). The intriguing factor of choosing FeB 4 is that the material was proposed as a "conventional" Fe-based superconductor, in contradiction to the discovery of an "unconventional" Febased superconductor because of its large electron-phonon coupling. Here we report the exotic phase transition of FeB 4 from metal to semiconductor at 53.7 GPa, even though we started with the metallic orthorhombic phase Pnnm of FeB 4 , which shows the superconducting temperature T c up to 60 GPa. The new phase after 53.7 GPa has I4 1 =acd space group symmetry with a finite fundamental band gap, which increases along with pressure monotonically. All of the considered structures have been tested to have a thermodynamic stability from phonon dispersion calculations. The reason behind the phenomena could be the overlap of atomic cores at higher pressure ranges, which increases the hybridization of valence electrons and their repulsive interactions with core electrons. The immediate technological outcome of this scenario of metal-to-semiconducting phase transition could be to search for a transparent state of a material that is a metal under ambient conditions. This drastic change of electronic and structural properties can be observed in other materials as well, and hence this can open a field of studying them...

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Abstract:The use of solid waste for the development of new building materials has been an alternative to reduce environmental impacts through the preservation of natural resources. In this context, this paper evaluates the possibility of using agate gemstone waste, called rolled powder, which basically consists of silica (SiO 2 ), in the manufacture of aerated foamed concrete blocks completely replacing the natural sand. Preformed foam was used as the air entrained by mechanical stirring with a mixture of natural foaming agents derived from coconut. To produce test specimens, the water/cement ratio and foam concentrations were varied, with three and four levels, respectively. The specimens were left for 28 days at room temperature to be cured, and then underwent analysis to determine their compressive strength, density, and the distribution of air-voids. The experiments demonstrated that the best water/cement ratio was 1.28 for 18% (of total solid mass) addition of foam, which generated a sample with a density of 430 kg/m 3 , and a compressive strength of 1.07 MPa. The result for compressive strength is 11% smaller than the requirements of the Brazilian standard (NBR 13438) for autoclaved aerated concrete blocks, but the results are promising.

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