La Atoms Research Articles

Tailoring the room temperature ferromagnetism in TiO2 nanoparticles by modulating the concentration of surface oxygen vacancy via La incorporating

Abstract La-incorporated TiO2 nanoparticles (Ti1-xLaxO2) were synthesized by a sol-gel method followed by vacuum annealing at 500 °C for 4 h, and were characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), Raman scattering spectroscopy, and vibrating sample magnetometer (VSM), respectively. The results indicated that La ions were incorporated with TiO2 without distorting the tetragonal anatase structure, and a small amount of La ions were doped into TiO2 lattice by substituting the surface Ti sites, whereas most of the La atoms evenly distribute into TiO2 matrix in the form of La2O3. The incorporation of La ions with TiO2 matrix modulates the concentration of surface oxygen vacancy in Ti1-xLaxO2 nanoparticles. The room temperature ferromagnetism (RTFM) in Ti1-xLaxO2 nanoparticles varies with the concentration of surface oxygen vacancy due to ferromagnetic coupling interactions between singly ionized oxygen vacancy, thus RTFM can be tailored by modulating the concentration of surface oxygen vacancy via La ions incorporating.

Structural evolution of La2Ti2O7 at elevated temperatures.

Structural evolution of a La2Ti2O7 ferroelectric compound possessing perovskite-type slabs at elevated temperatures was investigated using the single-crystal X-ray diffraction technique. The monoclinic low-temperature phase (L) transformed into the orthorhombic high-temperature phase (H) via an incommensurately modulated phase (IC) between ∼989 and ∼1080 K. The L-IC transition was considered to be of the first order, with the L+IC two-phase co-existing region between ∼989 and ∼1027 K. The structure of IC was determined from the (3+1)-dimensional superspace representation with a modulation vector q = αao (α ≃ 0.49), where ao is the a-axis vector of the basic cell. The structural modulation originated from the variation of the tilt angle of the TiO6 octahedra in the perovskite-type slab in association with small positional displacements of La atoms. The IC-H transition took place at ∼1080 K and was close to the second order. During the IC-H transition, nanoscale flat plate domains having either a cell twin of the L-type structural modules or a cell twin of the alternating H- and L-type structural modules began to appear in the approximant structure of IC. The thickness of the flat plate domains then grew rapidly along the modulation vector in proportion to (½ - α)-1 as α approached ½ with decreasing temperature. In the two-phase L+IC co-existing region, the IC phase consisting of the two types of cell twins was gradually replaced with the low-temperature monoclinic phase L, which is not cell twinned but rather twinned macroscopically by the L-type structural modules.

First-principles study of structure, mechanical and optical properties of La- and Sc-doped Y2O3

The electronic, mechanical and optical properties of La-and Sc-doped Y2O3 were investigated using first-principles calculations. Two doping sites of Sc and La in Y2O3 were modeled. The calculated values of the energy of formation show that the most energetically favorable site for a La atom in Y2O3 is a d-site Y atom, while for Sc a b-site Y atom is the more stable position. The calculated band gap shows a slight decrease with increasing La or Sc concentration. The calculated results for the mechanical and optical properties of Y2–xRxO3 (R = Sc or La, 0 < x ≤ 0.1875) show that La- or Sc-doped Y2O3 would have enhanced strength, and thus an ability of resisting external shocks, and increased hardness and mechanical toughness. These improved mechanical properties are achieved without sacrificing the optical properties of the doped compounds. So the doping of La or Sc in Y2O3 is permissible in the preparation of Y2O3 transparent ceramics, of course, doping of La or Sc will benefit the sintering of transparent ceramics.

Critical current density and flux pinning in BaFe1.9Pt0.1As2 and La doped Ba0.95La0.05Fe1.9Pt0.1As2 polycrystals

We present the field and temperature dependence of the magnetizations of BaFe1.9Pt0.1As2 and Ba0.95La0.05Fe1.9Pt0.1As2 samples synthesized by solid-state reaction method. The samples were formed as a single phase in the ThCr2Si2-type structure. Replacing Ba with the smaller La atom results in a lattice shrinkage. The critical current, Jc (H, T) has been determined (using Bean’s critical state model) from magnetic hysteresis loops in a temperature range between T = 5 K and the superconducting transition temperatures (20 K), in fields up to H = 9 T. We find a nonmonotonic ‘fishtail’ shape (exhibiting a second peak) of the magnetization loops as well as a very large irreversibility. We observe a remarkable flux jump at T = 5 K for BaFe1.9Pt0.1As2 due to magneto-thermal instability, but a very sharp magnetization peak for Ba0.95La0.05Fe1.9Pt0.1As2 near H = 0, which corresponds to a much-reduced relaxation rate of vortices. Jc decreases exponentially with temperature as well as with field in lower temperatures and fields ranges. La doping causes a considerable increase in the irreversibility, leading to a significant enhancement of Jc. The analysis shows that the high Jc is mainly due to collective (weak) pinning of vortices by dense microscopic point defects with some contribution from a strong pinning mechanism.The normalized pinning force Fp/Fp,max as a function of the reduced magnetic field h = H/Hirr is also obtained. Using the approaches of Dew-Hughes (1974 Phil. Mag. 30 293) and Kramer (1973 J. Appl. Phys. 44 1360), we determine the nature of the pining sources. It is found that many different pinning mechanisms are active simultaneously. The modified expression of Fp/Fp,max based on collective pinning theory enables us to determine the field dependence of the relaxation rate S(H, T = 5 K) indirectly instead of using more difficult relaxation measurements.Finally, all drastic changes with La doping are clearly demonstrated and investigated under different models introduced in the literature.

Heteroatom-induced band-reconstruction of metal vanadates for photocatalytic cyclohexane oxidation towards KA-oil selectivity

Structure-function correlation constitutes a central theme in the selective photocatalytic oxidation of cyclohexane with molecular oxygen, as a result of precise tailoring band-structure towards KA-oil selectivity. Herein, we comparatively and systematically investigate the correlation among optical properties, electronic structure, and photocatalytic performance of two d°-vanadate photocatalysts (BiVO4 and Cu3V2O8) using theoretical calculations and experimental techniques. Results show that BiVO4 promotes the selective oxidation pathway under visible-light irradiation with higher efficiency (TOF = 7.5 h−1, based on the molar amount of V sites) and chemoselectivity (cyclohexanone/cyclohexanol molar ratio = 3.0) than the Cu3V2O8. Meanwhile, the photocatalytic performance of BiVO4 demonstrates high photocatalytic selectivity towards KA-oil (95%), while Cu3V2O8 seems to facilitate the accommodation of chlorine promoters, leading to very different chlorocyclohexane selectivity (46%). Such the distinct photocatalytic performances of BiVO4 and Cu3V2O8 can be ascribed to their unique electronic structures to facilitate the e−−h+ charge carriers and generation of reactive species during photoirradiation. The Bi3+6p states of BiVO4 are predominant components of the conduction band minimum (CBM) and hybridize with Bi3+6 s, and O2−2p and V5+3d orbitals at the valence band maximum (VBM); whereas the Cu2+3d and V5+3d orbitals contribute to the CBM of Cu3V2O8, and Cu2+3d, O2−2p and V5+3d orbitals at the VBM. So BiVO4 with s − p matrix elements is more effective than the Cu3V2O8 in producing OH, h+ and H2O2, which can rapidly oxidize the C − Cl band cleavage for chlorocyclohexane intermediate to regenerate newly Cl radicals in the next cycle reactions. Heteroatom-tuning of photocatalytic performance is further supported by universal evidences from experimental results by replacing Bi or Cu of the above vanadates with Ag, La, Sr, Fe or Ti atom and the study of the electrons, holes and radicals mediated reaction pathway by scavengers, respectively.

Magnetic splitting of La I lines studied by means of fluorescence depletion spectroscopy

The fluorescence depletion spectroscopy (FDS) was used to study the structure of 11 La I lines in the visible green-red region 579.5–645.8 nm. A discharge tube with hollow cathode was the source of free La atoms. The measurements were carried out for two mutually perpendicular states of linear polarization of the laser light. The spectra were recorded in the presence of a magnetic field of about 800G. We determined Landé gJ factors for 7 levels, we improved the precision of the hyperfine structure (hfs) data for 6 even parity levels and we reanalyzed gJ data for several other levels of La I.

Suppression of long-range ferromagnetic order in the CexLa1−xTiGe3 system

We report specific heat, magnetization, and resistivity measurements on single crystals of ${\mathrm{Ce}}_{x}{\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{TiGe}}_{3}$ systems. When the Ce concentration $x$ is increased, the system changes from a single-ion Kondo system for $x=0.05$ into a ferromagnetic Kondo lattice for $x=1$, where the magnetic part of electrical resistivity reveals a single-ion scaling with $x$. The isoelectric substitution of Ce by La atoms causes a change of the relative strength of competing energy scales of Kondo and RKKY interaction and crystalline electric field (CEF). The substitutions induce the continuous evolution of the Kondo temperature ${T}_{K}$ and the linear variation of ferromagnetic ordering temperature ${T}_{c}$, which are accompanied by a change of the CEF level scheme of the Ce ions. The composition-temperature ($x\text{\ensuremath{-}}T$) phase diagram for ${\mathrm{Ce}}_{x}{\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{TiGe}}_{3}$ is constructed by a combination of magnetization, specific heat, and resistivity measurements. The ferromagnetic ordering temperature is linearly suppressed as $x$ decreases and vanishes near the critical concentration ${x}_{c}=0.1$, but conventional quantum criticality is absent near ${x}_{c}$. The specific heat measurement for $x=0.05$ reveals the power law increase of the electronic specific heat coefficient ${C}_{m}/T\ensuremath{\propto}1/T$ with a large value of $\ensuremath{\sim}3.5$ J/mol ${\mathrm{K}}^{2}$ at $T=0.4\phantom{\rule{0.28em}{0ex}}\mathrm{K}$. The magnetic susceptibility for $x=0.05$ also shows a power law dependence $\ensuremath{\chi}(T)\ensuremath{\propto}1/T$ below 10 K.

Preparation and molecular structure of lanthanum–FcCOO−–DTBbpy complexes

Two new lanthanum complexes, [La2(μ2-OOCFc)4(DTBbpy)2(NO3)2] (1·2CH3CN) and [La2(μ2-OOCFc)4(μ-HOOCFc)2(DTBbpy)2(HOCH3)2](ClO4)2 (2·2CH3OH); (Fc = ferrocene and DTBbpy = 4, 4′-di-tert butyl bipyridyl) were prepared and characterized by single crystal X-ray diffraction. The reaction of sodium ferrocene carboxylate (FcCOONa) with La(NO3)·6H2O (1:1) in methanol at 80 °C followed by the addition of 4, 4′-di-tert-butyl bipyridyl (DTBbpy) resulted in the formation of (1). The use of La(ClO4)3·6H2O as a precursor under identical synthetic condition yielded (2).In 1 and 2, the La atoms are bridged by four FcCOO- ligands forming the [La2(μ2-OOCFc)4] core (La…La = 4.0357(4) Å in 1 and 4.3789(3) Å in 2). The coordination number of the La atoms is 9 for 1 and 8 for 2.

Contrasting Bonding-Interaction-Induced Distinct Relaxation in La65Ni35 and La65Al35 Glass-Forming Alloys.

The α and β relaxations are two fundamental processes in glass-forming materials, and quite important for many of the properties. Although intensive studies have found that α and β relaxations can be tuned by changing the constituent elements, the underlying structural basis is still elusive. Here, we explored the effect of two key elements of Al and Ni on distinct β and α relaxations in La65Al35 and La65Ni35 glass-forming alloys via classical and ab initio molecular dynamics simulations combined with dynamical mechanical spectroscopy. Unexpected coupling of relaxation in both β and α relaxation time scales is observed for La and Al atoms in the La65Al35 system, which drastically suppresses the relaxation dynamics. It is revealed that the dynamic coupling of La and Al results from the covalent-like bonding interaction between Al atoms, which connect Al together, forming a network-like structure. The bonding network not only drastically slows down the dynamics of Al but also couples the motion of La and Al together. This finding elucidates the underlying basis of Al and Ni elements for distinct β and α relaxation and sheds light on tuning the formation and properties of metallic glasses by minor alloying.

Superconductivity in filled skutterudite LaxRh4P12 (0.5 < x ≤ 1): Experimental and computational studies

The superconductivity in filled skutterudites LaxRh4P12 (0.5 < x ≤ 1) was investigated by experiments and first-principles calculations. LaxRh4P12 species with varying La contents (x) were synthesized at high pressures and high temperatures. Increasing the synthesis pressure resulted in an increase in x. Moreover, TC was found to increase with increasing values of x. The highest value of TC was found to be 16.4 K for x = 0.99 (3). Electronic structure calculations for RhP3 and LaRh4P12 showed that filling of La into RhP3 significantly increased the density of states (DOS) at the Fermi energy EF, N (EF). This was attributed to the fact that an increase in the number of valence electrons due to La filling shifts the EF to higher energies, at which the DOS has a moderate value. Phonon calculations showed that the filling of La atoms into RhP3 leads to a La phonon band and modification of RhP phonon bands in the relatively low-energy region. The increase in N (EF) and modification of phonon spectra caused by La filling enhances the electron–phonon coupling constant, leading to superconductivity in LaRh4P12. The TC value calculated assuming the Bardeen–Cooper–Schrieffer mechanism was consistent with the experimentally observed TC. A comparison between LaRh4P12 and a conventional filled skutterudite showed that the former is an intercalation-type compound, the antibonding states of which are important for its transport properties, while the latter is a Zintl-phase-type compound, for which the bonding states are important.

Ab Initio Molecular-Dynamics Simulation Liquid and Amorphous Al94-xNi6Lax (x=3-9) Alloys

Ab initio molecular-dynamics simulations have been used to investigate the liquid and amorphous Al94-xNi6Lax (x=3-9) alloys. Through calculating the pair distribution functions and partial coordination numbers, the structure and properties of these alloys are researched, which will help the design bulk metallic glass. The concentration of La atoms can affect the short-range order of Al94-xNi6Lax alloys, which is also studied in this calculation result.

The study on high &lt;i&gt;n&lt;/i&gt; Rydberg state of La II

We analyze ionic spectrum of lanthanum via intermediate state (Xe)&lt;inline-formula&gt;&lt;tex-math id="M191"&gt;\begin{document}$ 5d6d \; ^3F_2 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M191.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M191.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; in the energy region 89872-91783 cm&lt;sup&gt;–1&lt;/sup&gt;, and the spectrum is obtained using five-laser resonance excitation in combination with a method of sequential ionization by a pulsed electric field and a constant electric field, and has been recalibrate in this work. Both of one strong and one weak autoionization Rydberg series converging to the La&lt;sup&gt;2+&lt;/sup&gt; state are determined. Meanwhile, the two autoionization Rydberg series are assigned by relativistic multichannel theory (RMCT) within the framework of multi-channel quantum defect theory (MQDT). More specifically, the strong autoionization Rydberg series is assigned to &lt;inline-formula&gt;&lt;tex-math id="M192"&gt;\begin{document}$ 5dnp\left(\dfrac{5}{2},\dfrac{1}{2}\right)_3 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M192.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M192.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and/or &lt;inline-formula&gt;&lt;tex-math id="M193"&gt;\begin{document}$ 5dnp\left(\dfrac{5}{2},\dfrac{1}{2}\right)_2 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M193.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M193.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;, and the weak autoionization Rydberg series is assigned to &lt;inline-formula&gt;&lt;tex-math id="M194"&gt;\begin{document}$ 5dnf\left(\dfrac{5}{2},\dfrac{5}{2}\right)_3 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M194.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M194.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; and/or &lt;inline-formula&gt;&lt;tex-math id="M195"&gt;\begin{document}$ 5dnf\left(\dfrac{5}{2},\dfrac{5}{2}\right)_2 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M195.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M195.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. We focus on the behavior of quantum defect with excitation energy for high &lt;inline-formula&gt;&lt;tex-math id="M196"&gt;\begin{document}$ n $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M196.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M196.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; Rydberg states, which are sensitive to the existence of a external field. We find the breakdown of quantum defect regular behavior for a specific Rydberg series and autoionization Rydberg series of La&lt;sup&gt;+&lt;/sup&gt; as the effective quantum number &lt;inline-formula&gt;&lt;tex-math id="M197"&gt;\begin{document}$ n^\star&gt;67 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M197.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M197.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;. Due to that our calculations, which are obtained by relativistic multichannel theory and included configuration interactions, are in basically agreement with that for experimental low &lt;inline-formula&gt;&lt;tex-math id="M198"&gt;\begin{document}$ n $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M198.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M198.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; (&lt;inline-formula&gt;&lt;tex-math id="M199"&gt;\begin{document}$ n^\star&lt;67 $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M199.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20181980_M199.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt;) Rydberg states as well as small stray electric fields, we suggest that plasma formed by photoionization of La atoms in the second excitation step may be responsible for the breakdown of quantum defect regular behavior.

La2O3 nanoplate: An efficient electrocatalyst for artificial N2 fixation to NH3 with excellent selectivity at ambient condition

Identification of new effective and selective N2 reduction electrocatalyst is still of critical importance for fundamental and application research. Here, we report La2O3 nanoplate performing as an efficient metal oxide catalyst for electrochemical N2 fixation to NH3, which exhibits excellent selectivity and stability with a high Faradaic efficiency of 4.76% and a NH3 yield rate of 17.04 μg h−1 mg−1cat. at −0.8 V vs. reversible hydrogen electrode (RHE) in 0.1 M Na2SO4 solution under atmospheric pressure. Density functional theory (DFT) calculation results show that La atoms in La2O3 act as the active sites for efficiently adsorbing N2. The optimal adsorption approach of N2 molecule on the (011) face of La2O3 is end-on-two configuration which is highly activated. Thus La2O3 exhibits high performance for electrochemical reduction of N2.

Mass-analyzed threshold ionization spectroscopy of lanthanide imide LnNH (Ln = La and Ce) radicals from N-H bond activation of ammonia.

Ln (Ln = La and Ce) atom reactions with ammonia are carried out in a pulsed laser vaporization supersonic molecular beam source. Lanthanide-containing species are observed with time-of-flight mass spectrometry, and LnNH molecules are characterized by mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical calculations. The theoretical calculations include density functional theory for both Ln species and a scalar relativity correction, electron correlation, and spin-orbit coupling for the Ce species. The MATI spectrum of LaNH exhibits a single vibronic band system with a strong origin band and two weak vibronic progressions, whereas the spectrum of CeNH displays two band systems separated by 75 cm-1 with each being like the LaNH spectrum. By comparing with the theoretical calculations, both LaNH and CeNH are identified as linear molecules with C∞v symmetry, and the two vibronic progressions are attributed to the excitations of Ln-N stretching and Ln-N-H bending modes in the ions. The additional band system observed for CeNH is due to the spin-orbit splitting from the interactions of triplet and singlet states. The ground valence electron configurations of LaNH and CeNH are La 6s1 and Ce 4f16s1, and the ionization of each species removes the Ln 6s1 electron. The remaining two electrons that are associated with the isolated Ln atoms or ions are in a doubly degenerate molecular orbital that is a bonding combination between Ln 5dπ and N pπ orbitals.

La-mediated dehydrogenation and C[sbnd]C bond cleavage of 1,4-pentadiene and 1-pentyne: Spectroscopy and formation of La(C5H6) and La(C3H4) radicals

La atom reactions with 1,4-pentadiene and 1-pentyne are carried out in a laser-vaporization molecular beam source. Both reactions yield a predominant La(C5H6) radical from ligand dehydrogenation and a minor La(C3H4) species from CC bond cleavage. The metal-hydrocarbon radicals are characterized with mass-analyzed threshold ionization (MATI) spectroscopy and quantum chemical computations. The MATI spectra of each species formed by the two reactions are essentially identical and consist of a single vibronic band system for La(C5H6) and two band systems for La(C3H4). Each band system exhibits a strong origin band and several weak vibronic ones. Adiabatic ionization energies, metal-ligand vibrational frequencies, and low-frequency ligand-based modes are measured for the two species. La(C5H6) is identified as a six-membered lanthanacycle [La(CHCHCHCHCH2)] (Iso A, C1), whereas two isomers of La(C3H4) are a four-membered metallacycle La(CHCHCH2) (Iso 1, C1) and a three-membered ring La(CHCCH3) (Iso 2, Cs). The ground electronic state of each radical is a doublet and that of the singly charged cation is a singlet. The remaining two electrons that are associated with the isolated La atom or ion are spin paired in a molecular orbital that is bonding combination between a La 5d orbital and a π* antibonding orbital of the C5H6 or C3H4 fragment. For the 1,4-pentadiene reaction, the formation of the six-membered metallacycle La(C5H6) involves La addition to a C=C double bond, La insertion into two C(sp3)H bonds, and concerted H2 elimination, whereas the formation of the three- and four-membered La(C3H4) rings involves two hydrogen migrations followed by CC bond breakage to eliminate an ethylene molecule. For the 1-pentyne reaction, the formation of each species requires isomerization of a La(1-pentyne) adduct to a La insertion species and then proceeds with the same elemental steps as those for the diene reaction.

Lattice expansion and local lattice distortion in Nb- and La-doped SrTiO3 single crystals investigated by x-ray diffraction and first-principles calculations

Electron-doped $\mathrm{SrTi}{\mathrm{O}}_{3}$ (where the dopant can be Nb or La) has been widely investigated for both its fundamental interest in condensed matter physics and for industrial applications. Its electronic properties are closely related to the Ti-O bonding states in the $\mathrm{SrTi}{\mathrm{O}}_{3}$ crystal. To further develop and control these properties, it is crucial to understand the factors controlling the change in lattice parameters and local lattice distortion upon doping with various atoms. Herein, we report the changes in lattice parameters and local lattice distortion in Nb- and La-doped $\mathrm{SrTi}{\mathrm{O}}_{3}$ single crystals, investigated by in-plane x-ray diffraction and first-principles calculations. The lattice parameter of Nb- and La-doped $\mathrm{SrTi}{\mathrm{O}}_{3}$ single crystals increased with dopant concentration. The broad intensities around the Bragg peak observed in the in-plane x-ray-diffraction experiments indicated that the local lattice expansion and contraction, or local lattice distortions, in the crystal were caused by the dopant atoms. First-principles calculations similarly showed that the lattice expansion and local lattice distortions in the $\mathrm{SrTi}{\mathrm{O}}_{3}$ crystals were caused by doped Nb and La atoms. Atoms surrounding Schottky pairs of O and Sr vacancies were displaced both away from and towards the vacancies, resulting in a reduction in the lattice expansion of donor-doped $\mathrm{SrTi}{\mathrm{O}}_{3}$. Donor atoms and Schottky pairs thus play an important role in determining the lattice parameters of $\mathrm{SrTi}{\mathrm{O}}_{3}$ crystals. These fundamental structural analyses provide a useful basis to further investigate the electronic conductivity of electron-doped $\mathrm{SrTi}{\mathrm{O}}_{3}$.

Progress in Finding New Energy Levels Using Laser Spectroscopy

The necessary tools for determining a fast and, during an experimental run, possible location of a new energy level are presented, using the findings and characterization of a new level of the La atom as an example. Due to the corresponding computer programs, the observations gained during the experiment can be immediately used.

Enhanced antimonate (Sb(V)) removal from aqueous solution by La-doped magnetic biochars

A novel La-doped magnetic biochar was synthesized by a co-precipitation method for efficient Sb(V) removal. In contrast to pristine biochar and un-doped magnetic biochar, the Sb(V) adsorption capacity in La-doped magnetic biochar was greatly improved, increasing from 2.22 mg/g and 4.85 mg/g to 18.92 mg/g at pH of 7.0, respectively. The enhanced Sb(V) adsorption remained over a wide pH range (2–10), despite the existence of Cl−, SO42−, NO3−, HCO3−, or H2PO4−. These competing anions had little interference with Sb(V) sorption except HCO3− and H2PO4−. The combined results of TEM, XRD, FTIR and XPS further confirmed that La atom was successfully doped into the Fe3O4 structure. The point of zero charge of the biochar increased accordingly with a number of hydroxyl groups (i.e. LaOH) formed on the surface. Although the magnetic performance decreased after La doping, La-doped magnetic biochar still showed high separation potential. The comparison of FTIR and XPS analyses before and after Sb(V) adsorption revealed that the formation of inner-sphere LaOSb complex was the dominant contribution for Sb(V) sorption enhancement. Meanwhile, other mechanisms such as hydrogen bonding, electrostatic attraction and ligand exchange were also involved. All the results suggested that La-doped magnetic biochars could serve as promising adsorbents for Sb(V) pollution minimization.

Electron doping in Sr3Ir2O7 : Collapse of band gap and magnetic order

The electron-doping-driven collapse of the charge gap and staggered magnetization of the spin-orbit-assisted Mott insulator ${\mathrm{Sr}}_{3}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ is explored via first-principles computational methods. In the antiferromagnetic phase, the gap and magnetization are observed to decrease slowly with increasing doping, with an abrupt collapse of both the gap and the magnetization at an electron concentration corresponding to 4.8% substitution of Sr with La, in excellent agreement with experiment. Additionally, we describe the structural effects of electron doping in ${\mathrm{Sr}}_{3}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$ via a competition between the steric effect from smaller La atoms substituted within the lattice and the dominant doping-driven deformation-potential effect. Curiously, our first-principles calculations fail to capture the low-temperature structural distortion reported in the low-gap phase of ${\mathrm{Sr}}_{3}{\mathrm{Ir}}_{2}{\mathrm{O}}_{7}$, supporting the notion that this distortion arises as a secondary manifestation of an unconventional electronic order parameter in this material.

Experimental and theoretical approaches for the investigation of proton conductive characteristics of La1-xBaxYbO3-δ

The proton conductive characteristics of La1-xBaxYbO3-δ (x = 0.02, 0.06, 0.10) were examined by an impedance analysis in the temperature range of 873–1473 K. The maximum proton concentrations in La1-xBaxYbO3-δ determined by the weight changes were almost 1/5 of the oxygen vacancies formed by the substitution of Ba. This result indicated that at least two types of oxygen vacancies, a hydratable oxygen vacancy and hydration independent one, exist in the crystal. The bond distances and electronic structure of the Ba-substituted LaYbO3 supercell with or without an oxygen vacancy were investigated by the first-principles molecular dynamics calculations. The substitution of Ba for the La-site of LaYbO3 was found to induce the local structure change of oxygen atoms surrounding the La atom.