Boosting Piezocatalytic Performance of BaTiO3 by Tuning Defects at Room Temperature.

Defect engineering constitutes a widely-employed method of adjusting the electronic structure and properties of oxide materials. However, controlling defects at room temperature remains a significant challenge due to the considerable thermal stability of oxide materials. In this work, a facile room-temperature lithium reduction strategy is utilized to implant oxide defects into perovskite BaTiO3 (BTO) nanoparticles to enhance piezocatalytic properties. As a potential application, the piezocatalytic performance of defective BTO is examined. The reaction rate constant increases up to 0.1721 min-1, representing an approximate fourfold enhancement over pristine BTO. The effect of oxygen vacancies on piezocatalytic performance is discussed in detail. This work gives us a deeper understanding of vibration catalysis and provides a promising strategy for designing efficient multi-field catalytic systems in the future.

Anomalous Hall effect in Nd-doped Bi1.1Sb0.9STe2 topological insulator single crystals.

Topological insulators are emerging materials with insulating bulk and symmetry protected nontrivial surface states. One of the most fascinating transport behaviors in a topological insulator is the quantum anomalous Hall effect, which has been observed in magnetic-topological-insulator-based devices. In this work, we report successful doping of rare-earth element Nd into Bi1.1Sb0.9STe2 bulk-insulating topological insulator single crystals, in which the Nd moments are ferromagnetically ordered at ∼100 K. Benefiting from the in-bulk-gap Fermi level, electronic transport behaviors dominated by the topological surface states are observed in the ferromagnetic region. At low temperatures, strong Shubnikov-de Haas oscillations with a nontrivial Berry phase are observed. The topological insulator with long range magnetic ordering in Nd-doped Bi1.1Sb0.9STe2 single crystals provides a good platform for quantum transport studies and spintronic applications.

The developments of cyan emitting phosphors to fulfill the cyan emission gap of white-LEDs.

Future generations of solid-state lighting (SSL) will prioritize the development of innovative luminescent materials with superior characteristics. The phosphors converted into white light-emitting diodes (white LEDs) often have a blue-green cavity. Cyan-emitting phosphor fills the spectral gap and produces "full-visible-spectrum lighting." Full-visible spectrum lighting is beneficial for several purposes, such as light therapy, plant growth, and promoting an active and healthy lifestyle. The design of cyan garnet-type phosphors, like Ca2LuHf2Al3O12 (CLHAO), has recently been the subject of interest. This review study reports a useful cyan-emitting phosphor based on CLHAO composition with a garnet structure to have a cyan-to-green emitting color with good energy transfer. It could be employed as cyan filler in warm-white LED manufacturing. Due to its stability, ability to dope with various ions suitable for their desired qualities, and ease of synthesis, this garnet-like compound is a great host material for rare-earth ions. The development of CLHAO cyan-emitting phosphors has exceptionally high luminescence, resulting in high CRI and warm-white LEDs, making them a viable desire for LED manufacturing. The development of CLHAO cyan-emitting phosphors with diverse synthesis techniques, along with their properties and applications in white LEDs, are extensively covered in this review paper.

High-mobility spin-polarized two-dimensional electron gas at the interface of EuTiO3/SrTiO3heterostructures.

Spin polarization of two-dimensional electron gas (2DEG) at the interface of EuTiO3/SrTiO3(STO) heterostructures has been theoretical predicted and experimentally observed via x-ray magnetic circular dichroism and polarized x-ray absorption spectroscopy, which, however, is lack of magnetotransport evidence. Here, we report the fabrication of high-quality EuTiO3/STO heterostructures by depositing antiferromagnetic insulating EuTiO3thin films onto STO substrates. Shubnikov-de Haas oscillation, Hall, and magnetoresistance (MR) measurements show that the interface is not only highly conducting, with electron mobility up to5.5×103cm2V-1s-1at 1.8 K, but also shows low-field hysteretic MR effects. MR of ∼9% is observed at 1.8 K and 20 Oe, which is one order of magnitude higher than those observed in other spin-polarized 2DEG oxide systems. Moreover, the heterostructures show ferromagnetic hysteresis loops. These results demonstrate that the high-mobility 2DEG is spin polarized, whose origin is attributed to the interfacial Ti3+-3dstates due to oxygen deficiency and the exchange interactions between interfacial Eu spins and itinerant Ti-3delectrons.

Domain Matching Strategy for Orientation Control of van der Waals Epitaxial Perovskite Thin Films.

The advantages of van der Waals epitaxy have attracted great interest because they can meet the requirements that conventional epitaxy struggles to satisfy. The weak adatom-substrate interaction without directional covalent bonding drastically relaxes the lattice matching limitation. However, the weak adatom-substrate interaction also leads to ineffectiveness in directing the crystal growth structure, limiting it to one orientation in epitaxial growth. In this work, we propose a domain matching strategy to guide the perovskite-type crystal epitaxial growth on 2D substrates, and we have demonstrated selective deposition of highly (001)-, (110)-, and (111)-oriented epitaxial Fe4N thin films on mica substrates using applicable transition structure design. Our work makes it possible to achieve and control different orientations of van der Waals epitaxy on the same substrate.

Coexistence of logarithmic and SdH quantum oscillations in ferromagnetic Cr-doped tellurium single crystals.

We report the synthesis of transition-metal-doped ferromagnetic elemental single-crystal semiconductors with quantum oscillations using the physical vapor transport method. The 7.7 atom% Cr-doped Te crystals (Cr:Te) show ferromagnetism, butterfly-like negative magnetoresistance in the low temperature (<3.8 K) and low field (<0.15 T) region, and high Hall mobility, e.g. 1320 cm2V-1s-1at 30 K and 350 cm2V-1s-1at 300 K, implying that Cr:Te crystals are ferromagnetic elemental semiconductors. WhenB// [001] // I, the maximum negative MR is ∼-27% atT= 20 K andB= 8 T. In the low temperature semiconducting region, Cr:Te crystals show strong discrete scale invariance dominated logarithmic quantum oscillations when the direction of the magnetic fieldBis parallel to the [100] crystallographic direction (B// [100]) and show Landau quantization dominated Shubnikov-de Haas oscillations forB// [210] direction, which suggests the broken rotation symmetry of the Fermi pockets in the Cr:Te crystals. The findings of coexistence of multiple quantum oscillations and ferromagnetism in such an elemental quantum material may inspire more study of narrow bandgap semiconductors with ferromagnetism and quantum phenomena.

Spin Reorientation Transition and Negative Magnetoresistance in Ferromagnetic NdCrSb3 Single Crystals.

High-quality NdCrSb3 single crystals are grown using a Sn-flux method, for electronic transport and magnetic structure study. Ferromagnetic ordering of the Nd3+ and Cr3+ magnetic sublattices are observed at different temperatures and along different crystallographic axes. Due to the Dzyaloshinskii-Moriya interaction between the two magnetic sublattices, the Cr moments rotate from the b axis to the a axis upon cooling, resulting in a spin reorientation (SR) transition. The SR transition is reflected by the temperature-dependent magnetization curves, e.g., the Cr moments rotate from the b axis to the a axis with cooling from 20 to 9 K, leading to a decrease in the b-axis magnetization f and an increase in the a-axis magnetization. Our elastic neutron scattering along the a axis shows decreasing intensity of magnetic (300) peak upon cooling from 20 K, supporting the SR transition. Although the magnetization of two magnetic sublattices favours different crystallographic axes and shows significant anisotropy in magnetic and transport behaviours, their moments are all aligned to the field direction at sufficiently large fields (30 T). Moreover, the magnetic structure within the SR transition region is relatively fragile, which results in negative magnetoresistance by applying magnetic fields along either a or b axis. The metallic NdCrSb3 single crystal with two ferromagnetic sublattices is an ideal system to study the magnetic interactions, as well as their influences on the electronic transport properties.

Correction: Magnetotransport and magnetic properties of Cr-modified Mn2Sb epitaxial thin films.

Correction for 'Magnetotransport and magnetic properties of Cr-modified Mn2Sb epitaxial thin films' by Ting-Wei Chen et al., Phys. Chem. Chem. Phys., 2023, 25, 5785-5794, https://doi.org/10.1039/D2CP05442F.

Magnetotransport and magnetic properties of Cr-modified Mn2Sb epitaxial thin films.

High-quality Mn2-xCrxSb (x = 0.01, 0.04, and 0.1) epitaxial thin films were grown on SrTiO3 (STO) (001) single-crystal substrates using molecular beam epitaxy. Magnetotransport and magnetic measurements reveal that the x = 0.01 sample undergoes a quasi-ferrimagnetic (I) [Q-FIM(I)]-to-ferrimagnetic (II) [FIM(II)] spin reorientation (SR) transition and a giant magnetoresistance (MR) associated first-order ferrimagnetic(II)-to-antiferromagnetic (AFM) phase transition upon cooling, resulting in the AFM ground state with a weak in-plane net moment. Upon increasing the doping level from x = 0.01 to 0.1, both the SR transition and the first-order magnetic transition are suppressed. For x = 0.1, the former transition is suppressed, leaving only the Q-FIM(I)-to-AFM transition within the whole temperature region. TAFM-FIM shows almost similar changes upon the application of either in-plane or out-of-plane magnetic fields. TAFM-FIM values of the x = 0.01 and 0.04 samples are much higher than those of the Mn2-xCrxSb bulk with similar doping levels, which can be understood by the clamping effect from STO substrates. For each thin-film sample, the MR effect is observed near TAFM-FIM and disappears in the high temperature Q-FIM(I) phase and low temperature AFM phase, indicating that MR is related to the spin-dependent electron scattering during the first-order magnetic phase transition. Based on the magnetotransport and magnetic data, a magnetic phase diagram is established for the Mn2-xCrxSb films in the low doping level region.

Colossal Magnetoresistance in Ti Lightly Doped Cr2Se3 Single Crystals with a Layered Structure.

Stoichiometric Cr2Se3 single crystals are particular layer-structured antiferromagnets, which possess a noncollinear spin configuration, weak ferromagnetic moments, moderate magnetoresistance (MR ∼14.3%), and poor metallic conductivity below the antiferromagnetic phase transition. Here, we report an interesting >16 000% colossal magnetoresistance (CMR) effect in Ti (1.5 atomic percent) lightly doped Cr2Se3 single crystals. Such a CMR is approximately 1143 times larger than that of the stoichiometric Cr2Se3 crystals and is rarely observed in layered antiferromagnets and is attributed to the frustrated spin configuration. Moreover, the Ti doping not only dramatically changes the electronic conductivity of the Cr2Se3 crystal from a bad metal to a semiconductor with a gap of ∼15 meV but also induces a change in the magnetic anisotropy of the Cr2Se3 crystal from strong out-of-plane to weak in-plane. Further, magnetotransport measurements reveal that the low-field MR scales with the square of the reduced magnetization, which is a signature of CMR materials. The layered Ti:Cr2Se3 with the CMR effect could be used as two-dimensional (2D) heterostructure building blocks to provide colossal negative MR in spintronic devices.

Nontrivial Giant Linear Magnetoresistance in Nodal-Line Semimetal ZrGeSe 2D Layers.

Linear magnetoresistance (LMR) is usually observed in topological quantum materials and plausibly connected with the topologically nontrivial surface state with Dirac-cone-like linear dispersion because the frequently encountered large Hall resistivity can be trivially mixed into the LMR via charge inhomogeneity. Herein, by applying an optimal gate voltage to nodal-line semimetal ZrGeSe two-dimensional (2D) layers with specific thicknesses, we observe a giant nonsaturated LMR of 8 × 104% at 2 K and a magnetic field of 9 T. This giant LMR is accompanied by a very small Hall resistivity, which is inconsistent with the charge inhomogeneity mechanism. Our systematic results confirm that the giant LMR is maximized when the topological semimetal is in the "even-metal" regime and suppressed upon evolution to the normal "odd-metal" regime. The "even-to-odd" transition is universal regardless of the thicknesses of the crystals. A comparison with Abrikosov's quantum LMR theory indicates that the observed LMR cannot be trivial.

Magnetotransport and magnetic properties of the layered noncollinear antiferromagnetic Cr2Se3 single crystals.

We report on the growth of high-quality stoichiometric layered Cr2Se3 single crystals with metallic and noncollinear antiferromagnetic ground state using the chemical vapor transport (CVT) method. The crystals show weak ferromagnetism in the in-plane and out-of-plane directions below the Neél temperature (T N), however, the field-cooled out-of-plane magnetization at 500 Oe and 10 K (∼0.24 µ B/f.u.) is approximately 15 times larger than that of the in-plane one, indicating strong c-axis easy uniaxial magnetic anisotropy, which is further supported by the in-plane and out-of-plane isothermal anisotropic magnetic hysteresis loops and the angular dependent magnetoresistance (MR). The latter also reveals a decrease of the coercive field of the crystal upon the tilting of the weak ferromagnetic easy axis away from the direction of the magnetic field. Further, the out-of-plane isothermal MR are negative below T N and show butterfly shapes for T < 10 K and couple with the magnetic hysteresis M(H) loop. These results may help researchers better understand the interplay between the weak ferromagnetism and the magnetotransport properties of 2D itinerant noncollinear antiferromagnetic systems.

Magnetotransport properties of square-net compounds of NbSiSb and NbGeSb single crystals.

We successfully grew single crystals of Si- and Ge-square-net compounds of NbSiSb and NbGeSb whose excellent crystalline quality are verified using single-crystal x-ray diffraction θ-2θ scans, rocking curves, scanning and transmission electron microscopies. Since these two compounds share major crystallographic similarity with the topological nodal-line semimetals of ZrSiS family, we employ density functional theory (DFT) calculations and magnetotransport measurements to demonstrate their band structures as well as the electron scattering mechanisms. DFT calculations show that the fermiology displays strong anisotropy from the crystallographic c-axis to the ab-plane and weak anisotropy within the ab plane, which is consistent with the strong anisotropic magnetotransport behaviors. Following the Kohler's scaling rule we prove that similar interband and intraband electron-phonon scattering mechanisms work in both the NbSiSb and NbGeSb compounds. The study of electronic transport mechanism in the presence of external magnetic field renders deep insight into topological behavior together with its Fermi surface, and the high similarity of crystallography and strong difference in band structures between the present single crystals and that of ZrSiS family provides the possibility to tune the band structure via element doping.

Photoflexoelectric effect in halide perovskites.

Harvesting environmental energy to generate electricity is a key scientific and technological endeavour of our time. Photovoltaic conversion and electromechanical transduction are two common energy-harvesting mechanisms based on, respectively, semiconducting junctions and piezoelectric insulators. However, the different material families on which these transduction phenomena are based complicate their integration into single devices. Here we demonstrate that halide perovskites, a family of highly efficient photovoltaic materials1-3, display a photoflexoelectric effect whereby, under a combination of illumination and oscillation driven by a piezoelectric actuator, they generate orders of magnitude higher flexoelectricity than in the dark. We also show that photoflexoelectricity is not exclusive to halides but a general property of semiconductors that potentially enables simultaneous electromechanical and photovoltaic transduction and harvesting in unison from multiple energy inputs.

Phosphorus Incorporation into Co9 S8 Nanocages for Highly Efficient Oxygen Evolution Catalysis.

The improvement of activity of electrocatalysts lies in the increment of the density of active sites or the enhancement of intrinsic activity of each active site. A common strategy to realize dual active sites is the use of bimetal compound catalysts, where each metal atom contributes one active site. In this work, a new concept is presented to realize dual active sites with tunable electron densities in monometal compound catalysts. Dual Co2+ tetrahedral (Co2+ (Td )) and Co3+ octahedral (Co3+ (Oh )) coordination active sites are developed and adjustable electron densities on the Co2+ (Td ) and Co3+ (Oh ) are further achieved by phosphorus incorporation (P-Co9 S8 ). The experimental results and density functional theory calculations show that the nonmetal P doping can systematically modulate charge density of Co2+ (Td ) and Co3+ (Oh ) in P-Co9 S8 and simultaneously improve the electrical conductivity of Co9 S8 , which substantially enhances oxygen evolution reaction performance of P-Co9 S8 .

Nonvolatile Control of the Electronic Properties of In2-xCrxO3 Semiconductor Films by Ferroelectric Polarization Charge.

A series of Cr-doped In2-xCrxO3 (ICO) semiconductor thin films were epitaxially grown on (111)-oriented 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-0.29PT) single-crystal substrates by the pulsed laser deposition. Upon the application of an electric field to the PMN-0.29PT substrate along the thickness direction, we realized in situ, reversible, and nonvolatile control of the electronic properties and Fermi level of the films, which are manifested by abundant physical phenomena such as the n-type to p-type transformation, metal-semiconductor transition, metal-insulator transition, crossover of the magnetoresistance (MR) from negative to positive, and a large nonvolatile on-and-off ratio of 5.5 × 104% at room temperature. We also strictly disclose that both the sign and the magnitude of MR are determined by the electron carrier density of ICO films, which could modify the s-d exchange interaction and weak localization effect. Our results demonstrate that the ferroelectric gating approach using PMN-PT can be utilized to gain deeper insight into the carrier-density-related electronic properties of In2O3-based semiconductors and provide a simple and energy efficient way to construct multifunctional devices which can utilize the unique properties of composite materials.

Nonvolatile and Reversible Ferroelectric Control of Electronic Properties of Bi2Te3 Topological Insulator Thin Films Grown on Pb(Mg1/3Nb2/3)O3-PbTiO3 Single Crystals.

Single-phase (00 l)-oriented Bi2Te3 topological insulator thin films have been deposited on (111)-oriented ferroelectric 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-PT) single-crystal substrates. Taking advantage of the nonvolatile polarization charges induced by the polarization direction switching of PMN-PT substrates at room temperature, the carrier density, Fermi level, magnetoconductance, conductance channel, phase coherence length, and quantum corrections to the conductance can be in situ modulated in a reversible and nonvolatile manner. Specifically, upon the polarization switching from the positively poled Pr+ state (i.e., polarization direction points to the film) to the negatively poled Pr- (i.e., polarization direction points to the bottom electrode) state, both the electron carrier density and the Fermi wave vector decrease significantly, reflecting a shift of the Fermi level toward the Dirac point. The polarization switching from Pr+ to Pr- also results in significant increase of the conductance channel α from -0.15 to -0.3 and a decrease of the phase coherence length from 200 to 80 nm at T = 2 K as well as a reduction of the electron-electron interaction. All these results demonstrate that electric-voltage control of physical properties using PMN-PT as both substrates and gating materials provides a simple and a straightforward approach to realize reversible and nonvolatile tuning of electronic properties of topological thin films and may be further extended to study carrier density-related quantum transport properties of other quantum matter.

Ultrasensitive negative photoresponse in 2D Cr2Ge2Te6 photodetector with light-induced carrier trapping.

Cr2Ge2Te6, a layered ferromagnetic semiconductor, has triggered extensive research interest due to its fantastic ferromagnetism and semiconducting characteristics as well as potential applications in next-generation spintronic and nanoelectronic devices. On the basis of its ferromagnetism, combined with rich electronic and optical properties, Cr2Ge2Te6 could be a promising candidate for optoelectronics including magnetophotonics and photodetectors. However, there are no relevant studies addressing this to date. In this work, we comprehensively investigated the photoresponse characteristics of few-layer Cr2Ge2Te6-based detectors. An uncommon negative photoconductivity (NPC) and correlated mechanism are explored with the Cr2Ge2Te6 photodetector. It is found that, both NPC and positive photoconductivity (PPC) may exist in an individual Cr2Ge2Te6 device, which are adjustable by control of the incident light intensity. More significantly, the NPC behavior enables ultrasensitive photoresponses of the Cr2Ge2Te6 photodetectors, where the detection of a weak light with an incident power intensity as low as 0.04 pW and a high responsivity of 340 AW-1 is achieved. This extraordinary performance demonstrates that the two-dimensional (2D) Cr2Ge2Te6 holds great promise for applications in ultraweak light detection.

Integration of Oxide Semiconductor Thin Films with Relaxor-Based Ferroelectric Single Crystals with Large Reversible and Nonvolatile Modulation of Electronic Properties.

We report the fabrication of 0.71Pb(Mg1/3Nb2/3)O3-0.29PbTiO3 (PMN-0.29PT)-based ferroelectric field effect transistors (FeFETs) by the epitaxial growth of cobalt-doped tin dioxide (SnO2) semiconductor thin films on PMN-0.29PT single crystals. Using such FeFETs we realized in situ, reversible, and nonvolatile manipulation of the electron carrier density and achieved a large nonvolatile modulation of the resistance (∼330%) of the SnO2:Co films through the polarization switching of PMN-0.29PT at 300 K. Particularly, combining the ferroelectric gating with piezoresponse force microscopy, X-ray diffraction, Hall effect, and magnetoresistance (MR), we rigorously disclose that both sign and magnitude of the MR are intrinsically determined by the electron carrier density, which could modify the s-d exchange interaction of the SnO2:Co films. Furthermore, we realized multilevel resistance states of the SnO2:Co films by combining the ferroelectric gating with ultraviolet light illumination, demonstrating that the FeFETs have potential applications in multistate resistive memories and electro-optical devices.

Tuning the Weak Ferromagnetic States in Dysprosium Orthoferrite.

RFeO3 orthoferrites, where R is a rare-earth ion of the lanthanide series, are attracting attention mostly because of their promising fast spin dynamics. The magnetic properties of these materials seem to crucially depend on whether the magnetizations of the R and Fe ions' weak ferromagnetic (WFM) components are parallel or antiparallel to each other. Here, we report an extensive investigation of a high-quality DyFeO3 single crystal in which the induced Dy3+ magnetization (FDy) has a natural tendency to be antiparallel to Fe3+ sublattice magnetization (FFe) within a large temperature window. Moreover, we find that specific variations of temperature and applied magnetic fields allow us to make FDy parallel to FFe, or force a spin-flip transition in FFe, among other effects. We found three different magnetic states that respond to temperature and magnetic fields, i.e. linear versus constant or, alternatively, presenting either behavior depending on the history of the sample. An original magnetic field-versus-temperature phase diagram is constructed to indicate the region of stability of the different magnetic phases, and to reveal the precise conditions yielding sudden spin switching and reversals. Knowledge of such a phase diagram is of potential importance to applications in spintronics and magnetic devices.