XRD Rietveld Refinement Research Articles

Impurity doping approach on bandgap narrowing and improved photocatalysis of Ca2Bi2O5

To modify the band natures and photochemical properties of Ca2Bi2O5, partial substitutions of La3+-, Na+-, Te4+-ions on Bi-sites were respectively conducted. The phase formations were investigated via XRD Rietveld refinements. High spontaneous polarization can be induced by the special geometry of BiO polyhedra with see-saw -like arrangement. Ca2Bi2O5 has a band energy of 2.49 eV (498 nm) with a direct allowed transition nature. La3+-, Na+-, Te4+-substitution can modify UV–vis absorption via the band-gap narrowing and the induced defects. Especially, the band energy of Te4+-doped Ca2Bi2O5 was reduced to 2.29 eV (541 nm) indicating a significant harvest of visible-light. The photocatalysis was evaluated on MB photodegradation. The impurity substitution can improve photocatalysis of Ca2Bi2O5. XPS, emission, and decay times were applied to discuss the mechanism. La3+-, Na+-, Te4+-doping in Ca2Bi2O5 can depress the recombination of light-induced charges via prolonging the decay times. The results could be referred to investigate multifunctional optical applications of bismuth semiconductors.

Optical and photochemical characteristics of Aurivillius-like semiconductor Bi9P2O18Cl synthesized via sol–gel-assisted solid-sate reaction

Bi3+-containing compounds with Aurivillius-like structure have been intensively investigated for multifunctional applications. In this work, a new Aurivillius-like semiconductor Bi9P2O18Cl was prepared via sol-gel routine combined with solid-state reaction method. XRD Rietveld refinement was conducted to investigate the detailed structural characteristics. This is a typical Aurivillius oxide semiconductor with high polarization ability. The optical absorption, band structure, luminescence and decay lifetimes were reported. Bi9P2O18Cl has a band energy of 2.58 eV characterized with an indirect transition nature. To detect its photochemical activities, the degradation of Rhodamine B (RhB) by Bi9P2O18Cl was studied. The results show that Bi9P2O18Cl has a strong ability to harvest visible-light. The luminescence is not efficient under UV or near UV excitation. However, Bi9P2O18Cl shows efficiently photocatalytic abilities under visible light irradiation. The results could be reliable reference in the booming development of Aurivillius Bi-oxide semiconductors.

B‐site‐doped BiFeO3‐based piezoceramics with enhanced ferro/piezoelectric properties and good temperature stability

AbstractHere, B‐site doped 0.725BiFe0.98M0.02O3‐0.275BaTiO3 (M = Fe, Sc, Ga, and Al) + 0.8 mol% MnO2 (abbreviated as BF, BS, BG, and BA) (BFM‐BT) ceramics were designed and prepared to modulate octahedral distortions. According to bond‐valence calculations based on XRD Rietveld refinement data, B‐site doped BFM‐BT ceramics tended to have a higher distortion as the radius of the doping ion decreases, and obtained a great improvement of ferroelectric and piezoelectric performances. B‐site‐doped BFM‐BT ceramics significantly inhibited the formation of impurities, leading to better ferroelectric and piezoelectric performances. The BFM‐BT ceramics exhibited high Curie temperature of 519‐530℃ and good temperature stability for piezoelectric performances. The d33 values of BF, BS, and BA ceramics remained the room temperature value ranging from room temperature to 470℃. Meanwhile the content of impure phases, oxygen vacancies and valence of Fe3+ to Fe2+ decreased with the decreasing radii of B‐site doping ions.

Role of energy band structure on the luminescence performance of double perovskite La2LiMO6:Eu3+ (M=Sb, Ta, Nb) red emitting phosphors

Abstract Monoclinic double perovskite La2LiMO6:Eu3+(M = Sb, Ta, Nb) phosphors were prepared by high temperature solid state reaction method in air. The material microstructures were characterized by XRD Rietveld refinement. All La2LiMO6:Eu3+ exhibited Eu3+ - emission in the red region under excitation by ultraviolet-blue light at room temperature. In the order of M = Sb, Ta, Nb, the emission of Eu3+ in La2LiMO6:Eu phosphor declined under charge transition band (CTB) excitation in turn, while enhanced gradually under 394 nm and 465 nm excitation. The optical band gap energy was calculated through the UV–Vis reflectance spectra of La2LiMO6:Eu indicating that photoionization is the quenching scheme in La2LiMO6:Eu. Co - doped with Bi3+ ions further reduces the energy band (i.e. forbidden bandwidth) of LLN:Eu, resulting in the significant enhancement of Eu3+- emission under 465 nm excitation, which demonstrates its potential application value as the red component of a blue chip based-white LED.

Rearranging cations on B sites to modify luminescence in layered-perovskite-like La3Ti2TaO11:Eu3+ ceramic phosphors

Compounds with the layered perovskite-like structure are well-known engineering materials because of the multifunctionality. In this work, a novel La3-xEuxTi2TaO11 (0 ≤ x ≤ 0.45) solid-solution with a typical layered perovskite-like structure was synthesized via the traditional solid-state reaction ceramic technique. The optimal emission happened in La3-xEuxTi2TaO11 (x = 0.3). To modify the luminescence properties, La2.7Eu0.3Ti2-5y/4Ta1+yO11 (y = 0.04, 0.05, 0.08, 0.1, 0.12, 0.14) phosphor was developed via stoichiometric alteration of (Ta5+→Ti4+) in “B” sites. The research motivation is on the fact that the framework distortion due to cation-disorders is an efficient method to modify the luminescence and improve the thermal stability of a rare earth ion (RE)-activated phosphor. The phase formations were conducted by XRD measurements and Rietveld refinements. The morphology was characterized by SEM and EDS. The luminescence properties such as luminescence, emission excitation wavelength, and decay lifetimes showed a dependence on the distortion of the framework. Cation alteration of (Ta5+→Ti4+) in La3-xEuxTi2TaO11 (x = 0.03–0.45) greatly modified the red-luminescence activities, such as improved efficiency, pure red chromaticity, and thermal stability. The excess of Ta5+ on Ti4+ sites bring about the distortion of octahedron surrounding resulting in intensive changes in the crystal-field environment around Eu3+ activators. The framework distortion due to substitutions of multiple cations is effective to enhance the emission efficiencies and thermal stability of RE3+-activated phosphors. The cation-disorder was discussed via luminescence features in 5D0→7F0 transition region. The results are helpful to introduce Eu3+ as a probe for rare-earth dopant site microstructure in phosphor materials.

Improved near-IR emission in Yb3+-condensed fluorosilicate apatite Sr4Yb6(SiO4)6F2 via Eu3+ doping

This work reports a new luminescence host, Yb3+-condensed fluorosilicate apatite Sr4Yb6(SiO4)6F2. Pure and Eu3+-doped Sr4Yb6(SiO4)6F2 dense ceramics were prepared via the solid-state reactions. The apatite-like structural features were confirmed via XRD Rietveld refinements. The optical absorption, down-conversion (DC) and up-conversion (UC) luminescence, and dynamic decays of Sr4Yb6-6xEu6x(SiO4)6F2 (x = 0, 0.01, 0.05, 0.1, 0.15) were investigated. In the DC with UV-light excitation, near-IR emission efficiency of Sr4Yb6(SiO4)6F2 can be greatly enhanced by Eu3+-doping via significant energy transfer from Eu3+ ions to Yb3+. The luminescence mechanisms were explained on the cross-relaxation (CR) processes between Eu3+ donors and Yb3+ acceptors. Up-conversion (UC) luminescence was detected via 974 nm excitation into 2F7/2 states of Yb3+, which occurs in green cooperative luminescence (CL) from Yb-pairs and UC red emissions of Eu3+ ions. Unlike the case of DC luminescence under UV light, CL of Yb3+ decreases quickly with the increase of Eu3+ doping; meanwhile, the up-converted red luminescence of Eu3+ shows only a small increase. The energy transfer mechanism was discussed via cross-relaxation between Yb3+ and Eu3+ ions.

Induced Synthesis of a New Intermetallic NiSn5 Phase and Electrochemical Mechanism Investigation

MSn5 (M=Fe, Co, Fe0.5Co0.5) are a series of metastable tin-based alloys discovered by Han’s group. Because of the high Sn content and high conductivity of alloying metals (Fe and Co et. al), the MSn5 phases exhibit superior electrochemical properties in lithium ion batteries. For example, 30-50 nm FeSn5 nanospheres can deliver a high capacity of 750 mA h g-1 at 50 mA g-1, and CoSn5 nanospheres exhibit good cycle stability up to 100 cycles. Although these three transition metals Fe, Co, and Ni show similar physical and chemical properties, we fail to synthesize NiSn5 phase by using the same polyol wet chemical method. In this work, we firstly synthesized the new NiSn5 intermetallic phase by adopting an induction synthesis method using Fe3+ and/or Co2+ as induction agent. Furthermore, the crystal structure was resolved using the charge-flipping method, and the growth and electrochemical mechanism were investigated using TEM and ex situ synchrotron XRD.The resutl shows the NiSn5 phase belongs to tetragonal phase in P4/mcc space group, and has stoichiometric Ni atom defects, the actual chemical formula is Ni0.62Sn5. Growth mechanism study reveals that the FeSn5/CoSn5 seed crystal formed after addition of trace of Fe3+/Co2+ plays a vital role in the formation of NiSn5 phase. The existence of FeSn5/CoSn5 seed crystal can effectively reduced the nucleation barrier of NiSn5, and the NiSn5 nanospheres final form through Kirkendall diffusion. The phase evolution investigation reveals that the NiSn5 phase is irreversible after initial discharging/charging processes, unlike the reversible transformation of MSn5 (M=Fe, Co, Fe0.5Co0.5). This result accounts for the failure of NiSn5 synthesis using traditional polyol wet chemical method and the relatively low cyclability of NiSn5. We believe this method can be expanded to synthesize other new alloys which are difficult to produce using the traditional methods. Figure 1 (a) The reaction mechanism of induced synthesis of NiSn5 phase. (b) Synchrotron XRD pattern and Rietveld refinement of NiSn5 phase. (c,d) TEM images of Sn and NiSn5 nanospheres. Acknowledgments This work is supported by the National Natural Science Foundation of China (Grant No. 51901206). Figure 1

The insight into promoting sodium storage mechanism of α-CrPO4-type NaV3(PO4)3 anode material for sodium-ion batteries

Exploitation of reliable insertion anode material with long cyclability and proper working potential is very meaningful to promote application of sodium ion battery (SIB). Herein, a type of porous anode material based on NaV3(PO4)3 (NVP) nanoparticles coated by robust carbon is reported for efficient Na storage with increasing capacity and decreasing potential plateau during ultra-long cycles for the first time. According to Na-NMR characterization and XRD Rietveld refinement, it is found that the Na+ ions partially occupy all the three sites with different percentage (11.5% 4b site, 24.3% 4c site and 64.2% 4e site). The systematical characterizations of in-situ and ex-situ XRD, SEM, XPS show a gradual transformation from the α-CrPO4-type crystal structure to an amorphous phase of NVP, which may reduce the activation barrier of Na+ ions especially those in 4e sites gradually. More Na+-ion sites are involved in the intercalation and de-intercalation processes and the voltage plateau decreased from 1.18 to 0.85 V vs. Na+/Na. Additionally, the full battery assembled by combining NVP/C anode with the typical Na3V2(PO4)3 cathode is also demonstrated with a long cycle life. The high performance of as-prepared NVP material provide a possible choice of reliable insertion anode material for long life span SIB.

(Pr0.75La0.25)0.7Sr0.3MnO3:Agx (0 ≤ x ≤ 0.25) polycrystalline ceramics with room-temperature TCR improvement for uncooled infrared bolometers

In this work, perovskite manganite (Pr0.75La0.25)0.7Sr0.3MnO3:Agx (PLSMO:Agx, x = 0, 0.05, 0.10, 0.15, 0.20 and 0.25) ceramics were successfully prepared by sol-gel route and solid-state reaction. The surface morphologies, peak temperature variation behaviors of temperature coefficient of resistivity (TCR), microstructural and electrical transport properties of all the specimens were analyzed by various testing methods like XRD, SEM, EDS, R-T and XPS. XRD Rietveld refinement data demonstrated that Mn–O bond length, Mn–O–Mn bond angles and the unit cell volume increased along with the rise in x. Consequently, the bandwidth describing the overlap between the O2p and Mn3d orbitals reduced, and this change further affected the electrical transport properties. Scanning electron microscopy (SEM) images indicated that silver was helpful in increasing the grain size. The metal-insulator transition temperature increased due to the enhancement in double exchange (DE) interaction. X-ray photoelectron spectroscopy (XPS) fitting data (percentage of Mn4+ and O2−) along with XRD Rietveld refinement data confirmed the enhancement in DE interaction. The most remarkable thing was that the reduction in resistivity occurred gradually, which resulted in a significant improvement in the TCR. The TCR value achieved 11.35% K−1 with the peak temperature being 300.69 K (room-temperature ~ 300 K) at x = 0.15. Obviously, obtaining a large room-temperature TCR value (≥10% K−1) in praseodymium perovskite oxides was encouraging since such results have not been explored previously. Overall, the proposed PLSMO:Ag0.15 ceramic with large room-temperature TCR value look prospective candidates for future advanced uncooled infrared bolometers.

A new color-adjustable self-emitting in SrGa2Ge2O8 substituted by Eu3+, energy transfer and the determination of luminescence center

To explore a new color-adjustable self-emitting in SrGa2Ge2O8:Eu phosphors, a series of experiments and characterization were carried out in this paper. Through a classic solid state method, we successfully synthesized the SrGa2-yGe2-zO8:xEu (0 ≤ x, y, z ≦ 0.2) phosphors. The resulting SrGa2-yGe2-zO8:xEu (0 ≤ x, y, z ≦ 0.2) phosphors had been structurally characterized by X-ray Powder Diffraction Refinements (XRD) and Energy Disperse Spectrometer (EDS). In the present study, it was found that under the excitation of 277 nm, by changing the concentration of doped europium ions, a series of color changes from cyan to white are obtained in SrGa2Ge2O8. The energy transfer from the host to the Eu ions occurs. And the energy transfer ability from the host to Eu3+ were shown to be induced when aluminum was substituted to the nominal composition. The bond energy calculation result shows that the doped Sr2+, Ga3+, Ge4+ ions are substituted by Eu3+, Al3+ and Si4+, respectively, which is consistent with the XRD Rietveld refinement analysis. Also, the EDS analysis shows that atomic ratio is 10:19:20 for Sr/Ga/Ge in SrGa2Ge2O8, which is consistent with the XRD result. Diffuse reflection (DR) spectra and electronic structure display the energy band gap is 4.49 and 3.487eV, respectively. Excited by the 260 nm light, it presents a broad band peaks from 350 to 650 nm with the peak at 441 nm. When Al3+/Si4+ ions are doped in it, the red-shift of the matrix and the photoluminescence improvement of SrGa2Ge2O8: Eu can be found.

Synthesis and characterization of semiconductor heterojunctions based on Zr6Nb2O17 nanoparticles

Semiconductor heterojunctions based on substrate of Zr6Nb2O17 were easily synthesized via in situ co-precipitation method. In the synthesis, chemical composition deviation of Nb and Zr in raw materials from stoichiometric requirements of Zr6Nb2O17 resulted in Zr6Nb2O17/Nb2O5 and Zr6Nb2O17/ZrO2 heterojunctions, respectively. XRD measurements and Rietveld refinements were applied to confirm the phase formation and characteristics. The substrate Zr6Nb2O17 is characterized by the indirect transition nature with band energy of 2.78 eV. The conduction-band and valence-band are constructed by Nb(6d) and O-2p orbitals, respectively. The photocatalytic activities of Zr6Nb2O17, Zr6Nb2O17/Nb2O5 and Zr6Nb2O17/ZrO2 on the degradation of RhB and phenol solutions were evaluated. Zr6Nb2O17/Nb2O5 and Zr6Nb2O17/ZrO2 heterojunctions got the improved photocatalytic effects in comparison with the single Zr6Nb2O17. Especially, Zr6Nb2O17/Nb2O5 showed an optimal photocatalytic ability. The photocatalytic mechanism was investigated via emission spectra and lifetimes of photo-created charges. In the heterojunction construction, light-created charge-carriers were efficiently separated resulting in the enhanced photocatalytic effects.

Versatile fluorescent CaGdAlO4:Eu3+ red phosphor for latent fingerprints detection

Latent fingerprint detection is one of the promising technique in forensic science. Here, an oxide based red-emitting phosphors, CaGdAlO4:Eu3+ (CGA:Eu3+), have been successfully synthesized by a solvothermal reaction method. The structural phase was characterized with the XRD Rietveld refinement and TEM analyses. The luminescence properties and dynamics of Eu3+ in CGA were studied in detail by room temperature emission, excitation and decay curve measurements. Intense red emission peaking at 620 nm due to 5D0→7F2 transitions of Eu3+ under the excitation at 283 nm was obtained and the optimal Eu3+ ion concentration was found to be about 7 mol%. The CIE chromaticity coordinate evaluated from the PL spectra and exhibited (0.6410, 0.3581) coordinates within the pure red region of the CIE 1931 diagram with a close proximity to the commercial red phosphor (Y2O2S:Eu3+). Furthermore, with the use of the CGA:7Eu3+ phosphors, the developed latent fingerprint fluorescent images were well visualized and identified their level 1, 2 and 3 details with high contrast, selectivity and sensitivity. These results indicate that CGA:7Eu3+ has great potential for practical applications in the latent fingerprint detection.

Shape-controlled CuxCe1-xO2 nanorods catalyst and the active components functioned in selective oxidation of CO in hydrogen-rich stream

A novel shape-controlled CuxCe1-xO2 nanorods catalyst is synthesized with a simple coprecipitation method at room temperature and Cu(I) chloride as copper sources for the first time. Various analysis methods (XRD Rietveld Refinement, N2 adsorption-desorption, dynamic OSC, XPS, HRTEM, H2-TPR and In situ DRIFTs) and catalytic activity test techniques are used to investigate the structural properties and the catalytic performance of the catalysts in CO-PROX. Introducing copper dopant into ceria nanorods has positive effect on enriching the lattice distortion, oxygen vacancy concentration and the lattice oxygen mobility of ceria support. The incorporation of copper ions generates two main types of active copper species that play different roles in CO-PROX. Specifically, the highly dispersed CuOx species determine the low-temperature CO oxidation activity, while strongly bound Cu-[Ox]-Ce species at the copper-ceria interface regulates the high-temperature CO oxidation activity of the catalyst. Appropriate copper doping (7–11 wt %) is in favor of forming sufficient CuOx species highly dispersed on the surface of ceria nanorods and accelerating the oxygen mobility, as well as strengthening the copper-ceria interaction in the catalyst, which significantly improves its catalytic activity and broadens the temperature window in CO-PROX.

Improvement of emission and thermal stability induced by selected occupation of Al3+ in Ba3Si6O12N2:Eu2+ phosphors

Oxynitride Ba3Si6O12N2:Eu2+ phosphor can usually exhibit high color purity emission spectrum and outstanding thermal stability because of its rigid structure which can be widely used in WLEDs. With the aim of further optimizing the emission intensity, color purity and thermal stability, Al3+-doped Ba3Si6O12N2:Eu2+ green phosphors were successfully prepared by a high-temperature sintering method in the current work. The crystal structure was clearly investigated by the XRD patterns and Rietveld refinement. The expanding volume and elemental analysis proved that Si4+ ions can be efficiently substituted by Al3+ ions in the Ba3Si6O12N2:Eu2+ phosphor. With increasing doping of Al3+ ions, the full width at half maximum decreased from 66.88 to 65.12 nm with an optimal color purity of 65.95%, and the reason was clearly elucidated by the Gaussian fitting spectrum and decay times. Moreover, the emission intensity of Ba3Si6O12N2:0.1Eu2+, 0.03Al3+ was 120% of the intensity of the Al-free sample, and the internal quantum efficiency could reach 70%. The thermal stability was also remarkably enhanced as Al3+ substituted Si4+ in Ba3Si6O12N2:0.1Eu2+, and Ba3Si6O12N2:0.1Eu2+, 0.03Al3+ exhibited only 8% emission loss at 200 °C compared with that at ambient temperature. The outstanding thermal stability was clearly explained by the thermoluminescence spectra and configurational coordinate diagram. The results indicate that the introduction of Al3+ ions can be a versatile method to improve the optical properties of silicon oxynitride.

Structural Refinement and Optoelectronic Properties of (MoxTi1‐2xO2‐δ)1‐y(RGO)y Nanocomposites and Their Photovoltaic Studies with Natural Pigments as Sensitizers

AbstractIn the present investigation, the optoelectronic properties of the binary TiO2/RGO nanocomposites modified through the insertion Mo(VI) ions and thereafter these ternary nanocomposites (NCs) have been tested for I–V measurements using natural pigments as sensitizers. Initially, a series of (MoxTi1‐2xO2‐δ)1‐y(RGO)y [x=0.5 to 3.0 mol %; y=0.75 wt.%] NCs was prepared by using in‐situ chemical approach. XRD Rietveld refinement reveals the formation of single phase only with substitution of two Ti(IV) ions by single Mo(VI) ions in the ternary NCs. After the well characterizations, these NCs are deposited on the FTO substrate using binder‐free doctor blade technique and then these are sensitized with N719 dyes (model protocol) as well as natural pigments and measured under solar simulator for knowing the photovoltaic performances. Among the different photoelectrodes, I–V and IPCE measurements of (Mo0.100Ti0.980O1.990)0.925(RGO)0.075 NCs sensitized with N719 showing the highest power conversion efficiency of 7.58% which is higher to that of TiO2/RGO (η=5.81%) based photoelectrodes. For the optimized photoelectrode composition with N719, natural pigment Betalain based dye sensitized solar cells (DSSCs) show the highest efficiency of 2.23% which opposes to an efficiency of 0.38, 1.29, and 1.13% for Lawsone, Curcumin and Anthocyanin sensitized DSSCs, respectively.

Fast response of CO2 room temperature gas sensor based on Mixed-Valence Phases in Molybdenum and Tungsten Oxide nanostructured thin films

Molybdenum - tungsten oxide (Mo1-xWxO3, x = 1, 0.8, and 0.6) nanostructured thin films-based room temperture (RT) gas sensors are prepared by means of reactive RF magnetron co-sputtering at 400 °C. The structural, morphology, topography, optical, and electrical characterizations of the prepared sensors are carried out by XRD Rietveld structure refinement analyses, SEM, AFM, UV-VIS spectrophotometer, and source meter. By controlling the deposition temperture of 400 °C, a co-existing phase of MoO3 and MoO2 in WO3 matrix is presented with high oxygen vacancies concentration as calculated from the XRD Rietveld Refinement analyses. By increasing the Mo content, the calculated oxygen vacancies concentration increases by factor of 1.36. The optical characterization of Mo0.2W0.8O3 thin film shows a high transparent of 99.6% at 500 nm. The prepared thin films have successfully tested to detect carbon dioxide (CO2) at RT (20 °C) with high selectivity and repeatability. The Mo0.4W0.6O3 sensor film shows an electrical Schottky contact with fast response and recovery times towards CO2 under UV light activation. Mo0.4W0.6O3 thin film under dark and UV conditions were able to detect low CO2 concentration of 2 and 0.5 sccm CO2 at RT, respectively. Under UV illumination, Mo0.4W0.6O3 film shows a fast response and recovery time of 6.53 and 8.05 s at 0.5 sccm with sensitivity of 29.19%. Under UV photonic activation, higher electron concentration is presented in the oxide surface, which leads to high probability for reaction with CO2 molecules, and consequently enhanced the chemisorption of CO2. The enhanced CO2 gas sensitivity and fast response may refer to the high oxygen vacancies concentration and the active role of the grain boundaries in MoO2, MoO3 and WO3 mixed-valence nanostructured under UV activation.

Preparation and photochemical properties of Sb3Nb3O13 nanoparticles and the derived semiconductor heterojunctions

In this work, Sb3Nb3O13 nanoparticles were synthesized via in situ co-precipitation and a subsequent heating route. The composition deviation of Nb and Sb from stoichiometric requirements of Sb3Nb3O13 resulted in the final products of Sb3Nb3O13/Nb2O5 and Sb3Nb3O13/Sb2O3 heterojunctions, respectively. XRD measurements and Rietveld refinements were applied to study phase formation and structure characteristics. The substrate Sb3Nb3O13 has band energy of 2.66 eV characterized by the indirect transition natures. The conduction-band is mainly constructed by Nb(6d) and the valence-band is O-2p orbitals. The photo-degradation activity of Sb3Nb3O13 on RhB dye solutions was conducted, which was significantly improved with the coupling with Sb2O3 and Nb2O5. Especially, Sb3Nb3O13/Nb2O5 heterojunction showed optimal photocatalytic abilities, which has a degradation rate more than 4 times higher than pure substrate Sb3Nb3O13. The photocatalytic mechanism was investigated via emission spectra and lifetimes of photo-created charges. In the heterojunction construction, light-created charge-carriers were efficiently separated resulting in high photocatalytic effects.

Room temperature multiferroic properties of hexagonal Lu0.85Sr0.15FeO3 ceramics

The structural, electric and magnetic properties of bulk hexagonal Lu1-xSrxFeO3 (x = 0 and 0.15) ceramics are investigated. XRD data and rietveld refinement confirm the hexagonal structure with P63cm space group. Magnetic measurements for Sr-doped sample indicate a ferromagnetic-like behavior at the room temperature with a very high coercivity of the order of ∼ 4.4 kOe. P-E hysteresis loops show an enhanced ferroelectric property with Sr doping. Hence, towards the realization of applications, the multiferroic properties of hexagonal LuFeO3 are improved remarkably by 15% Sr substitution at Lu site.

Multiferroic properties of lead-free 0.2(Ni0.8 Zn0.2Fe2O4)-0.8(Ba0.85Ca0.15Zr0.1Ti0.9O3) magnetoelectric composite

In this work the structural, electric and magnetic characteristics of 0.2(Ni0.8 Zn0.2Fe2O4 (NZF))-0.8 (Ba0.85Ca0.15Zr0.1Ti0.9O3 (BCZT)) multiferroic composite is investigated. The constituent phases were synthesized by sol-gel process, and mixed in an appropriate ratio to form the composite. The XRD data and Rietveld refinement confirm that the composite exists in cubic+tetragonal+orthorhombic mixed phases. The P-E loop of the composite shows a finite loop opening with a decrease in the polarization compared to the pure BCZT. The M-H loops show a saturated loop at an applied field ∼ 1 kOe and the values of magnetization decreased nearly by four orders, compared to the pure NZF.

Unveiling the origin of high reversible capacity in Li-rich layered oxide in Li-ion batteries

Lithium-rich layered oxides are promising cathode candidates for Li-ion batteries due to their high specific capacity than the commercial cathode material, LiCoO2. However, the mechanism of the incredibly high capacity and inherent problems of lithium-rich layered oxides, such as low initial Columbic efficiency and poor capacity retention, has not been explored in detail. Herein, lithium-rich layered oxide, Li1.2 Mn0.54Ni0.13Co0.13O2, has been synthesized by sol-gel method, which could be charged to 5 V (versus Li/Li+) and delivered a specific capacity of 248 mAh g−1. Then, a combination of XRD Rietveld refinement and HRTEM analysis has been employed to investigate the microstructure and phase composition of as-prepared Li1.2 Mn0.54Ni0.13Co0.13O2. The results revealed that Li1.2 Mn0.54Ni0.13Co0.13O2 nanoparticles consist of different phases, including LiCoO2 with R-3m symmetry, LiNiO2 with R-3m symmetry, LiMnO2 with R-3m symmetry, Li2MnO3 with c2/m symmetry, and Li2MnO3 with cmc/21 symmetry. It has been demonstrated that O2-Li2MnO3 phase with cmc/21 symmetry is responsible for the high reversible capacity of Li1.2 Mn0.54Ni0.13Co0.13O2 compound. However, the complex phase composition caused abundant stacking faults in the nanoparticles, which led to poor rate performance. The present study provides useful insights into the charge storage mechanism of a promising Li-ion battery cathode, Li1.2 Mn0.54Ni0.13Co0.13O2, which can be used for the development of novel electrode materials for next-generation LIBs due to its lower consumption of element Co and good electrochemical performance.