Lanthanum Nitride Research Articles

Pressure driven structural phase transitions and modulations in optical properties of lanthanum nitride: an account from on the fly molecular dynamics and SCF vis-à-vis non-SCF first-principle calculations

The paper is focused to explore the pressure induced structural phase transitions and modulations of optical properties of lanthanum nitride (LaN) for the first time with the aid of first-principle density functional theory and Born–Oppenheimer on the fly molecular dynamics calculations. Crystal structures, Gibbs free energies and phonon dispersion spectra of the compound in its various phases under ambient and external pressures have been critically investigated. The key phonon modes responsible for these pressure driven transitions have also been unveiled. Electronic band structures and associated optoelectronic properties of the systems have been studied in detail from both the self-consistent field and non-self-consistent field calculations. The early signature of topological insulator for the high pressure phase of LaN has been addressed from the electronic band structure calculations. We believe that this study will not only help for futuristic designs of improved functionalized systems with LaN compound but also can augment their applications such as pressure sensors, pressure conducting switches, dissipationless transistors and in optoelectronic devices.

Defect rocksalt structures in the La-Na-N system.

Sodium azide (NaN3) is a versatile nitrogen source that can be used for the synthesis of new nitrides under high-pressure and temperature conditions. Reactions between lanthanum nitride (LaN) and sodium azide (NaN3) at 800°C under 8 GPa pressure have led to the discovery of two defect rocksalt phases which are the first reported ternaries in the La-Na-N system. Preliminary structure assignments have been made based on fits to powder X-ray diffraction profiles. One phase is La1-xNa3xN with vacancies at octahedral La sites and interstitial tetrahedral Na cations. This phase has a tetragonally distorted rocksalt structure (space group I4[Formula: see text]mmm, a = 3.8704(2) and c = 5.2098(3) Å for nominal x = 0.10) and the distortion decreases with increasing Na content (space group I4[Formula: see text]mmm, a = 3.8060(2) Å, c = 5.2470(3) Å for nominal x = 0.14), further giving a cubic phase (a = 5.3055(2) Å) for nominal x = 0.25. This coexists with another cubic [Formula: see text] phase (a = 5.1561 (5) Å), tentatively identified as rocksalt 'NaN1/3' stabilized by a small amount of La; NaLayN(1+3y)/3 with y ≈ 1%. These initial investigations reveal that the high-pressure La-Na-N phase diagram may be rich in defect rocksalt-type materials although further work using neutron diffraction will be needed to confirm the structures. This article is part of the theme issue 'Exploring the length scales, timescales and chemistry of challenging materials (Part 1)'.

Ultralow lattice thermal conductivity, negative thermal expansion, elastic and thermoelectric properties of Lanthanum Nitride: Insights from first-principle calculations

Ultralow lattice thermal conductivity, negative thermal expansion and thermoelectric properties for the face centered cubic phase of lanthanum nitride (LaN) have been explored for the first time from first-principle density functional theory and ab-initio molecular dynamics calculations. The elastic constants, phonon dispersion relations, mode Grüneisen parameter, phonon group velocity and phonon-phonon scattering rates have been studied to unveil the ultralow lattice thermal conductivity ( = 1.08 Wm−1K−1) of the compound at room temperature (T = 300 K). The negative thermal expansion of LaN has been estimated from the mode Grüneisen parameter. The electronic band structure, hole-electron effective masses and the thermoelectric properties including the Seebeck coefficient, electrical conductivity, electronic thermal conductivity and thermoelectric power factor have been investigated to estimate the high thermoelectric figure of merit (ZT ∼ 0.98) of the system at room temperature. We believe that the present study will help to unfold LaN for its applications in thermoelectric power generators, fibre-optic communications, fuel cells and in clean and global energy conservation.

Novel nitrogen-rich lanthanum nitrides induced by the ligand effect under pressure.

N-rich La-N compounds have been studied by first-principles calculations in this work. We identified nine unknown polynitrides, which reveals that the miraculous ligand effect of La plays an important role in the electronic properties and hybridization of nitrogen atoms. Unique tri-coordination atoms with alternate sp2 and sp3 hybridizations are formed in the N18 ring of LaN8. The ligand effect of La induces a novel 1-D chain-like N10 cage polymeric structure in LaN10 and stabilizes it under mild pressure (25 GPa). Moreover, the ligand effect of the introduced La atom on the N10 cage has been clarified by the analysis of the structural evolution behavior from I4̄3m-N10 to Imm2-LaN10. In addition, Imm2-LaN10 with excellent energy (4.56 kJ g-1) and explosive performance (Vd = 16.88 km s-1, Vp = 1887.53 kbar) is a good energetic material candidate.

Dinitrogen fixation mediated by lanthanum hydride

Dinitrogen fixation is one of the key reactions in chemistry, which is closely associated with food, environment, and energy. It has been recently recognized that the hydride materials containing negatively charged hydrogen (H‾) show promises for N2 fixation and hydrogenation to ammonia. Herein, we report that rare earth metal hydrides such as lanthanum hydride can also fix N2 either by heating to 200 °C or ball milling under ambient N2 pressure and temperature. The N2 fixation by lanthanum hydride may proceed via an intermediate lanthanum hydride-nitride (La-H-N) structure to form the final lanthanum nitride product. The hydride ion functions as an electron donor, which provides electrons for N2 activation possibly mediated by the lanthanum atoms. It is observed that N–H bond is not formed during the N2 fixation process, which is distinctly different from the alkali or alkaline earth metal hydrides. The hydrolysis of La-H-N to ammonia is feasible using water as the hydrogen source. These results provide new insights into the nitrogen fixation by hydride materials and more efforts are needed for the development of rare earth metal-based catalysts and/or nitrogen carriers for ammonia synthesis processes.

Semiconducting character of LaN: Magnitude of the bandgap and origin of the electrical conductivity

Lanthanum nitride (LaN) has attracted research interest in catalysis due to its ability to activate the triple bonds of N2 molecules, enabling efficient and cost-effective synthesis of ammonia from N2 gas. While exciting progress has been made to use LaN in functional applications, the electronic character of LaN (metallic, semi-metallic, or semiconducting) and magnitude of its bandgap have so far not been conclusively determined. Here, we investigate the electronic properties of LaN with hybrid density functional theory calculations. In contrast to previous claims that LaN is semi-metallic, our calculations show that LaN is a direct-bandgap semiconductor with a bandgap value of 0.62 eV at the X point of the Brillouin zone. The dispersive character of the bands near the band edges leads to light electron and hole effective masses, making LaN promising for electronic and optoelectronic applications. Our calculations also reveal that nitrogen vacancies and substitutional oxygen atoms are two unintentional shallow donors with low formation energies that can explain the origin of the previously reported electrical conductivity. Our calculations clarify the semiconducting nature of LaN and reveal candidate unintentional point defects that are likely responsible for its measured electrical conductivity.

Na2La4(NH2)14·NH3, a lanthanum-rich intermediate in the ammonothermal synthesis of LaN and the effect of ammonia loss on the crystal structure

Abstract Single crystals of Na2La4(NH2)14·NH3 were obtained from supercritical ammonia under ammonobasic conditions at a temperature of 573 K and 120 MPa pressure. It represents a lanthanum-rich intermediate in the ammonothermal synthesis of LaN. Upon aging, the title compound loses the crystal ammonia, resulting in pale crystals of Na2La4(NH2)14, the original space group P212121 being retained in a very similar unit cell. However, the crystal structure reacts to subtle changes in the composition as well as to the modified coordination of particularly the sodium cations interconnecting lanthanum amide layers within a third dimension. Results of Raman spectroscopic studies are reported. The observations of thermal analysis measurements indicating the formation of lanthanum nitride, in combination with the observed retrograde solubility in liquid ammonia, contribute to the knowledge of the ammonothermal crystal growth of lanthanum nitride.

Vacancy-enabled N2 activation for ammonia synthesis on an Ni-loaded catalyst

Ammonia (NH3) is pivotal to the fertilizer industry and one of the most commonly produced chemicals1. The direct use of atmospheric nitrogen (N2) had been challenging, owing to its large bond energy (945 kilojoules per mole)2,3, until the development of the Haber-Bosch process. Subsequently, many strategies have been explored to reduce the activation barrier of the N≡N bond and make the process more efficient. These include using alkali and alkaline earth metal oxides as promoters to boost the performance of traditional iron- and ruthenium-based catalysts4-6 via electron transfer from the promoters to the antibonding bonds of N2 through transition metals7,8. An electride support further lowers the activation barrier because its low work function and high electron density enhance electron transfer to transition metals9,10. This strategy has facilitated ammonia synthesis from N2 dissociation11 and enabled catalytic operation under mild conditions; however, it requires the use of ruthenium, which is expensive. Alternatively, it has been shown that nitrides containing surface nitrogen vacancies can activate N2 (refs. 12-15). Here we report that nickel-loaded lanthanum nitride (LaN) enables stable and highly efficient ammonia synthesis, owing to a dual-site mechanism that avoids commonly encountered scaling relations. Kinetic and isotope-labelling experiments, as well as density functional theory calculations, confirm that nitrogen vacancies are generated on LaN with low formation energy, and efficiently bind and activate N2. In addition, the nickel metal loaded onto the nitride dissociates H2. The use of distinct sites for activating the two reactants, and the synergy between them, results in the nickel-loaded LaN catalyst exhibiting an activity that far exceeds that of more conventional cobalt- and nickel-based catalysts, and that is comparable to that of ruthenium-based catalysts. Our results illustrate the potential of using vacancy sites in reaction cycles, and introduce a design concept for catalysts for ammonia synthesis, using naturallyabundant elements.

In situ and real-time monitoring of structure formation during non-reactive sputter deposition of lanthanum and reactive sputter deposition of lanthanum nitride.

Lanthanum and lanthanum nitride thin films were deposited by magnetron sputtering onto silicon wafers covered by natural oxide. In situ and real-time synchrotron radiation experiments during deposition reveal that lanthanum crystallizes in the face-centred cubic bulk phase. Lanthanum nitride, however, does not form the expected NaCl structure but crystallizes in the theoretically predicted metastable wurtzite and zincblende phases, whereas post-growth nitridation results in zincblende LaN. During deposition of the initial 2-3 nm, amorphous or disordered films with very small crystallites form, while the surface becomes smoother. At larger thicknesses, the La and LaN crystallites are preferentially oriented with the close-packed lattice planes parallel to the substrate surface. For LaN, the onset of texture formation coincides with a sudden increase in roughness. For La, the smoothing process continues even during crystal formation, up to a thickness of about 6 nm. This different growth behaviour is probably related to the lower mobility of the nitride compared with the metal. It is likely that the characteristic void structure of nitride thin films, and the similarity between the crystal structures of wurtzite LaN and La2O3, evoke the different degradation behaviours of La/B and LaN/B multilayer mirrors for off-normal incidence at 6.x nm wavelength.

Density functional theory characterization of lanthanum nitride endohedral fullerene: La3N@C92

Systemic investigations on lanthanum nitride endohedral metallofullerene La3N@C92 are carried out by a hybrid density functional theory technique combined with statistical mechanics treatment. A novel isolated-pentagon-rule (IPR) isomer with C2 symmetry is determined as the most suitable host cage for the encapsulation of La3N with the lowest energy and predominant thermodynamic stability related to fullerene formation. Natural electron configuration analyses reveal that electron transfer between the La3N cluster and C92 cage is mainly contributed by the 6s orbital of lanthanum atoms. The present work may supply some information reliable for synthesis and experimental characterization of large trimetallic nitride endohedral fullerenes.

First-principles lattice dynamical study of lanthanum nitride under pseudopotential approximation

The present paper reports a comprehensive first-principles calculation of lattice dynamical properties of lanthanum nitride, using the relativistic separable dual-space Gaussian pseudopotentials and local density approximation. Our results concerning equilibrium lattice parameter and bulk modulus agree well with the available experimental and previous theoretical data. The phonon dispersion curves and related properties in both ambient rocksalt (RS) and high pressure cesium chloride (CsCl) structures are reported for the first time which shows rocksalt as more stable structure similar to other calculations. The electronic and mechanical properties are also discussed.

Gas-Phase Reactions of Atomic Lanthanide Cations with Ammonia: Room-Temperature Kinetics and Periodicity in Reactivity

Reactions of (14) atomic lanthanide cations (excluding Pm(+)) with ammonia have been surveyed in the gas phase by using an inductively coupled plasma/selected-ion flow tube (ICP/SIFT) tandem mass spectrometer to measure rate coefficients and product distributions in He at 0.35 +/- 0.01 Torr and 295 +/- 2 K. Primary reaction channels were observed corresponding to H(2) elimination with formation of the protonated lanthanum nitride and NH(3) addition. H(2) elimination was seen only in the reactions with La(+), Ce(+), Gd(+), and Tb(+) and occurs with these ions exclusively. NH(3) addition was seen with Pr(+), Nd(+), Sm(+), Eu(+), Dy(+), Ho(+), Er(+), Tm(+), Yb(+), and Lu(+). Higher-order sequential addition of up to five NH(3) molecules was observed with the Ln(+)(NH(3)) and LnNH(+) ions. The reaction efficiency of the primary reactions is seen to decrease as the energy required to promote an electron to make two non-f electrons available for bonding increases. The periodic trend in reaction efficiency along the lanthanide series matches quite closely the periodic trend in the electron-promotion energy required to achieve a d(1)s(1) or d(2) excited electronic configuration in the lanthanide cation. With La(+), Ce(+), Gd(+), and Tb(+), the electrostatic attraction between the atomic lanthanide cation and ammonia is sufficiently strong to provide enough energy to achieve electron promotion and to overcome any barriers to subsequent N-H bond insertion and H(2) loss, but this is not the case with the other lanthanide cations with which collisional stabilization of the intermediate adduct ion, with or without insertion of Ln(+), predominates.

The first-principles study on the LaN

We present the results of ab-initio study on the structural, elastic, thermodynamics, and electronic properties of the nonmagnetic Lanthanum nitride (LaN) using the plane-wave pseudopotential approach to the density-functional theory within the generalized-gradient approximation implemented in VASP (Viena Ab-initio Simulation Package). The calculated structural parameters (the lattice constant, bulk modulus, cohesive energy), the phase transition pressure from NaCl (B1) to CsCl (B2) phase, elastic constants, Zener anisotropy factor ( A), Poisson ratio ( ν), Young's modulus ( Y), Shear modulus ( C′), Debye temperature, and band structures are presented. The obtained results are compared with the available experimental and the other theoretical results.

Synthesis of new La nitrides at high pressure and temperature

We have succeeded in synthesizing two new lanthanum nitrides in a supercritical nitrogen fluid at high pressure (about 30 GPa) and high temperature (about 2000 K), using a diamond anvil cell and a YAG laser heating system. These nitrides were found to be stable down to 5 GPa and ∼300 K in a nitrogen atmosphere. One of the new lanthanum nitrides is a cubic P lattice-type phase, which is a main phase synthesized nitride. The calculated lattice parameter is a = 11.979 Å at 5 GPa, 300 K. The other nitride is of a trigonal P lattice-type. The calculated lattice parameters are a = 3.889 Å and c = 6.691 Å at 5 GPa, 300 K. The most likely phase of the former new La nitride is Pa 3 ̄ La 2 N 3 + δ , the structure of which may be similar to the Ia 3 ̄ Mn 2O 3-type (Ia80). The phase of the latter nitride is P 3 ̄ m 1 La 2 N 3 + δ , the structure of which is the same as the P 3 ̄ m 1 La 2O 3-type (hP5).

La4N2S3: Ein neues Nitridsulfid des Lanthans mit beispielloser Kristallstruktur

AbstractLa4N2S3: A New Nitride Sulfide of Lanthanum with Unprecedented Crystal StructureThe oxidation of lanthanum powder with sulfur and cesium azide (CsN3) in the presence of lanthanum tribromide (LaBr3) yields lanthanum nitride sulfide with the composition La4N2S3 when appropriate molar ratios of the reactants are used. Additional cesium bromide (CsBr) as a flux secures fast reactions (7 d) at 900 °C in evacuated silica tubes as well as the formation of almost black single crystals. The orthorhombic crystal structure (Pnnm, Z = 2) was determined from single crystal X‐ray diffraction data (a = 641.98(4), b = 1581.42(9), c = 409.87(3) pm). Two crystallographically different La3+ cations are present, La1 resides in sixfold coordination of two N3− and four S2− anions forming a trigonal prism and La2 is coordinated by two N3− and five S2− in the shape of a monocapped trigonal prism. However, the main feature of the crystal structure comprises N3−‐centred (La3+)4 tetrahedra which arrange as pairs [N2La6]12+ of edge‐shared [NLa4]9+ units and which are further connected via four vertices to form double chains $^{1}_{\infty}\rm \{[N_{2}La_{2}La^{\prime}_{4/2}]^{6+}\}$. They get bundled along [001] like a hexagonal rod packing and are held together by two crystallographically different S2− anions. Further motifs for the connectivity of [NM4]9+ tetrahedra in crystal structures of nitride chalcogenides and halides of the rare‐earth elements (M = Sc, Y, La; Ce – Lu) with ratios of N : M = 1 : 2 are presented and discussed for comparison.

Synthesis by sol–gel route of oxyapatite powders for dense ceramics: Applications as electrolytes for solid oxide fuel cells

Solid oxide fuel cells have considerable interest in recent years, because of their high efficiency and environmentally friendly nature. Such systems required oxygen-conducting electrolytes and now the most common electrolyte is yttria stabilized zirconia (YSZ). This compound exhibits high oxide ion conductivity at elevated temperatures (850–1000 °C). However, this high working temperature causes problems in terms of materials selection and lifetime. One solution is to develop new oxide ions conductors exhibiting high oxide ion conductivity at intermediary temperatures (700–800 °C). Recent work has identified Ln 10− x Si 6O 26± z (Ln = rare earths) as a good fast oxide ion conductor. Undoped and doped Ln 10− x B 6O 26± z (B = Si or Ge) oxides are currently prepared by solid-state methods. In that work, we propose a sol–gel process to synthesize powders of La 9.33Si 6O 26 type-silicated apatites. The main advantage is to decrease the crystallization temperature in comparison to the conventional methods, allowing the synthesis of reactive powders with nanometric particles size. These oxides are synthesized using silicon alkoxide and lanthanum nitride as precursors. In the litterature, no study refers to the synthesis of mixed oxides with silicon alcoxides. However, there are several studies on sol–gel synthesis of glasses with this precursor. In this study, several processing parameters have been investigated (the hydrolysis ratio, the concentration of metallic precursors in the sol and the role of organic compounds) in order to synthesize pure phases after the decomposition of the sols. Pure powders of La 9.33Si 6O 26 type-silicated apatites are obtained at 800 °C. These powders were used to prepare ceramics. Several processing parameters as morphology of powders (agglomeration, particle sizes) and, heating profiles have been studied on the densification. Dense ceramics (90–95%) have been prepared at temperatures around 1400 °C. The used of sol–gel powders allow the decrease of the sintering temperature of about 200 °C.

Structural phase stability and superconductivity of LaN

Results of a theoretical investigation on the structural phase stability of lanthanum nitride (LaN) is reported. We predict that LaN, which crystallizes in NaCl structure, undergoes a transition from NaCl to CsCl type structure at around 26.9 GPa with a volume collapse of 12.5%. In addition, the superconducting transition temperature ( T c) is also calculated theoretically for the first time. The high-pressure phase of LaN is CsCl structure and not the tetragonal structure as observed in other lanthanum pnictides, which has been predicted by the total energy minimization. In addition, the basic ground state properties such as the equilibrium lattice parameter, bulk modulus, cohesive energy, heat of formation, electronic specific heat coefficient are computed and compared with the available experimental and other theoretical results. The band structure and density of states are plotted for ambient and high-pressure structures. The possible reasons for the occurrence of superconductivity and the structural phase transition are also discussed.

Ionic conductivity of nitrides

Electrical conductivity of nonmetallic aluminium, magnesium, calcium and lanthanum nitrides has been measured in nitrogen, ammonium and argon over the temperature range 973–1673 K. The nature of the conductivity has been investigated using the emf method in a cell with separate gas compartments, using controlled nitrogen partial pressure. It has been shown, that the investigated nitrides of the II and III groups of the Mendelleev's periodic table are mixed conductors, the ionic conductivity part of which varies on temperature and nitrogen partial pressure.

ChemInform Abstract: MISCIBILITY OF THORIUM CARBIDE WITH LANTHANUM NITRIDE, CERIUM NITRIDE (CEN), PRASEODYMIUM NITRIDE, NEODYMIUM NITRIDE, SAMARIUM NITRIDE (SMN), GADOLINIUM NITRIDE AND ERBIUM NITRIDE

Chemischer InformationsdienstVolume 12, Issue 3 Physical Inorganic Chemistry ChemInform Abstract: MISCIBILITY OF THORIUM CARBIDE WITH LANTHANUM NITRIDE, CERIUM NITRIDE (CEN), PRASEODYMIUM NITRIDE, NEODYMIUM NITRIDE, SAMARIUM NITRIDE (SMN), GADOLINIUM NITRIDE AND ERBIUM NITRIDE P. ETTMAYER, P. ETTMAYERSearch for more papers by this authorJ. WALDHART, J. WALDHARTSearch for more papers by this authorA. VENDL, A. VENDLSearch for more papers by this authorG. BANIK, G. BANIKSearch for more papers by this author P. ETTMAYER, P. ETTMAYERSearch for more papers by this authorJ. WALDHART, J. WALDHARTSearch for more papers by this authorA. VENDL, A. VENDLSearch for more papers by this authorG. BANIK, G. BANIKSearch for more papers by this author First published: January 20, 1981 https://doi.org/10.1002/chin.198103026Read the full textAboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat No abstract is available for this article. Volume12, Issue3January 20, 1981 RelatedInformation

Isotope exchange of nitrogen on magnesium, calcium and lanthanum nitrides

It has been found that calcium nitride possesses a high catalytic activity in the isotope exchange of nitrogen. The catalytic activity of nitrides is shown to be independent of the heat of their formation. The effect of H2 and O2 on the isotope exchange of nitrogen is studied.