Photocatalytic La4Ti3O12 nanoparticles fabricated by liquid-feed flame spray pyrolysis

Hexagonal plate-like nanoparticles (NPs) of the layered perovskite La₄Ti₃O₁₂ were fabricated using liquid-feed flame spray pyrolysis (LF-FSP) followed by subsequent heat-treatments. Their photocatalytic activity was evaluated using decolorization of methyl orange solutions under Uv irradiation. LF-FSP combusts metalloorganic precursor aerosols to produce mixtures of cubic simple perovskite (ABO₃) phase and lanthanum oxycarbonate (La₂O_4·846C_0.846) phase with very low agglomeration and average particle sizes (APSs) of 23 nm (as-produced NPs). Rietveld refinement of synchrotron XRD powder patterns verified that the simple perovskite in the as-produced NPs is LaTiO₃ (originally cubic Pm-3m-type space group) and heat-treating gives NPs of the trigonal layered perovskite La₄Ti₃O₁₂ (R-3-type space group). La₄Ti₃O₁₂ NPs heat-treated at 1100 °C/3-6h/air exhibits hexagonal plate-like morphology and high crystallinity offering enhanced photocatalytic degradation of methyl orange solutions compared to the as-produced NPs. The LF-FSP approach to obtaining layered perovskite La₄Ti₃O₁₂ NPs provides a simple route to photocatalytic materials in reasonable quantities.     

The effect of group-I elements on the structural and optical properties of ZnO nanoparticles

Undoped and group-I elements doped ZnO nanoparticles (NPs) (Zn_1?yX_2yO, X=Li, Na, K, and y=0.05) were synthesized by a sol–gel method. Structural and morphological studies of the resulting products were carried out by X-ray diffraction analysis (XRD) and transmission electron microscopy (TEM). The XRD results revealed that the sample products were crystalline with a hexagonal wurtzite phase. The TEM images showed ZnO NPs with nearly spherical shapes with particle size distributed over the nanometer range. In addition, the XRD and TEM results showed a decrease in crystallite and particle sizes of NPs from Li-doped to K-doped ZnO NPs. Crystalline development in the ZnO NPs was investigated by X-ray peak broadening. The size-strain plot (SSP) method was used to study the individual contributions of crystallite sizes and lattice strain on the peak broadening of the undoped and doped ZnO NPs. The effect of doping on the optical band-gap and crystalline quality was also investigated by using photoluminescence (PL) and Raman spectrometers. The Raman spectra of the all ZnO NPs showed a strong E₂(high) peak. The PL spectra exhibited a strong peak in the ultraviolet (UV) region of the electromagnetic spectrum for the all ZnO NPs. The UV peak of the doped ZnO NPs was red-shifted with respect to that of the undoped ZnO NPs.     

Tailoring the structural,magnetic and dielectric properties of Ni-Zn-CdFe2O4 spinel ferrites by the substitution of lanthanum ions

In this paper, we have tailored the structural, magnetic and dielectric properties of Ni_0.5Zn_0.3Cd_0.2Fe_2-yLa_yO₄ (y?=?0.0–0.21) nano-structured spinel ferrites by the substitution of La³⁺ ions. The investigated samples were synthesized by Sol-gel auto-combustion method and were characterized using XRD, SEM, VSM, FTIR and dielectric measurements. Single phase nanostructure formation of synthesized material was confirmed by XRD analysis. The effect of La³⁺ ions on crystallite size, grain size, lattice constant and bulk densities was calculated and it was found that lattice constant first increased upto concentration y?=?0.105 then decreased with further substitution of dopant ions. FTIR results for all synthesized samples demonstrated two absorption bands at υ₁ =?540.8?cm^?1 and υ₂ =?490.8?cm^?1 corresponds to tetrahedral and octahedral sites of spinel structure respectively. With the increase in La³⁺ ions concentration, saturation magnetization and remanence both found to be decreased down to lowest M_s value of 34.1?emu/g which is not yet reported in the literature according to best of our knowledge. Dielectric results showed that by decreasing frequency, both dielectric loss and dielectric constant decreases. AC conductivity has two regions, at low frequency region ac conductivity increases while at high frequency region, it decreases with increasing frequency. The measured results for all synthesized nano-ferrites suggested that synthesized nanoferrites are recommended for high frequency and microwave absorbing applications.     

Energy transfer and photoluminescent analysis of a novel color-tunable Ba2Y1-xV3O11:xSm3+ nanophosphor for single-phased phosphor-converted white LEDs

Metal nitrates are used to synthesize a series of novel Ba₂Y_1-xV₃O₁₁:xSm³⁺ nanophosphors via urea-assisted solution combustion route. X-ray diffraction (XRD), diffuse reflectance (DR), transmission electron microscopy (TEM) and photoluminescence (PL) spectroscopy were employed to analyse the structure, morphology, photoluminescent behaviour and energy transfer mechanism. Rietveld analysis over Ba₂Y_0.98Sm_0.02V₃O₁₁ showed that Y³⁺ ions can be well-replaced by trivalent samarium ions without resulting any major alteration in the crystal structure of host lattice. Furthermore, the lattice parameters were determined for both the host as well as the doped composition. The Scherrer equation yielded an average particle size of 44?nm, which in turn was further confirmed by TEM micrographs. The optical band-gap of the host (3.92?eV) was calculated from the diffuse reflectance spectra. Moreover, the photoluminescence spectral studies showed that under near ultra-violet (NUV) excitation of 340?nm, our nanophosphor powder exhibits the characteristic emission peaks of trivalent samarium along with the emission of VO₄^3? (501?nm) group. The excitation energy transfer from vanadate group to Sm³⁺ produced a systematic color tunablity in white region itself. The optimum Sm³⁺ concentration for better luminescence was found to be 2?mol%. The critical distance for energy transfer was calculated to be 29.02?Å, which in turn assisted to shortlist the mechanism responsible for luminescence-quenching (dipole-dipole) arising from the over-doping of the activator. The photoluminescence decay curves revealed the decay kinetics of ⁴G_5/2 electronic state. Finally, the calculation of CIE color coordinates from emission spectra in MATLAB program unveiled a somewhat white-light emitter which may find potential applications in phosphor-converted white light emitting diodes (PC-WLED) under near-ultraviolet (NUV) excitation.     

Ultrasound and Microwave-Assisted Co-precipitation Synthesis of La<Subscript>0.75</Subscript>Sr<Subscript>0.25</Subscript>MnO<Subscript>3</Subscript> Perovskite Nanoparticles from a New Lanthanum(III) Coordination Polymer Precursor

In the present study nano-sized strontium-doped lanthanum manganite, La_0.75Sr_0.25MnO₃ (LSM), were synthesized by three simple different methods (a) co-precipitation, (b) ultrasonic and (c) microwave-assisted co-precipitation. A lanthanum(III) coordination polymer, [pyda.H]₂[La₂(pydc)₄(H₂O)₄]·2H₂O, where [pyda.H]⁺?=?2,6-diaminopyridinium, and (pydc)^2??=?2,6-pyridinedicarboxylate, was used as a new precursor. The products were characterized by Fourier transform infrared spectroscopy (FT-IR), X-ray powder diffraction (XRD), field emission scanning electron microscope (FESEM), thermal gravimetric (TG) and differential thermal analyses (DTA), as well as by Energy-dispersive X-ray spectroscopy (EDX). The XRD results showed that the crystal lattice of the product obtained was orthorhombic perovskite structure. The porosity, particle size and homogeneity of calcinated LSM were strongly dependent on the preparation method. In addition, the results proved that the product formation time was decreased considerably when ultrasonic or microwave irradiation methods were used.     

Particle Size and Crystal Phase Dependent Photoluminescence of La2Zr2O7:Eu3+ Nanoparticles

Herein, La₂Zr₂O₇:5% Eu³⁺ nanoparticles (NPs) with different sizes have been synthesized for the first time through a modified facile molten salt process using a single‐source complex precursor of La(OH)₃·ZrO(OH)₂:Eu(OH)₃·nH₂O. It was found that the concentration of the added ammonia to co‐precipitate the corresponding metallic ions to form the precursor can influence the final particle size of the fluorite La₂Zr₂O₇:5%Eu³⁺ NPs. Furthermore, the crystal phase of the La₂Zr₂O₇:5%Eu³⁺ NPs was transferred from fluorite to pyrochlore after thermal treatment at 1000°C. The relationship between photoluminescence (PL), quantum yield (QY), particles size and crystal phase has been further investigated through fluorescence decay, site symmetry, and Judd–Ofelt (J–O) analysis. Specifically, PLQY and lifetime increase with increasing particle size of the fluorite La₂Zr₂O₇:5%Eu³⁺ NPs. Additionally, crystal phase transfer from fluorite to pyrochlore resulted in large PLQY decrease and moderate lifetime increase in the La₂Zr₂O₇:5%Eu³⁺ NPs.     

Facile preparation and characterization of lanthanum oxide powders by the calcination of lanthanum carbonate hydrate in microwave field

Micron-sized lanthanum oxide powders are prepared by the calcination of lanthanum carbonate hydrate in microwave field. The decomposition process of lanthanum carbonate hydrate was analyzed by TG-DSC and indicates the reaction undergoes three stages, resulting in the generation of lanthanum oxide at 770 °C. For microwave assisted calcination, XRD patterns demonstrate that hexagonal La₂O₃ structure is initially formed after calcination at 650 °C for 2 h, and FT-IR analyses confirm the decomposition of precursor is complete after calcination at 750 °C for 2 h. SEM investigations reveal that 800 °C is the optimal calcination temperature to generate La₂O₃ powders with uniform morphologies. In comparison, conventionally calcination experiments are carried out in electrical furnace. Both XRD and FT-IR analyses are in consistence with TG-DSC, which indicate the temperature required for fully decomposition of lanthanum carbonate hydrate by conventional heating is higher than that of microwave heating. SEM images present irregular morphologies and wide particle size distribution of conventionally prepared samples. All the techniques are utilized to prove the feasibility of decomposing La₂(CO₃)₃ to generate La₂O₃ in microwave field and highlight the advantages of microwave heating.     

A novel one-pot biosynthesis of pure alpha aluminum oxide nanoparticles using the macroalgae Sargassum ilicifolium: A green marine approach

A novel biological method is proposed for producing ceramic alpha aluminum oxide nanoparticles using an extract of the algae Sargassum ilicifolium. The algal extract functions as a bioreducing as well as a stabilizer agent. The presence of an absorption peak at 227?nm, confirmed the formation of the aluminum oxide nanoparticles using a UV–visible spectroscopy. FTIR analysis indicated that bioreduction of aluminum ions and nanoparticle stabilization probably occurred by interactions between aluminum and the biofunctional groups of algal extract. The XRD pattern revealed that after calcination at ~ 1200?°C, the Al₂O₃ nanoparticles were alpha crystalline in nature with a diameter of 35?nm and had a rhombohedral structure. TEM indicated that the alumina nanoparticles were well-dispersed and spherical in shape with an average size of 20?±?2.1?nm. EDX spectroscopy revealed that the sample contained only aluminum (46.31%) and oxygen (53.69%), confirming the high purity of the alumina nanopowder. The results demonstrated that alpha alumina NPs has an optical band gap of 5.46?eV.     

Impact of nano-perovskite La2CuO4 on dc-conduction,opto-electrical sensing and thermal behavior of PVA nanocomposite films

ABSTRACT

Nanocomposite (NC) films of poly vinyl alcohol (PVA) incorporated with varying amounts of perovskite lanthanum cuprate (La₂CuO₄) nanoparticles (NPs) have been fabricated by solution intercalation technique. TEM result showed the size of NPs between 91-134nm. The effects of NPs content on structural and morphological behaviors of PVA have been established by XRD, FTIR and SEM methods. Electrical properties of NC films were performed using LCR-meter. Current (I)–voltage (V) data displayed dc-conductivity increased with increasing NPs content and trends of I–V indicate the dominant Ohmic behavior at voltage <5V and above that Poole–Frenkel emission is the dominant conduction mechanism. Ac-conductivity increases with increase in frequency and dosage of NPs. The maximum ac-conductivity obtained in this investigation is 2.43X10^?5S/cm for PVA/2wt% La₂CuO₄ with lowest activation energy of 0.147 eV at 25^°C. Cyclic voltammetry (CV) revealed the specific capacitance of PVA-NC improved compared to pristine PVA. The reduction in T_g with increment NPs contents was observed. The optical behaviors of NCs were deduced by UV-visible spectroscopy where the result showed band gap energy was reduced from 5.23eV to 3.25eV whereas refractive index increased from 1.71 to 2.44 for pure PVA and PVA/2wt%La₂CuO₄, respectively.     

Influence of rare earth (RE=Nd,Y, Pr and Er) doping on the microstructural and optical properties of ceria nanostructures

Nanopowders of Ce_0.9RE_0.1O_1.95 (RE=Nd, Y, Pr and Er) were synthesized by nitrate-fuel combustion method and calcinated at 700 °C for 2 h to obtain completely crystalline structures. The effect of RE dopants on the crystalline nature, lattice parameters, and microstructural parameters such as microstrain, stress, and deformation energy density of ceria was evaluated through uniform deformation model (UDM), uniform deformation stress model (UDSM) and uniform deformation energy density model (UDEDM) by using the X-ray diffraction (XRD) data. The results revealed that the microstructural parameters were considerably altered with respect to the dopants. The transmission electron microscope (TEM) graphs and their corresponding selected area diffraction (SAED) patterns of ceria nanoparticles confirmed that all doped ceria powders are crystalline with the wide range of particle size distributions aligned in all the directions. The optical diffuse reflectance spectroscopy (DRS) measurements showed a band at around 340 nm attributed to the transitions of charge-transfer between O 2p and Ce 4f orbitals in cerium oxide and RE doped CeO₂ exhibited the reflectance band in the visible regions due to the transition of 4f energy levels of RE ions. Photoluminescence (PL) spectra of RE doped ceria showed the blue-green emission bands.     

Study on the crystal structure of (Gd2−xCex)Ti2O7 (0 ≤ x ≤ 0.8) pyrochlore

Synthesis, characterisation and crystal structure analysis studies of oxides in (Gd_2?x Ce_x)Ti₂O₇ series have been reported, Ce³⁺ used as a surrogate for Pu³⁺ because they have similar physical and chemical properties. In the present report, a series of pyrochlore-type crystal with composition (Gd_2?x Ce_x)Ti₂O₇ (0?≤?x?≤?0.8) were successfully synthesised by the solution combustion followed by high temperature calcining. The phase purity and crystal structure of samples were investigated by X-ray diffraction analysis as well as Rietveld refinement. It was observed that the solubility of Ce³⁺ in the lattice of Gd₂Ti₂O₇ pyrochlore is 39.62?mol.-%. The calculated lattice parameters and the simulated XRD patterns of (Gd_2?x Ce_x)Ti₂O₇ (x?=?0, 0.5, 1) were obtained based on the density functional theory. The results of theoretical calculation are quite consistent with the results of the experiment. Additionally, the grain size and the visual information about the microscopic structure of the (Gd_2?x Ce_x)Ti₂O₇ crystals were obtained by transmission electron microscopy.     

Green gelatine-assisted sol–gel synthesis of ultrasmall nickel oxide nanoparticles

Nickel oxide nanoparticles (NiO NPs) were synthesised using a sol–gel method in a gelatinous medium. Gelatine was used as a size-limiting polymerisation agent for the growth of NiO NPs. X-ray diffraction (XRD) analysis revealed that increasing the calcination temperature increased the crystallite size and decreased the size of the lattice constant. The size-strain plot method (SSP) was used to measure the individual contribution of grain sizes and micro strain on the peak broadening of NiO NPs. Transmission electron microscopy (TEM) showed the ultrasmall size of the NiO NPs with a narrow size distribution(10±0.2 nm). The band gap value of NiO NPs was calculated using ultraviolet–visible (UV–Vis) spectroscopy and decreased with increased calcination temperature.     

Formation of anatase TiO2 nanoparticles by simple polymer gel technique and their properties

Pure anatase nano-TiO₂ powders were successfully prepared by a simple polymer gel technique using poly-(vinylpyrrolidone) (PVP) as the polymer. The products were systematically characterized by X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), field-emission scanning electron microscopy (FE-SEM), high resolution transmission electron microscopy (HR-TEM), UV–visible spectroscopy and photoluminescence studies. The XRD and XPS results indicate that the prepared powder had a pure anatase nano-TiO₂ structure with lattice parameters a and c of 0.378 and 0.951 nm, respectively. The particle size analysed by TEM ranged between 7 and 12 nm. The maximum UV absorption for the TiO₂ nanoparticles was below 400 nm with an estimated direct band gap (Eg) of 3.55 eV. The photoluminescence peaks of the nanopowder were observed at 391 and 468 nm. The nanosized materials were produced using a simple and cost effective polymer gel technique.     

Magneto Optical Properties of FeB<Subscript>x</Subscript>Fe<Subscript>2−x</Subscript>O<Subscript>4</Subscript> Nanoparticles

In this study, FeB_xFe_2?xO₄ nanoparticles (NPs) were synthesized by the polyol method. The M–H hysteresis curves exhibit superparamagnetic characteristics that are both coercivity and remanent magnetization values are negligible. The particle size dependent Langevin function was applied to calculate the magnetic particle dimensions around 9 nm. The measured magnetic moments of NPs are in range of (1.52–2.2) µ_B and almost half or less with respect to 4 µ_B of bulk Fe ferrite. Magnetic anisotropy was specified as uniaxial and calculated effective anisotropy constants (K _eff ) are between 43.3 × 10⁴ and 19.4 × 10⁴ emu/g. The UV–Vis diffuse reflectance spectroscopy and Kubelka–Munk theory were used to determine the optical properties. The estimated optical band gap values (2.15–2.48 eV) of FeB_xFe_2?xO₄ NPs are bigger with respect to reported values (1.88–2.12 eV) for Fe₃O₄ NPs in the literature. The bigger E _g values are mainly attributed to B concentration and partly to quantum confinement effect.     

Synthesis and Characterization of Antibacterial Activity of Spinel Chromium-Substituted Copper Ferrite Nanoparticles for Biomedical Application

Metal ferrite nanoparticles (NPs) attracted much attention due to their superparamagnetic, catalytic properties and surface area to volume ratio. Among these spinel ferrite NPs have shown immense potential in nanomedicine. The objective of present research work was the synthesis of chromium-substituted spinel copper ferrite NPs [(CuCr_xFe_2?xO₄ (0.0?≤?x?≤?1.0)] by coprecipitation method and characterization of their antibacterial activity against E. coli. The synthesized ferrite NPs were characterized by X-ray diffraction, FT-IR, UV- Vis diffuse reflectance, SEM, Brunauer-Emmett-Teller (BET) and Barrett–Joyner–Halenda (BJH) techniques. XRD analysis confirmed that the all the samples were cubic spinel in structure with crystal size of 43.3–20.2 nm. It has been found that as the amount of dopant (Cr) increases, size of the NPs decreased. The E_g values were found in the range of 1.20–1.80 eV for CuCrxFe_2???xO₄ (0.0?≤?x?≤?1.0) NPs as analyzed by UV–Visible diffuse reflectance spectroscopy. The BET surface area of Cr-substituted ferrite NPs decreases as Cr content increased while the pore diameter increases when moved from CuFe₂O₄ to CuCrFeO₂ analyzed by BJH. The antibacterial activity increases as the concentration of dopant (Cr) increased. It has been found that CuCr_xFe_2?xO₄ NPs inhibit bacterial growth in a size dependent manner i.e., small size NPs (CuCr_xFe_2?xO₄; 20.2 nm; x?=?1.0) exhibit strong antibacterial activity (MIC; 2.5 mg/ml), whereas large size NPs (CuCr_xFe_2?xO_4; 43.3 nm; x?=?0.0) inhibit bacterial growth at concentration of more 16 mg/ml. SEM micrograph shows that CuCr_xFe_2?xO₄ NPs get adhered to bacterial cell surfaces and damaged the cell membrane due to interaction between NPs and cell membrane. Cells treated with CuCr_xFe_2?xO₄ NPs were irregular and abnormal in shape with distorted cell membrane. CuCr_xFe_2?xO₄ NPs severely damaged E. coli cells might be because of formation of pits, indentation, deformation and distortion of cell wall and membrane, indicating significant loss of membrane integrity that may lead to cell death.     

Structural,morphological and mechanical insights from La2O3 doped machinable silicate glass ceramics for biomedical applications

Machinable glass ceramics attracted much attention in recent years due to its improved mechanical and therapeutic performances. La₂O₃ doped SiO₂–Al₂O₃–MgO–K₂CO₃–CaO–MgF₂ glass and glass ceramics (GCs) were synthesized using melt-quenching and solid-state reaction methods. Herein, doping impact of La₂O₃ on physical, optical, morphological, mechanical, and biological properties were studied. XRD reveals the major phase formation of monoclinic cuspidine, Ca₄F₂Si₂O₇ with some minor phases. 3 mol% of La₂O₃ GCs shows a new major crystalline phase of akermanite, Ca₂MgSi₂O₇. FTIR study shows that La₂O₃ acts as a network modifier and non-bridging oxygens presented in the glassy structure tends to be increased. Optical band gap and particle size were lies in the range of 4.18–4.10 eV, and 50–57 nm, respectively. Rod-like morphology and their elemental distributions were confirmed via SEM and EDS techniques. TEM studies suggested that the lattice planes agreed with the XRD results and confirmed a major phase formation of Ca₂MgSi₂O₇. Enhanced mechanical properties were observed using Universal Testing Machine. The cell viability and cell cytotoxicity, were performed by MTT and ALP assay.     

High temperature thermal stabilization of alumina modified by lanthanum species

The effects of precursor pretreatment and addition methods of lanthanum species on stabilization of alumina (surface area loss, phase transformations and high temperature interaction with lanthanum species) have been investigated by BET specific surface area measurements (BET), X-ray powder diffraction (XRD), N₂ adsorption–desorption isotherms, thermal analysis and X-ray photoelectron spectroscopy (XPS) in the range of 600–1150°C. Although powder La₂O₃, which is mechanically mixed with γ-Al₂O₃ or pseudo boehmite, can effectively retard the α phase transformation by solid phase interaction with Al₂O₃, it does not show a positive effect on retarding the loss of surface area. Compared with the direct impregnation of γ-Al₂O₃, the gelation of pseudo boehmite by acidification accelerates phase transformations and weakens the stabilizing influence of lanthanum species. At 600°C and for atomic ratio of La/Al up to 0.1 or at 1150°C and La/Al≤0.02, the lanthanum species is highly dispersed in alumina. With the increase of calcination temperature or lanthanum content, lanthanum species is present as dispersed La₂O₃, LaAlO₃ and crystalline La₂O₃. At T≤1000°C the surface area loss of alumina is mainly attributed to the sintering of particles. The follow-up loss at T>1000°C results from both sintering and phase transformations. The highly dispersed lanthanum species retard both sintering and phase transformations, and their associated surface area loss. However, the formation of LaAlO₃ mainly retards the surface area loss resulting from the α phase transformation. Having considered the purely mechanical mixing effect of additive on the surface area loss of alumina, an influence criterion of lanthanum species on retarding the surface area loss whether resulting from sintering or from α phase transformation at high temperature ≥1000°C has been proposed in this paper.     

Synthesis and thermal stability of Re2Zr2O7, (Re = La,Gd) and La2(Zr1−xCex)2O7−δ compounds under reducing and oxidant atmospheres for thermal barrier coatings

Rare-earth zirconates and cerates have attracted particular interest for thermal barrier coating (TBC) applications due to their advantageous thermal properties, such as a low conductivity and efficient phase stability at elevated temperatures. This study focuses on synthesising La₂Zr₂O₇, Gd₂Zr₂O₇, La₂Ce₂O_7?γ and La₂(Zr_0.7Ce_0.3)O_7?γ compounds via two soft chemistry processes, alkoxide and citrate synthesis. Thermal analysis, X-ray diffraction (XRD) and scanning electron microscope observations were used to analyse the powder after calcinations under air. Chemical reactivity tests under a reducing atmosphere were performed at 1400 °C and investigated by XRD analysis. It was found that the lanthanum and gadolinium zirconates are the most stable and interesting materials under an Ar_(g)/3%H_2(g) atmosphere.     

Thermophysical properties of (La0.25Sm0.25Gd0.25Yb0.25)2Ce2+xO7+2x(x=0.1, 0.2, and 0.3) high entropy oxides

A series of high-entropy oxides (La_0.25Sm_0.25Gd_0.25Yb_0.25)₂Ce_2+xO_7+2x were synthesised adopting a improved sol-gel technique and fritting method. The crystal-lattice, microstructure, elemental constitution, and thermal-physical performances were studied. The results showed that the synthesised high-entropy oxides have a single-fluorite lattice structure. The bulk specimen exhibits a compact microstructure, and clear grain boundaries. The thermal conductivities of the obtained high-entropy oxides are lower than those of CeO₂ and 7YSZ due to lattice strains and numerous oxygen vacancies. The obtained high-entropy oxides have greater thermal expansion coefficients than 7YSZ. The thermal conductivity and expansion coefficient are elevated because of the addition of excess CeO₂. The synthesised high-entropy oxides also exhibit outstanding lattice steadiness up to 1200 °C.     

Synthesis of β-Bi2O3 nanoparticles via the oxidation of Bi nanoparticles: Size,shape and polymorph control,anisotropic thermal expansion,and visible-light photocatalytic activity

Bismuth trioxide (Bi₂O₃) is known for its simple composition but rich polymorphism that allows a number of phase-dependent physicochemical properties and technical applications. We here report our controllable synthesis of highly discrete β-Bi₂O₃ (tetragonal) nanoparticles (NPs) via the thermal oxidation of nearly-monodisperse Bi NPs. The size and shape (spherical and tear- or rod-like) of β-Bi₂O₃ NPs are tunable by the size of parent Bi NPs whereas β and α (monoclinic) polymorphs can be selectively achieved by tailoring the oxidation temperature. The phase stability of β polymorph from room temperature to 450 °C enables us to perform an in situ high-temperature XRD study on the temperature dependence of its lattice parameters, which reveals a marked thermal expansion anisotropy in β-Bi₂O₃ with a linear thermal expansion coefficient of +35.1 × 10^?6 °C^?1 in the c axis, fifteen times higher than that in the a axis. Meanwhile, the narrow band gap (2.27 eV for β vs. 2.77 eV for α) and strong visible-light absorption endow β-Bi₂O₃ NPs with a good photocatalytic activity for the visible-light Rhodamine B dye degradation. We expect that our work could be a valuable reference for the studies on the size, shape and polymorph control, thermal property, and photocatalytic application of Bi₂O₃.