Showing papers on "Tetragonal crystal system published in 2022"

Zoology of Multiple‐Q Spin Textures in a Centrosymmetric Tetragonal Magnet with Itinerant Electrons

Abstract: Magnetic skyrmion is a topologically stable particle‐like swirling spin texture potentially suitable for high‐density information bit, which was first observed in noncentrosymmetric magnets with Dzyaloshinskii–Moriya interaction. Recently, nanometric skyrmion has also been discovered in centrosymmetric rare‐earth compounds, and the identification of their skyrmion formation mechanism and further search of nontrivial spin textures are highly demanded. Here, magnetic structures in a prototypical skyrmion‐hosting centrosymmetric tetragonal magnet GdRu2Si2 is exhaustively studied by performing the resonant X‐ray scattering experiments. A rich variety of double‐Q magnetic structures, including the antiferroic order of meron(half‐skyrmion)/anti‐meron‐like textures with fractional local topological charges are identified. The observed intricate magnetic phase diagram is successfully reproduced by the theoretical framework considering the four‐spin interaction mediated by itinerant electrons and magnetic anisotropy. The present results will contribute to the better understanding of the novel skyrmion formation mechanism in this centrosymmetric rare‐earth compound, and suggest that itinerant electrons can ubiquitously host a variety of unique multiple‐Q spin orders in a simple crystal lattice system.

Effect of Ag doped MnO2 nanostructures suitable for wastewater treatment and other environmental pollutant applications

Abstract: A modest sol-gel method has been employed to prepare the pure and Ag doped MnO2 nanoparticles and methodologically studied their physical, morphological, and photosensitive properties through XRD, TEM, EDAX, Raman, UV, PL and N2 adsorption - desorption study. Tetragonal crystalline arrangement with spherical nanoparticles was found out through XRD and TEM studies. The EDAX studies further supported that formation Ag in the MnO2 crystal matrix. The bandgap energy of Ag doped MnO2 was absorbed through UV spectra. Photo -generated recombination process and surface related defects were further recognized by PL spectra. Through visible light irradiation, the photo - degradation of methyl orange (MO) and phenol dye solutions were observed. The optimum condition of (10 wt% of Ag) Ag doped MnO2 catalyst showed tremendous photocatalytic efficiency towards MO than phenol under same experimental study.

Charge-two Weyl phonons with type-III dispersion

Abstract: In recent years, charge-two Weyl point phonons (WPPs) have attracted increasing attention. Charge-two WPPs not only provide a new platform for realizing phonon-based unconventional Weyl points (WPs) but also help in realizing specific phonon-based transport behaviors. Herein, based on the first-principles calculations and symmetry analysis, we propose a realistic material with the $P{3}_{1}21$ space group, ${\mathrm{BaZnO}}_{2}$, which has a charge-two WPP and two charge-one WPPs at high-symmetry points. These three unpaired WPPs form a unique triangular Weyl complex. Unlike previously reported material candidates with type-I or type-II charge-two WPPs, the proposed ${\mathrm{BaZnO}}_{2}$ has a type-III charge-two WPP, which has a constant frequency surface that contains two electronlike or holelike states connected at the charge-two WP. ${\mathrm{BaZnO}}_{2}$ can support double-helicoid phonon surface states that cover the entire (001) surface Brillouin zone. The clean type-III WPP, unique triangular Weyl complex, and clear and long surface states in ${\mathrm{BaZnO}}_{2}$ suggest that it is an excellent platform for further research into the physics and applications of type-III charge-two WPPs. Furthermore, we pointed out that charge-two WPPs with type-III band dispersion may appear at high-symmetry points in space groups 75--80, 89--98, 143--146, 149--155, 168--173, 177--182, 196, 207--210. Besides trigonal ${\mathrm{BaZnO}}_{2}$, some material candidates, including tetragonal ${\mathrm{MgTiO}}_{4}$, trigonal ${\mathrm{Li}}_{2}{\mathrm{GeF}}_{6}$, hexagonal ${\mathrm{CaSO}}_{4}$, and cubic ${\mathrm{Li}}_{10}{\mathrm{B}}_{14}{\mathrm{Cl}}_{2}{\mathrm{O}}_{25}$, are also shown to be the hosts of type-III charge-two WPPs.

Study on Properties of Potassium Sodium Niobate Coating Prepared by High Efficiency Supersonic Plasma Spraying

Abstract: In order to realize the construction of environmentally friendly potassium sodium niobate ceramic coating on metal surface, potassium sodium niobate ceramic coating was prepared by supersonic plasma spraying technology. The morphology, element extension and phase structure of such coating were investigated. The dielectric and ferroelectric properties were also analyzed. The results show that the coating has good quality and tetragonal phase structure. When test frequency ≥ 2 MHz, the dielectric constant is stable at about 300, and also dielectric loss is stable at about 0.05. The coating exhibits good hysteresis loops under different applied electric fields. When the applied electric field is 16 KV/cm, residual polarization value of as-prepared coating reaches 17.02 μC·cm−2.

Strain Adjustment Realizes the Photocatalytic Overall Water Splitting on Tetragonal Zircon BiVO4

Abstract: Overall water splitting to generate H2 and O2 is vital in solving energy problem. It is still a great challenge to seek efficient visible light photocatalyst to realize overall water splitting. In this work, the tetragonal zircon BiVO4 is prepared by epitaxial growth on FTO substrate and its overall water splitting reaction is studied. Under the influence of epitaxial strain, the conduction band position shifts negatively and beyond H+/H2 reduction potential (0 V vs NHE), which enables it to possess the photocatalytic hydrogen evolution activity. After loading cocatalysts, the overall water splitting (λ > 400 nm) is realized (H2: ≈65.7 µmol g−1 h−1, O2: ≈32.6 µmol g−1 h−1), and the value of solar hydrogen conversion efficiency is 0.012%. The single‐particle photoluminescence (PL) spectra and PL decay kinetics tests demonstrate the cocatalysts are beneficial to the separation and transfer of carriers. The new strategy of adjusting the band structure by strain is provided.

Simultaneously achieving giant piezoelectricity and record coercive field enhancement in relaxor-based ferroelectric crystals

Abstract: A large coercive field (EC) and ultrahigh piezoelectricity are essential for ferroelectrics used in high-drive electromechanical applications. The discovery of relaxor-PbTiO3 crystals is a recent breakthrough; they currently afford the highest piezoelectricity, but usually with a low EC. Such performance deterioration occurs because high piezoelectricity is interlinked with an easy polarization rotation, subsequently favoring a dipole switch under small fields. Therefore, the search for ferroelectrics with both a large EC and ultrahigh piezoelectricity has become an imminent challenge. Herein, ternary Pb(Sc1/2Nb1/2)O3-Pb(Mg1/3Nb2/3)O3-PbTiO3 crystals are reported, wherein the dispersed local heterogeneity comprises abundant tetragonal phases, affording a EC of 8.2 kV/cm (greater than that of Pb(Mg1/3Nb2/3)O3-PbTiO3 by a factor of three) and ultrahigh piezoelectricity (d33 = 2630 pC/N; d15 = 490 pC/N). The observed EC enhancement is the largest reported for ultrahigh-piezoelectric materials, providing a simple, practical, and universal route for improving functionalities in ferroelectrics with an atomic-level understanding.

Ultrahigh Energy-Storage Performances in Lead-free Na0.5Bi0.5TiO3-Based Relaxor Antiferroelectric Ceramics through a Synergistic Design Strategy.

Abstract: Dielectric ceramics with outstanding energy-storage performances are nowadays in great demand for pulsed power electronic systems. Here, we propose a synergistic design strategy to significantly enhance the energy-storage properties of (1 - x)(0.94Na0.5Bi0.5TiO3-0.06BaTiO3)-xCaTi0.75Ta0.2O3 solid solution ceramics through introducing polar nanoregions, shifting rhombohedral to tetragonal phase transition below room temperature (stable antiferroelectric characteristic), as well as increasing the band gap in the system. Ultrahigh energy-storage properties with a record value of recoverable energy-storage density Wrec ∼ 9.55 J/cm3 and a high efficiency η ∼ 88% are achieved in Na0.5Bi0.5TiO3-based bulk ceramics with x = 0.24. Moreover, high Wrec (>3.4 J/cm3) and η (>90%) with a variation of less than 6% can be observed in a wide frequency and temperature frequency range of 5-200 Hz and 25-140 °C. Our research result not only indicates the great possibility of Na0.5Bi0.5TiO3-based lead-free compositions to replace lead-based energy-storage ceramics but also gives an effective strategy to design ultrahigh energy-storage performances for eco-friendly ceramics.

The emergence of valency in colloidal crystals through electron equivalents

Abstract: Colloidal crystal engineering of complex, low-symmetry architectures is challenging when isotropic building blocks are assembled. Here we describe an approach to generating such structures based upon programmable atom equivalents (nanoparticles functionalized with many DNA strands) and mobile electron equivalents (small particles functionalized with a low number of DNA strands complementary to the programmable atom equivalents). Under appropriate conditions, the spatial distribution of the electron equivalents breaks the symmetry of isotropic programmable atom equivalents, akin to the anisotropic distribution of valence electrons or coordination sites around a metal atom, leading to a set of well-defined coordination geometries and access to three new low-symmetry crystalline phases. All three phases represent the first examples of colloidal crystals, with two of them having elemental analogues (body-centred tetragonal and high-pressure gallium), while the third (triple double-gyroid structure) has no known natural equivalent. This approach enables the creation of complex, low-symmetry colloidal crystals that might find use in various technologies.

MnO2-SnO2 Based Liquefied Petroleum Gas Sensing Device for Lowest Explosion Limit Gas Concentration

Abstract: In this work, MnO2-SnO2 nanocomposite based below lower exposure limit (0.5–2.0 vol%) sensing device for liquefied petroleum gas (LPG) is reported. The synthesized material is highly crystalline with an average crystallite size of 16.786 nm, confirmed by the X-ray diffraction pattern. Williamson-Hall plot shows that the induced strain of 2.627 × 10−4, present in the nanocomposite, lies between the induced strains of both of its constituents. The XRD pattern of nanocomposite contains the cubic phase of MnO2 and the tetragonal phase of SnO2. Tauc plot shows the optical energy band gap of MnO2, SnO2, and MnO2-SnO2 of 3.407 eV, 3.037 eV, and 3.202 eV respectively. The surface morphological investigation shows the brush-like structure which enhances sensor performance by providing activation sites. The energy dispersive X-ray (EDS) spectrum found that materials are highly pure because other peaks are not observed. The functional group analysis by using FTIR found to be Sn–O and Mn–O both vibration bands existed. The highest sensor response was found to be 2.42 for 2.0 vol% whereas for a lower concentration of 0.5 vol% the sensor response was observed to be 1.44. The fast response and recovery of this sensing device were found to17.30 and 23.25 s respectively for 0.5 vol% of LPG.

Comparative Study of Sonophotocatalytic, Photocatalytic, and Catalytic Activities of Magnesium and Chitosan-Doped Tin Oxide Quantum Dots

Abstract: The present study demonstrates the hydrothermal synthesis of SnO2 quantum dots (QDs) doped with different concentrations (2, 4 wt %) of magnesium (Mg) and a fixed amount of chitosan (CS). The obtained samples were investigated through a number of characterizations for optical analysis, elemental composition, crystal structure, functional group presence, interlayer spacing, and surface morphology. The XRD spectrum revealed the tetragonal structure of SnO2 with no significant variations occurring upon the addition of CS and Mg. The crystallite size of QDs was reduced by incorporation of dopants. The optical absorption spectra revealed a red shift, assigned to the reduction of the band gap energy upon doping. TEM analysis proved that the few nanorod-like structures of CS overlapped with SnO2 QDs, and agglomeration was observed upon Mg doping. The incorporation of dopants little enhanced the d-spacing of SnO2 QDs. Moreover, the synthesized nanocatalyst was utilized to calculate the degradation percentage of methylene blue (MB) dye. Afterward, a comparative analysis of catalytic activity, photocatalytic activity, and sonophotocatalytic activity was carried out. Notably, 4% Mg/CS-doped QDs showed maximum sonophotocatalytic degradation of MB in basic medium compared to other activities. Lastly, the prepared nanocatalyst was found to be efficient for dye degradation in any environment and inexpensive.

Modified, Solvothermally Derived Cr-doped SnO2 Nanostructures for Enhanced Photocatalytic and Electrochemical Water-Splitting Applications

Abstract: Cr-doped SnO2 nanostructures with a dopant concentration ranging from 1 to 5% have been successfully prepared using low-temperature modified solvothermal synthesis. The as-prepared nanoparticles showed a rutile tetragonal structure with a rough undefined morphology having no other elemental impurities. The particle shape and size, band gap, and specific surface area of the samples were investigated by scanning electron microscopy, transmission electron microscopy (TEM), high-resolution TEM, UV–visible diffused reflectance spectroscopy, and Brunauer–Emmett–Teller surface area studies. The optical band gap was found in the range of 3.23–3.67 eV and the specific surface area was in the range of 108–225 m2/g, which contributes to the significantly enhanced photocatalytic and electrochemical performance. Photocatalytic H2 generation of as-prepared Cr-doped SnO2 nanostructures showed improved effect of the increasing dopant concentration with narrowing of the band gap. Electrochemical water-splitting studies also stressed upon the superiority of Cr-doped SnO2 nanostructures over pristine SnO2 toward hydrogen evolution reaction and oxygen evolution reaction responses.

Multiple Skyrmion Crystal Phases by Itinerant Frustration in Centrosymmetric Tetragonal Magnets

Abstract: A skyrmion crystal (SkX) expressed as a multiple number of spiral modulations manifests itself not only in its peculiar magnetic texture but also in nontrivial transport properties originating from an emergent magnetic field. We here report our numerical results for multiple SkXs in a centrosymmetric tetragonal crystal system. By performing simulated annealing for an effective spin model for itinerant magnets, we find that three types of the SkXs with the skyrmion numbers of one and two, which are characterized by different superpositions of helices, are stabilized in the ground state, and are transformed by an external magnetic field. The essence of the emergent multiple SkXs lies in itinerant frustration where exchange interactions are competed in momentum space due to the nature of itinerant electrons.

Morphotropic Relaxor Boundary Construction Highly Boosts the Piezoelectric Properties of Bi-Based Lead-Free Thin Films.

Abstract: To achieve large electrostrain and low hysteresis, we further optimized a morphotropic phase boundary (MPB) by modulating its local polar symmetries. The construction of a morphotropic relaxor boundary (MRB) in thin films can be achieved by suitable introduction of Bi(Fe0.95Mn0.03Ti0.02)O3 into (Bi0.5Na0.5)TiO3-SrTiO3 to form a solid solution. The designed thin film achieves surprising piezoelectric properties with an inverse piezoelectric coefficient of 179.7 pm V-1 and negligible hysteresis. The composition of two relaxors with different local polar symmetries (tetragonal nanoregions and rhombohedral nanoregions), namely, an MRB, and the coexistence of multiscale domain structures can greatly weaken the anisotropy of polarization, degrade the energy barrier, attenuate the discontinuity of polarization, and achieve a large electrostrain and low hysteresis. The domain dynamics of the PNRs under the action of an external excitation field are analyzed to clarify the enhancement mechanism. This construction of MRBs is feasible for producing lead-free piezoelectric films with high-voltage electrical properties and low hysteresis, and various experimental design and theoretical references are provided.

Modulating polarization rotation to stimulate the high piezocatalytic activity of (K, Na)NbO3 lead-free piezoelectric materials

Abstract: The strategy of modulating polarization rotation of potassium sodium-niobate ((K 0.5 Na 0.5 )NbO 3 , KNN) lead-free piezoelectric materials was reported to boost piezoelectric properties and resultant piezocatalytic activities. The effectiveness of modulating polarization rotation was proved by degrading Rhodamine B (RhB) using three KNN-based samples with different phase structures (i.e., orthorhombic (O) phase, orthorhombic-tetragonal (O-T) coexistence phase, and rhombohedral-orthorhombic-tetragonal (R-O-T) coexistence phase). Poled samples with the R-O-T coexistence phase show a reaction rate constant of 0.091 min −1 owing to the easiest polarization rotation, 2.12 times more than that of poled O-phase featured samples with the most difficult polarization rotation. Enhanced piezocatalytic activities primarily originate from the easier polarization rotation and improved carrier concentration, accompanied by the trace of the mechano-charge generation. Therefore, modulating polarization rotation effectively boosts piezocatalysis of KNN-based materials, promising for harnessing natural energy and disease treatment. • lead-free (K, Na)NbO 3 materials are eco-friendly piezocatalyst. • Proposing a new strategy to enhance there piezocatalysis. • Obtaining a high k value of 0.091 min −1 , much superior to those of other materials. • Unveiling the physical mechanisms of the superior piezocatalytic activities.

Flame-made ternary Pd-In2O3-ZrO2 catalyst with enhanced oxygen vacancy generation for CO2 hydrogenation to methanol

Abstract: Palladium promotion and deposition on monoclinic zirconia are effective strategies to boost the performance of bulk In2O3 in CO2-to-methanol and could unlock superior reactivity if well integrated into a single catalytic system. However, harnessing synergic effects of the individual components is crucial and very challenging as it requires precise control over their assembly. Herein, we present ternary Pd-In2O3-ZrO2 catalysts prepared by flame spray pyrolysis (FSP) with remarkable methanol productivity and improved metal utilization, surpassing their binary counterparts. Unlike established impregnation and co-precipitation methods, FSP produces materials combining low-nuclearity palladium species associated with In2O3 monolayers highly dispersed on the ZrO2 carrier, whose surface partially transforms from a tetragonal into a monoclinic-like structure upon reaction. A pioneering protocol developed to quantify oxygen vacancies using in situ electron paramagnetic resonance spectroscopy reveals their enhanced generation because of this unique catalyst architecture, thereby rationalizing its high and sustained methanol productivity.