Narrow Results

The primary aim of the current research is to explore the impact of yttrium-doping in barium stannate titanate (Ba${}_{1-1.5x}$Y_xTi${}_{1-z}$Sn_zO₃) to investigate the variation in its structural and electrical properties. The specimens were synthesized using a solid-state method, wherein the precursors were heated together until they reacted to form the desired compounds. Subsequently, X-ray diffractometric analysis was employed to confirm the crystallographic phases. Archimedes’ method was used to determine the density of the material. An Electron Paramagnetic Resonance (EPR) study was conducted to examine the nature of defect centers and impurity ions within the synthesized ceramics. Furthermore, the impact of yttrium (Y) substitution on the system’s morphology and grain growth was evaluated through SEM micrographs. Selective compositions were found with enhanced dielectric properties of barium titanate ceramic, exhibiting a dielectric constant of 9816 at the transition point. The highest value among all studied samples had a clear indication of DC conductivity. Piezoelectric coefficient (d${}_{33}$) and P-E hysteresis loops were also investigated for these samples, indicating potential applications in electronic devices for the modified material’s improved ferroelectric properties.

An aim of the experiments is to study alloying techniques of dollop-like MM, as-cast and extruded Mg-MM master alloy in die casting AZ91D magnesium alloy at conventional cold chamber die casting temperature. The as-cast AZ91D-1.2wt%MM alloys were prepared and MM was added by different way at 720°C. The results showed that the efficiency of alloying achieved less than 50% within 30 min when dollop-like MM was added. When MM was added by as-cast and extruded Mg-21wt%MM master alloy, the efficiency of alloying was improved significantly. The microstructure and analytical studies were carried out using optical microscopy and differential scanning calrimetry (DSC). Testing results showed the Mg-MM master alloy could melt easily down at die casting temperature because Mg-RE phases with lower melting point were formed. The grain refining efficiency of the master alloy was improved by extrusion. The improvement could be attributed to the decrease in Mg-RE particle size and increase in the number of nucleating sizes for Mg. Then die-casting AZ91D-0.44wt%MM test bars were produced with addition of extruded Mg-21wt%MM master alloy and the efficiency of alloying was around 80%.

First-principles calculations of the electronic structure of substitutional rare earth (RE) impurity (Eu and Gd) in wurtzite ZnO have been performed using density functional theory within a Hubbard potential correction to the RE 4f states. For Eu-doped ZnO, the magnetic coupling between Eu ions in the nearest neighbor sites is ferromagnetic (FM). The room temperature (RT) ferromagnetism (FM) can be enhanced by an appropriate hole doping into the sample. The ZnO:Gd is found to favor the antiferromagnetic (AFM) phase. The FM can be achieved by high electron doping. The native defects effect (V${}_{\mathrm{\text{O}}}$, V${}_{\mathrm{\text{Zn}}}$) on the FM is also studied. The oxygen vacancies seem to play an important role in the generation of the FM in both ZnO:Eu and ZnO:Gd, which is in good agreement with recent experimental results.

The optical properties of Eu${}^{3+}$ ions in tellurite glass ceramics with the chemical composition 50TeO₂–29B₂O₃–10ZnO–10Na₂O–1Eu₂O₃-based precursor glasses were presented. These precursor glasses have been prepared by melt quenching method in air, followed by thermal annealing at 550${}^{\circ }$C for 12 h, 24 h and 36 h. After thermal annealing process, the micro–crystals appeared in host tellurite glasses. Judd–Ofelt (JO) parameters were calculated from the photoluminescence (PL) spectral measurements. The ${\mathrm{\Omega }}_2$, ${\mathrm{\Omega }}_4$ and ${\mathrm{\Omega }}_6$ parameters have been used to estimate the radiative properties of Eu${}^{3+}$ ions in tellurite glass ceramics such as transition probabilities, branching ratio, radiative lifetimes and stimulated emission cross-section. The results of tellurite glass ceramic have been discussed and compared with the similar studies.

This paper discusses the influence of Vietnam rare earth (RE) with the composition of 69.4% Ce and 30.5% La (modification content of 4% and 6%) on the microstructure and mechanical properties of Al–5Zn–3.5Mg–1.2Cu alloy when the temperature modification is changed at $750^{\circ }\mathrm{\text{C}}$ in 150, 200, 250 s. By optical microscopy, the results showed that the microstructure of the modified sample is finer than the nonmodified sample. By the SEM and EDS analysis, at the grain boundaries of this alloy, ${\mathrm{\text{MgZn}}}_2$ and/or ${\mathrm{\text{Mg}}}_3{\mathrm{\text{Zn}}}_3{\mathrm{\text{Al}}}_2$ intermetallic phases appeared. The modified elements (La, Ce) in RE and aluminum were formed in the intermetallic ${\mathrm{\text{Al}}}_{11}{\mathrm{\text{RE}}}_3$ and ${\mathrm{\text{Al}}}_2\mathrm{\text{RE}}$ phases, which prevents the development of the dendritic $\alpha$ phase. The result showed Al–5Zn–3.5Mg–1.2Cu alloy modified with 4% RE in 150 s which is the most optimal result, the grain size is $6.67\mu \mathrm{\text{m}}$ and the hardness is 107 HB.

The rare earth kagome systems R₃Ga₅SiO${}_{14}$ (R = Nd or Pr), which are weakly frustrated antiferromagnets, do not exhibit long-range order at temperatures down to 40 mK as revealed by neutron scattering. The neutron experiments provide evidence for the emergence at low temperatures of correlated spins in nanoscale cluster regions with magnetic field-dependent correlation lengths. A variety of techniques have been used to determine the magnetic and thermal properties of these systems. In particular, high-field electron spin resonance (ESR), nuclear magnetic resonance (NMR) and muon spin resonance ($\mu$SR) experiments have established that dynamic correlation of spins remains significant at temperatures well above 1 K. ESR provides evidence for spin wave excitations in spin clusters and the spectra have been interpreted using a Heisenberg model approach. While Nd${}^{3+}$ (J = 9/2) is a Kramers ion Pr${}^{3+}$ (J = 4) is not. This difference leads to contrasts in the magnetic properties of the two systems. This review surveys the information that has been obtained on the properties of these kagome materials over the past decade.

The structural, electronic, mechanical and thermodynamic properties for ${\mathrm{\text{Al}}}_{23}{\mathrm{\text{REMg}}}_{34}$ and ${\mathrm{\text{Al}}}_{24}{\mathrm{\text{Mg}}}_{33}\mathrm{\text{RE}}$ (RE = Sc, Y, La, Sm and Gd) compounds have been calculated by first-principles theory. The obtained structural parameters and elastic constants of two kinds of doped ${\mathrm{\text{Al}}}_{12}{\mathrm{\text{Mg}}}_{17}$ are compared with some theoretical and experimental data. The electronic structure analysis, such as density of states, explains the bonding character of Al–Mg–RE. All the doped ${\mathrm{\text{Al}}}_{12}{\mathrm{\text{Mg}}}_{17}$ are influenced by the high-energy electrons directly. Furthermore, the basic mechanical properties which are derived from the elastic constants and the thermal stability of doped ${\mathrm{\text{Al}}}_{12}{\mathrm{\text{Mg}}}_{17}$ are discussed. The predicted brittleness of ${\mathrm{\text{Al}}}_{23}{\mathrm{\text{REMg}}}_{34}$ and ${\mathrm{\text{Al}}}_{24}{\mathrm{\text{Mg}}}_{33}\mathrm{\text{RE}}$ is consistent with the available experiments.

Laser cladding is one kind of advanced surface modification technology and has the abroad prospect in making the wear-resistant coating on metal substrates. However, the application of laser cladding technology does not achieve the people's expectation in the practical production because of many defects such as cracks, pores and so on. The addiction of rare earth can effectively reduce the number of cracks in the clad coating and enhance the coating wear-resistance. In the paper, the effects of rare earth on metallurgical quality, microstructure, phase structure and wear-resistance are analyzed in turns. The preliminary discussion is also carried out on the effect mechanism of rare earth. At last, the development tendency of rare earth in the laser cladding has been briefly elaborated.

The synergism of CeCl₃ (Ce) with cysteine (Cys) on the corrosion of P110 carbon steel in 3% NaCl solutions was investigated by electrochemical methods and surface analysis. The results showed that CeCl₃ and cysteine do little to inhibit the corrosion of carbon steel, but the combination of CeCl₃ with cysteine has obvious synergistic effect on the corrosion of carbon steel and the corrosion inhibition efficiency was improved significantly. The potentiodynamic polarization curves indicated that the mixture of CeCl₃ and cysteine acts as a cathodic inhibitor. Scanning electron microscope (SEM) and Infrared (IR) reflection spectra showed the synergistic inhibition effect was formed by the complexes between rare earth Ce(III) ion and amino acid.

The effect of different metal ions on the photocatalytic property of TiO₂ film prepared by micro-arc oxidation was studied. Photocatalytic experiments showed that the impregnation of metal ions increased the photocatalytic efficiency of TiO₂. The increase of transition element Fe${}^{3+}$ and the rare earth element Dy${}^{3+}$ is more obvious, and the optimum concentration is 0.1mol/L. The SEM results showed that there was no significant change on the surface of TiO₂ film before and after metal ion immersion. The results of EDS surface scanning showed that Fe and Dy elements were uniformly distributed on the surface of TiO₂ film after metal ion impregnation, and the deposition amounts were 0.81% and 3.39%, respectively. XRD results showed that a new phase was formed in Fe${}^{3+}$-impregnated TiO₂, which could improve the photocatalytic efficiency.

Surface degradation (oxidation/corrosion/erosion) at elevated temperature is encountered commonly in engineering industries like gas turbines and thermal power plants. MCrAlX coatings which came into the picture in 1960s were used widely for surface protection in the elevated-temperature section of the gas turbine engines and in boilers to combat oxidation/corrosion/erosion. Among them, MCrAlY ($M=\mathrm{\text{Ni}}$, Co or $\mathrm{\text{Co}}+\mathrm{\text{Ni}}$) were developed to be used as the overlay coatings and bond coat (BC), which offer a combination of multiple features such as oxidation, corrosion and ductility. MCrAlY coatings form a second layer of aluminum oxide beneath the chromium oxide layer at elevated temperatures which minimizes the oxidation/corrosion/erosive wear rates. But the desire to increase combustion efficiencies of power plants and gas turbine engines along with lower CO₂ emissions poses a significant challenge for coating design. As the temperature surpasses 900^∘C, NiCrAlY coating degrades quickly due to nonregeneration of chromia or alumina. The research and development (R&D) efforts are focusing continuously on improving the existing MCrAlX coatings or developing new sustainable MCrAlX coatings with improved oxidation performance. In this review, the roles of the alloying elements, microstructures, post-deposition treatment techniques and different deposition processes in the elevated-temperature oxidation/corrosion performance of MCrAlX-based alloys have been explored in detail.

The upconversion (UC) fluorescences from 300 nm to 500 nm of NaYF₄:La³⁺(Er³⁺, Tb³⁺) nanocrystals under 532 nm laser excitation were investigated at room temperature. These UC luminescences have potential applications in UC lasers.

Ultrafine Sm-Lu mixed oxide powder with an overall composition Sm_1.0Lu_1.0O₃ was processed by inductive radio frequency plasma treatment using two different approaches: spraying a mixture of pure Sm₂O₃ and Lu₂O₃ with and without sintering pretreatment. Due to the insufficient reaction time and contact, the mixture sprayed without sintering shows only a marginal reaction between the two materials. Therefore, an alternative approach was adopted. The mixed oxide was first synthesized by solid state reaction at 1600°C. Then, the as-sintered pellets were crushed and ground, followed by plasma treatment. In this way, ultrafine particles of Sm_1.0Lu_1.0O₃ mixed oxide were obtained.

Heteroleptic porphyrinato/phthalocyaninato rare earth(III) triple-decker compounds M₂(Por)₂(Pc') (1a-4a) and M₂(Por)(Pc')₂ (1c-4c) (M = Eu, Tb; Por = TDOPP, Pc' = OOPc or Por = TpClPP, Pc' = Pc where H₂(TDOPP) = 5,10,15,20-tetrakis(4-n-dodecyloxyphenyl)porphyrin, H₂[OOPc] = 2,3,9,10,16,17,23,24-octakis(n-octyloxy)phthalocyanine, H₂(TpClPP) = 5,10,15,20-tetrakis(4-chlorophenyl)porphyrin, H₂(Pc') = general phthalocyanine, and H₂(Pc) = unsubstituted phthalocyanine) were obtained by the cyclic tetramerization of the corresponding dicyanobenzenes 7 using monoporphyrinato rare earth(III) acetylacetonates M(Por)acac as templates with catalysis by the organic base 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU). Double-decker complexes M(Por)(Pc') (M = Eu, Tb; Por = TDOPP, Pc' = OOPc or Por = TpClPP, Pc' = Pc) (1b-4b) were isolated as side products. For the purpose of comparative study, homo- and hetero-dinuclear rare earth triple-deckers with one porphyrinato and two phthalocyaninato ligands M₂(Por)(Pc')₂ (1c, 2c) (M = Eu, Tb; Por = TDOPP, Pc' = OOPc) and (Por)M(Pc')M'(Pc')(M ≠ M' = Eu, Tb) (5c, 6c) were also prepared using the raise-by-one-story method. The complexes were characterized by UV-vis, near-IR, IR and mass spectra. The comparison between ¹H NMR spectra of the two series of triple-decker compounds a and c, and also between the substituted phthalocyanine- and unsubstituted phthalocyanine-containing europium triple-deckers, renders it possible to assign the aromatic proton signals unambiguously.

Over the past two decades and in particular the past five years, numerous sandwich-type rare earth complexes containing naphthalocyanine ligands have been synthesized. The more extended delocalized π-electron system of naphthalocyanine in comparison with phthalocyanine generates unique physical, spectroscopic, electrochemical and photoelectrochemical properties which have aroused significant research interest in these compounds. This review summarizes recent progress in research on this important class of molecular materials and overviews the current status of the field.

A novel tetraazaporphyrinato and phthalocyaninato mixed heteroleptic double-decker sandwich rare-earth compound with photochromic and electrochromic features has been facilely synthesized by one-pot reaction using Eu(acac)₃·nH₂O, metal-free phthalocyanine H₂Pc′ (Pc′ = 2,3,9,10,16,17,23,24-octakis(decyloxy)phthalocyanine), and the photochromic precursor 1,2-dicyano-l,2-bis(2,3,5-trimethyl-3-thienyl)ethane as starting materials. The compound was well characterized by elemental analysis and various spectroscopic methods including UV-vis, IR, ¹H NMR, and mass spectroscopies. The electrochemical behavior of this compound was studied by cyclic voltammetry (CV) and differential pulse voltammetry (DPV) methods, which showed up to three one-electron oxidation and four one-electron reduction processes, demonstrating an electro-active compound for high-density information storage. The photochromic performance of the compound was detected by electronic absorption spectra, suggesting the compound to be a good candidate for non-destructive readout by means of UV-vis spectroscopy.

The Raman spectra of the mixed (naphthalocyaninato)[tetrakis(4-$n$-butylphenyl)porphyrinato] rare earth double-decker compounds M(Nc)(TBPP) (M = Y, La, Ce, Eu, Dy, Lu) were studied with Density Functional Theory for the first time. The results reveal the fingerprint band for naphthalocyanine to be around 1455–1615 cm${}^{-1}$ and porphyrin around 693–749 cm${}^{-1}$. Coupled Nc–Por ring–ring interaction vibration modes are also detected at 1470–1522 cm${}^{-1}$, owing to the stretching between the central metal and the N atoms. These vibration modes are recognized as the dominating components in the Raman spectra of those double-decker compounds.

Y₂O₃:Eu nanopowders were synthesized by urea combustion method containing different concentration of Eu. The synthesized Y₂O₃:Eu nanopowders were characterized by X-ray diffractometry, scanning electron microscopy (SEM), transmission electron microscopy (TEM), high resolution transmission electron microscopy (HRTEM), selected area electron diffraction (SAED), energy dispersive X-ray analysis (EDX) and photoluminescence spectroscopy (PL). The particle size was calculated to be in the range of 15–30 nm using Scherrer's formula. The Ia-3 structure of synthesized Y₂O₃:Eu nanopowders were confirmed with X-ray diffractometry. The crystallinity of Y₂O₃:Eu nanopowders were confirmed by SAED and TEM images. The ⁵D₀–∑⁷F_J (J = 0, 1, 2, 3) and ⁵D₁–⁷F₁ transitions bands were observed at 575–650 and 530–550 ranges in the photoluminescence spectrum. The concentration quenching was estimated to be about 5 mol% of Eu. The best chromaticity to the standard red color was observed with the sample containing 3 mol% of Eu.

Upconverting lanthanide nanoparticles overcome many of the problems associated with more traditionally used luminescent contrast agents, such as photobleaching, autofluorescence, cytotoxicity and phototoxicity. For this reason, they are an attractive choice for biomedical imaging applications, particularly for imaging in living tissues. The last decade has seen numerous improvements to these nanocrystals, but a comprehensive guide to the synthesis of upconverting lanthanide nanoparticles has not yet been written. Methods vary from paper to paper and from group to group, and results vary between research groups for each method. For this reason, development of these nanoparticles remains a significant endeavor for any research group interested in joining the field. In this review, we look at the varying synthetic methods employed over the last decade and detail methodology for a select few that have been favored in the field.

Cubic-like CeO₂ nanocrystals about 11 nm long were successfully synthesized via an ethanolamine-assisted hydrothermal route using (NH₄)Ce(NO₃)₄ as a precursor at 180°C for 24 h. The CeO₂ nanocubes were modified onto the glassy carbon electrode by adsorption to fabricate the modified electrode. The reliability and stability of the CeO₂ NC/GC electrode offer a good possibility for applying the technique on routine analysis of ascorbic acid (AA) in clinical use. In addition, the catalytic effect of the CeO₂ nanocubes for thermal decomposition of ammonium perchlorate (AP) was investigated by DTA and TG. The catalytic performance of CeO₂ nanocubes is superior to that of commercial CeO₂ powder.