Recent advances in the synthetic growth of nanowires have given access to crystal phases that in bulk are only observed under extreme pressure conditions. Here, we use first-principles methods based on density functional theory and many-body perturbation theory to show that a suitable mixing of hexagonal Si and hexagonal Ge yields a direct bandgap with an optically permitted transition. Comparison of the calculated radiative lifetimes with typical values of nonradiative recombination mechanisms indicates that optical emission will be the dominant recombination mechanism. These findings pave the way to the development of silicon-based optoelectronic devices, thus far hindered by the poor light emission efficiency of cubic Si
Systematic studies on polycrystalline Hf1–xZrxO2 films with varying Zr contents show that HfO2 films are paraelectric (monoclinic). If the Zr content is increased, films become ferroelectric (orthorhombic) and then antiferroelectric (tetragonal). HfO2 shows very good insulating properties and it is used in metal-oxide-semiconductor field-effect devices, while ZrO2 shows good piezoelectric properties, but it is antiferroelectric. In between, Hf0.5Zr0.5O2 shows good ferroelectric properties at the expense of poorer insulating and piezoelectric properties than HfO2 and ZrO2, respectively.
About ten years after ferroelectricity was first reported in doped HfO2 polycrystalline films, there is tremendous interest in this material and ferroelectric oxides are once again in the spotlight of the memories industry. Great efforts are being made to understand and control ferroelectric properties. Epitaxial films, which have fewer defects and a more controlled microstructure than polycrystalline films, can be very useful for this purpose. Epitaxial films of ferroelectric HfO2 have been much less investigated, but after the first report in 2015 significant progress has been achieved.
We report here a structural study of RBaMn2O6 (R=La, Pr, and Nd) compounds by means of synchrotron radiation x-ray powder diffraction and Raman spectroscopy. The three compounds are A-site ordered perovskites adopting the prototypical tetragonal structure at high temperature. A ferromagnetic transition is observed in the LaBaMn2O6 sample and the lattice parameters undergo anisotropic changes at TC related to the orientation of the magnetic moments.
The layered perovskite YBaCuFeO5 (YBCFO) is considered one of the best candidates to high-temperature chiral multiferroics with strong magnetoelectric coupling. In RBaCuFeO5 perovskites (R: rare-earth or Y) A-site cations are fully ordered whereas their magnetic properties strongly depend on the preparation process. They exhibit partial cationic disorder at the B-site that generates a magnetic spiral stabilized through directionally assisted long range coupling between canted locally frustrated spins.
We report the synthesis and theoretical study of two new colorimetric chemosensors with special selectivity and sensitivity to Ni2+ and Cu2+ ions over other metal cations in the CH3CN/H2O solution. Compounds (E)-4-((2-nitrophenyl)diazenyl)-N,N-bis(pyridin-2-ylmethyl)aniline (A) and (E)-4-((3-nitrophenyl)diazenyl)-N,N-bis(pyridin-2-ylmethyl)aniline (B) exhibited a drastic color change from yellow to colorless, which allows the detection of the mentioned metal cations through different techniques.