GaO4 Tetrahedra Research Articles

Crystal structure of the quaternary lithogallate Sr2LiGaO4

Abstract The new quaternary lithogallate Sr2LiGaO4 was prepared by conventional solid-state synthesis in a welded tantalum ampoule at T = 850 °C. Single-crystal X-ray diffraction was used to elucidate the crystal structure of the compound, which crystallizes in the orthorhombic space group Pnma (no. 62) with the lattice parameters a = 11.2434(4), b = 5.6879(2), and c = 6.6983(2) Å. The phase composition of the powder sample was determined by Rietveld refinement based on X-ray diffraction data. The crystal structure is composed of layers of corner-sharing LiO4 and GaO4 tetrahedra with alternating orientation parallel to the crystallographic bc plane. The eightfold coordinated strontium atoms are arranged in a zigzag manner between the layers forming two types of double-capped trigonal prismatic SrO8 units with common faces. The crystal structure of Sr2LiGaO4 is isotypic to that of the lithoaluminate derivate Sr1.85Ba0.15LiAlO4.

Reduction of vacancy defects induced by thermal annealing in β-Ga2O3 epilayer

The effects of annealing in oxygen atmosphere of β-Ga2O3 epilayers were investigated by X-ray photoelectron spectroscopy, photoluminescence and Fourier-transform infrared spectroscopy. The increasing proportions of Ga3+ and OL (lattice oxygen) signifies the reduction of VO as the annealing temperature rising. The variations of the photoluminescence emissions demonstrate the improvement of the crystal quality and reduction of VO(1), VO(2) and VGa. VO and VGa are filled with oxygen atoms and gallium atoms after annealing, mainly attributed to the bonds constructions of Ga (1)–O (1) and Ga (1)–O (2) in GaO4 tetrahedra. These results offer detailed information and guidelines for removing intrinsic point defects in β-Ga2O3.

Synthesis, structure, characterization, and electronic structure calculation of a new molecule-inclusion strontium gallate Sr6(Ga12O24)·Bi2O3

Inorganic oxide crystalline materials have been attractive owing to unusual structural and physical properties including superconductivity, nonlinear optics, photocatalytic degradation, molecular sieve and solar cells. Herein, a new molecule-inclusion strontium gallate, Sr6(Ga12O24)·Bi2O3, has been obtained by solid-state method. The compound crystallizes in the centrosymmetric space group R3¯(no. 148), and exhibits a three-dimensional network structure composed by corner-sharing connected GaO4 tetrahedra and edge-sharing connected SrO9 polyhedra with Bi atoms located in hexagonal tunnels. Spectral analysis shows that the compound exhibits strong Raman peak. Synthesis, crystal structure, versatile characterizations as well as theory calculations of Sr6(Ga12O24)·Bi2O3 are presented in this work.

Synthesis, chiral crystal structure, and magnetic properties of Ba3Ga2O5Cl2.

A new compound, Ba3Ga2O5Cl2, isostructural with Ba3Fe2O5Cl2, was synthesized by solid-state reaction in air. Through single-crystal and powder X-ray diffraction analysis, the crystal structure was determined to be cubic with chiral space group I213 and unit-cell parameter a= 9.928 (1) Å. The Ga3+ ions in Ba3Ga2O5Cl2 are coordinated by O atoms and form GaO4 tetrahedra. Ten neighboring GaO4 tetrahedra are further bridged through corner sharing and rotation along the body diagonal, producing the chiral structure. Magnetization measurements indicate temperature-independent diamagnetic behavior, which is qualitatively consistent with core diamagnetism from all the constituent elements.

Electronic states of gallium oxide epitaxial thin films and related atomic arrangement

Amorphous, crystallized, and Mg-doped β-Ga2O3 thin films are investigated to understand the evolution of electronic states and the related atomic arrangement. In the process from the amorphous to crystallized phase of Ga2O3 films, disordered atoms transform into six-fold GaO6 octahedra. The denser structure creates more electron density. The crystallized phase widens the band gap, because of the conduction band changes attributed to the Ga 4s states hybridized with O 2s states. The Mg dopants create four-fold GaO4 tetrahedron deficiency. Moreover, the distances between Ga atoms become shorter for the doped film; however, the Ga–O distance is independent of the dopant. Mg dopants affect the oxygen states in valence band and Ga–O interaction at conduction band, which results in a slightly smaller band gap. The electronic evolution of the amorphous, crystallized and doped films is confirmed by the calculated density of states results. These results will be beneficial for the design of more effective semiconductive films.

Three Inorganic-Organic Hybrid Gallo-/Alumino-Borates with Porous-Layered Structures Containing [MB4O10(OH)] (M = Al/Ga) Cluster Units.

Three inorganic-organic hybrid gallo-/alumino-borates [Ga2B7O14(OH)]·H2dah (1, dah = 1,6-diaminohexane), K2[Ga2B7O14(OH)(en)0.5] (2, en = ethylenediamine), and K2[Al2B7O14(OH)(en)0.5]·H2O (3) were synthesized under solvothermal conditions. Compound 1 features a 3D porous-layered structure built by the alternation of [GaB4O10(OH)]6-, [B3O6]3- clusters and GaO4 tetrahedra, in which the novel [GaB4O10(OH)]6- cluster is first observed. Compounds 2 and 3 are isostructural and made by [MB4O10(OH)]6-, [B3O6(en)0.5]3- clusters and MO4 tetrahedra (M = Ga/Al); their 3D porous layers are similar to those of 1 and further bridged by en linkers through the rare B-N-C covalent bonds, resulting in the 3D inorganic-organic hybrid framework. This is the first main-group metal borate with organic molecules participating in the oxoboron frameworks through B-N bonds. Optical diffuse-reflectance spectra reveal that 1, 2, and 3 are potential wide-band-gap semiconductors.

Crystal structure and temperature-dependent properties of Na2H4Ga2GeO8 – a novel gallogermanate

Abstract Synthesis, crystal structure and temperature-dependent behavior of Na2H4Ga2GeO8 are reported. This novel gallogermanate crystallizes in space group I41/acd with room-temperature powder diffraction lattice parameters of a = 1298.05(1) pm and c = 870.66(1) pm. The structure consists of MO4 (M = Ga, Ge) tetrahedra in four-ring chains, which are connected by two different (left- and right-handed) helical chains of NaO6 octahedra. Protons coordinating the oxygen atoms of the GaO4 tetrahedra not linked to germanium atoms ensure the charge balance. Structure solution and refinement are based on single crystal X-ray diffraction measurements. Proton positions are estimated using a combined approach of DFT calculations and NMR, FTIR and Raman spectroscopic techniques. The thermal expansion was examined in the range between T = 20(2) K and the compound’s decomposition temperature at 568(5) K, in which no phase transition could be observed, and Debye temperatures of 266(11) and 1566(65) K were determined for the volume expansion.

Salt-flux synthesis, crystal structure and theoretical characterization of Rb0.74Ga6.62Ti0·38O11

Single crystals of Rb0.74Ga6.62Ti0·38O11 (RGTO) were grown from a mixed RbCl–RbF flux at 850 °C. The compound crystallizes in the RbGa7O11 structure type, which is reminiscent of the hollandite and β-Ga2O3 structure types. RGTO crystallizes in the monoclinic space group P2/m with lattice parameters a = 8.3355 (8) Å, b = 3.0286 (3) Å, c = 9.5028 (9) Å, and β = 114.620 (3)°. The crystal structure of RGTO is comprised of GaO6 and mixed (Ga/Ti)O6 octahedra and GaO4 tetrahedra connected in a complex three-dimensional, anionic framework exhibiting eight-sided channels that are occupied by disordered Rb cations required for charge balance. First-principles calculations in the form of density functional theory were performed, which indicated the complex to be a charge transfer semiconductor.

Brownmillerite-Type Sr2ScGaO5 Oxide Ion Conductor: Local Structure, Phase Transition, and Dynamics.

Brownmillerite-type Sr2ScGaO5 has been investigated by a range of experimental X-ray and neutron scattering techniques (diffraction, total scattering, and spectroscopy) and density functional theory calculations in order to characterize its structure and dynamics. The material undergoes a second-order phase transition on heating during which a rearrangement of the (GaO4/2)∞ tetrahedral chains occurs, such that they change from being essentially fully ordered in a polar structure at room temperature to being orientationally disordered above 400 °C. Pair distribution function analysis carried out using neutron total scattering data suggests that GaO4 tetrahedra remain as fairly rigid units above and below this transition, whereas coordination polyhedra in the (ScO6/2)∞ layers distort more. Inelastic neutron scattering and phonon calculations reveal the particular modes that are associated with this structural change, which may assist ionic conductivity in the material at higher temperatures. On the basis of the correlations between these findings and the measured conductivity, we have synthesized a derivative compound with increased conductivity and suggest a possible conduction mechanism in these brownmillerite-type solid electrolytes.

Synthesis and Characterization of a New Layered Gallium Phosphonate Oxalate [C2H10N2]0.5[Ga3(PO3CH3)4(C2O4)].H2O

A new layered gallium phosphonate-oxalate hybrid material, [C2H10N2]0.5[Ga3(PO3CH3)4(C2O4)].H2O, denoted as MOP-1, was synthesized under mild hydrothermal conditions (150 °C) in the presence of ethylenediammonium ion (H2en)2+ as structure-directing agent. The compound was structurally characterized by single-crystal X-ray diffraction (SCXRD), Fourier transformed infra-red spectroscopy (FTIR), and thermogravimetric analysis (TGA). Its structure consists of gallium phosphonate double layers formed of GaO6 octahedra, GaO4 tetrahedra, and PO3CH3 groups sharing corners. The double layers are cross-linked by oxalate ligands to form a three-dimensional framework with intersecting channels where the ammonium ions and water molecules are located. The bridging oxalate ligand acts as a bidentate ligand to each Ga in octahedral coordination environment. Crystal data are as follows: Monoclinic P21/n (14), a = 8.7530(5) A; b = 16.3427(8) A; c = 14.7522(8) A; β = 93.284(1)°, V = 2106.8(2) A3 and Z = 4.

Synthesis, Structure, and Thermal Properties of Ca5Ga6O14

Calcium gallate Ca5Ga6O14 is synthesized by solid-phase means. Its melting point is 1325 ± 2°C. A phase transition of the second kind is observed in the temperature interval of 750–800°C. The temperature dependence of a thermal linear expansion coefficient within 200–900°C is given. Vibrational spectroscopy data confirm that Ca5Ga6O14 contains not only GaO4 tetrahedra but also GaO6 octahedra.

Cs3LiZn2(WO4)4 and Rb3Li2Ga(MoO4)4: different filled derivatives of the cation-deficient Cs6Zn5(MoO4)8 structure.

Two new compounds, namely cubic tricaesium lithium dizinc tetrakis(tetraoxotungstate), Cs3LiZn2(WO4)4, and tetragonal trirubidium dilithium gallium tetrakis(tetraoxomolybdate), Rb3Li2Ga(MoO4)4, belong to the structural family of Cs6Zn5(MoO4)8 (space group I-43d, Z = 4), with a partially incomplete (Zn5/6□1/6) position. In Cs3LiZn2(WO4)4, this position is fully statistically occupied by (Zn2/3Li1/3), and in Rb3Li2Ga(MoO4)4, the 2Li + Ga atoms are completely ordered in two distinct sites of the space group I-42d (Z = 4). In the same way, the crystallographically equivalent A+ cations (A = Cs, Rb) in Cs6Zn5(MoO4)8, Cs3LiZn2(WO4)4 and isostructural A3LiZn2(MoO4)4 and Cs3LiCo2(MoO4)4 are divided into two sites in Rb3Li2Ga(MoO4)4, as in other isostructural A3Li2R(MoO4)4 compounds (AR = TlAl, RbAl, CsAl, CsGa, CsFe). In the title structures, the WO4 and (Zn,Li)O4 or LiO4, GaO4 and MoO4 tetrahedra share corners to form open three-dimensional frameworks with the caesium or rubidium ions occupying cuboctahedral cavities. The tetrahedral frameworks are related to that of mayenite 12CaO·7Al2O3 and isotypic compounds. Comparison of isostructural Cs3MZn2(MoO4)4 (M = Li, Na, Ag) and Cs6Zn5(MoO4)8 shows a decrease of the cubic lattice parameter and an increase in thermal stability with the filling of the vacancies by Li+ in the Zn position of the Cs6Zn5(MoO4)8 structure, while filling of the cation vacancies by larger Na+ or Ag+ ions plays a destabilizing role. The series A3Li2R(MoO4)4 shows second harmonic generation effects compatible with that of β'-Gd2(MoO4)3 and may be considered as nonlinear optical materials with a modest nonlinearity.

Cubic Sr2ScGaO5 Perovskite: Structural Stability, Oxygen Defect Structure, and Ion Conductivity Explored on Single Crystals.

Oxygen-deficient Sr2ScGaO5 single crystals with a cubic perovskite structure were grown by the floating-zone technique. The transparent crystals of this pure 3D oxygen electrolyte are metastable at ambient temperature, showing one-sixth of all oxygen positions vacant. While neutron single-crystal diffraction, followed by maximum entropy analysis, revealed a strong anharmonic displacements for the oxygen atoms, a predominant formation of ScO6 octahedra and GaO4 tetrahedra is indicated by Raman spectroscopic studies, resulting in a complex oxygen defect structure with short-range order. Temperature-dependent X-ray powder diffraction (XPD) and neutron powder diffraction (NPD) studies reveal the cubic Sr2ScGaO5 to be thermodynamically stable only above 1400 °C, while the stable modification below this temperature shows the brownmillerite framework with orthorhombic symmetry. Cubic Sr2ScGaO5 remains surprisingly kinetically stable upon heating from ambient temperature to 1300 °C, indicating a huge inertia for the retransformation toward the thermodynamically stable brownmillerite phase. Ionic conductivity investigated by impedance spectroscopy was found to be 10-4 S/cm at 600 °C, while oxygen 18O/16O isotope exchange indicates a free oxygen mobility to set in at around 500 °C.

Microwave dielectric properties of spinel-structured Li0.5Ga2.5O4 ceramics with cation ordering on octahedral sites

The effect of firing temperature on the cation distributions of Li+ and Ga3+ in the tetrahedral and octahedral sites of Li0.5Ga2.5O4 ceramics was investigated and the microwave dielectric properties of the ceramics were also characterized in this study. 7Li and 71Ga solid-state nuclear magnetic resonance (NMR) spectra revealed the preferential occupations of the Ga3+ cations in tetrahedral sites of the Li0.5Ga2.5O4 ceramics, whereas the octahedral sites of the ceramics were occupied by the Li+ and Ga3+ cations. Moreover, the order/disorder behavior of Li+ and Ga3+ cations on the octahedral sites was examined by Raman spectroscopy and crystal structure refinements; the fractions of disordered (Fd3m) Li0.5Ga2.5O4 ceramic increased from 0.9 to 10.3%, depending on the firing temperature. From this result, it is considered that the coexistence of the ordered (P4332) and disordered Li0.5Ga2.5O4 ceramics is suggested. As a result, the covalency of the cation–oxygen bonds in the GaO4 tetrahedron and MO6 octahedron (M = Li+ and Ga3+) was strongly affected by the order/disorder behavior of the Li+ and Ga3+ cation in the tetrahedral and octahedral sites. The εr of the ceramics increased from 6.1 to 10.1 with increasing firing temperature, depending on the relative density and fraction of the disordered phase. Q · f also markedly improved from 18,546 to 237,962 GHz.

First-Principles Study of CuGaO2 Polymorphs: Delafossite α-CuGaO2 and Wurtzite β-CuGaO2.

The electronic structures of delafossite α-CuGaO2 and wurtzite β-CuGaO2 were calculated based on density functional theory using the local density approximation functional including the Hubbard correction (LDA+U). The differences in the electronic structure and physical properties between the two polymorphs were investigated in terms of their crystal structures. Three major structural features were found to influence the electronic structure. The first feature is the atomic arrangements of cations. In the conduction band of α-CuGaO2 with a layered structure of Cu2O and Ga2O3, Cu and Ga states do not mix well; the lower part of the conduction band mainly consists of Cu 4s and 4p states, and the upper part consists of Ga 4s and 4p states. By contrast, in β-CuGaO2, which is composed of CuO4 and GaO4 tetrahedra, Cu and Ga states are well-mixed. The second feature is the coordination environment of Cu atoms; the breaking of degeneracy of Cu 3d orbitals is determined by the crystal field. Dispersion of the Cu 3d valence band of β-CuGaO2, in which Cu atoms are tetrahedrally coordinated to oxygen atoms, is smaller than those in α-CuGaO2, in which Cu atoms are linearly coordinated to oxygen atoms; this results in a larger absorption coefficient and larger hole effective mass in β-CuGaO2 than in α-CuGaO2. The interatomic distance between Cu atoms-the third feature-also influences the dispersion of the Cu 3d valence band (i.e., the effective hole mass); the effective hole mass decreases with decreasing interatomic distance between Cu atoms in each structure. The results obtained are valuable for understanding the physical properties of oxide semiconductors containing monovalent copper and silver.

NaBa4(GaB4O9)2X3 (X = Cl, Br) with NLO-Active GaO4 Tetrahedral Unit: Experimental and ab Initio Studies

Two gallium borates, NaBa4(GaB4O9)2X3 (X = Cl, Br), were synthesized by high temperature solution method. The title compounds crystallize in the same space group P42nm. Their structures feature a 3D [GaB4O9]∞ framework composed of GaO4 tetrahedra and B4O9 groups. NaBa4(GaB4O9)2X3 (X = Cl, Br) compounds show the largest second harmonic generation responses among alkali metal and alkaline-earth metal gallium borates that are 1.5 and 1.1 times that of KH2PO4 (KDP), respectively, and are type I phase-matchable. Combined electronic structure and SHG density calculations as well as local dipole moment analysis have revealed that B–O groups and GaO4 tetrahedron play major roles in SHG response.

Structural, elastic and vibrational properties of nanocrystalline lutetium gallium garnet under high pressure.

An ab initio study of the structural, elastic and vibrational properties of the lutetium gallium garnet (Lu3Ga5O12) under pressure has been performed in the framework of the density functional theory, up to 95 GPa. Pressure dependence of the elastic constants and the mechanical stability are analyzed, showing that the garnet structure is mechanically unstable above 87 GPa. Lattice-dynamics calculations in bulk at different pressures have been performed and compared with Raman scattering measurements of the nanocrystalline Tm(3+)-doped Lu3Ga5O12 up to 60 GPa. The theoretical frequencies and pressure coefficients of the Raman active modes for bulk Lu3Ga5O12 are in good agreement with the experimental data measured for the nano-crystals. The contributions of the different atoms to the vibrational modes have been analyzed based on the calculated total and partial phonon density of states. The vibrational modes have been discussed in relation to the internal and external modes of the GaO4 tetrahedron and the GaO6 octahedron. The calculated infrared modes and their pressure dependence are also reported. Our results show that with this nano-garnet size the sample has essentially bulk properties.

Synthesis and crystal structure of Sr2MnGaO5-dFx, layered oxyfluorides

Sr2MnGaO5 brownmillerite has an interesting structure. In this compound, MnO6 octahedra and GaO4 tetrahedra are ordered along c-axis. The MnO6 octahedra are deformed due to Jahn-Teller effect with four short equatorial Mn-O distances and two long apical one. Oxygen vacancies in the GaO layer provide distorted tetrahedral coordination for the Ga cation. The oxide and/or fluoride ions are introduced into the vacancies in GaO layer. The synthesis of Sr2MnGaO4.78F1.22 using XeF2 as a fluorinating agent is reported, while the small amount SrF2 impurity is contained[1]. On the other hand, low temperature fluorination using polyvinylidenefluoride (PVDF) is powerful method for the synthesis of oxyfluoides from brownmillerite[2]. In this study, we synthesize the Sr2MnGaO5-dFx (x=0.5, 1.0, 1.5, 2.0) using PVDF and investigate the variation of crystal structure with x. Sr2MnGaO5 brownmillerites were prepared sold state reaction method. Starting materials were SrCO3, Mn2O3 and Ga2O3. The mixture was heated twice in Ar at 13000C for 72h. For the preparation of Sr2MnGaO5-dFx (x=0.5, 1.0, 1.5, 2.0), stoichiometric amounts of Sr2MnGaO5 brownmillerite and PVDF were ground and the mixture were heated in N2 at 4000C for 8h. And then, the as prepared materials were subsequently heated in O2 at 4000C for 8h. The Sr2MnGaO5-dFx were obtained without impurities. As shown in Fig., the orthorhombic distortion reduced with the increase in x. The X-ray diffraction data of Sr2MnGaO5-dF1.0 could be refined on the structure model belonging the space group Icmm. the bond valence sum of Ga3+ calculated from Ga-O bond length indicates that the fluoride ions are introduced into GaO layer preferentially. The measurements of magnetic properties for Sr2MnGaO5-dFx are in progress.

Lattice Dynamics Study of Nanocrystalline Yttrium Gallium Garnet at High Pressure

This work reports an experimental and theoretical lattice dynamics study of nanocrystalline Y3Ga5O12 (YGG) garnet at high pressures. Raman scattering measurements in nanocrystalline Tm3+-doped YGG garnet performed up to 29 GPa have been compared to lattice dynamics ab initio calculations for bulk garnet carried out up to 89 GPa. Good agreement between the theoretical vibrational modes of bulk crystal and the experimental modes measured in the nanocrystals is found. The contribution of GaO4 tetrahedra and GaO6 octahedra to the different phonon modes of YGG is discussed on the basis of the calculated total and partial phonon density of states. Symmetries, frequencies, and pressure coefficients of the Raman-active modes are discussed. Moreover, the calculated infrared-active modes and their pressure dependence are reported. No pressure-induced phase transition has been observed in nano-YGG up to 29 GPa. This is in agreement with theoretical results, which show a mechanical instability of YGG above 84 GPa, si...

Solvothermal synthesis, crystal structure, and second-order nonlinear optical properties of a new noncentrosymmetric gallium-organic framework material, [N(C3H7)4]3Ga3[C6H3(CO2)3

A novel noncentrosymmetric (NCS) gallium-organic framework material, [N(C3H7)4]3Ga3[C6H3(CO2)3]4 (CAUMOF-11) has been synthesized by a solvothermal reaction using Ga(NO3)3·xH2O, 1,3,5-C6H3(CO2H)3, N(C3H7)4Cl, HNO3, and HCON(CH3)2 at 180°C. The structure of the reported material has been determined by single-crystal X-ray diffraction. CAUMOF-11 has an anionic three-dimensional framework with aligned four-coordinate GaO4 tetrahedra and 1,3,5-benzenetricarboxylate groups. Tetrapropylammonim cations reside within the channel and maintain the charge balance. Detailed structural analyses with full characterization including infrared spectroscopy, thermogravimetric analysis, elemental analysis, ion-exchange reactions, topotactic decomposition, and gas adsorption experiments are reported. Powder second-harmonic generating (SHG) measurements on CAUMOF-11, using 1064nm radiation, exhibit SHG efficiency of 15 times that of α-SiO2 and the material is phase-matchable (type-1).