Tetragonal Structure Research Articles

Enhanced dielectric, ferroelectric and piezoelectric properties of lead-free (Ba,Ca)(Sn,Ti)O3 ceramics by optimisation of sintering temperature

Lead-zirconate-titanate [Pb(Zr,Ti)O3 PZT] crystals possess superior ferroelectric, dielectric and piezoelectric properties. However, due to the toxicity of lead there is a demand for lead-free alternatives. In the present work, we focus on the production of the lead-free (Ba,Ca)(Sn,Ti)O3 (BCST) ceramics via solid-state synthesis method. BCST ceramics calcined at 1050°C, 1100°C, 1150°C, 1200°C and 1250°C were characterized using XRD analysis which showed that at temperatures above 1150°C the structure was free from impurities. Rietveld refinements confirmed a tetragonal structure with P4mm space group for the material calcined at 1150°C. Scanning electron microscopy image analysis of samples sintered at 1200°C, 1250°C and 1300°C showed an increase in grain size and density with temperature. The material sintered at 1300°C had a higher dielectric constant compared to other ceramics. A larger grain size facilitated high ferroelectric polarisation (3.38 μC/cm2), dielectric constant (6100) and d33 piezoelectric coefficient (236 pC/N) for the ceramics. This study demonstrates the potential for using lead-free BCST ceramics for device applications, such as piezoelectric actuators, transducers and ultrasonic motors.

Synthesis and Characterization of the Electrical and Energy Storage Properties of New Barium Titanate - Europium Titanate Solid Solution

In the present work, the investigation of the structural, dielectric, ferroelectric and energy storage properties of polycrystalline samples of (1-x)BaTiO3 – xEuTiO3 (BT-ET) solid solution materials prepared by conventional solid-state reaction method has been carried out. X-ray diffraction analyses have revealed the formation of a single-phase tetragonal structure with the P4mm space group. Furthermore, the temperature dependence of the dielectric constants marked the presence of the following sequence of structural phase transitions, namely from rhombohedral to orthorhombic, from orthorhombic to tetragonal and from tetragonal to cubic phase transitions with the increase of temperature. A diffuse phase transition has been observed from the dielectric permittivity peak and has been analyzed using the modified Curie-Weiss law and the degree of diffuseness is found to be in the range of 1.16 - 1.76 due to the existence of different states of polarization. A phase diagram has been established based on the temperature-dependent dielectric permittivity studies. The room temperature ferroelectric properties point to a coercive field larger than that of BaTiO3 ceramics. Broad dielectric peaks associated with diffuse phase transition appear in a wide temperature range (40 - 100 °C) with the highest dielectric permittivity ε’ = 6498 found in the x = 0.05 ceramics. Moreover, an improved energy storage performance is obtained in the 0.95BaTiO3-0.05EuTiO3 ceramic with a recoverable energy density of Wrec = 0.797 J/cm3, coupled with an efficiency η = 73% at 170 kV/cm and the highest storage energy density of Wst = 1.571 J/cm3 is obtained for 0.90BaTiO3-0.10EuTiO3, which is superior to other lead-free BT-based ceramics. All these features demonstrate that the BT-ET ceramics can be widely used in energy storage applications and also in high-temperature multilayer capacitors for automotive, aerospace and related industries.

Optoelectronic properties of BiCuOSe p-type oxychalcogenides

BiCuOSe systems are proposed as candidates to develop transparent p-type semiconductors in the visible region. This work reports the characterization results obtained for the BiCuOSe powders, synthesized by the solid-state reaction (SSR) method through mechanical milling, and nanostructured thin films deposited from the same processed powders using the pulsed laser deposition (PLD) technique. Structural characterization through X-ray diffraction (XRD) showed that the material presents a tetragonal structure with an average crystallite size of 21 nm and a preferential orientation in the (1 0 2) plane. The morphological and particle size evolution of BiCuOSe powders is presented as a function of the milling time. Transmission and scanning electron microscopies confirmed the spherical geometry of the particles in the powders and nanosheets like structure for the films. Particle sizes were also estimated, ranging from 10 to 100 nm for powders and 60 to 70 nm for films. The bandgap values, EG, for BiCuOSe powders were estimated from diffuse reflectance spectra using the Kubelka–Munk method, yielding values close to 0.7 eV. For thin films, EG values were estimated using the Tauc method, obtaining values in the range of 0.8–3.5 eV, depending on the annealing treatment. Additionally, electrical properties were measured in all deposited thin films, confirming the p-type conductivity, a minimal resistivity of 0.0735 Ω cm, hole mobility on the order of 88 cm2/Vs, and carrier concentration of 9.7 × 1018 cm−3.

Nanomechanical behavior, adhesion and wear resistance of tin oxide coatings for biomedical applications

AbstractThis study investigates the properties of tin oxide coatings employed in biomedical applications. The films were deposited on a clean glass substrate, preheated at 450 °C, applying the spray pyrolysis technique as the latter produces crystallized thin films without the need for further heat treatment. X‐ray diffraction analysis showed that tin oxide films had a tetragonal structure characterized by a preferential orientation (111). The measurements of reflectance and transmittance revealed a wide optical band gap of 4.0 eV. Nanoindentation tests showed that the tin oxide coating, with a hardness of 5.9 GPa and a Young's modulus of 78 GPa, exhibited elastic‐plastic behavior. In addition, tribological tests indicated that tin oxide coating had a very low coefficient of friction (μ=0.06), high wear resistance (wear rate 2.10−5 mm3 N−1 m−1) and good adhesion to the substrate (critical adhesion load of 5.55 N). It was also noticed that tin oxide thin films had antibacterial activity due to their nanocrystalline impurities. These properties make tin oxide perfectly acceptable for biomedical applications.

Structural, magnetic, impedance and electric modulus response and dielectric relaxation in Co-doped inverse spinel [formula omitted] nanoferrite

In this research work, we report synthesis, structural, electric and magnetic properties of Cu1−XCoXFe2O4(x = 0.05, 0.10, 0.15, 0.20) nanoferrite. All the samples are synthesized using sol-gel auto-combustion method. X-ray diffraction patterns validate the formation of single phase tetragonal structure at room temperature for all the samples. Absence of secondary phases confirms the successful substitution of Cu2+ by Co2+ ions in CuFe2O4 matrix. Dielectric analysis reveals that all the materials exhibit remarkable single dielectric relaxation. The dielectric relaxation peaks are observed between 150–225 °C. In addition, Co-doped CuFe2O4 exhibit marked enhancement of dielectric constant value for potential technological applications. Further, the correlated barrier hopping (CBH) model well explains the conduction phenomena in all the samples. Activation energy values are analyzed by applying the Arrhenius equation. Impedance analysis indicates that both grain and grain boundary effects contributed the electrical response in the ferrites which is confirmed from the plot of Z″ vs. Z′. The bulk and grain boundary response are further determined by modeling the impedance data with an equivalent circuit. Modulus study confirms the existence of non-Debye type of relaxation in the synthesized ferrites. Magnetic study shows the improved value of magnetic parameters such as saturation magnetization (Ms), remanent magnetization (Mr) and coercive field (Hc).

A comparative study on green synthesis and characterization of Mn doped ZnO nanocomposite for antibacterial and photocatalytic applications

Biological and green synthesis of nanomaterial is a superior choice over chemical and physical methods due to nanoscale attributes implanted in a green chemistry matrix, have sparked a lot of interest for their potential uses in a variety of sectors. This research investigates the growing relevance of nanocomposites manufactured using ecologically friendly, green technologies. The transition to green synthesis correlates with the worldwide drive for environmentally sound procedures, limiting the use of traditional harsh synthetic techniques. Herein, manganese was decorated on ZnO NPs via reducing agent of Withania-extract and confirmed by UV-spectrophotometry with highest peak at 1:2 ratio precursors, and having lower bandgap energy (3.3 eV). XRD showed the sharp peaks and confirms the formation of nanoparticles, having particle size in range of 11–14 nm. SEM confirmed amorphous tetragonal structure while EDX spectroscopy showed the presence of Zn and Mn in all composition. Green synthesized Mn-decorated ZnO-NPs screened against bacterial strains and exhibited excellent antimicrobial activities against gram-negative and gram-positive bacteria. To check further, applicability of synthesized Mn-decorated Zn nanocomposites, their photocatalytic activity against toxic water pollutants (methylene blue (MB) dye) were also investigated and results showed that 53.8% degradation of MB was done successfully. Furthermore, the installation of green chemistry in synthesizing nanocomposites by using plant extract matrix optimizes antibacterial characteristics, antioxidant and biodegradability, helping to build sustainable green Mn decorated ZnO nanomaterial. This work, explains how biologically friendly Mn-doped ZnO nanocomposites can help reduce the environmental impact of traditional packaging materials. Based on these findings, it was determined that nanocomposites derived from biological resources should be produced on a wide scale to eradicate environmental and water contaminants through degradation.

Effect of Zr substitution on photocatalytic and magnetic properties of lanthanum titanate

Abstract Photocatalysis is considered a highly promising method to treat water samples contaminated with organic pollutants. Zirconium-doped lanthanum titanate (LaTi1−x Zr x O3, where x = 0 (LTO) and 0.05 (LZTO)) NPs were synthesized by the auto-combustion method and characterized by X-ray diffraction analysis (XRD), UV–visible diffuse reflectance spectroscopy (UV–vis DRS), Fourier transform infrared (FTIR), field emission scanning electron microscope (FE-SEM), and Raman spectroscopy. LTO and LZTO have tetragonal structure with an average crystalline size of 16 nm and 13 nm respectively. The band gap from UV–vis DRS was estimated to be 3.52 and 3.36 eV, respectively. The analysis of surface morphology indicates that the addition of Zr disrupted the crystal structure of LTO and transformed its spherical morphology into a rod-like structure. The Raman spectra of the LTO and LZTO crystal structure revealed the presence of A g and B 2g symmetry phonons. The magnetic properties were analysed by vibrating sample magnetometer (VSM) which confirmed the ferromagnetic behaviour. LZTO nanoparticles have been shown to have an efficiency of 92 % after 80 min of degradation. The synthesized LZTO samples exhibited enhanced ferromagnetic behaviour and improved photoactivity for the degradation of methylene blue dye as compared to those of pure LTO, make LZTO a good choice for magnetically separable photocatalysts that effectively purify contaminated water.

Sol-gel spin-coated Y-doped SnO2 nanostructured thin films for various optoelectronic device applications

The effect of various concentrations of Y-doped SnO2 thin films (Y: SnO2) on structural, optical, and electrical properties was investigated. XRD showed the polycrystalline tetragonal structure of all the films. SEM analysis showed homogenous growth of the films with spherical structure. XPS revealed the oxidation states of Sn, Y, and O, also it provides the presence of oxygen vacancies in Y: SnO2 films. The UV–visible spectrometer studies showed that all the films were above 76% of optical transmittance in the visible region. The optical band gap energy was found to be 3.91 eV for pure SnO2, whereas Y: SnO2 films have shown a decrease of band gap with Y content and reached down to 3.74 eV in 5 at% Y: SnO2 film. The 3 at% Y: SnO2 film showed the lowest sheet resistance (Rsh) of 34.2 Ω/Sq and the highest figure of merit (ɸ) of 3.55 × 10−3 Ω−1 among the others.

Growth of MAPbI3 perovskite films on MWCNT-modified TiO2 thin films for solar cell applications

In this work, we have modified titanium dioxide (TiO2) films by incorporating multi-walled carbon nanotubes (MWCNTs) in TiO2-sol. TiO2 and MWCNT-modified TiO2 thin films have been prepared via solution processing spin coating route. Further, the structural, optical, and surface morphology of methyl ammonium lead iodide (MAPbI3) films have been studied onto pristine TiO2 and MWCNT-modified TiO2 films. We extensively analyze how different MWCNT concentrations impact the TiO2 and perovskite film structure, optoelectronic properties, and surface characteristics. The findings highlight that the MAPbI3 films maintain a tetragonal structure with enhanced crystallinity compact and smooth surface morphology in MWCNT-modified TiO2/MAPbI3 films. Besides this, enhanced optical absorbance in MAPbI3 films have also been observed on perovskite films fabricated onto MWCNT-modified TiO2 films with enlarged grains and a red shift in optical band gap has been observed for MWCNT-modified TiO2 films and MWCNT-modified TiO2/ MAPbI3 films. Further, various critical electrical parameters such as charge carrier concentration, Hall mobility, sheet resistance, and resistivity have been investigated to understand the effects of the incorporation of MWCNT on TiO2 films. The value of carrier concentration enhances from 3.76 × 1024 cm−3 to 6.39 × 1024 cm−3 on incorporation of MWCNT in TiO2 films. Furthermore, an enhancement in crystallinity, optical absorbance, and grain size has been observed in perovskite films fabricated onto TiO2/MWCNT films. Thus, TiO2 modification with MWCNT can tune the optical and charge transport properties of charge-transporting layer TiO2 films for perovskite photovoltaics and other optoelectronic devices.

In situ biosynthesis, characterization, and degradation of methylene blue dyes from Solanum Crispum flower extracts

Through a natural process of obtaining Solanum Crispum flower extract, Tin-oxide nanoparticles (SnO2 NPs) have been synthesized using an eco-friendly process. The physico-chemical properties of the synthesized SnO2 NPs were assessed by Ultraviolet–Visible, Fourier transforms infrared (FTIR), Raman, XRD, SEM, EDX, and TEM. A distinctive absorption peak at 267 nm, coupled with a 3.5 eV band gap, was observed in UV–visible spectral analysis. SnO functional groups of synthesized NPs were determined through FTIR at 596 cm−1. An active structural mode and a vibrational mode were identified using Raman spectroscopy, and the crystallographic nature and lattice parameters were studied by X-ray diffraction, and the crystallites were 12 nm in size. Photoluminescence (PL) was used to investigate the existence of defects/vacancies in the lattice site. The surface shape was revealed by SEM analysis. EDX was used to identify the elemental constitution. TEM evidence provided a tetragonal rutile structure for SnO2 NPs, and EDX analysis revealed their chemical purity. The DPPH testing technique was used to determine photo-antioxidant properties. The photocatalytic activity of synthesized SnO2 NPs was also investigated, A better result was obtained with these NPs than with commercially available SnO2 NPs.

Manipulating the phase stability of a halide perovskite, CH3NH3PbI3 by high-pressure cycling

Methylammonium lead iodide perovskite, CH3NH3PbI3 (MAPbI3) is a highly promising photovoltaic material, whose structural and electronic properties are very sensitive to applied stresses. Here, we show that the phase stability of a MAPbI3 crystal can be controlled by structural defects and strains. We synthesized a single crystal of MAPbI3 and measured its electrical properties across two successive structural phase transitions under applied pressure up to 4–9 GPa under multiple high-pressure cycling. We revealed three types of effects of this high-pressure treatment. (i) An increasing the level of defects and strains in the crystal greatly delays the first reconstructive phase transition, conserving the ambient-pressure tetragonal phase up to a record pressure of ∼1.4 GPa, much higher compared to its typical stability range of up to 0.3–0.5 GPa only. (ii) A time exposure of the crystal at a fixed pressure corresponding to the beginning of the second phase transition to a “destabilized” structure eliminated some of defects and strains; it down-shifted the phase boundaries back. (iii) A recrystallization of the sample after pressure-induced amorphization enhanced its structural stability against amorphization upon subsequent pressurization cycle. We proposed that the most abundant defects and strains, which could appear in the pressure-cycled MAPbI3 crystals, were related to migration of iodine atoms from their regular sites to the MA interstices. Temperature-dependent photoluminescence measurements indicated that the sample recovered after the high-pressure cycling crystallized back into the initial tetragonal crystal structure. Whereas, its stability range expanded toward lower temperatures by 20 K and a band gap slightly increased, from 1.59 to 1.625 eV (at 290 K). Using this organic-inorganic perovskite as an example, we show how the phase stability of such materials can be manipulated by creation and elimination of structural defects and local strains.

Magnetic suppression for a possible Fe-poor organic–inorganic hybrid superconductor Fe14Se16(tepa)0.8 (tepa = tetraethylenepentamine) with a superconducting transition at ∼42 K

Composition/structure-dependent superconductivity for FeSe-based superconductors attracted great attention not only due to their high superconducting transition temperatures (TC), but also for understanding the origin of iron-based superconductivity. Here, we report a new Fe-poor organic-inorganic hybrid material Fe14Se16(tepa)0.8 with a paramagnetic-diamagnetic transition at ∼42 K grown by a high-temperature organic-solution-phase method with soluble iron/selenium sources in a tepa solution, alternative to previous intercalation strategies. The Fe14Se16(tepa)0.8 phase is in a tetragonal layered hybrid structure with a nanoplate shape. Composition analyses reveal a Fe-poor characteristic of the hybrid in contrast to previous FeSe-intercalated superconductor, and selected area electron diffraction pattern is featured by Fe3Se4 superstructures with a √2 × √2 of Fe vacancy order. Ab initio density functional calculations show that minus Fe3Se4 ions are stable in the hybrid and ∼0.25e−/Fe0.75Se is obviously larger than the reported values of approximately 0.2e−/FeSe in other FeSe-intercalated superconductors. Typical hysteresis loops and temperature dependence of dc/ac susceptibilities of the Fe14Se16(tepa)0.8 measured below ∼42 K suggest a presence of the Meissner effect in this material. Effects of synthesis conditions on structures and magnetic properties of the hybrids show a magnetic evolution from a long-range ferrimagnetic (FIM) order of Fe14Se16(tepa) to a coexistence of FIM and superconducting (SC) orders of Fe14Se16(tepa)0.9 and an SC order of Fe14Se16(tepa)0.8. X-ray absorption spectrum (XAS) confirms the presence of ferric/ferrous irons. Mössbauer studies reveal that the high-TC superconductivity originates from a suppression of the FIM order through tuning the spin states of irons from high-spin Fe3+ (S = 5/2) and Fe2+ (S = 2) in the Fe14Se16(tepa) to low-spin Fe3+ (S = 1/2) and Fe2+ (S = 0) in the Fe14Se16(tepa)0.8. Although no zero resistance is detected even at a temperature of 2 K, the resistivity at 2 K decreases by more than 1600 times compared to that in a normal state calculated by a variable range hopping (VRH) model, suggesting that the high-TC superconductivity of Fe14Se16(tepa)0.8 is possible.

Crystallographic parameters and their systematics within the CeCuAl3-related family of intermetallics

Rare-earth RTX3 compounds (T stands for a transition d-metal and X is a p-metal) form a large family of intermetallics, revealing a variety of intriguing physical properties. Among them, CeTX3 compounds represent a particularly studied group, due to their frequently complex magnetic structures, Kondo physics, pressure-induced superconductivity, or recently highlighted quantum quasi-bound states. We report on the structural properties and their systematics within the CeCuAl3-related intermetallics crystallising in the tetragonal structure of the BaNiSn3-type. Our synchrotron X-ray diffraction data of 14 selected alloys allow us to follow the evolution of crystallographic parameters of the CeCuAl3-based substitution series. Substitutions of R, T and X elements are shown to have significant impact on the unit cell volume, virtual lattice expansion and free fraction coordinates of individual Wyckoff sites. Structural parameters are discussed within the framework of physical properties of investigated compounds.

Exploration of Photoluminescence, Colorimetric, and Decay Performance of Sm-activated CaWO4 Ceramic.

This paper represents structure, photoluminescence, and colorimetric investigations of Sm-activated CaWO4 ceramic made with the help of a solid-state reaction process. Structures of the ceramics are examined through X-ray diffraction spectroscopy. It indicates that these materials have a tetragonal structure and I41/a space group without having any other secondary phase. Energy band gaps are increased with the higher concentrations of Sm dopants. Photoluminescence analyses show that concentration quenching is found at x = 0.02 Sm incorporated CaWO4. The critical distance of energy transfer is obtained as about 20Å. Q-value is observed approximately equal to 6 which denotes that dipole-dipole interactions occur in the materials that create the critical energy transfer distance in them. Chromaticity values are described in that the ceramics emit orange-red color as well as excellent colorimetric parameters. Quantum efficiency of x = 0.02 Sm composition in CaWO4 is measured under 405nm EX wavelength. Photoluminescence decay behaviors are observed and average lifetime values are evaluated.

Structural, optical, and electrical properties of strontium-doped tin dioxide films for high photoconductivity

In this work, tin dioxide (SnO₂) films with different concentrations of strontium (Sr) were prepared using sol-gel and immersing methods. The structural, morphological, optical, and electric properties of Sr-doped SnO₂ films were investigated for photoconductivity applications. X-ray diffraction patterns revealed a tetragonal rutile structure for the deposited films with lattice parameters (a = b = 4.726 Å, c = 3.182 Å). Adding 4.71 at.% of Sr (optimal doping ratio) into SnO2 film leads to a significant decrease in the crystallite size. Consequently, the highest electrical conductivity of Sr-doped SnO₂ films is attained at 4.71 at.%. The transmittance and optical bandgap of Sr-doped SnO₂ films exhibit a significant decrease at a high Sr doping ratio of 10.07 at.%. Additionally, the electrical conductivity of undoped SnO2 and Sr-doped SnO2 (4.71 at. %) films increases from 0.22 S/cm and 2.18 S/cm to 0.43 S/cm and 4.95 S/cm under UV-irradiation, respectively, with good consistency and repeatability. The findings of this work indicate that Sr-doped-SnO2 films are potential candidate materials for a wide range of applications, especially photoconductivity, photodetectors, and photoconductive materials.

Ultra-bright green emitting Sr2MgSi2O7:Tb3+ nanophosphors: unveiling multi-security applications in anti-counterfeiting, flexible films, optical thermometry and latent fingerprint visualization

In this study, we synthesized facile green-emitting Sr2MgSi2O7:Tb3+ (1–11 mol %) nanophosphors (SMSO:Tb3+ NPs) using a solid-state reaction method. Characterization through X-ray diffraction (XRD) revealed a tetragonal crystal structure in the as-synthesized SMSO:Tb3+ NPs. Crystallographic data obtained from Rietveld refinements identified the specific sites of Tb3+ ions in the host material. Chemical and photo-luminescent properties are explored using X-ray photo-electron spectroscopy (XPS) and Photoluminescence (PL) spectroscopy, respectively. The NPs exhibited vibrant green emission at 547 nm, attributed to the Tb3+ ions' 5D4→7F5 transition, with a high quantum yield of 63.10 %. Optimal doping concentration is determined as 7 mol % (SMSO:7 Tb3+), overcoming concentration quenching primarily due to dipole-dipole (d-d) interaction. Impressively, SMSO:7 Tb3+ NPs demonstrated a correlated colour temperature (CCT) of 5549 K, colour purity (CP) of 91.60 %, and excellent colour stability. These phosphors are effectively applied in latent fingerprints (LFPs) development, revealing distinct ridge features useful for personal identification. Additionally, SMSO:7 Tb3+ NPs, combined with soluble PVA, are used to create a transparent anti-counterfeiting (AC) film, exhibiting intense green emission under UV 365 nm light. Notably, the film flexibility, durability, and foldability enhance its applicability in AC techniques. This study showcases SMSO:Tb3+ NPs as versatile luminous platforms with applications in flexible displays, high-colour quality lighting, fingerprint (FP) visualization, and anti-counterfeiting.

Barium oxide nanorods: Catalyst concentration and surface defects' role in degrading methylene blue organic pollutant

In this study, BaO nanorods (NRs) were synthesized with inherent surface defects using the chemical coprecipitation process. The rich oxygen defect BaO NRs exhibited enhanced light sensitivity and effectively interacted with the organic pollutant methylene blue (MB) dye under UV-light illumination for wastewater treatment. The X-ray diffraction (XRD) analysis confirmed the highly crystalline tetragonal structure of the BaO NRs. Microstructural characteristics were examined using theoretical approaches such as Debye-Scherrer (DS), Williamson-Hall (W-H), and Size-Strain Plot (SSP), revealing an average crystallite size of approximately 30 nm. Field emission scanning electron microscopy (FE-SEM) revealed the rod-shaped structure of the BaO nanorods, with particles aligned on top of each other. UV–visible absorption studies demonstrated an increased optical bandgap in the BaO NRs compared to the bulk material. Photoluminescence spectroscopy revealed the presence of oxygen traps and surface defects, which aided the photodegradation process. The photocatalytic activity of the BaO NRs was assessed by degrading MB dye. We found that a concentration of 150 mg of BaO NRs exhibited the highest degradation efficiency at 85 %.

Molecular dynamics simulation of mechanical properties of decagonal quasicrystal approximate phase Al2Fe

By using the molecular dynamics method, the tensile and elastic mechanical properties of Al2Fe (tI6 and oF24) alloys for decagonal quasicrystals approximation are simulated. Structural models for tI6 and oF24 are first established and then the appropriate embedded atom method (EAM) potential function is selected to analyze the effects of temperature and strain rate on the stress-strain relation, atomic structure and deformation mechanism. Furthermore, all the elastic constants Cij of tI6 and oF24 are calculated by the molecular dynamics explicit deformation method, and the crystal structure and stability of tI6 and oF24 are also judged. Besides, the elastic mechanical properties of tI6 and oF24 including bulk modulus, shear modulus, elastic modulus, and Poisson's ratio, are derived by means of both the general formula and the independent crystal system formula. The results show that the elastic modulus and tensile strength of tI6 and oF24 almost decrease linearly with increasing temperature. An increase of strain rate has little effect on the elastic modulus of tI6 and oF24, but it can result in an obvious increase of the tensile strength and ultimate strain. By calculating, tI6 possesses a stable tetragonal crystal structure and oF24 has a stable orthorhombic crystal structure, which are consistent with the previous results derived by the first-principle. The Young's modulus, shear modulus and Poisson's ratio display high anisotropy except for the bulk modulus. The anisotropic of oF24 is higher than that of tI6, while the stiffness and hardness of tI6 are greater than those of oF24. The present work can provide a theoretical reference for analyzing the mechanical properties of the approximate phase of decagonal quasicrystal as well as a novel numerical calculation method for determining the mechanical properties of related materials.

Blue emission and color-tunable behavior in Tm3+ singly- and Dy3+/Tm3+ co-doped CaLaGa3O7 phosphors

Tm3+ singly- and Dy3+/Tm3+ co-doped CaLaGa3O7 phosphors were prepared successfully by a high-temperature solid-state reaction method and their structure, spectroscopic properties, as well as energy transfer processes between Dy3+ and Tm3+ were studied. The XRD measurements show that all the prepared phosphors have a tetragonal structure. The emission proved that under excitation by 355 nm, 455 nm blue light was obtained in Tm3+: CaLaGa3O7 phosphor with a high color purity (99%). For Dy3+/Tm3+: CaLaGa3O7, the emission spectra exhibited the typical yellow emissions of Dy3+ and blue light of Tm3+. More importantly, the relative emission intensity of Dy3+ and Tm3+ can be varied by modifying the concentration of Tm3+ and the exciting wavelength, indicating that the luminescence color is tunable. Further, optimal white-light emission was achieved when co-doped 0.01 Tm3+ and 0.02 Dy3+ under 355 nm excitation. Meanwhile, the CIE chromaticity coordinates, color temperature value and color purity of the 0.02 Dy3+/0.01 Tm3+: CaLaGa3O7 phosphor were calculated to be (x = 0.3321, y = 0.3231), 5515 K and 7.18%, respectively, which are close to the standard white-light illumination. Moreover, the study on the decay curves indicates that mutual energy transfers between Dy3+ and Tm3+ take place in the Dy3+/Tm3+: CaLaGa3O7 phosphor. The above findings suggest that the prepared phosphors have potential applications in light emission devices.

Opportunity of ferrimagnetic (CZLF)/ferroelectric (BZT) composite materials in high frequency applications

The ferrimagnetic Zn0.35Co0.65 La0.02Fe1.98O4 (CZLF) ferrite with cubic spinel structure (space group Fd3m) was made into composite by mixing with ferroelectric Ba0.5Zr0.5TiO3 (BZT) perovskite with tetragonal structure (space group P4mm) at the mass ratio. Disk-shaped composite powder was finally heated at 1100 °C to study the structure, dielectric and ferroelectric properties. The structural characterization for synthesized samples were carried out using Fourier transform infrared and Transmission Electron Microscopy. Fourier transform infrared show the successful formation of composite samples which is also observed from x-ray diffraction pattern. In compared to their ferrite counterparts before the composite, dielectric response and ferroelectric characteristics of the composite samples are noticeably altered. Compared to the ferrite samples, the composite system exhibits a higher permittivity. In composite samples, the space charge polarization, which was primarily effective at low frequencies and high measurement temperatures, is much diminished. The mechanical properties and indentation creep of these bearing alloys were studied by Vickers indentation testing at room temperature. The remnant polarization of BZT/CZLF increases with decreasing BZT content, which may be suitable for permanent memory device applications. Graphical abstract