Structural and optical properties of Ga2O3:In films deposited on MgO (1 0 0) substrates by MOCVD

Ga₂O₃:In films with different indium (In) content x [x=In/(Ga+In) atomic ratio] have been deposited on MgO (1 0 0) substrates by metalorganic chemical vapor deposition (MOCVD). Structural analyses revealed that the film deposited with actual In content (x′) of 0.09 was an epitaxial film and the films with x′=0.18 and 0.37 had mixed-phase structures of monoclinic Ga₂O₃ and bixbyite In₂O₃. The absolute average transmittance of the obtained films in the visible region exceeded 95%, and the band gap was in the range of 4.74-4.87 eV. Photoluminescence (PL) measurements were performed at room temperature, in which the visible luminescences were strong and could be seen by the naked eye. The strong emissions in the visible light region were proposed to originate from the gallium vacancies, oxygen deficiencies and other defects in these films.     

A new phase in the system lithium-aluminum: Characterization of orthorhombic Li2Al

Investigation of the Li rich part of the binary Li-Al system revealed the existence of a new phase, orthorhombic Li₂Al, which is isostructural to Li₂Ga and Li₂In. The crystal structure was determined from single crystal X-ray diffraction data (Cmcm, a=4.658(2) Å, b=9.767(4) Å, c=4.490(2) Å, Z=4). Refinement of atomic position site occupancies yielded a composition Li_1.92Al_1.08 (64 at% Li) indicating a small homogeneity range, Li_2−xAl_1+x. Li₂Al is the peritectic decomposition product of the stoichiometric compound Li₉Al₄, which is stable below 270±2 °C. Li₂Al itself decomposes peritectically to Li₃Al₂ and Li rich melt at 335±2 °C. The discovery of Li₂Al (Li_2−xAl_1+x) settles a long standing inconsistency in the Li-Al phase diagram which was based on the assumption that Li₉Al₄ possesses a high temperature modification.     

Structural Investigation of Mixed Nitrided Galloaluminophosphates “AlGaPON” by EELS, XAS, and XPS Spectroscopies

Amorphous nitrided galloaluminophosphates “AlGaPON” catalysts with nitrogen contents varying from 0 to 23.3 wt% N were obtained by nitriding an Al_0.5Ga_0.5PO₄ precursor under ammonia flow at 750°C in a tubular furnace. The structural changes induced by this treatment were investigated by electron energy loss spectroscopy (EELS), X-ray absorption spectroscopy (XAS), and X-ray photoelecton spectroscopy (XPS). XANES and XPS results indicate that the first-coordination spheres of P, Ga, and Al atoms are modified by nitridation. In particular, the comparison of the P XANES spectra recorded on “AlGaPON” and on a PON phosphorus oxynitride (reference of mixed PO₂N₂ tetrahedra) reveals that mainly PO₂N₂ tetrahedra are present in highly nitrided samples. Moreover, the replacement of oxygen by nitrogen probably concerned P-O-Ga bonds rather than P-O-Al. EELS investigation reveals that the precursor is homogeneous at the used probe scale, but indicates that nitridation is accompanied by a loss of homogeneity of the material.     

Crystal structure of Eu-doped magnetoplumbite-type lanthanum aluminum oxynitride with emission site splitting

Eu-doped lanthanum aluminum oxynitride (LaAl₁₂(O,N)₁₉) with magnetoplumbite structure was prepared by nitridation of the oxide precursor obtained from aluminum glycine gel and subsequent post-annealing. Eu-doped lanthanum aluminum oxynitride exhibited blue light emission at 440 nm with a shoulder at 464 nm under excitation at 254 nm. Isostructural Eu-doped calcium aluminum oxide (CaAl₁₂O₁₉) exhibited a single emission peak at 415 nm. Structural refinement using neutron powder diffraction indicated that the lanthanum site occupied partially by Eu²⁺ splits into 2d and 6h sites in the aluminum oxynitride. The longer emission and the shoulder peak in the former aluminum oxynitride were observed in relation to the increasing covalency as well as crystal field splitting around doped Eu²⁺ induced by site splitting involved with the two kinds of anions.     

Darstellung und Strukturen neuartiger Triphenylsilylund Triphenylgermyl‐substituierter Gallane und Oligogallane – [Ga3(GePh3)6]–, das erste lineare Trigallan

Chemistry of Gallium. 20. Synthesis and Structures of Novel Triphenylsilyl and Triphenylgermyl Substituted Gallanes and Oligogallanes – [Ga₃(GePh₃)₆]^–, the First Linear Trigallane From the raction of sonochemically prepared “GaI” with LiEPh₃ (E = Si, Ge) the compounds [Li(THF)₂][GaI(EPh₃)₃] (E = Si: 22 , E = Ge: 24 ), [Li(THF)₄][GaI(SiPh₃)₃] ( 23 ), [Li(THF)₄][Ga₂(SiPh₃)₅] ( 21 ) and [Li(THF)₄][Ga₃(GePh₃)₆] ( 25 ) as well as polymeric Li(THF)I ( 20 ) were obtained and structurally characterized. 21 is a monoanionic digallane, exhibiting a trigonal planar and a tetrahedrally coordinated gallium centre. 25 has a linear Ga₃ core, where the terminal gallium atoms bear three GePh₃‐groups, each. The central Ga atom is only 2‐coordinated. Thus, 25 may be a valuable hint to the formation of larger gallium clusters with “naked” gallium atoms. Derivatives of 21 and 25 have been studied by DFT methods.     

Donorstabilisierte Galliumdihalogenide Ga2X4·2D (X = Cl,Br; D = Donormolekül): Ein experimenteller Beitrag zu den Variationsmöglichkeiten der Ga‐Ga‐Einfachbindung

Donor‐stabilized Galliumdihalides Ga₂X₄·2D (X = Cl, Br; D = Donor): An Experimental Contribution on the Variation of the Gallium‐Gallium Single Bond During the disproportionation of metastable GaX‐solutions (X= Cl, Br) donor‐stabilized galliumdihalides are formed as oxidized products. According to X‐ray structure analyses they all exhibit dimeric entities DX₂Ga‐GAX₂D (D= THF, NHEt2, NEt3, 4‐^tButylpyridin or Br^‐), which means these compounds are isoelectronic with ethane and could schematically be regarded as representatives of catenulate or alkane‐like gallium subhalides: Ga_n(X, D)_2n+2. The gallium‐gallium bond in these compounds is shorter than in the organometallic compounds such as R₂Ga‐GaR₂. The comparison of the bonding situation in the galliumdihalides, particularly of the gallium‐gallium bond, shows clearly the influence by donor molecules as well as by halogen ligands.     

Subvalente Galliumtriflate – mögliche Ausgangsverbindungen für Clusterverbindungen des Galliums

Subvalent Gallium Triflates – Potentially Useful Starting Materials for Gallium Cluster Compounds By reaction of GaCp* with trifluormethanesulfonic acid in hexane a mixture of gallium trifluormethanesulfonates (triflates, OTf) is obtained. This mixture reacts readily with lithiumsilanides [Li(thf)₃Si(SiMe₃)₂R] (R = Me, SiMe₃) to afford the cluster compounds [Ga₆{Si(SiMe₃)Me}₆], [Ga₂{Si(SiMe₃)₃}₄] and [Ga₁₀{Si(SiMe₃)₃}₆]. By crystallization from various solvents the gallium triflates [Ga(OTf)₃(thf)₃], [HGa(OTf)(thf)₄]⁺ [Ga(OTf)₄(thf)₃]⁻, [Cp*GaGa(OTf)₂]₂ and [Ga(toluene)₂]⁺ [Ga₅(OTf)₆(Cp*)₂]⁻ were isolated and characterized by single crystal X ray structure analysis.     

Searching for gallium bioactive compounds: Gallium(III) complexes of tridentate salicylaldehyde semicarbazone derivatives

In the search for gallium bioactive compounds five Ga(III) complexes, [Ga^III(L-H)₂](NO₃), with tridentate salicylaldehyde semicarbazone derivatives as ligands (L) have been synthesized and characterized in the solid state and in solution by different techniques. The crystal structure of [Ga^III(L4-H)₂](NO₃)·2H₂O, where L4 is 3-ethoxysalicylaldehyde semicarbazone, was solved by X-ray diffraction methods. The gallium(III) ion is in a distorted octahedral environment, coordinated to two nearly planar and mutually perpendicular 3-ethoxysalicylaldehyde semicarbazonato anions acting as tridentate ligands through their phenol and carbonyl oxygen atoms and their azomethine nitrogen atom. Their biological potential has been explored by evaluating their activity on Mycobacterium tuberculosis, causative agent of tuberculosis, and their cytotoxicity on tumor cell lines. Three different human tumor cell lines were selected that show different degrees of resistance to metallodrugs: ovarian A2780 (low resistance), breast MCF7 (medium resistance) and prostate PC3 (high resistance) cells. Although the complexes have not shown activity on M. tuberculosis, complexation with gallium has led to the enhancement of the cytotoxic potencies of the organic compounds. Those complexes that contain a bromide substituent at the phenolate ring have shown the highest cytotoxicities. In particular, [Ga^III(L2-H)₂](NO₃), where L2 is 5-bromosalicylaldehyde semicarbazone,·has shown a remarkable cytotoxicity on A2780 tumor cell line with an IC₅₀ value of the same order than cisplatin (IC_{50 Ga-L2} = 2.4 ± 0.3 μM; IC_{50 cisplatin} = 2.0 ± 0.1 μM, 72 h incubation at 37 °C). Interestingly, this complex has also shown moderate cytotoxicity against MCF7 and PC3 cells (IC_{50 MCF7} = 30 ± 6; IC_{50 PC3} = 18 ± 3 μM). Therefore, this gallium compound could be considered a promising wide spectrum potential anti-tumor agent.     

Syntheses, X-ray structures and CVD studies of diorganoalkoxogallanes

Structural studies by X-ray crystallography have been carried out for a range of diorganoalkoxogallanes incorporating donor-functionalized ligands. The compounds [Et₂Ga(μ-OR)]₂ (1, R = CH₂CH₂NMe₂; 2, R = CH(CH₃)CH₂NMe₂; 3, C(CH₃)₂CH₂OMe; 4, R = CH(CH₂NMe₂)₂) adopt dimeric structures with a planar Ga₂O₂ ring, and each gallium atom is coordinated in a distorted trigonal bipyramidal geometry. Low pressure chemical vapor deposition (CVD) of 2 and 4 resulted in the formation of oxygen deficient gallium oxide thin films on glass. However, the reaction of Et₃Ga and ROH (R = CH₂CH₂NMe₂, CH(CH₃)CH₂NMe₂, C(CH₃)₂CH₂OMe, CH(CH₂NMe₂)₂) in toluene under aerosol assisted (AA)CVD conditions afforded stoichiometric Ga₂O₃ thin films on glass. This CVD technique offers a rapid, convenient route to Ga₂O₃, which involves the in situ formation of diethylalkoxogallanes, of the type [Et₂Ga(μ-OR)]₂, the structures of which are described in this paper. The gallium oxide films were deposited at 450 °C and analyzed by scanning electron microscopy (SEM), X-ray powder diffraction, wavelength dispersive analysis of X-rays (WDX), X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy.     

Ga2Br2R2 und Ga3I2R3 [R = C(SiMe3)3] — zwei neue elementorganische Galliumsubhalogenide mit einer bzw. zwei Ga‐Ga‐Bindungen

Ga₂Br₂R₂ and Ga₃I₂R₃ [R = C(SiMe₃)₃] — Two New Organoelement Subhalides of Gallium Containing One or Two Ga‐Ga Single Bonds The oxidation of the tetrahedral tetragallium cluster Ga₄[C(SiMe₃)₃]₄ ( 1 ) with elemental bromine in the presence of AlBr₃ yielded the corresponding gallium subhalide Ga₂Br₂R₂ [ 4 , R = C(SiMe₃)₃], which remains monomer even in the solid state and in which the Ga^II atoms are connected by a short Ga‐Ga single bond [243.2(2) pm]. The analogous diiodide Ga₂I₂R₂ ( 3 ), which was obtained on a similar route by our group only recently, did not react with lithium tert‐butanolate by substitution as originally expected. Instead, partial disproportionation occurred with the formation of the trigallium diiodide Ga₃I₂R₃ ( 6 ), in which three Ga atoms are connected by two Ga‐Ga single bonds (255.1 pm on average). Both terminal Ga atoms have a coordination number of four owing to the bridging function of both iodine atoms, while the inner one which has an oxidation number of +1 remains coordinatively unsaturated. An average oxidation state of 1.66 resulted for all atoms of the chain. The Ga^III compound {[GaI(R)(OCMe₃)(OH)]Li}₂ ( 7 ) was isolated as the second product of the disproportionation. It is a dimer in the solid state via Li‐O bridges and shows a hindered rotation of its tert‐butyl group.     

Vacancy ordering and oxygen dynamics in oxide ion conducting La1−xSrxGa1−xMgxO3−x ceramics: Ga, Mg and O NMR

The oxygen vacancies distribution in the rigid lattice and the thermally activated motion of oxygen atoms are studied in La_1−xSr_xGa_1−xMg_xO_3−x (x=0.00; 0.05; 0.10; 0.15 and 0.20) compounds. For that ⁷¹Ga, ²⁵Mg and ¹⁷O NMR was performed from 100 K up to 670 K, and ion conductivity measurements were carried out up to 1273 K. The comparison of the electric field gradients at the Ga- and Mg-sites evidences that oxygen vacancies appear exclusively near gallium cations as a species trapped below room temperature in local clusters, GaO_5/2-□-GaO_5/2. These clusters decay at higher temperature into mobile constituents of the structural octahedra Ga(O_5/6□_1/6)_6/2. At the same time, the nearest octahedral oxygen environment of magnesium cations persists at different doping levels. The case of two adjacent vacant anion sites is found highly unlikely within the studied doping range. The thermally activated oxygen motion starts to develop above room temperature as is observed from both the motional narrowing of ¹⁷O NMR spectra and the ¹⁷O nuclear spin-lattice relaxation rate. The obtained results show that two types of motion exist, a slow motion and a fast one. The former is a long-range diffusion whereas the latter is a local back and forth oxygen jumps between two adjacent anion sites. These sites are strongly differentiated by the probability of the vacancy formation, like the vacant apical site and the occupied equatorial site in the orthorhombic compositions x <0.15.     

Formation of apatite oxynitrides by the reaction between apatite-type oxide ion conductors, La8+xSr2−x(Si/Ge)6O26+x/2, and ammonia

Following growing interest in the use of ammonia as a fuel in solid oxide fuel cells (SOFCs), we have investigated the possible reaction between the apatite silicate/germanate electrolytes, La_8+xSr_2−x(Si/Ge)₆O_26+x/2, and NH₃ gas. We examine how the composition of the apatite phase affects the reaction with ammonia. For the silicate series, the results showed a small degree of N incorporation at 600 °C, while at higher temperatures (800 °C), substantial N incorporation was observed. For the germanate series, partial decomposition was observed after heating in ammonia at 800 °C, while at the lower temperature (600 °C), significant N incorporation was observed. For both series, the N content in the resulting apatite oxynitride was shown to increase with increasing interstitial oxide ion content (x/2) in the starting oxide. The results suggest that the driving force for the nitridation process is to remove the interstitial anion content, such that for the silicates the total anion (O+N) content in the oxynitrides approximates to 26.0, the value for an anion stoichiometric apatite. For the germanates, lower total anion contents are observed in some cases, consistent with the ability of the germanates to accommodate anion vacancies. The removal of the mobile interstitial oxide ions on nitridation suggests problems with the use of apatite-type electrolytes in SOFCs utilising NH₃ at elevated temperatures.     

Oxygen Nonstoichiometry, Conductivity, and Seebeck Coefficient of La0.3Sr0.7Fe1−xGaxO2.65+δ Perovskites

The total electrical conductivity and the Seebeck coefficient of perovskite phases La_0.3Sr_0.7Fe_1−xGa_xO_2.65+δ (x=0-0.4) were determined as functions of oxygen nonstoichiometry in the temperature range 650-950°C at oxygen partial pressures varying from 10⁻⁴ to 0.5 atm. Doping with gallium was found to decrease oxygen content, p-type electronic conduction and mobility of electron holes. The results on the oxygen nonstoichiometry and electrical properties clearly show that the role of gallium cations in the lattice is not passive, as it could be expected from the constant oxidation state of Ga³⁺. The nonstoichiometry dependencies of the partial molar enthalpy and entropy of oxygen in La_0.3Sr_0.7(Fe,Ga)O_2.65+δ are indicative of local inhomogeneities, such as local lattice distortions or defect clusters, induced by gallium incorporation. Due to B-site cation disorder, this effect may be responsible for suppressing long-range ordering of oxygen vacancies and for enhanced stability of the perovskite phases at low oxygen pressures, confirmed by high-temperature X-ray diffraction and Seebeck coefficient data. The values of the electron-hole mobility in La_0.3Sr_0.7(Fe,Ga)O_2.65+δ, which increases with temperature, suggest a small-polaron conduction mechanism.     

Structure and electron density analysis of electrochemically and chemically delithiated LiCoO2 single crystals

Single crystals of Li_0.68CoO₂, Li_0.48CoO₂, and Li_0.35CoO₂ were successfully synthesized for the first time by means of electrochemical and chemical delithiation processes using LiCoO₂ single crystals as a parent compound. A single-crystal X-ray diffraction study confirmed the trigonal R3¯m space group and the hexagonal lattice parameters a=2.8107(5) Å, c=14.2235(6) Å, and c/a=5.060 for Li_0.68CoO₂; a=2.8090(15) Å, c=14.3890(17) Å, and c/a=5.122 for Li_0.48CoO₂; and a=2.8070(12) Å, c=14.4359(14) Å, and c/a=5.143 for Li_0.35CoO₂. The crystal structures were refined to the conventional values R=1.99% and wR=1.88% for Li_0.68CoO₂; R=2.40% and wR=2.58% for Li_0.48CoO₂; and R=2.63% and wR=2.56% for Li_0.35CoO₂. The oxygen-oxygen contact distance in the CoO₆ octahedron was determined to be shortened by the delithiation from 2.6180(9) Å in LiCoO₂ to 2.5385(15) Å in Li_0.35CoO₂. The electron density distributions of these Li_xCoO₂ crystals were analyzed by the maximum entropy method (MEM) using the present single-crystal X-ray diffraction data at 300 K. From the results of the single-crystal MEM, strong covalent bonding was clearly visible between the Co and O atoms, while no bonding was found around the Li atoms in these compounds. The gradual decrease in the electron density at the Li site upon delithiation could be precisely analyzed.     

Neutron powder diffraction study of tetragonal Li7La3Hf2O12 with the garnet-related type structure

We have successfully synthesized a polycrystalline sample of tetragonal garnet-related Li-ion conductor Li₇La₃Hf₂O₁₂ by solid state reaction. The crystal structure is analyzed by the Rietveld method using neutron powder diffraction data. The structure analysis identifies that tetragonal Li₇La₃Hf₂O₁₂ has the garnet-related type structure with a space group of I4₁/acd (no. 142). The lattice constants are a=13.106(2) Å and c=12.630(2) Å with a cell ratio of c/a=0.9637. The crystal structure of tetragonal Li₇La₃Hf₂O₁₂ has the garnet-type framework structure composed of dodecahedral La(1)O₈, La(2)O₈ and octahedral HfO₆. Li atoms occupy three types of crystallographic site in the interstices of this framework structure, where Li(1) atom is located at the tetrahedral 8a site, and Li(2) and Li(3) atoms are located at the distorted octahedral 16f and 32g sites, respectively. These Li sites are filled with the Li atom. The present tetragonal Li₇La₃Hf₂O₁₂ sample exhibits bulk Li-ion conductivity of σ_b=9.85×10⁻⁷ S cm⁻¹ and grain-boundary Li-ion conductivity of σ_gb=4.45×10⁻⁷ S cm⁻¹ at 300 K. The activation energy is estimated to be E_a=0.53 eV in the temperature range of 300-580 K.     

Gallium-containing sulfide binary and ternary materials by atomic layer deposition: precursor reactivities and growth fine chemistries

Gallium sulfide (Ga_xS) and copper gallium sulfide (Cu_xGa_yS_z) were synthetized by atomic layer deposition (ALD), using copper acetylacetonate Cu(acac)₂, hexakis(dimethylamino)digallium [Ga(NMe₂)₃]₂ and hydrogen sulfide (H₂S). Thanks to the compatibility of the Cu_xS and Ga_xS ALD windows, a supercycle strategy that combines single growth cycles of the two binary compounds was used to generate the ternary material. A wide range of compositions and properties can be obtained from Ga-rich to Cu-rich via copper gallium sulfide thin films. Structural, morphological, and optoelectronic characterizations were performed on all films. Surface and in-depth chemical compositions were determined by X-ray photoelectron spectroscopy profiling, allowing a better understanding of the chemical reactions involved during the growth process. In the case of Ga_xS films, other Ga precursors have been tested. Our experimental observations, combined with reported ones and density functional theory calculation results have highlighted the specific reactivity of alkylamido precursor in ALD chemistry. Compositional studies revealed a significant O content which origin is discussed and represents an important challenge to address in ALD of sulfide materials in general.     

Aluminum, gallium, and indium oxopivalates: Thermodynamic characteristics of gallium oxopivalates

Aluminum, gallium, and indium oxopivalates were synthesized by a heterophase method, and their evaporation was studied by the Knudsen effusion method with the mass-spectral analysis of the gas phase. It was shown that oxopivalates can be considered within binary systems as compounds of the type mM(piv)₃ · nM₂O₃. The standard enthalpies of formation of gallium oxopivalates Ga₃O(piv)_7(gas), 7Ga(piv)₃ · Ga₂O_3(solid), 4Ga(piv)₃ · Ga₂O_3(solid), and 7Ga(piv)₃ · 2Ga₂O_3(solid) were found.     

Gallium and indium dithiocarboxylates: Synthesis, spectroscopic characterization and structure of [MeGa(S2Ctol)2]

Several gallium and indium dithiocarboxylate complexes of the type [Me_nM(S₂CR)_3−n] (M = Ga, In; n = 0, 1, 2; R = phenyl (Ph), p-tolyl (tol), mesityl (Mes)) have been synthesized. These complexes were characterized by elemental analysis, IR, UV-vis and NMR (¹H,¹³C{¹H}) spectroscopy. Structure of [MeGa(S₂Ctol)₂] was established by X-ray crystallography. The gallium atom adopts a distorted five coordinate geometry which is intermediate between trigonal bipyramidal and square pyramidal configurations. The complex [Me₂InS₂Ctol] underwent a two-step thermal decomposition leading to the formation of tetragonal β-In₂S₃.     

Studies on controlled potential coulometric determination of gallium in sodium perchlorate and sodium thiocyanate

Controlled potential coulometric (CPC) studies were carried out for developing a method to determine gallium at milligram levels, in the mixed supporting electrolyte medium (4 M NaClO₄ + 0.5 M NaSCN), employing stirring mercury as a working electrode. Investigations for optimization of working electrode potentials, quantity of charge, level of background current and electrolysis time for achieving quantitative reduction of Ga(III) to Ga and its oxidation back to Ga(III), were undertaken. Effect of gallium content and interference of zinc in of gallium determination were also studied. The developed methodology was employed for the determination of gallium in pure Ga as well as in synthetic U + Ga mixture solutions. Accuracy and precision values of better than 0.5% were obtained at 1-2 mg levels.     

Kinetics of Oxidation Processes in the System Co/Ga studied by in situ X‐Ray Diffraction

Oxidation processes in the system Co/Ga were studied by in situ X‐ray diffraction at temperatures between 800 and 1000 °C. Experiments were performed with metal powders and planar substrates. Oxidation of cobalt‐rich alloys, Co_1‐xGa_x, results in the formation of mixtures of cobalt‐ and gallium‐containing oxides. During oxidation of the intermetallic compounds CoGa and CoGa₃ only gallium is oxidized, and dense tarnishing layers of β‐Ga₂O₃ are formed. In all cases the oxide products are only intermediate products on the way to thermodynamic equilibrium, i.e. total oxidation of both metals. The kinetics during oxidation of the intermetallic compound CoGa was studied in detail by time resolved in situ X‐ray diffraction. After an induction time the kinetics can be described by a parabolic rate law with an activation energy of 312 kJ mol^—1. From the decrease of the parabolic rate constant with decreasing oxygen partial pressure and the observation of pore formation at the metal‐oxide interface it can be concluded that (i) outward diffusion of Ga‐ions through β‐Ga₂O₃ is the rate determining step during this solid state reaction, and (ii) Ga‐ions are mobile by means of gallium vacancies.