Room-temperature Polarization Research Articles

Achieving high electromechanical response in lead-free BNT-BT ceramics through synergistic A/B-site doping

Lead-free Bi0.5Na0.5TiO3-based ceramics show great promise for achieving high unipolar strain. However, it remains challenging to implement an effective strategy for microstructural designs with high electromechanical response. Herein, a direct composition-engineering method based on A/B-sites doping is adopted to introduce a synergistic effect of reduced oxygen vacancies, lattice distortion, ferroelectric-to-relaxor phase transition, and nano-sized domains, resulting in a high piezoelectric strain coefficient d*33 of 857 pm/V at a small electric field of 4 kV/mm. Furthermore, a large room-temperature maximum polarization (Pm) of 72.4 μC/cm2 was observed at high electric field. A phase transition from coexisting rhombohedral–tetragonal to pseudocubic was engineered by finely tuning the contents of NaTaO3, leading to a decrease in both remnant polarization (Pr) and coercive field (Ec). The phase diagram of 1-x[0.935(Bi0.5Na0.5TiO3)-0.065(BaTi0.99Nb0.01O3)]-x(NaTaO3) (x = 0–0.04) is proposed, providing a roadmap for engineering high-performance piezoelectric ceramics with enhanced electrostrain responses, which may find potential applications as piezoelectric actuators.

Electrical and optical properties of environmental friendly Li(1‐x)Smx/3NbO3 ceramics for high‐temperature energy storage applications

AbstractThis research article delves into the synthesis and characterization of Li(1‐x)Sm(x/3)NbO3 ceramic, employing a high‐energy ball milling process. The investigation explores the incorporation of Sm3+ at the Li+1 site across a range of compositions (x = 0, 0.01, 0.02, 0.03, 0.04, 0.05). Structural analysis, using x‐ray diffraction (XRD) and Rietveld structural refinement, establishes that within the investigated composition range, no significant changes in the crystal structure are evident. The x‐ray photoelectron spectroscopy revealed the presence of oxygen vacancies as well as the stable oxidation state of different elements like O2−, Nb5+, Sm3+, and Li1+. At sintering temperature 1050°C, the average grain sizes vary approximately from 1.5 to 3.8 μm for different compositions with regular grain morphology. The UV‐Vis analysis reveals a noteworthy reduction in the band gap to 3.09 eV for the x = 0.01 composition. Photoluminescence studies exhibit distinct green, orange, and red bands, with the highest intensity observed for x = 0.01, showcasing promising optical properties. The dielectric permittivity of Sm‐substituted compositions surpasses the response of pure LiNbO3, demonstrating an increasing trend with temperature in the frequency range 100 Hz‐1 MHz intriguingly, no Curie temperature is observed up to 500°C for any composition. The polarization vs electric field hysteresis loop response highlights better polarization characteristics at the room temperature and maximum polarization is 0.66 μC/cm2 for the composition x = 0.05. The energy storage response of the developed compositions is investigated, which reveals a maximum efficiency of 46.64% for x = 0.04 in Li(1‐x)Sm(x/3)NbO3. The tunable optical properties, enhanced dielectric response, and notable energy efficiency of these high TC ceramics suggest their utility across diverse applications. These findings not only contribute to the understanding of functional ceramic materials but also pave the way for their optimized utilization in advanced technological applications, particularly in energy storage devices under nonambient conditions at high temperatures.

Effect of Ce infusion on the structural, dielectric, optical, transport and polarization behavior of Nd-modified triple-layered Aurivillius phase ceramic Bi3NdTi3O12

Herein, the effect of cerium substitution on the structural, dielectric, optical, impedance and leakage current characteristics of Nd modified triple layered Aurivillius phase compound of chemical composition Bi3NdTi3-xCexO12 is investigated. The polycrystalline samples are synthesized via ceramic fabrication technology. Room temperature X-ray analysis confirms their orthorhombic symmetry. Scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS) analysis affirm microstructure and elemental composition of the compounds. The temperature-dependent dielectric study indicates diffused phase transition (DPT) behavior possibly induced by compositional fluctuations and random occupancy of equivalent crystallographic sites. Signature peaks pertaining to metal-oxide bond vibrations are also identified by FTIR study. Impedance spectroscopic study unravels negative temperature coefficient of resistance (NTCR) and non-Debye type relaxation in the samples. UV–Visible spectroscopy reveals a reduction in band-gap from 3.1 eV to 2.83 eV with cerium infusion from x = 0 to x = 0.3. It is due to the introduction of localized mid-gap states thus, suggesting the possibility of photovoltaic applications. Further analysis of electric modulus and impedance characteristics propounds prominent short-range carrier hopping with higher cerium percentage. The room temperature I–V study suggests an increase in the voltage-dependent non-linearity with cerium incorporation. Leakage current analysis reveals a transition from Ohmic to space charge limited conduction (SCLC) type behavior with high electric field. Room temperature polarization study confirms their ferroelectric property. Frequency dependent ac conductivity obeys Jonscher double power law clearly indicating the presence of two dispersive regions dominated by grain and grain boundary effects. Reduced bandgap, enhanced voltage dependent non-linearity, NTCR type property and saturated P-E loops observed in the sample unravel the multifunctional aspects of the fabricated compound.

Structural analysis and polarization study of CoCr2O4 nanoparticles

We present the room temperature polarization study of the multiferroic compound CoCr2O4. The co-existence of two elements (Co and Cr) in partially filled d-blocks makes these compounds exhibit a wide range of physical properties. The Cr3+ions almost invariably cover the octahedral (Oh) sites as the crystal field stabilization energy (CFSE) is more than 224 kJ mol −1. The chemical based Sol-gel self-combustion method has been used to successfully synthesize CoCr2O4 chromite. Laboratory X-ray diffraction (LXRD) and synchrotron X-ray diffraction (SXRD) investigations approve the single-phase face centered crystalline structure. The obtained space group is Fd3m. The average crystallite size has been determined by Debye Scherrer’s method and the Williamson Hall [W-H] method. The obtained size is found to be ~ 27 and 17 nm respectively, for both methods when the data is measured by SXRD. The scanning electron micrograph (SEM) shows the agglomeration of particles, which is confirmed by surface topography. Room temperature polarization study exposes the weaker strength of ferroelectricity, which is principally due to charge reversal in the CoCr2O4 compound. The experimental value for retaining polarization is found to be ~ 65% at room temperature (300K).

Achieving ultralow coercive electric field in (Ca1-1.5xGdx)3Ti2O7 ceramics via dual inhibitory effects on oxygen vacancies

(Ca1-1.5xGdx)3Ti2O7 ceramics with ultralow coercive field were obtained by the flowing oxygen sintering combined with donor doping, and their microstructure, dielectric properties ferroelectric properties, and negative piezoelectric properties were studied. The Gd3+ was introduced into A sites of Ca3Ti2O7 ceramics when x is less than 0.75%, but the Gd3+ occupied B sites of Ca3Ti2O7 ceramics when x is above 0.75%. The introduction of Gd3+ suppresses grain growth and leads to a transition from rod-like grain to irregularly shaped grain. The variation of oxygen vacancy induced by the doping of Gd3+ leads to the change of dielectric and ferroelectric properties of (Ca1-1.5xGdx)3Ti2O7 ceramics. The ultralow coercive field of (Ca1-1.5xGdx)3Ti2O7 (x = 0.25%) sample obtained at PUND and DHM modes reached 58.80 kV/cm and 45.76 kV/cm, respectively, and the higher room-temperature remnant polarization (1.797 μC/cm2/PUND and 2.055 μC/cm2/DHM) was achieved simultaneously. These results indicate that the inhibition of oxygen vacancies contributes to realizing the ultralow coercive field in (Ca1-1.5xGdx)3Ti2O7 ceramics. These findings demonstrate that introducing rare-earth ions as donor dopants into the A site of Ca3Ti2O7 ceramics combined with the flowing oxygen sintering is an essential strategy to achieve ultralow coercive field for Ca3Ti2O7-based materials.

Bandgap engineered BaTiO3-based ferroelectric oxides for photovoltaic applications

Ferroelectric oxides have gained research attention in the field of ferroelectric photovoltaics (PV) after the discovery of power conversion efficiency exceeding the Shockley–Queisser limit in BaTiO3 (BTO) crystals. However, advancement in this field is hindered by the wide bandgap (>3 eV) nature of ferroelectric oxides. In this work, a novel lead-free ferroelectric (1 − x)BTO − xBi(Ni2/3Nb1/3)O3 system was proposed and demonstrated to show bandgap reduction without compromising the polarization. Notably, the system displayed a bandgap reduction from 3.1 to 2.4 eV upon varying the composition from x = 0.0 to 0.05. Particularly, the optimal composition x = 0.02 showed enhancement in polarization (Pmax = 16 μC/cm2) and anomalous PV response with an open-circuit voltage of 6 V at 300 K. The origin of the bandgap reduction and polarization retention is explored experimentally by Raman spectroscopic measurements and analyzed theoretically by density functional theory. Our results revealed that the oxygen octahedral distortions and Ni2+ doping favor bandgap lowering, and Bi3+ ions stabilize the ferroelectric polarization. This study provides insight into the origin of bandgap tuning and paves the route for exploring new low-bandgap ferroelectric material with room temperature polarization.

Enhanced room temperature relative permittivity and low dielectric loss ferroelectric double perovskite for energy storage applications

The polycrystalline ceramic oxide, BaBi1.2Fe0.8TiO6 is synthesized by a mixed oxide method at 1000 °C. XRD and Rietveld's analysis suggests a tetragonal system and P4mm space group. The closely spaced dense micro grains of various shapes and sizes in scanning electron micrograph (SEM) image support the polycrystalline single-phase compound. The UV–Visible spectroscopy results in a convenient value of threshold wavelength (610 nm), absorption bandgap energy (2.23 eV), and reflectance bandgap energy (2.31 eV) which are good responses to the IR and visible range and its possible application in photocatalytic devices. The room temperature (RT) polarization loop shows non-zero remanent polarization, i.e. ferroelectric property of the compound. Relatively higher room temperature dielectric permittivity (ɛr = 2455) with low loss tangent (tanδ) = 0.247 at 100 Hz, phase transition (Td > 200 °C), and Curie (Tc > 470 °C) temperature values are supporting to be as good dielectric material for ceramic capacitors. Transport property shows lower RT current density is in order of 1E-9 at 300 V/cm. The compound follows the Arrhenius equation and results in imminent values of activation energy in ac conductivity (Ea = 0.847 eV at 100 Hz) and dc conductivity (Ea = 0.838 eV) analysis. Based on the results, the present compound is likely to be used as a dielectric material in ceramic capacitors, energy and memory storage devices, and photocatalytic devices.

Room-temperature electric field-induced out-of-plane ferroelectric polarization in strain-free freestanding 2D SrTiO3 membranes

SrTiO3 (STO), a room-temperature paraelectric material in bulk form, has been a rich playground for emergent phenomena for decades. As an emerging material, great attention has been paid to freestanding 2D STO thin films. Recently, the room-temperature ferroelectricity has been unveiled in strained STO thin films; however, it remains an open question whether the strain-free freestanding 2D STO thin film is room-temperature ferroelectric or not. Here, we report the electric field-induced out-of-plane ferroelectric polarization in large-scale, freestanding, and strain-free 2D STO membranes at room temperature. High-resolution piezoresponse force microscopy measurements show that polarization in freestanding strain-free STO membranes can be switched by electric field and persist for an hour. The first-principles calculations suggest that the intrinsic defects such as oxygen vacancies could be linked to the observed spontaneous out-of-plane polarization in 2D STO membranes, which could be further enhanced by external electric field due to the induced symmetry breaking. Our work reports the unprecedented room-temperature ferroelectric polarization in strain-free freestanding 2D STO membranes, unlocking the great potential of freestanding 2D STO for the applications in novel electronic and logic-in-memory devices.

Persistent room-temperature valley polarization in graphite-filtered WS2 monolayer

Transition metal dichalcogenide (TMD) monolayers (1L) in the 2H-phase are two-dimensional semiconductors with two valleys in their band structure that can be selectively populated using circularly polarized light. The choice of the substrate for monolayer TMDs is an essential factor for the optoelectronic properties and for achieving a high degree of valley polarization at room temperature (RT). In this work, we investigate the RT valley polarization of monolayer WS2 on different substrates. A degree of polarization of photoluminescence (PL) in excess of 27% is found from neutral excitons in 1L-WS2 on graphite at RT, under resonant excitation. Using chemical doping through photochlorination we modulate the polarization of the neutral exciton emission from 27% to 38% for 1L-WS2/graphite. We show that the valley polarization strongly depends on the interplay between doping and the choice of the supporting layer of TMDs. Time-resolved PL measurements, corroborated by a rate equation model accounting for the bright exciton population in the presence of a dark exciton reservoir support our findings. These results suggest a pathway towards engineering valley polarization and exciton lifetimes in TMDs, by controlling the carrier density and/or the dielectric environment at ambient conditions.

Room-Temperature Ferroelectricity of Paraelectric Oxides Tailored by Nano-Engineering

Inducing clear ferroelectricity in the quantum paraelectric SrTiO3 is important for triggering methods to discover hidden phases in condensed matter physics. Several methods such as isotope substitution and freestanding membranes could introduce ferroelectricity in SrTiO3 toward nonvolatile memory applications. However, the stable transformation from quantum paraelectric SrTiO3 to ferroelectricity SrTiO3 at room temperature still remains challenging. Here, we used multiple nano-engineering in (SrTiO3)0.65/(CeO2)0.35 films to achieve an emergent room-temperature ferroelectricity. It is shown that the CeO2 nanocolumns impose large out-of-plane strains and induce Sr/O deficiency in the SrTiO3 matrix to form a clear tetragonal structure, which leads to an apparent room-temperature ferroelectric polarization up to 2.5 μC/cm2. In collaboration with density functional theory calculations, it is proposed that the compressive strains combined with elemental deficiency give rise to local redistribution of charge density and orbital order, which induce emergent tetragonality of the strained SrTiO3. Our work thus paves a pathway for architecting functional systems in perovskite oxides using a multiple nano-design.

Anion-induced robust ferroelectricity in sulfurized pseudo-rhombohedral epitaxial BiFeO3 thin films via polarization rotation.

Polarization rotation caused by various strains, such as substrate and/or chemical strain, is essential to control the electronic structure and properties of ferroelectric materials. This study proposes anion-induced polarization rotation with chemical strain, which effectively improves ferroelectricity. A method for the sulfurization of BiFeO3 thin films by introducing sulfur anions is presented. The sulfurized films exhibited substantial enhancement in room-temperature ferroelectric polarization through polarization rotation and distortion, with a 170% increase in the remnant polarization from 58 to 100.7 μC cm-2. According to first-principles calculations and the results of X-ray absorption spectroscopy and high-angle annular dark-field scanning transmission electron microscopy, this enhancement arose from the introduction of S atoms driving the re-distribution of the lone-pair electrons of Bi, resulting in the rotation of the polarization state from the [001] direction to the [110] or [111] one. The presented method of anion-driven polarization rotation might enable the improvement of the properties of oxide materials.

Nonvolatile Electrical Valley Manipulation in WS2 by Ferroelectric Gating.

Valleytronics in transition metal dichalcogenides has been intensively investigated for potential applications in next-generation information storage, data processing, and signal transmission devices. Here a ferroelectric gating approach is engaged in achieving nonvolatile electrical tuning of the valley-excitonic properties of monolayer and bilayer WS2. The gating effects include carrier doping and ferroelectric coupling, which are further distinguished by comparing two geometries where the gate electrodes are in direct contact with or insulated from the WS2 crystal. The results show that the carrier doping from gate electrodes acts on WS2 through carrier screening, which only moderately alters the valley polarization. In contrast, the ferroelectric gating promotes electron-phonon interaction, introduces a strong surface polarization field, and controls the interfacial charge trapping/detrapping, causing a Stark shift in exciton energy and strongly enhancing room-temperature valley polarization. In bilayer WS2, the intralayer-interlayer exciton transition is further induced, contributing to even higher valley polarization. The ferroelectric coupling effect can still be maintained after the removal of gate voltage, showing its nonvolatile nature. The role of ferroelectricity is further verified by the anomalous temperature dependence in valley polarization. This work has revealed effective electrical control over valley excitons in semiconductors through interaction with ferroelectric materials. The reported high room-temperature valley polarization in WS2 will boost the development of valleytronics devices.

Magnetic Domain Characterization and Physical Properties of Gd-Doped and (Gd, Al) Co-Doped ZnO Thin Films.

Undoped ZnO, Gd-doped ZnO with various doping concentration (1, 3, 5, and 7 at%), and 3 at% (Gd, Al) co-doped ZnO films were prepared on a glass substrate using the co-reactive sputtering method. The influence of the doping and co-doping process on the films was characterized using X-ray diffraction, FESEM, EDX, MFM, VSM, UV-VIS spectroscopy, and the Hall Effect measurement at room temperature. XRD study confirmed that the Gd and Al ions are incorporated into a ZnO lattice. EDX analysis confirmed the existence of Zn, O, Al, and Gd elements in the prepared Gd-doped ZnO and (Gd, Al) co-doped ZnO films, which suggests the successful doping procedure. All the deposited films obtained maximum optical transmittance above 80%, showing a high transparency of the films in the visible region. The optical band gap was found red-shifted from 3.11 to 3.21 eV with the increase in Gd doping concentration. The increase in band gap energy from 3.14 eV to 3.16 eV was obtained for 3 at% Gd and 3 at% (Gd, Al) co-doped ZnO films. The MFM measurement proved the existence of room-temperature ferromagnetism and spin polarization in Gd and (Gd, Al) co-doped ZnO films. By co-doping with Al, the result obtained from MFM shows the enhancement of magnetic properties, as it exhibited a smaller domain size with a shorter magnetic correlation length L, a larger phase shift Φrms, and the highest value of δfrms compared to the sample with 3 at% Gd incorporated into ZnO. The carrier concentration and electrical conductivity increased with the increase in Gd concentration, whereas the electrical resistivity and hall mobility showed a reverse trend. The similar trend of results obtained for 3 at% (Gd, Al) co-doped ZnO as compared to 3 at% Gd-doped ZnO also indicates greater electrical properties after a shallow donor such as aluminum was incorporated into Gd-doped ZnO thin films. In conclusion, for future applications, one should consider the possible influence of other types of shallow donor incorporation in an attempt to enhance the properties of new types of diluted magnetic semiconductors (DMSs).

Room-temperature polarization of individual nuclear spins in diamond via anisotropic hyperfine coupling and coherent population trapping

We employ the electronic spin of a single nitrogen-vacancy (NV) defect in diamond to detect and control the quantum state of remote nuclear spins coupled by hyperfine interaction. More precisely, our work focuses on individual ^{13}text {C} nuclei featuring a moderate hyperfine coupling strength (sim 1 MHz) with the NV’s electron spin. Two different methods providing an efficient room-temperature polarization of these peculiar ^{13}text {C} nuclear spins are described. The first one is based on a polarization transfer from the NV electron spin to the ^{13}text {C} nucleus, which is mediated by the anisotropic component of the hyperfine interaction. The second one relies on coherent population trapping (CPT) within a Lambda -type energy-level configuration in the microwave domain, which enables to initialize the ^{13}text {C} nuclear spin in any quantum state superposition on the Bloch sphere. This CPT protocol is performed in an unusual regime for which relaxation from the excited level of the Lambda -scheme is externally triggered by optical pumping and separated in time from coherent microwave excitations. For these two polarization techniques, we investigate the impact of optical illumination on the nuclear spin polarization efficiency. This work adds new methods to the quantum toolbox used for coherent control of individual nuclear spins in diamond, which might find applications in quantum metrology.Graphical

Fortified relaxor ferroelectricity of rare earth substituted 4-layered BaBi3.9RE0.1Ti4O15 (RE = La, Pr, Nd, and Sm) Aurivillius compounds

In this report, the effect of rare-earth (RE3+) ion substitution on structural, microstructural, and electrical properties in barium bismuth titanate (BaBi4Ti4O15) (BBTO) Aurivillius ceramics has been investigated. The Rietveld refinements on X-ray diffraction (XRD) patterns confirm that all the samples have an orthorhombic crystal system with A21am space group. Meanwhile, temperature dependent synchrotron XRD patterns reveal that the existence of dual phase in higher temperature region. The randomly oriented plate-like grains are experimentally strived to confirm the distinctive feature of bismuth layered Aurivillius ceramics. The broad band dielectric spectroscopic investigation signifies a shifting of ferroelectric phase transition (Tm) towards low temperature region with a decrease of the RE3+-ionic radii in BBTO ceramics. The origin of diffuse ferroelectric phase transitions followed by stabilization of the relaxor ferroelectric nature at high frequency region is explained using suitable standard models. The temperature dependent ac and dc conductivity results indicate the presence of double ionized oxygen vacancies in BBTO ceramics, whereas the dominance of single ionized oxygen vacancies is observed in RE-substituted BBTO ceramics. The room temperature polarization vs. electric field (P–E) hysteresis loops are shown to be well-shaped symmetric for BBTO ceramics, whereas slim asymmetric ferroelectric characteristics developed at RE-substituted BBTO ceramics.

Flash Sintered Potassium Sodium Niobate: High-Performance Piezoelectric Ceramics at Low Thermal Budget Processing.

Alternative sintering technologies promise to overcome issues associated with conventional ceramic sintering such as high thermal budgets and CO2 footprint. The sintering process becomes even more relevant for alkali-based piezoelectric ceramics such as K0.5Na0.5NbO3 (KNN) typically fired above 1100 °C for several hours that induces secondary phase formation and, thereby, degrades their electrical characteristics. Here, an ability of KNN ceramics to be of high performance is successfully demonstrated, using an electric field- and current-assisted Flash sintering technique at 900 °C only. Reported for the first time, Flash sintered KNN ceramics have room-temperature remnant polarization Pr = 21 μC/cm2 and longitudinal piezoelectric coefficient d33 = 117 pC/N, slightly superior to that of conventional ones due to the reduced content of secondary phases. High-performance KNN ceramics Flash sintered at a low-thermal budget have implications for the development of innovative low carbon technologies, electroceramics stakeholders, and piezoelectric energy harvesters.

Enhanced room-temperature spin-valley coupling in V-doped MoS2

Achieving room-temperature valley polarization in two-dimensional (2D) atomic layers (2D materials) by substitutional doping opens new avenues of applications. Here, monolayer ${\mathrm{MoS}}_{2}$, when doped with vanadium at low (0.1 atomic %) concentrations, is shown to exhibit high spin-valley coupling, and hence a high degree of valley polarization at room-temperature. The atomic layers of ${\mathrm{MoS}}_{2}$ (MS) and V-doped ${\mathrm{MoS}}_{2}$ (VMS) are grown via the chemical vapor deposition-assisted method. The formation of new energy states near the valence band is confirmed from band gap calculations and also from the density functional theory--based band structure analyses. Time-reversal symmetry broken energy shift in the equivalent valleys is predicted in VMS, and the room-temperature chirality-controlled photoluminescent (PL) excitation measurements indicate such a shift in valley exciton energies (\ensuremath{\sim}35 meV). An enhanced valley polarization in VMS (\ensuremath{\sim}42%) is observed in comparison to that in MS (12%), while in MS, the chirality-controlled excitations did not show the difference in emission energies. Spin Hall effect of light--based optical rotation measurements indicate the asymmetric absorption among the two different chiralities of the incident light, hence supporting the existence of room-temperature valley polarization. This study opens possibilities of room-temperature opto-spintronics using stable 2D materials.

Colossal Room-Temperature Ferroelectric Polarizations in SrTiO3/SrRuO3 Superlattices Induced by Oxygen Vacancies.

Artificial superlattices have demonstrated many unique phenomena not found in bulk materials. For this investigation, SrTiO3/SrRuO3 paraelectric/metallic superlattices with various stacking periods were synthesized via pulsed laser deposition. A robust room-temperature ferroelectric polarization (∼46 μC/cm2) was found in the superlattices with 2 unit cell (u.c.) thick SrRuO3 layers, despite the fact that neither SrTiO3 nor SrRuO3 is inherently ferroelectric. Results obtained from atomically resolved elemental mapping and X-ray photoelectron spectroscopy verified that oxygen vacancies accumulated at the SrTiO3/SrRuO3 interfaces, causing lattice distortions and increased tetragonality (c/a). The observed ferroelectric responses can be mainly attributed to the broken spatial inversion symmetry induced by the ordered distribution of oxygen vacancies at the SrTiO3/SrRuO3 interfaces, coupled with the triggering of external electric field. The resulting polarization mechanism induced by oxygen vacancies suggests viable ways for improving the electrical properties of ferroelectric materials, with the goal of expanding the functionality of a range of electronic devices.

Electrical Switching of the Off-Resonance Room-Temperature Valley Polarization in Monolayer MoS2 by a Double-Resonance Chiral Microstructure.

Enhancing and expanding the manipulated range of room-temperature valley polarization at off-resonance wavelength is extremely crucial to developing various functional valleytronic devices. Although these have been realized through the double-resonance strategy or twist-angle engineering, the demand for electrical control over the concepts remains elusive. Here, we fabricate a gate-tunable double-resonance chiral microstructure using a molybdenum disulfides (MoS2) monolayer. On the basis of the varied interface charge density, we demonstrate the huge photoluminescence (PL) tuning ability of this configuration. Furthermore, benefiting predominately from the screening of long-range e-h exchange interactions and the chiral Purcell effect, the electrical switching of the room-temperature valley polarization at off-resonance wavelength is also realized. Our work enriches the functions of TMDs-based optoelectronic devices and may create important applications in future valley-polarized encode and information processing devices.

Crystal structure, dielectric and impedance studies of a new lead free tungsten bronze ferroelectric oxide

The current manuscript describes the structure, dielectric and impedance nature of the ferroelectric ceramic Na2Ba2Y2W2Ti4Nb4O30 made by high temperature mixed oxide route. The compound formation with orthorhombic phase and surface morphology was verified by X-ray diffraction and scanning electron microscopy techniques respectively. The temperature variation of dielectric parameters (εr and tan δ) at selected frequencies of the material exhibits dual phase transitions at 323 and 573 K, respectively. The low temperature phase transition is considered as structural type in the ferroelectric phase and the high temperature (573 K) transition is related to transformation from ferroelectric phase to paraelectric phase. The room temperature polarization curve is plotted to assure the ferroelectricity in the ceramic. The frequency dependent impedance parameters at given temperature range determines the contribution of both bulk and grain boundary effects in it. The intrinsic resistance due to grains of the material follows opposite trend with temperature like semiconductors. Temperature dependent bulk resistance is used to obtain various thermistor parameters and their variation with temperature is discussed. Jonscher’s law is referred to understand the frequency dependent ac conductivity and it’s various temperature dependent parameters (A and n).