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The Sb2WO6 photocatalyst is synthesized by introducing oxygen vacancies through acetylene annealing. The number of oxygen vacancies can be adjusted by varying the annealing duration. Oxygen vacancy defects in Sb2WO6 change the surface chemical properties, enhance the separation of carriers, broaden the absorption of visible light, and activate the catalytic sites, resulting in overall enhancement of the photocatalytic properties. The significance of surface oxygen vacancies and pertinent mechanisms of photocatalytic oxidation are described. Our results reveal a promising method to improve the properties of Sb2WO6-based materials for applications such as the treatment of wastewater. [ABSTRACT FROM AUTHOR]

Electrical control of conductivity and magnetism in two-dimensional (2D) ferroelectric (FE) materials have attracted immense attention due to their fascinating properties and potential applications in designing field-effect transistors and high-density multistate data storage. Based on first-principles calculations and crystal field theory, we present an approach to obtain 2D intrinsic asymmetric multiferroics by replacing the In atom in the ferroelectric In2X3 monolayer (X = S, Se) with the Cr atom. Interestingly, it is found that the InCrX3 monolayers have two inequivalent polarized states, which are characterized by metal and semiconductor, respectively, which is related to the crystal field around Cr3+ ions. Thus, it provides a feasible way to realize electrical control of reversible metal–insulator transition induced by ferroelectric switching, indicating that the InCrX3 monolayers can be used as the channel materials in the FE memory technology. In addition, because of the existence of the Cr3+ ions, the InCrX3 monolayers also exhibit robust ferromagnetism with different Curie temperatures and magnetocrystalline anisotropy energies, which can provide a good platform for realizing the strong coupling between the magnetism and ferroelectricity. These interesting results provide a feasible way to design asymmetric FE materials with regulatable conductivity and magnetism that can enable a wide range of applications in nanodevices. [ABSTRACT FROM AUTHOR]

Using first-principles calculations, the structural, electronic, piezoelectric, and optical properties of Janus Sc2CXY (X ≠ Y, X/Y = F, Cl, Br, and I) MXenes were comprehensively investigated. All of the studied MXenes are structurally stable. Both Young's modulus Y and Poisson's ratio ν are isotropic and can be modulated by the surface-functionalized halogen atoms. In addition, the band gaps of all the Janus Sc2CXY MXenes can be modulated from 0.638 eV to 1.437 eV by different functional groups. Interestingly, the semiconductor–metal transition for Janus Sc2CXI (X = F, Cl, and Br) can occur when the compressive strain reaches 6%. Furthermore, because of their symmetric breaking, the Janus Sc2CXY MXenes exhibit excellent in-plane and out-of-plane piezoelectric properties. High optical absorption is found in the visible and ultraviolet ranges for all the studied MXenes, and it is expected that they can be utilized in the fields of piezoelectric and optoelectronic nanodevices. [ABSTRACT FROM AUTHOR]

The coupling of topological electronic states and ferroelectricity is highly desired due to their abundant physical phenomenon and potential applications in multifunctional devices. However, it is difficult to achieve such a phenomenon in a single ferroelectric (FE) monolayer because the two polarized states are topologically equivalent. Here, we demonstrate that the symmetry of polarized states can be broken by constructing a Janus structure in a FE monolayer. We illustrate such a general idea by replacing a layer of Te atoms in the In2Te3 monolayer with S atoms. Using first-principles calculations, we show that the In2Te2S monolayer has two asymmetric polarized states, which are characterized by a metal and semiconductor, respectively. Importantly, as the spin–orbit coupling is included, a band gap (50.4 meV) is created in the metallic state, resulting in a non-trivial topological phase. Thus, it proves to be a feasible method to engineer non-volatile FE control of topological order in a single-phase system. We also demonstrate the underlying physical mechanism of topological phase transition, which is unveiled to be related to the weakened intrinsic electric field resulting from charge transfer. These interesting results provide a general way to design asymmetric FE materials and shed light on their potential application in non-volatile multifunctional devices. [ABSTRACT FROM AUTHOR]

Due to their potential application in spintronic devices, two-dimensional (2D) ferromagnetic materials are highly desired. We used first-principles calculations and Monte Carlo simulations to investigate the electronic structure and magnetic characteristics of the MnOCl2 monolayers. We discovered two stable monolayer structures, Pmna-MnOCl2 and Pmmn-MnOCl2. Our findings show that the Pmna-MnOCl2 monolayer is an intrinsic ferromagnetic semiconductor with an indirect band gap of 0.152 eV and a Curie temperature (TC) of 202 K, while the Pmmn-MnOCl2 monolayer is an intrinsic ferromagnetic Dirac semimetal with a high TC (910 K) and triaxial magnetic anisotropy. We also show that a Pmmn-MnOCl2 monolayer with a nontrivial band gap of 6.2 meV can achieve the quantum anomalous Hall effect (QAHE) with Chern number C = 1. Additionally, the existence of a gapless edge state can be flexibly regulated by choosing the terminal edges. Our studies reveal that the Pmmn-MnOCl2 monolayer can serve as a candidate material to achieve high-temperature QAHE. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials with intrinsic ferromagnetism and piezoelectricity have received growing attention due to their potential applications in nanoscale spintronic devices. However, their applications are highly limited by the low Curie temperatures (TC) and small piezoelectric coefficients. Here, using first-principles calculations, we have successfully predicted that BiCrX3 (X = S, Se, and Te) monolayers simultaneously possess ferromagnetism and piezoelectricity by replacing one layer of Bi atoms with Cr atoms in Bi2X3 monolayers. Our results demonstrate that BiCrX3 monolayers are not only intrinsic ferromagnetic semiconductors with indirect band gaps, adequate TC values of higher than 300 K, and significant out-of-plane magnetic anisotropic energies, but also exhibit appreciable in-plane and out-of-plane piezoelectricity. In particular, the in-plane piezoelectric coefficients of BiCrX3 monolayers with ABCAB configuration are up to 15.16 pm V−1, which is higher than those of traditional three-dimensional piezoelectric materials such as α-quartz. The coexistence of ferromagnetism and piezoelectricity in BiCrX3 monolayers gives them promising applications in spintronics and nano-sized sensors. [ABSTRACT FROM AUTHOR]

Two-dimensional (2D) materials with intrinsic half-metallicity at or above room temperature are important in spin nanodevices. Nevertheless, such 2D materials in experiment are still rarely realized. In this work, a new family of 2D Cr 2 TeX 2 (X = I, Br, Cl) monolayers has been predicted using first-principles calculations. The monolayer is made of five atomic sublayers with ABCAB-type stacking along the perpendicular direction. It is found that the energies for all the ferromagnetic (FM) half-metallic states are the lowest. The phonon spectrum calculations and molecular dynamics simulations both demonstrate that the FM states are stable, indicating the possibility of experimentally obtaining the 2D Cr 2 TeX 2 monolayers with half-metallicity. The Curie temperatures from Monte Carlo simulations are 486, 445, and 451 K for Cr 2 TeI 2 , Cr 2 TeBr 2 , and Cr 2 TeCl 2 monolayers, respectively, and their half-metallic bandgaps are 1.72, 1.86 and 1.90 eV. The corresponding magnetocrystalline anisotropy energies (MAEs) are about 1185, 502, 899 μeV per Cr atom for Cr 2 TeX 2 monolayers, in which the easy axes are along the plane for the Cr 2 TeBr 2 and Cr 2 TeCl 2 monolayers, but being out of the plane in the Cr 2 TeI 2 . Our study implies the potential application of the 2D Cr 2 TeX 2 (X = I, Br, Cl) monolayers in spin nanodevices., Competing Interests: The authors have no conflicts of interest to disclose., (This journal is © The Royal Society of Chemistry.)

The coupling of topological electronic states and ferroelectricity is highly desired due to their abundant physical phenomenon and potential applications in multifunctional devices. However, it is difficult to achieve such a phenomenon in a single ferroelectric (FE) monolayer because the two polarized states are topologically equivalent. Here, we demonstrate that the symmetry of polarized states can be broken by constructing a Janus structure in a FE monolayer. We illustrate such a general idea by replacing a layer of Te atoms in the In 2 Te 3 monolayer with S atoms. Using first-principles calculations, we show that the In 2 Te 2 S monolayer has two asymmetric polarized states, which are characterized by a metal and semiconductor, respectively. Importantly, as the spin-orbit coupling is included, a band gap (50.4 meV) is created in the metallic state, resulting in a non-trivial topological phase. Thus, it proves to be a feasible method to engineer non-volatile FE control of topological order in a single-phase system. We also demonstrate the underlying physical mechanism of topological phase transition, which is unveiled to be related to the weakened intrinsic electric field resulting from charge transfer. These interesting results provide a general way to design asymmetric FE materials and shed light on their potential application in non-volatile multifunctional devices.

Due to their potential application in spintronic devices, two-dimensional (2D) ferromagnetic materials are highly desired. We used first-principles calculations and Monte Carlo simulations to investigate the electronic structure and magnetic characteristics of the MnOCl 2 monolayers. We discovered two stable monolayer structures, Pmna -MnOCl 2 and Pmmn -MnOCl 2 . Our findings show that the Pmna -MnOCl 2 monolayer is an intrinsic ferromagnetic semiconductor with an indirect band gap of 0.152 eV and a Curie temperature ( T C ) of 202 K, while the Pmmn -MnOCl 2 monolayer is an intrinsic ferromagnetic Dirac semimetal with a high T C (910 K) and triaxial magnetic anisotropy. We also show that a Pmmn -MnOCl 2 monolayer with a nontrivial band gap of 6.2 meV can achieve the quantum anomalous Hall effect (QAHE) with Chern number C = 1. Additionally, the existence of a gapless edge state can be flexibly regulated by choosing the terminal edges. Our studies reveal that the Pmmn -MnOCl 2 monolayer can serve as a candidate material to achieve high-temperature QAHE.

Two-dimensional (2D) materials with intrinsic ferromagnetism and piezoelectricity have received growing attention due to their potential applications in nanoscale spintronic devices. However, their applications are highly limited by the low Curie temperatures ( T C ) and small piezoelectric coefficients. Here, using first-principles calculations, we have successfully predicted that BiCrX 3 (X = S, Se, and Te) monolayers simultaneously possess ferromagnetism and piezoelectricity by replacing one layer of Bi atoms with Cr atoms in Bi 2 X 3 monolayers. Our results demonstrate that BiCrX 3 monolayers are not only intrinsic ferromagnetic semiconductors with indirect band gaps, adequate T C values of higher than 300 K, and significant out-of-plane magnetic anisotropic energies, but also exhibit appreciable in-plane and out-of-plane piezoelectricity. In particular, the in-plane piezoelectric coefficients of BiCrX 3 monolayers with ABCAB configuration are up to 15.16 pm V -1 , which is higher than those of traditional three-dimensional piezoelectric materials such as α-quartz. The coexistence of ferromagnetism and piezoelectricity in BiCrX 3 monolayers gives them promising applications in spintronics and nano-sized sensors.

Ferromagnetic (FM) semiconductors have been recognized as the cornerstone for next-generation highly functional spintronic devices. However, the development in practical applications of FM semiconductors is limited by their low Curie temperatures (T C ). Here, on the basis of model analysis, we find that the FM super-exchange couplings in the d 5 - d 3 system can be significantly strengthened by reducing the virtual exchange gap (G ex ) between occupied and empty e g orbitals. By first-principle calculations, we predict robust ferromagnetism in three rhombohedral RMnO 3 (R = Sc, Y, and Lu) compounds with the T C that is as high as ∼1510 K (YMnO 3 ). The oxygen breathing motions open a band gap and create an unusual Mn 2+ /Mn 4+ charge ordering of the Mn-d electrons, which play an important role in altering the G ex . Interestingly, the rhombohedral RMnO 3 compounds are also ferroelectric (FE) with a large spontaneous polarization approaching that of LiNbO 3 . These results not only deepen the understandings of magnetic couplings in d 5 - d 3 system, but also provide a way to design room-temperature FM-FE multiferroics.