Pressure-induced novel ZrN semiconductor materials with high dielectric constants: a first-principles study.

In addition to ZrN and ZrN compounds, zirconium nitrides with a rich family of phases always exhibit metal phases. By employing an evolutionary algorithm approach and first-principles calculations, we predicted seven novel semiconductor phases for the ZrN system at 0-150 GPa. Through calculating phonon dispersions, we identified four dynamically stable semiconductor structures under ambient pressure, namely, α-1̄, β-1̄, γ-1̄, and β-1 (with bandgaps of 1.

Pressure-Induced Phase Diagram and Electronic Structure Evolves during the Insulator-Metal Transition of Bulk BiFeO.

BiFeO is the most widely known multiferroic at room temperature, possessing both ferroelectricity and antiferromagnetism. It has high Curie temperature and Néel temperature, i.e.

Activating HfX (X = S, Se and Te) for the hydrogen evolution reaction by introducing defects: a first-principles study.

An ideal catalyst should have a relative hydrogen adsorption Gibbs free energy (Δ) close to zero [J. K. Nørskov, , 2005, , J23].

Prediction of the hardest BiFeO from first-principles calculations.

BiFeO is the only material with ferroelectric Curie temperature and Néel temperature higher than room temperature, making it one of the most well-studied multiferroic materials. Based on an evolutionary algorithm, we predicted a new cubic C-type antiferromagnetic structure (3̄-BiFeO) at ambient pressure. It was found that 3̄-BiFeO is the hardest BiFeO (Vickers hardness ∼ 9.

Defect-Induced Ultrafast Nonadiabatic Electron-Hole Recombination Process in PtSe Monolayer.

Defects are inevitable in two-dimensional materials due to the growth condition, which results in many unexpected changes in materials' properties. Here, we have mainly discussed the nonradiative recombination dynamics of PtSe monolayer without/with native point defects. Based on first-principles calculations, a shallow p-type defect state is introduced by a Se antisite, and three n-type defect states with a double-degenerate shallow defect state and a deep defect state are introduced by a Se vacancy.

Accurately Controlling the Occupation of Eu in Cs(K, Na)(LiSiO) to Achieve Narrow-Band Green Emission for Wide Color Gamut Displays.

The development of narrow-band phosphors for wide color gamut displays in multimodal phosphors through selective site occupancy engineering is an important challenge. In this work, by replacing Na ions with K ions in the cyan-green double-band emitting phosphor CsKNa(LiSiO): 10%Eu, the occupation of Eu in Cs(K, Na)(LiSiO) was accurately controlled from occupying three sites of Cs, K1, and Na to occupying only one site of K2/Na. The obtained phosphor CsKNa(LiSiO): 10%Eu exhibits a single narrow-band green emission at 531 nm (the full width at half-maximum of 46 nm) with excellent thermal stability of luminescence from 80 to 523 K (96.

Semiconductors with a chiral crystal structure in group IVB transition metal pernitrides.

Group IVB transition metal (TM) nitrides rarely exhibit the semiconductor phase, except for TMN (TM = Ti, Zr, and Hf) compounds. In this study, using the calculations based on density functional theory, we report two chiral crystal structures, namely 321 and 321, of TMN, which are dynamically stable at ambient pressure. Unlike conventional metal phases of transition metal dinitrides, the 321 and 321 configurations exhibit intriguing semiconductor properties (with bandgaps of 1.

Enhanced electronic and optical properties of multi-layer arsenic via strain engineering.

Solar cell is a kind of devices for renewable and environmentally friendly energy conversion. One of the important things for solar cells is conversion efficiency. While much attention has been drawn to improving efficiency, the role of strain engineering in two-dimensional materials is not yet well-understood.

New multiferroic BiFeO with large polarization.

BiFeO is one of the most widely studied multiferroic materials, because of its large spontaneous polarization at room temperature, as well as ferroelasticity and antiferromagnetism. Using an evolutionary algorithm, we found two new dynamically stable BiFeO structures (6 and 622) at ambient pressure. Their energy is only 0.

Zero Poisson's ratio in single-layer arsenic.

Zero (or near-zero) Poisson's ratio (ZPR) materials have important applications in the field of precision instruments because one of their faces is stable and will not be affected by strain. However, ZPR materials are extremely rare. Here, we report a novel ZPR material, two-dimensional 2/ arsenene, by first principles calculations.

A first principles study of p-type doping in two dimensional GaN.

Similar to most semiconductors, low-dimensional GaN materials also have the problem of asymmetric doping, that is, it is quite difficult to form p-type conductivity compared to n-type conductivity. Here, we have discussed the geometry, structure, and electronic defect properties of a two-dimensional graphene-like gallium nitride (g-GaN) monolayer belonging to the group III-V compounds, doped with different elements (In, Mg, Zn) at the Ga site. Based on first principles calculations, we found that substituting Ga (low concentration impurities) with Mg would be a better choice for fabricating a p-type doping semiconductor under N-rich conditions, which is essential for understanding the properties of impurity defects and intrinsic defects in the g-GaN monolayer (using the "transfer to real state" model).

The design of dual-switch fluorescence intensity ratio thermometry with high sensitivity and thermochromism based on a combination strategy of intervalence charge transfer and up-conversion fluorescence thermal enhancement.

Currently, the temperature sensing performances of inorganic photoluminescence materials based on fluorescence intensity ratio technology have become a research hotspot in the optical thermometry field due to their non-contact sensing, fast response and high stability. However, several problems have obstructed the development of optical temperature sensing materials, including low sensitivity and narrow temperature measurement ranges. In view of the above dilemma, a new optical thermometer La2Mo3O12:Yb3+,Pr3+ designed based on the combination strategy of intervalence charge transfer and up-conversion fluorescence thermal enhancement was developed.

New two-dimensional arsenene polymorph predicted by first-principles calculation: robust direct bandgap and enhanced optical adsorption.

In this work, we predict a new polymorph of 2D monolayer arsenic. This structure, named-As, consists of a centrosymmetric monolayer, which is thermodynamically and kinetically stable. Distinctly different from the previously predicted monolayer arsenic with an indirect bandgap, the new allotrope exhibits a direct bandgap characteristic.

Two-dimensional arsenene polymorph beyond the auxetic foam: high mechanical sensitivity and large, negative NPR.

Single-layer δ-As and γ-P have unique atomic arrangement, which belong to the Pmc21 and Pbcm space groups, respectively. Because of the coupling hinge structure, the physical properties of the two materials have obvious anisotropy. In this paper, we report the mechanical properties of the single-layer δ-As and γ-P.

Factors affecting the negative Poisson's ratio of black phosphorus and black arsenic: electronic effects.

Negative Poisson's ratio (NPR) materials (when stretched longitudinally, the thickness of these materials increases along the lateral direction) are widely used in engineering because of their good resistance to shear, denting, and fracture. Observance of a negative Poisson's ratio (NPR) in two-dimensional (2D) single-layer materials presently has two explanations. The first, from mechanical principles, is that it derives from the presence of a special structure (hinge structure), such as in single-layer black phosphorus (BP) or black arsenic (β-As).

Anti-twinning in nanoscale tungsten.

Nanomaterials often surprise us with unexpected phenomena. Here, we report a discovery of the anti-twinning deformation, previously thought impossible, in nanoscale body-centered cubic (BCC) tungsten crystals. By conducting in situ transmission electron microscopy nanomechanical testing, we observed the nucleation and growth of anti-twins in tungsten nanowires with diameters less than about 20 nm.

Tuning element distribution, structure and properties by composition in high-entropy alloys.

High-entropy alloys are a class of materials that contain five or more elements in near-equiatomic proportions. Their unconventional compositions and chemical structures hold promise for achieving unprecedented combinations of mechanical properties. Rational design of such alloys hinges on an understanding of the composition-structure-property relationships in a near-infinite compositional space.

Brittle Fracture of 2D MoSe.

An in situ quantitative tensile testing platform is developed to enable the uniform in-plane loading of a freestanding membrane of 2D materials inside a scanning electron microscope. The in situ tensile testing reveals the brittle fracture of large-area MoSe crystals and measures their fracture strength for the first time.