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Photoluminescence spectra are investigated in erbium‐doped GaLaS(O) glasses. Under optical pumping by a semiconductor laser diode operating at 808 nm, the samples demonstrate intense "green" emission bands centered at around 525 and 550 nm as well as much weaker "red" emission band centered at around 664 nm. The intensities of "green" and "red" emission bands are investigated as a function of pumping intensity. The cascade mechanism of generation of radiation from higher lying levels of the 4f‐shell Er3+ ions is discussed to interpret these experimental results and the theoretical description of the phenomenon is developed. [ABSTRACT FROM AUTHOR]

The present work deals with the fabrication of undoped lanthanum chromium oxide and indium doped lanthanum chromium oxide material by cost effective sol–gel method. The four sensors were fabricated by screen printing technique. The indium ion concentration was varied for LaCrO3 material from 0.1 M% to 0.7 M% to access the comparative gas sensing results. All the prepared materials were characterized by XRD, SEM, EDAX, TEM and IR to confirm their structural and chemical composition. The prepared sensors viz. 0.1 M% In3+ doped LaCrO3, 0.3 M% In3+ doped LaCrO3, 0.5 M% In3+ doped LaCrO3 and 0.7 M% In3+ doped LaCrO3 were investigated for gas sensing mechanism for selected gases such as petrol vapours, ethanol, ammonia, NO2, H2S and CO2 gases. The optimum response was recorded for tested gases for all the prepared sensors. The 0.3 M% In3+ doped LaCrO3 found to be exceptional for petrol vapour and highest response was recorded for petrol vapors for 0.3 M% In3+ doped LaCrO3 thick film sensor. All the indium doped are found to be good sensors for petrol vapours and moderate for other tested gases. The prime parameters for the sensors such as selectivity, response and recovery and reproducibility were recorded for the prepared sensor. The response and recovery was very rapid for 0.3 M% In3+ doped LaCrO3 sensor. The gas sensing mechanism for petrol vapours has been established for 0.3 M% In3+ doped LaCrO3 sensor via hole accumulation layer mechanism. The Schematic abstract exhibits the synthesis of In-doped LaCrO3 (0.1M%. 0.3M%, 0.5M% and 0.7M %) by the sol-gel manner. It also illustrates the characterization and optimal gas response to volatile petrol vapors among all the gases. [ABSTRACT FROM AUTHOR]

Two LaxMn1−xOy (LM1, LM2) and three LaxFe1−xOy (LF1, LF2, LF3) amorphous nanowire arrays (NWAs) were prepared by chemical co‐precipitation in anodic aluminium oxide (AAO) templates. The concentration of the reactant plays a crucial role in determining the morphology of LaxMn1−xOy NWAs. The AAO template was etched using a mixed nitrate solution that led to the exposure of LaxFe1−xOy NWAs on the template surface in the process of preparation, then the length of nanowires exposed to the template depends on the etching time. The LM2 NWAs exhibited obvious magnetic anisotropy after the template is almost eliminated by etching with NaOH solution, while the magnetic anisotropy of LaxFe1−xOy NWAs was manipulated by the length of nanowires outside the template. There is a regular change in the coercive force Hc and remanence ratio Mr/Ms with increasing length of nanowires outside the template. Therefore, the nanoarray materials with tunable magnetic anisotropy were obtained by controllable preparation, and they can be applied to high‐density magnetic memory nano‐devices. [ABSTRACT FROM AUTHOR]

Perovskite-type oxynitrides hold great potential for optical applications due to their excellent visible light absorption properties. However, only a limited number of such oxynitrides with modulated physical properties are available to date and therefore alternative fabrication strategies are needed to be developed. Here, we introduce such an alternative strategy involving a precursor microstructure controlled ammonolysis. This leads to the perovskite family member LaTa(IV)O2N containing unusual Ta4+ cations. The adjusted precursor microstructures as well as the ammonia concentration are the key parameters to precisely control the oxidation state and O:N ratio in LaTa(O,N)3. LaTa(IV)O2N has a bright red colour, an optical bandgap of 1.9 eV and a low (optically active) defect concentration. These unique characteristics make this material suitable for visible light-driven applications and the identified key parameters will set the terms for the targeted development of further promising perovskite family members. Perovskite-type oxynitrides hold great potential for optical applications due to their excellent visible light absorption properties. Here, a defined precursor microstructure is used to modulate the oxidation state of tantalum during ammonolysis leading to a bright red perovskite containing tantalum in a rare 4+ -state. [ABSTRACT FROM AUTHOR]

The work is a brief review of the current state of knowledge about high-pressure superconductors with a high value of critical temperature (Tc). The described results relate to hydrogen-rich superconductors with particular emphasis on well-known hydrogen sulfide compounds and also include newly-discovered lanthanum hydride compounds. Since in the considered systems the superconductivity is phononinduced, in theoretical predictions the Eliashberg equations formalism has been used, while some of the results were extended by including the results obtained in calculations using the density functional theory method. Theoretical predictions were compared with the results of experiments available in the literature. A holistic view of the latest results may lead the way to discover the superconductivity at room temperature. [ABSTRACT FROM AUTHOR]

The work is a brief review of the current state of knowledge about high-pressure superconductors with a high value of critical temperature (Tc). The described results relate to hydrogen-rich superconductors with particular emphasis on well-known hydrogen sulfide compounds and also include newly-discovered lanthanum hydride compounds. Since in the considered systems the superconductivity is phononinduced, in theoretical predictions the Eliashberg equations formalism has been used, while some of the results were extended by including the results obtained in calculations using the density functional theory method. Theoretical predictions were compared with the results of experiments available in the literature. A holistic view of the latest results may lead the way to discover the superconductivity at room temperature. [ABSTRACT FROM AUTHOR]

In this contribution, we describe the use of graphene as an efficient catalyst support and the role it plays in increasing the Lewis acidity of the supported metal complexes. By a density functional theory study, we show that the [La(N(SiMe3)2)3] complex can be easily grafted on graphene‐OH and ‐COOH functionalized surfaces. Two stable mono‐grafted compounds, (gO)‐[La(N(SiMe3)2)2] and (gOO)‐[La(N(SiMe3)2)2], are formed, behaving as stronger Lewis acids than the previously reported silica grafted analogues. To study the role of the graphene support in catalysis, we also computed the catalytic activity of the alkylated (gO)‐[La(CH3)2] and (gOO)‐[La(CH3)2] complexes in the ethylene and 1,3‐butadiene homo‐ and co‐polymerization reactions. Both compounds are efficient catalysts for the homo‐polymerization of the ethylene and 1,3‐butadiene. For the 1,3‐butadiene homo‐polymerization, the stereoselectivity outcome of the reaction differs according to the grafting site. The results computed for the co‐polymerization reaction, finally, show that the high stability of the allylic products leads to the formation of block copolymers. [ABSTRACT FROM AUTHOR]

In this work, two adsorbents were synthesized by loading lanthanum and iron ions on magnetized ETS‐4 titanosilicate. The sorbents were identified by Fourier‐transform infrared spectroscopy (FTIR), vibrating sample magnetometry (VSM), thermogravimetry, differential thermogravimetry (TG‐DTG), X‐ray diffraction (XRD), and Brunauer‐Emmette‐Teller techniques, and their adsorption performance for the sorption of fluoride was evaluated in a wide fluoride concentration range. The influence of various variables, including shaking time, fluoride concentration, pH, and temperature, on the uptake of fluoride was investigated. The maximal capacity of ETS‐4 impregnated with La and with Fe was 260.69 and 231.43 mg/g, respectively. The used sorbent was readily removed from the solution by using a magnet bar. The regenerated sorbent retained most of its capability after regeneration. The results of the kinetic study were described by a pseudosecond‐order model, indicating that the process was chemisorption in nature. The Freundlich isotherm well described the sorption data, which implied that the adsorption was multilayered and heterogeneous. [ABSTRACT FROM AUTHOR]

Lanthanum-doped zinc oxide (ZnO:La) thin films were deposited using a nebulizer spray technique with La concentrations 0, 1, 3 and 5 wt%. The structural, morphological and gas sensing properties were studied. All the film samples exhibit considerable ammonia sensing ability. The gas sensing results show that the ZnO:La film with 3 wt% of La doping exhibits remarkable sensing response and fast response/recovery times (39 s/11 s) for 100 ppm of NH3 at room temperature. The reasons for the enhanced sensing ability of the doped films have been addressed with the help of the underlying mechanism, atomic force microscopy (AFM) and photoluminescence (PL) results. [ABSTRACT FROM AUTHOR]

In this study, we prepared strontium-doped lanthanum ferrites with the perovskite-type structure for application as solid oxide fuel cell (SOFC) cathodes. We used the Pechini method to prepare strontium-doped lanthanum ferrites with the strontium:lanthanum molar ratios of 20:80 and 40:60. The resulting doped materials were characterized using various analytical tools. The calcination process was conducted at 450 °C because above this temperature, the stabilization of mass loss occurred and no phase transformation was observed. The X-ray diffraction results confirmed the mixing of the powder phases after the calcination process and the presence of a single powder phase in the air-sintered samples. The high-resolution transmission electron microscopy results revealed the presence of agglomerated nanoparticles smaller than 20 nm in size in the samples. The electrochemical impedance spectroscopy results revealed that the sample with 20% strontium exhibited a conductivity of 3.9 × 10−3 S cm−1 at 95 °C and activation energy of 0.37 eV. In contrast, the sample with 40% strontium exhibited a conductivity of 3.5 × 10−2 S cm−1 and activation energy of 0.29 eV. These results suggest that with an increase in the strontium content, the conductivity of the samples increased, where as the activation energy of the conduction process decreased. Therefore, the ferrites synthesized in this work are potential catalysts for SOFC cathodes. [ABSTRACT FROM AUTHOR]

Metal oxides hold great promise as robust sonosensitizers for sonodynamic therapy (SDT). However, they usually suffer from limited production yield of reactive oxygen species (ROS) due to the fast recombination of ultrasound‐triggered electrons and holes. Herein, porous lanthanum (La)‐doped MnO2 (LMO) nanoparticles are firstly developed as promising sonosensitizers in SDT. The strategic introduction of La dopants greatly promotes the separation efficiency of ultrasound‐triggered electrons and holes of MnO2, endowing them with significantly improved ROS yield. Consequently, the LMO with polyethylene glycol decoration exhibits good SDT activity toward breast cancer cells. This work highlights the doping strategy for the development of enhanced ROS production of metal oxide sonosensitizers for SDT. [ABSTRACT FROM AUTHOR]

The review is devoted to the conductive properties of the multielement compounds such as lanthanum and erbium cobaltites. These properties are associated with a dopant-controlled interaction of the delocalized electrons with the local magnetic moments. It is considered the basic physical mechanisms that determine the transport properties of perovskitelike materials. It is given main experimental results for lanthanum and erbium cobaltites, and it is considered the influence of the polycrystallinity factor of samples on their galvanomagnetic properties. [ABSTRACT FROM AUTHOR]

Direct CO 2 electrolysis has been explored as a means to store renewable energy and produce renewable fuels. La chromate-based perovskite oxides have attracted great attention as fuel electrode materials for solid oxide electrolyzer cells. However, the electrochemical catalytic activity of such oxides is relatively low, and their stability has not been confirmed. In this study, Pr is doped into La 0.75 Sr 0.25 Cr 0.5 Mn 0.5 O 3- δ (LSCM) and the applicability of the resulting fuel electrode to direct CO 2 electrolysis is investigated. The polarization resistance of the resulting electrode at 800 °C is decreased by 25%. Distribution function of relaxation times analysis indicates that the observed improvements may be attributed to increased oxygen ion conductivity. A full cell of Pr-doped LSCM-gadolinium-doped ceria (GDC)|scandia-stabilized zirconia|La 0.6 Sr 0.4 Co 0.2 Fe 0.8 O 3- δ -GDC achieves an electrolysis current of 0.5 A cm−2 at 1.36 V and a Faradaic efficiency close to 100%. Short-term (210 h) stability testing of the cell under an electrolysis current of 0.5 A cm−2 at 800 °C with pure CO 2 as the feedstock reveals a decrease in applied voltage at a rate of 7 mV kh−1, thereby indicating excellent stability. Thus, given its satisfactory performance and stability, the Pr-doped LSCM electrode may be considered a promising candidate material for direct CO 2 electrolysis. • Pr was doped into LSCM to develop an effective fuel electrode for CO 2 electrolysis. • Polarization resistance in CO 2 at 800 °C was reduced by 25% by doping Pr into LSCM. • Full cell with Pr-doped LSCM cathode, ScSZ electrolyte, LSCF-GDC anode was tested. • Full cell showed 0.5 A cm−2 at 1.36 V at 800 °C and Faradaic efficiency nearly 100%. • Full cell showed excellent stability in short-term test with 0.5 A cm−2 at 800 °C. [ABSTRACT FROM AUTHOR]

Fission isotopes contribute approximately 10% of the total radioactivity removed from the heat transport circuit of reactor systems during the chemical decontamination process. Simulated corrosion products (SCP) (CrFeO3 and MxCrFe1−xO3) and with fission isotope substituted in SCP [MxNiCrFe1−xO4 (M = La, Ce and Zr; x ≤ 0.05)] were synthesised and its dissolution behavior were studied in permanganate medium. Fission isotope metal ion substitution in SCP showed enhanced 'Cr' dissolution rates during the permanganate treatment. Among the fission isotope (La, Ce and Zr) substituted oxide dissolution studies, 'La' release was more compare to 'Ce' and 'Zr'. The release behavior of fission products studies showed that dissolved lanthanum is getting sorbed onto the insitu formed MnO2. [ABSTRACT FROM AUTHOR]

A strontium‐doped lanthanum cobaltite perovskite, La0.6Sr0.4CoO3, was prepared and utilized as a recyclable heterogeneous catalyst for the direct oxidative C(sp3)─H/C(sp2)─H coupling reaction between cyclic ethers and alkenes or coumarins to achieve corresponding α‐functionalized ethers. The α‐functionalization of cyclic thioethers or amides with alkenes or coumarins was also achieved via this protocol. The La0.6Sr0.4CoO3 catalyst exhibited better performance than a variety of homogeneous and heterogeneous catalysts. Utilizing a recyclable catalyst would offer a greener option for the direct oxidative C(sp3)─H/C(sp2)─H coupling reaction. To our best knowledge, the C(sp3)─H/C(sp2)─H coupling between olefins and ethers to generate α‐functionalized ethers using a heterogeneous catalyst has not been previously reported, and the α‐functionalization of cyclic thioethers or amides with alkenes or coumarins is new. [ABSTRACT FROM AUTHOR]

Herein, the influence of lanthanum concentration on the structural, thermal, optical, ferroelectric, and magnetic properties of Bi1-xLaxFeO3 (BLFO, x = 0, 0.05, 0.1, 0.15, 0.2, and 0.25) nanorods prepared by hydrothermal method was investigated. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy were performed to study the structural properties of BLFO nanoparticles for different lanthanum concentration. The Rietveld refinement and analysis of crystal structure revealed a single-phase perovskite structure with space group R3c. Transmission electron microscope (TEM) image of bismuth iron oxide nanorods exhibits average diameter of ~ 40 nm and length of ~ 2 μm. The ferroelectric Curie temperature of 833 °C (829 °C) was determined for BiFeO3 (Bi0.8La0.2FeO3) by differential thermal analysis (DTA). Diffuse reflectance UV-Vis spectra indicated that the optical band gap is decreased by increasing the lanthanum concentration. The ferroelectric properties of BiFeO3 nanoparticles also improved by adding lanthanum into the structure of bismuth iron oxide. Moreover, J-E curves showed that lanthanum doping can significantly decrease the leakage current of bismuth ferrite nanorods. Finally, vibrating sample magnetometer (VSM) measurements indicated that the weak ferromagnetic behavior is observed for as-prepared BLFO nanorods with x ≤ 0.15. However, for the 20 mol% lanthanum doping, a magnetic transition from weak ferromagnetic to antiferromagnetic occurred. [ABSTRACT FROM AUTHOR]

Powdery photocatalyst has been deeply studied due to its great potential in water treatment, yet its low recyclability is the bottleneck hindering its practical application. In this work, magnetically recyclable lanthanum-doped TiO2/calcium ferrite/diatomite (La-TCD) ternary composite was synthesized by sol-gel method. The physicochemical properties of this material were characterized and studied, and the photocatalytic property was evaluated by the decomposition of antibiotic oxytetracycline (OTC) and disinfection of bacteria Escherichia coli under visible light irradiation. The formation of heterojunction between La-doped TiO2 and calcium ferrite hindered the recombination of photo-induced charge carriers and improved the photocatalytic activity. Besides, the photodecomposition of OTC was enhanced by the high adsorption ability of substrate diatomite, in other words, the adsorption and decomposition synergistic behavior between catalyst and diatomite. The optimal La doping amount, as well as composite dosage, was determined. The composite could simply be recovered from waterbody by an external magnet, and the repetition tests indicated no obvious decrease of photoactivity after five cycles. Above all, this composite presented good potential to be applied in wastewater remediation process. [ABSTRACT FROM AUTHOR]

A solid-phase microextraction was performed using Fe3O4 nanoparticle coated with the chitosan, as a green and biodegradable polymer, for the pre-concentration of La (III) in aqueous solutions. The Fe3O4 magnetic nanoparticles were initially synthesized and properly coated with chitosan as adsorbent, and desorption step was successfully conducted using nitric acid. After desorption, analyte was determined with ICP-OES. The effects of different parameters, including pH, nanoparticle amount, concentration and volume of desorption acid, adsorption and desorption time, stirring rate, temperature and salt effect on the microextraction process, were investigated. The calibration curve was plotted, and a linear response range of 0.008–0.1 ng L−1 with a detection limit of 0.008 ng L−1 was obtained. This method was successfully implemented on two samples of river water, and favorable results were observed. [ABSTRACT FROM AUTHOR]

We have made measurements of the de Haas-van Alphen (dHvA) effect and the magnetic susceptibility of La1-x Smx B6 for x=0, 0.05, and 0.10 and Ce1-x Cax B6 for x=0 0.01, 0.03, and 0.05 in order to see changes in the Fermi surface (FS) volume with doping using lower valence substitutions for La and Ce. The FS volume decrease in La1-x Smx B6 is found to be directly proportional to the decrease in the number of electrons contributing to the boron-based conduction band by the decrease in valence of the divalent element. Two overlapping pieces of FS in the same portion of the Brillouin zone are seen to decrease in volume to the extent that they no longer overlap. In the case of Ce1-x Cax B6 the combination of increased disorder decreasing the mean-free path due to doping and heavy effective masses results in the damping of the dHvA oscillations and no signals are observed above x=0.05. Due to the mixed valence of the Ce atoms the volume decrease is not proportional to the percent valence change. Additional magnetic-susceptibility and magnetization measurements show the changing magnetic phase diagram in Ce1-x Cax B6. In the antiferroquadrapolar state of all of the Ce1-x Cax B6 samples the near-zero applied field magnetization is seen to increase with decreasing temperature terminating in a transition to the antiferromagnetic state. © 2009 The American Physical Society.

We have made measurements of the de Haas-van Alphen (dHvA) effect and the magnetic susceptibility of La1-x Smx B6 for x=0, 0.05, and 0.10 and Ce1-x Cax B6 for x=0 0.01, 0.03, and 0.05 in order to see changes in the Fermi surface (FS) volume with doping using lower valence substitutions for La and Ce. The FS volume decrease in La1-x Smx B6 is found to be directly proportional to the decrease in the number of electrons contributing to the boron-based conduction band by the decrease in valence of the divalent element. Two overlapping pieces of FS in the same portion of the Brillouin zone are seen to decrease in volume to the extent that they no longer overlap. In the case of Ce1-x Cax B6 the combination of increased disorder decreasing the mean-free path due to doping and heavy effective masses results in the damping of the dHvA oscillations and no signals are observed above x=0.05. Due to the mixed valence of the Ce atoms the volume decrease is not proportional to the percent valence change. Additional magnetic-susceptibility and magnetization measurements show the changing magnetic phase diagram in Ce1-x Cax B6. In the antiferroquadrapolar state of all of the Ce1-x Cax B6 samples the near-zero applied field magnetization is seen to increase with decreasing temperature terminating in a transition to the antiferromagnetic state. © 2009 The American Physical Society.

The solution behavior of dopants, Si, La, and N, in HfO2 polymorphs, monoclinic, tetragonal, and cubic was investigated by using a first principles calculation based on density functional theory within the local density approximation. It was found that the Si and La solutions are more preferable under oxidization atmosphere than reduction atmosphere, and the most efficient nitridation condition for the HfO2 is NO/NO2 atmosphere. By comparing the energy difference between the monoclinic and the tetragonal phases, it was found that the energy difference is decreased by the Si or La doping, whereas influence of the N doping is small, indicating that the phase transition from the monoclinic to tetragonal phase would be enhanced by the Si or La doping. [ABSTRACT FROM AUTHOR]

A study of the magnetic, electrical resistivity and hyperfine properties of polycrystalline La2RuO5 compounds is presented in this work. This compound forms in a monoclinic phase (space group P21/c). Magnetic susceptibility measurements yield an effective magnetic moment which is consistent with spin S = 1 of Ru ions, and a negative paramagnetic Curie temperature which indicates the presence of antiferromagnetic interactions. Below T ∼ 165 K, the magnetization shows a sudden decrease, precisely where the electrical resistivity shows a change in the activation energy. Room-temperature perturbed angular correlation spectrum is well fitted considering two electric-quadrupole components. The temperature dependences of electric-quadrupole frequencies and asymmetry parameters corroborate the occurrence of a phase transition at T ∼ 170 K. Moreover, below 170 K, magnetic-dipole interactions, which coexist with electric-quadrupole interactions, are observed at Ru sites. This is considered as a strong evidence for the preservation of S = 1 moment of Ru ions in the triclinic phase. The temperature dependence of the magnetic hyperfine field shows an unusual behavior, not consistent with the Brillouin function, and suggests a first-order magnetic transition, associated with either a structural transition or an orbital ordering induced by the Ru-Ru pair formation. [ABSTRACT FROM AUTHOR]

The structural and optoelectronic properties of LaAlO3 under pressure have been investigated for the first time using the highly accurate all electrons full potential linearized augmented plane wave method. The calculated lattice parameter at zero pressure is found in excellent agreement with the experimental results. Furthermore, with the increase in the external pressure, the lattice constant as well as bonds length decreases in accordance with the experimental results. The compound at zero pressure is an indirect bandgap semiconductor, while interestingly the indirect nature shifts to direct one with the increase of the pressure. The bonding in the material is of mixed covalent and ionic nature. In optical properties, frequency dependent parameters such as real and imaginary parts of dielectric function, refractive index, reflectivity, optical conductivity, absorption coefficient, and sumrules are calculated under pressure. [ABSTRACT FROM AUTHOR]

Scaled layers of HfO2 on LaGeOx on Ge grown by molecular beam deposition and their electrical properties and passivation are discussed. The interfacial LaGeOx thickness as well as the deposition temperature of the HfO2 cap are varied and the effects thereof on properties like peak mobility and interface trap distributions are compared. We report on negative threshold voltages, around -0.8 V, in combination with scaled devices with a minimum EOT of 1.4 nm, which shows beneficial characteristics for the LaGeOx passivation of Ge. The effect of various post-metallization anneals in FG and O2 is shown to improve the gate stack properties of the scaled samples, yielding higher peak mobilities with maximum values of about 120 cm2/Vs for annealed samples. The impact of LaGeOx interfacial layer thickness and HfO2 deposition temperature on the density of interface traps (Dit) distributions for as-deposited and annealed samples is discussed, and Hf in-diffusion into the LaGeOx is shown to be detrimental to its passivation of Ge. The Dit distributions are measured by the full conductance technique on MOSFETs at room temperature as well as 233 K and are then correlated with the mobilities extracted from the same devices. [ABSTRACT FROM AUTHOR]

Thin films of YBCO have been deposited on bare and La0.67Sr0.33MnO3 (LSMO) nanoparticle decorated single crystal SrTiO3 (STO) substrates. The effect of ferromagnetic LSMO nanoparticles, present at the substrate/film interface, on the superconducting properties of YBa2Cu3O7-δ (YBCO) thin film has been investigated by temperature dependent magnetization studies. The YBCO thin film on LSMO decorated STO substrate shows significant improvement in the critical current density and pinning force density as compared to the YBCO thin film deposited on the undecorated substrate, and this improvement is more significant at higher applied magnetic field. The presence of LSMO nanoparticles at YBCO/STO interface seems to introduce structural defects, which might be in the form of threading dislocations along the c-axis acting as correlated pinning centers leading to improved flux pinning properties of the YBCO thin film. The LSMO nanoparticles are ferromagnetic, which can also act as magnetic pinning centers and may result in the enhancement of flux pinning properties of the YBCO thin film deposited on the LSMO decorated STO substrate. [ABSTRACT FROM AUTHOR]

In this work, photoelectron spectroscopy is used to characterize the band alignment of lanthanum aluminate heterostructures which possess a wide range of potential applications. It is found that our experimental slope parameter agrees with theory using the metal-induced gap states model while the interface induced gap states (IFIGS) model yields unsatisfactory results. We show that this discrepancy can be attributed to the correlation between the dielectric work function and the electronegativity in the IFIGS model. It is found that the original trend, as established largely by metals, may not be accurate for larger band gap materials. By using a new correlation, our experimental data shows good agreement of the slope parameter using the IFIGS model. This correlation, therefore, plays a crucial role in heterostructures involving wider bandgap materials for accurate band alignment prediction using the IFIGS model. [ABSTRACT FROM AUTHOR]

The properties of the d-band structure of the transition metal atom in cubic LaBO3 and SrBO3 perovskites (where B = Sc, Ti, V, Cr, Mn, Fe, Co, Ni, and Cu) and their dependence on strain, d-band filling, and oxidation state were investigated using density functional theory calculations and atom-projected density of states. The strain dependence of the d-band width is shown to depend systematically on the size of the B atom. We show that the transition metal d-band width and center are linearly correlated with each other in agreement with a rectangular band model. A simple matrix element formalism based on the solid state table can readily predict the strain dependence of the d-band width. [ABSTRACT FROM AUTHOR]

The structural and electrical transport properties of LaMn1-xFexO3 (0.1 ≤ x ≤ 0.6) bulk samples have been investigated. The powder x-ray diffraction patterns at room temperature show that all samples are formed in single phase. The temperature dependent resistivity data have been fitted with the Mott's variable-range hopping (VRH) model for an entire studied range of the temperature (77-300 K) to calculate the hopping distance (Rh) and the density of states at Fermi level (N(EF)). It is found that all parameters vary systematically with the increase in Fe concentration. Moreover, the resistivity data were also fitted in the small polaron hopping (SPH) model. The non-adiabatic SPH conduction mechanism is followed by all samples. This type conduction mechanism is far accompanied by subtle electronically induced structural changes involving in Fe-O-Fe and Fe-O-Mn bond angles and bond lengths. Thus we suggest that the transport properties can be explained according to the additional localization of charge carriers induced by Fe doping. [ABSTRACT FROM AUTHOR]

Lanthanum dimer (La2) was studied by mass-analyzed threshold ionization (MATI) spectroscopy and a series of multi-configuration ab initio calculations. The MATI spectrum exhibits three band systems originating from ionization of the neutral ground electronic state, and each system shows vibrational frequencies of the neutral molecule and singly charged cation. The three ionization processes are La2+ (a2∑g+) ← La2 (X1∑g+), La2+ (b2Π3/2, u) ← La2 (X1∑g+), and La2+ (b2Π1/2, u) ← La2 (X1∑g+), with the ionization energies of 39 046, 40 314, and 40 864 cm-1, respectively. The vibrational frequency of the X1Σg+ state is 207 cm-1, and those of the a2Σg+, b2Π3/2, u and b2Π1/2, u are 235.7, 242.2, and 240 cm-1. While X1Σg+ is the ground state of the neutral molecule, a2Σg+ and b2Πu are calculated to be the excited states of the cation. The spin-orbit splitting in the b2Πu ion is 550 cm-1. An X4Σg- state of La2+ was predicted by theory, but not observed by the experiment. The determination of a singlet ground state of La2 shows that lanthanum behaves differently from scandium and yttrium. [ABSTRACT FROM AUTHOR]

The behavior of temperature dependences of electrical resistance and magnetoresistance of polycrystalline substituted lanthanum manganite (La0.5Eu0.5)0.7Pb0.3MnO3 at low temperatures was thoroughly studied. A broad hysteresis was found in the field dependences of electrical resistance in the low-temperature region. Above 40 K, no hysteresis feature was observed. The temperature T = 40 K corresponds to the temperature of minimum electrical resistance and the temperature TN to the antiferromagnet-paramagnet phase transition of the material of the intergrain boundaries. In this work we propose a model which explains the observed features of the ρ(T) and ρ(H) curves at temperatures below TN by the formation of a network of ferromagnet-antiferromagnet-ferromagnet tunnel contacts. [ABSTRACT FROM AUTHOR]

We have performed a systematic structural, vibrational, and optical study of LaF3:Eu3+ nanoparticles capped with oleic acid (OA) or OA and sensitized with thenoyltrifluoroacetone (TTA). The average nanoparticle size was around 11 nm for all Eu3+ concentrations. A shift in the energy of the Raman active modes is observed with increasing Eu3+ concentration that can be accounted for by a decrease in the unit cell volume. Sensitization by TTA was observed and resulted in an 18 000% increase in the photoluminescence (PL) intensity for TTA/OA capped LaF3:Eu3+ nanoparticles when compared with OA capped LaF3:Eu3+ nanoparticles. There is also a large increase in the 5D0→7F2 PL intensity, when normalized to the 5D0→7F1 PL magnetic dipole transition intensity, for TTA/OA capped nanoparticles. The changes in the PL intensities, PL lifetimes, Judd-Ofelt parameters, stimulated emission cross sections, and quantum efficiencies, for OA and TTA/OA capped LaF3:Eu3+ nanoparticles with increasing Eu3+ concentration can be accounted for by a model that separates the Eu3+ sites into sites near the surface and Eu3+ sites in the core as well as nonradiative recombination sites near the surface. The large increase in PL intensity due to TTA sensitization means that TTA capped LaF3:Eu3+ can potentially be used for applications that include optical amplification. [ABSTRACT FROM AUTHOR]

Rectifying and photoelectronic properties of the La0.67Ba0.33MnO3/SrTiO3:Nb junctions with the film thickness from d=0.5 to 30 nm have been systematically studied. It is found that the electronic transport of the junction is dominated by quantum tunneling or thermoionic emission when film thickness is below or above 1 nm. The rectifying ratio and ideality factor, correspondingly, experience a sudden change as film thickness grows from 0.5 to 1 nm and a smooth variation with film thickness above 1 nm. The threshold film thickness for the establishment of a mature depletion layer is therefore 1 nm. The photoemission properties of the junctions also exhibit a strong dependence on film thickness. As experimentally shown, the photocurrent vanishes in the zero thickness limit, and grows rapidly with the increase in film thickness until d=6 nm, where a maximal photocurrent of ∼770 nA/mm2 under the irradiance of the laser of 5 mW and 532 nm is obtained. After this maximum, an increase-to-decrease turning appears with further increasing film thickness. Taking into account the finite diffusion distance of the photocarriers and the strain-enhanced charge trapping in ultrathin film junctions, a theoretical description that well reproduces the experiment results can be obtained, which reveals the severe depression of finite diffusion distance of the extra carriers on photocurrent. The maximal diffusion distance thus obtained is ∼3.5 nm. Similar analyses have been performed for the La0.67Ca0.33MnO3/SrTiO3:Nb junctions, and the corresponding diffusion distance there is ∼1.5 nm. [ABSTRACT FROM AUTHOR]

The electrical conduction mechanism in La3Ta0.5Ga5.5O14 (LTG) was studied from the standpoint of defect formation during growth caused by the nonstoichiometry of the crystal. Since the stoichiometric composition of LTG does not coincide with the congruent composition, single crystals grown from the stoichiometric melt under an atmosphere of O2/Ar in the oxygen partial pressure range from 0.005 to 1 atm was Ta-poor. Ta vacancies were formed during the growth, and their population was predominated by the growth-pO2. With increasing temperature up to 600 °C, the Ta vacancies were ionized to yield holes, and thus the electrical conductivity of the LTG crystal varied with temperature and growth-pO2. In contrast, Ga vacancies as a carrier source would form by Ga evaporation during growth under pO2 below 0.005 atm. The growth-pO2 dependence of the electrical conductivity was opposite to the case for Ta vacancies. For the case of sintered LTG with the exact stoichiometric composition, impurity defects dominated electrical conduction below 600 °C, where the impurity concentration was higher than the cation vacancies arising from the nonstoichiometry of the sintered LTG. Thus, electrical conductivity was almost independent of the sintering atmosphere of pO2. Above 700 °C, the dominant carrier in both single crystal and sintered LTG was ions related to oxygen defects formed by the anion Frenkel reaction. [ABSTRACT FROM AUTHOR]

Metal-oxide-semiconductor capacitors and n-channel metal-oxide-semiconductor field-effect transistors with La2O3 gate dielectric were fabricated. The positive bias temperature instability was studied. The degradation of threshold voltage (ΔVT) showed an exponential dependence on the stress time in the temperature range from 25 to 75 °C. The degradation of subthreshold slope (ΔS) and gate leakage (IG) with stress voltage was also measured. The degradation of VT is attributed to the oxide trap charges Qot. The extracted activation energy of 0.2 eV is related to a degradation dominated by the release of atomic hydrogen in La2O3 thin films. [ABSTRACT FROM AUTHOR]

The electrical conduction mechanism in La3Ta0.5Ga5.5O14 (LTG) was studied from the standpoint of defect formation during growth caused by the nonstoichiometry of the crystal. Since the stoichiometric composition of LTG does not coincide with the congruent composition, single crystals grown from the stoichiometric melt under an atmosphere of O2/Ar in the oxygen partial pressure range from 0.005 to 1 atm was Ta-poor. Ta vacancies were formed during the growth, and their population was predominated by the growth-pO2. With increasing temperature up to 600 °C, the Ta vacancies were ionized to yield holes, and thus the electrical conductivity of the LTG crystal varied with temperature and growth-pO2. In contrast, Ga vacancies as a carrier source would form by Ga evaporation during growth under pO2 below 0.005 atm. The growth-pO2 dependence of the electrical conductivity was opposite to the case for Ta vacancies. For the case of sintered LTG with the exact stoichiometric composition, impurity defects dominated electrical conduction below 600 °C, where the impurity concentration was higher than the cation vacancies arising from the nonstoichiometry of the sintered LTG. Thus, electrical conductivity was almost independent of the sintering atmosphere of pO2. Above 700 °C, the dominant carrier in both single crystal and sintered LTG was ions related to oxygen defects formed by the anion Frenkel reaction. [ABSTRACT FROM AUTHOR]

The annealing behavior of a lanthanum oxide thin film deposited on a silicon (001) substrate by electron-beam evaporation has been studied by aberration-corrected transmission electron microscopy (TEM), scanning TEM (STEM), and electron energy loss spectroscopy (EELS). We have developed a procedure for the precise measurement of thickness and interfacial roughness by taking advantage of features of aberration correction combined with the statistics of fluctuating crystalline edge positions. The results of the measurements and quantitative elemental analyses by STEM-EELS have revealed atomic diffusion and reactions during deposition and postdeposition annealing (PDA) at 300 and 500 °C. The channel mobility could be limited by Coulomb scattering before PDA, and by remote roughness scattering and remote phonon scattering after PDA at 500 °C. When we consider the large leakage current caused by oxygen defects in the as-deposited sample and the large equivalent oxide thickness of the thick Si-rich layer in the 500 °C-PDA sample, the gate properties of the 300 °C-PDA sample should be better than those of other samples, as shown by electrical measurements. [ABSTRACT FROM AUTHOR]

Magnetic properties and spin state transfer in Ga doping perovskite cobaltites La0.7Ca0.3(Co1-yGay)O3 (y=0, 0.1, 0.2, 0.3, and 0.4) are carefully investigated in this work. On Ga doping, the Curie temperature sharply decreases and the magnetization is greatly reduced, indicating Ga doping breaks the ferromagnetic interaction in the system. For y≥0.2, the ferromagnetic and antiferromagnetic transitions have been observed in thermal magnetization measurement whereas the dominated antiferromagnetic interaction is confirmed by the negative Curie–Weiss temperatures. Evaluation of the effective moment of Co ions seems to imply that Ga doping stablizes Co-ion high spin state. [ABSTRACT FROM AUTHOR]

Dynamic structural change in Pd-perovskite automotive catalyst, LaFe0.9Pd0.1O3, which has a high catalytic activity during aging, was studied by in situ time-resolved dispersive x-ray absorption fine structure spectroscopy at 200–500 °C. An Al2O3-based conventional catalyst was also studied. In a reductive atmosphere, both catalysts showed similar temperature dependences of structural transformation from an oxide to a metal. However, different temperature dependence was observed in an oxidative atmosphere. A faster response in the structural change was observed in the Pd-perovskite catalyst than in the Pd/Al2O3 catalyst. It was revealed that Pd-perovskite shows a considerably fast structural change to the oxidized state via the movement of Pd atoms into the perovskite crystal, in comparison with Pd/Al2O3 showing two-step structural change for making PdO. [ABSTRACT FROM AUTHOR]

Bi1-xLaxFe1-yCoyO3 (x=0, 0.1; y=0, 0.05, 0.1) polycrystalline thin films were fabricated on Pt/Ti/SiO2/Si(111) substrates via chemical solution deposition method. X-ray diffraction analysis revealed a phase transition in La–Co codoped BiFeO3 (BFO) thin films. Saturated ferroelectric hysteresis characteristics in La–Co codoped BFO thin films were observed, and the conduction behavior of Bi1-xLaxFe1-yCoyO3 thin films investigated to understand the leakage mechanisms. In the low applied field, the conduction mechanism of Bi1-xLaxFe1-yCoyO3 thin films was found to be dominantly Ohmic. In the high applied field, the conduction mechanisms of pure and La doped BFO thin films were found to be trap-filled-limited and Poole–Frenkel emission, and that of Co doped and La–Co codoped BFO thin films Schottky emission. The dielectric constant of Bi0.9La0.1Fe0.9Co0.1O3 thin film, in the frequency range of 1 to 2000 kHz, was nearly two times higher than that of pure BFO thin film while the dielectric loss tan δ was small at values below 0.07. It was found that saturation magnetization in BFO thin films could be enhanced by La or Co doping, and obviously by La–Co codoping too. [ABSTRACT FROM AUTHOR]

Strong blue and green visible lights are obtained in Tm3+/Ho3+-codoped LaOF tetragonal nanocrystals (NCs) through down and up fluorescence conversions when the sample is excited selectively with ultraviolet and infrared photons, respectively. The excitation spectrum by detecting at 545 nm (Ho3+:5S2→5I8) reveals two peaks at 348 nm (Ho3+:5I8→5G3) and 355 nm (Tm3+:3H6→1D2), which indicates that the energy transfer process from Tm3+ to Ho3+ has occurred when Tm3+ is excited with 355 nm photons in Tm3+/Ho3+:LaOF. There is no energy transfer from Ho3+ to Tm3+ when Ho3+ is excited with 348 nm photons in codoped samples because the near resonant Ho3+ levels are significantly quenched by multiphonon relaxation. But enhanced green fluorescence of Ho3+ is obtained due to the ion situated at the low symmetry site in Ho3+/Tm3+:LaOF NCs. The intensity patterns of the up-conversion fluorescence would be fine-tuned by adjusting Tm3+ concentration and excitation wavelength. Spectroscopic analyses in down- and up-conversion processes indicate that Tm3+ ions possibly prefer to stay at the surface of NCs than Ho3+ ions. [ABSTRACT FROM AUTHOR]

Magnetic properties and spin state transfer in Ga doping perovskite cobaltites La0.7Ca0.3(Co1-yGay)O3 (y=0, 0.1, 0.2, 0.3, and 0.4) are carefully investigated in this work. On Ga doping, the Curie temperature sharply decreases and the magnetization is greatly reduced, indicating Ga doping breaks the ferromagnetic interaction in the system. For y≥0.2, the ferromagnetic and antiferromagnetic transitions have been observed in thermal magnetization measurement whereas the dominated antiferromagnetic interaction is confirmed by the negative Curie–Weiss temperatures. Evaluation of the effective moment of Co ions seems to imply that Ga doping stablizes Co-ion high spin state. [ABSTRACT FROM AUTHOR]

The temperature dependencies of the current-voltage (I-V) characteristics for the La2-xSrxCuO4 (LSCO) (x=0.10, 0.16, and 0.20)/1.0 wt % Nb-doped SrTiO3 (SNTO) heterojunctions were investigated under magnetic fields up to 14 T. The junction resistances for different heterojunctions show remarkable jumps as soon as the superconductivities of LSCO films occur. The diffusion voltages Vd and the fitting parameters E00 in the field emission/thermionic-field emission formula, as well as the in-plane resistivities of LSCO films have the similar temperature and magnetic field dependencies. It is believed that both of the superconductivities of LSCO films and the inhomogeneous Schottky interfaces between LSCO and SNTO are responsible for the I-V characteristics of the heterojunctions. [ABSTRACT FROM AUTHOR]

We report an investigation of the electronic structure of LaB6 nanopolycrystalline pulsed laser deposited (PLD) film and single crystal with x-ray absorption near edge structures (XANES) spectroscopy at the B K-edge. The experimental results are compared with theoretical calculations using density functional theory, and real space multiple scattering. It is found that (i) the LaB6 PLD film is of high quality and metallic albeit it is a polycrystalline phase of nanocrystallites and (ii) the B K-edge XANES for the single crystal specimens exhibit well defined spectral features corresponding to the theoretical partial densities of states of B p character and the threshold energy is relatively low and free electronlike, revealing its metallic character. The implications of these observations to the enhancement in electron emission from the PLD films are discussed. [ABSTRACT FROM AUTHOR]