Space Group Immm Research Articles

Imparting Superhydrophobicity to Porphyrinic Coordination Frameworks Using Organotin

Imparting Superhydrophobicity to Porphyrinic Coordination Frameworks Using Organotin

Synthesis and Characterizations of Two Tellurides β-BaGa2Te4 and Ba5Ga2Ge3Te12 with Flexible Chain Structure.

Demands for IR birefringent materials are increasing due to the rapid developments of IR laser applications. Herein, two new chain tellurides β-BaGa2Te4 and Ba5Ga2Ge3Te12 have been discovered. β-BaGa2Te4 crystallizes in the orthorhombic space group Imma (no. 74) with unit cell constants of a = 23.813(3) Å, b = 11.9673(19) Å, and c = 6.7215(9) Å, while Ba5Ga2Ge3Te12 crystallizes in the monoclinic space group P21/c (no. 14) with unit cell constants of a = 13.6540(3) Å, b = 9.6705(2) Å, and c = 23.1134(7) Å. The structure of β-BaGa2Te4 can be considered to be the antiparallel arrangement of one-dimensional (1D) [GaTe2] chains formed by edge-sharing GaTe4 tetrahedra, which are separated by Ba2+ cations. In the crystal structure of Ba5Ga2Ge3Te12, two kinds of 1D chains, namely chain 1 ∞1[(GaGe)3Te8] and chain 2 ∞1[(GaGe)2Te4], are stacked alternately and put together by the coulomb force with Ba2+ cations. In addition, First-principles calculations indicate that β-BaGa2Te4 has a large birefringence, ∼0.325 at 2050 nm, derived from the superposition of the polarizabilities of GaTe4 tetrahedra, implying that it has potential as an IR birefringent material. This work may provide some guidance for exploring new IR birefringent crystals.

Revisiting the Structure of Calcined and Hydrated AlPO-11 with DFT-Based Molecular Dynamics Simulations*.

Published crystal structures of the AEL‐type aluminophosphate AlPO‐11 in its calcined form (space group Ima2 ) show some peculiar features, such as unusually short Al−O and P−O bonds and near‐linear Al−O−P angles. Although experimental evidence for the presence of dynamic disorder was presented, the nature of the associated distortions remained unresolved. In this study, ab initio molecular dynamics (AIMD) calculations in the framework of density functional theory (DFT) were employed to study the dynamic behaviour of this zeotype. At 100 K, static local distortions that break the Ima2 symmetry are present in the time‐averaged structures computed from the AIMD trajectories. At 300 and 500 K, the time‐averaged structures approach Ima2 symmetry. Although shortened Al−O and P−O bonds and near‐linear Al−O−P angles were found in the average structures, an analysis of radial and angular distribution functions confirmed their absence in the instantaneous structures. This deviation is due to a precession‐like motion of some oxygen atoms around the Al−P connection line, which moves their time‐averaged positions closer to this line. In hydrated AlPO‐11, some of the water molecules are coordinated to framework Al atoms, leading to an octahedral coordination of 1/5 of the Al sites. DFT optimisations and AIMD simulations on partially hydrated models delivered evidence for a preferential adsorption at the Al1 site. No dynamic disorder was observed for the hydrated form.

Identification and characterisation of a new orthorhombic Ti6Sn5O0.9 structure

The orthorhombic phase of Ti6Sn5 in the Ti-Sn binary system is regarded as a low-temperature or metastable phase. The motivation of the present study was to clarify the presence of this orthorhombic phase. This phase could not be synthesized by heating a mixture of Ti and Sn powder at 873 K, whereas single crystals of a novel suboxide, Ti6Sn5O0.88 (orthorhombic, a = 5.72790(10) Å, b = 9.1379(2) Å, c = 16.9275(3) Å, space group Immm), were obtained by heating powders of Ti, Sn, and TiO2 at 1273 K in an Ar atmosphere, followed by slow cooling. Crystal structure analysis of single-crystal X-ray diffraction data indicated that the O atoms are located at a 4 g site in the Ti tetrahedron of the orthorhombic Ti6Sn5 structure. An almost single-phase polycrystalline bulk sample of Ti6Sn5O0.9 was prepared by heating a compacted powder mixture of Ti, Sn, SnO2 at 1173 K. The bulk sample exhibited metallic electrical properties.

Ambient pressure synthesis and properties of LaCu3Fe2TiSbO12: New A-site ordered ferrimagnetic quadruple perovskite

A large number of quadruple perovskites are synthesized and reported under high pressure while ambient pressure synthesized quadruple perovskites are limited in number. Recently, ambient pressure synthesis of quadruple perovskites has gained much interest.1 The A-site ordered quadruple perovskite, LaCu3Fe2TiSbO12, reported for the first time, is synthesized by high-temperature solid-state reactions at ambient pressure. Rietveld structure refinement using P-XRD data reveal formation of LaCu3Fe2TiSbO12 in body centered cubic Im-3 space group with lattice parameter of 7.4465(7) Å. The compound shows complete 1:3 order of A-site La with A′-site Cu and B/B′-site disorder of Fe with Ti and Sb instead of both A- and B-site order in CaCu3Fe2Sb2O12 (Larregola et al., 2014; Chen et al., 2013) [1,2]. The magnetic transitions observed in the compound around 160 and 60 ​K are attributed to short-range orders. The static disorder at the B-sublattice introduced by non-magnetic Ti and Sb precludes the possibility of long-range magnetic order in the compound. Lower saturation magnetization presumably supports antiferromagnetic ordering of A-site Cu2+ and B-site Fe3+ spins interrupted by the B-site disorder restricting it to a short-range phenomenon. The ferrimagnetic quadruple perovskite also show reasonably high dielectric constant in the low-frequency region and a low dielectric loss at room temperature. The stabilization of LaCu3Fe2TiSbO12 under ambient pressure despite having a fairly large global instability index (GII, calculated with SPuDS) of 0.276 v.u. is interesting and may suggest accessibility of many new quadruple perovskites at atmospheric pressure.

Crystal structure of new ternary disilicide of platinum and erbium

Crystal structure of the ternary compound ErPtSi2 (diffractometer HZG-4a, CuK-radiation, structure type YIrGe2, Pearson symbol oI32, space group Immm, a=4.19395(6) Å, b=8.41465(13) Å, c=15.85404(19) Å, RB=0.0639, Rp=0.0424, and 2=1.11) was studied by X-ray powder diffraction method. Intermetallide ErPtSi2 is the first representative of YIrGe2 structure type in R–Pt–Si systems. Crystal structures of ternary compounds in the system Er–Pt–Si were analyzed and the structural relationships between them were established according to the systematics of the nearest coordination environment around the less electronegative Er atoms. Compounds, found in the system, were divided into two main types based on the nearest coordination environment, namely on the derivatives of hexagonal and pentagonal prisms with different amounts of additional atoms. These polyhedra exist both alone and in the combination with each other and with cubooctahedra in the structures of the different ternary silicides of erbium. Such a relatively small coordination environment of rare-earth metal atoms can be explained by the structural peculiarities of the ErPt3 binary compound. The coordination polyhedra of the smallest atoms are trigonal prisms with different amounts of additional atoms or cubooctahedra.

Enhancement of A′-site Mn3+ spin ordering by B-site Mn4+ substitution in quadruple perovskite PbMn3Cr3MnO12

An A-site ordered but B-site disordered quadruple perovskite oxide PbMn3Cr3MnO12 was synthesized by high-pressure and high-temperature methods. The compound crystallizes in space group Im-3 with the charge distribution of Pb2+Mn3+3Cr3+3Mn4+O12. Three antiferromagnetic phase transitions are found to occur at TN1 ≈ 155, TN2 ≈ 81, and TN3 ≈ 74 K, respectively, due to the complex B-site and A′-B intersite spin interactions. Compared with the isostructural LaMn3Cr4O12 with negligible A′-B intersite spin coupling, the substitution of Mn4+, which has identical electronic configuration to that of Cr3+ (t2g3), into the B site can introduce A′-B intersite spin interactions. As a result, the A′-site spin-related ordering temperature increases significantly, while the B-site one remains little changed in the current PbMn3Cr3MnO12. This work opens up a way to enhance the A′-site spin ordering temperature in quadruple perovskite oxides.

Synthesis and spectroscopic characterization of Ba2Sb2O7:Eu3+ orange-red emitting phosphor for WLEDs

A series of Eu3+ doped Ba2Sb2O7 phosphors were prepared by the solid-state reaction method. XRD analysis confirmed its orthorhombic structure with the space group Imma. The photoluminescence spectra implies that the phosphors exhibit characteristic emission peaks corresponding to 5D0→7FJ transitions of Eu3+ ions under NUV excitation. The CIE chromaticity coordinates reveal reddish-orange emission in the warm CCT region with high color purity. The mechanism for concentration quenching was found to be quadrupole–quadrupole interaction and the decay lifetime of the phosphors is in the millisecond range. The results suggest that the prepared phosphors are a potential candidate for phosphor-converted white light-emitting diodes and optoelectronic devices.

New compound Sm2Ru3Sn5 with a structure derived from Ru3Sn7

Abstract Ternary intermetallic compound Sm2Ru3Sn5 was synthesized in the system Sm-Ru-Sn by arc-melting and annealing at 600 °C in the field with high content of Sn. Its crystal structure was determined using single crystal X-ray diffraction data (at 240 K). The compound crystallizes in cubic system with space group I 4 ‾ 3m (No. 217), unit cell parameter is a = 9.4606 (8) Å, Z = 4, Pearson symbol c/40. The intermetallic compound Sm2Ru3Sn5 represents an ordered version of the centrosymmetric Ru3Sn7 structure (space group Im 3 ‾ m), in which 16f Sn-filled crystallographic site is split into two 8c sites, each of which is solely occupied of one sort of atoms – Sn or Sm. The occupation of these two 8c sites leads to a reduction of symmetry due to the removal of the inversion center.

Os Doping Suppressed Cu-Fe Charge Transfer and Induced Structural and Magnetic Phase Transitions in LaCu3Fe4-xOsxO12 (x = 1 and 2).

B-site Os-doped quadruple perovskite oxides LaCu3Fe4-xOsxO12 (x = 1 and 2) were prepared under high-pressure and high-temperature conditions. Although parent compound LaCu3Fe4O12 experiences Cu-Fe intermetallic charge transfer that changes the Cu3+/Fe3+ charge combination to Cu2+/Fe3.75+ at 393 K, in the Os-doped samples, the Cu and Fe charge states are found to be constant 2+ and 3+, respectively, indicating the complete suppression of charge transfer. Correspondingly, Os6+ and mixed Os4.5+ valence states are determined by X-ray absorption spectroscopy for x = 1 and x = 2 compositions, respectively. The x = 1 sample crystallizes in an Fe/Os disordered structure with the Im3̅ space group. It experiences a spin-glass transition around 480 K. With further Os substitution up to x = 2, the crystal symmetry changes to Pn3̅, where Fe and Os are orderly distributed in a rocksalt-type fashion at the B site. Moreover, this composition shows a long-range Cu2+(↑)Fe3+(↑)Os4.5+(↓) ferrimagnetic ordering near 520 K. This work provides a rare example for 5d substitution-suppressed intermetallic charge transfer as well as induced structural and magnetic phase transitions with high spin ordering temperature.

Composition adjustment verifies structure-property correlation in narrow-band green-emitting Zn4-xMgxB6O13: Mn2+ phosphor

A variety of optoelectronic devices such as photovoltaics and light-emitting diodes need stable performance of phosphors and the most important factor in liquid-crystal display (LCD) backlights will be the color purity. Here, a novel rare-earth-free narrow-band green-emitting phosphor based on the substitution of Mg2+ for Zn2+ in the lattice of Zn3.98-xMgxB6O13:0.02Mn2+ has been assembled via a solid-state reaction method. According to XRD and Rietveld refinement results, Zn3.98-xMgxB6O13:0.02Mn2+ can achieve perfect solid solution phases at 0 ≤ x ≤ 0.2 in terms of the same cubic structure of Zn4B6O13 with space group I-43m (217). Under the excitation at 450 nm in blue region, Zn3.98-xMgxB6O13:0.02Mn2+ phosphors possess the green emission band at λmax ~542 nm and its full-width at half-maximum (FWHM) has been found to be only 39 nm. In addition, the emission intensity can be enhanced by increasing Mg content (x) from 0 to 0.1. It has to be mentioned that the thermal stability for the composition-optimized x = 0.1 sample is superior to that of the unsubstituted sample (x = 0). The underlying mechanism for this luminescence improvement has been verified. By virtue of assembling a green-emitting Zn3·97Mg0·1B6O13:0.02Mn2+ phosphor and a commercial red-emitting K2SiF6:Mn4+ phosphor as light converters, a warm white light has been achieved based on InGaN-based blue-LED (450 nm) and such device gives rise to wide color gamut of 105% National Television System Committee (NTSC) and good color-rendering index Ra of 90.6 at a correlated color temperature of 3683 K. Our results pave a new way in developing Mn2+-activated thermally stable narrow-band green-emitting phosphors with improving luminescence performance by simple compositional adjustments.

Dielectric properties of Ni and Nb doped CaCu3Ti4O12 ceramics

CaCu2.8Nb0.2Ti4-xNixO12 (x=0.1, 0.2, 0.3) and CaCu3Ti4O12 ceramics were successfully fabricated through the solid-state reaction method. All the samples were methodically examined by X-ray diffraction (XRD), scanning electron microscopy (SEM), impedance and dielectric properties measurements. XRD analyses verified the constitution of a cubic perovskite structure with Im-3 space group. The average grain size of CaCu3Ti4O12 ceramics reduced with Ni and Nb ions doping, especially decreased significantly with the increase of Ni content. Compared with un-doped CaCu3Ti4O12, Ni and Nb ions doped CaCu3Ti4O12 ceramics presented greatly enhanced dielectric constant range from 102 Hz to 106 Hz, illustrating the Ni and Nb ions have great influence on improving the dielectric constant. The CaCu2.8Nb0.2Ti3.8Ni0.2O12 sample achieves the highest dielectric constant, possesses the lowest dielectric loss and acquires the largest grain boundary resistance in the doped samples. Therefore, it has optimal dielectric performance.

A Vacancy-Driven Intermetallic Phase: Rh3Cd5-δ (δ ∼ 0.56).

A nonstoichiometric line phase, Rh3Cd5-δ (δ ∼ 0.56), is found in close vicinity to RhCd and structurally characterized by single-crystal X-ray diffraction and energy-dispersive X-ray spectroscopy. The compound crystallizes in the cubic space group Im3m (No. 229) with lattice constant a = 6.3859(9) Å and represents a 2 × 2 × 2 superstructure of RhCd, which accommodates a vacancy concentration of nearly 6% in its crystal structure. The first-principles electronic structure calculation on a hypothetical ordered configuration of Rh3Cd5-δ reveals that Rh-Cd heteroatomic interaction plays a major role in the stability of the compound. A combination of the total energy, formation energy, and crystal orbital Hamilton population calculations on hypothetical model configurations establishes that the compound upholds an optimum vacancy concentration in the Cd2a (Cd1) site for the stability of the phase.

Above Room Temperature Organic Dielectric Switchable and NLO Co‐crystal: [C4H4O4][C8H19N

AbstractA new pure organic co‐crystal compound 1, [C4H4O4][C8H19N] ([C4H4O4]=maleic acid, [C8H19N]=diisobutylamine/DIBA) was discovered to undergo an above room temperature reversible phase transition at around 353/343 K. The variable‐temperature single‐crystal X‐ray structural measurements reveal that space group of the structural phase transition is from space group Cmm2 to space group Imm2. The phase transition of compound 1 is mainly ascribed to the twisted movement of diisobutylamine molecules. Meanwhile, nonlinear optical (NLO) properties were also observed in compound 1.

Complex Dirac-like Electronic Structure in Atomic Site-Ordered Rh3In3.4Ge3.6

We report the synthesis via an indium flux method of a novel single-crystalline compound Rh3In3.4Ge3.6 that belongs to the cubic Ir3Ge7 structure type. In Rh3In3.4Ge3.6, the In and Ge atoms choose to preferentially occupy, respectively, the 12d and 16f sites of the Im-3m space group, thus creating a colored version of the Ir3Ge7 structure. Like the other compounds of the Ir3Ge7 family, Rh3In3.4Ge3.6 shows potential as a thermoelectric displaying a relatively large power factor, PF ~ 2 mW/cmK2, at a temperature T ~ 225 K albeit showing a modest figure of merit, ZT = 8 x 10-4, due to the lack of a finite band gap. These figures might improve through a use of chemical substitution strategies to achieve band gap opening. Remarkably, electronic band structure calculations reveal that this compound displays a complex Dirac-like electronic structure relatively close to the Fermi level. The electronic structure is composed of several Dirac type-I and type-II nodes, and even Dirac type-III nodes that result from the touching between a flat band and a linearly dispersing band. This rich Dirac-like electronic dispersion offers the possibility to observe Dirac type-III nodes and study their role in the physical properties of Rh3In3.4Ge3.6 and related Ir3Ge7-type materials.

The crystal structure of Cu2GeSe3 and the structure-types of the I2-IV-VI3 family of semiconducting compounds

Almost 50 years after the initial report, the crystal structure of Cu2GeSe3, a I2-IV-VI3 semiconductor, has been revised using modern single-crystal X-ray diffraction data. The structure of this material can be properly described in the monoclinic space group Cc (No. 9) with unit-cell parameters a = 6.7703 (4) Å, b = 11.8624 (5) Å, c = 6.7705 (4) Å, β = 108.512 (6)°, V = 515.62 (5) Å3, Z = 4, rather than in the orthorhombic space group Imm2 (No. 44) with unit-cell parameters a = 11.860 (3), b = 3.960 (1), c = 5.485 (2) Å, V = 257.61 Å3, Z = 2, as originally proposed [Parthé & Garín (1971). Monatsh. Chem. 102, 1197–1208]. Contrary to what was observed in the orthorhombic structure, the distortions of the tetrahedra in the monoclinic structure are consistent with the distortions expected from considerations derived from the bond valence model. A brief revision of the structures reported for the I2-IV-VI3 family of semiconducting compounds (I: Cu, Ag; IV: Si, Ge, Sn; and VI: S, Se, Te) is also presented.

OI20-carbon: A new superhard carbon allotrope

A new orthorhombic carbon crystal denoted oI20‑carbon possessing the Immm space group was designed. Its structure is formed by stacking of a cage structure, which consists of 32 carbon atoms. Its stability and structural, mechanical and electronic properties were investigated by first-principles simulations. Density functional theory calculations show that this new carbon allotrope is thermodynamically stable (even more stable than synthesized T‑carbon and supercubane). Ab initio molecular dynamics (AIMD) simulations show that it can maintain the structure above a temperature of 1000 K, indicating its excellent thermal stability. oI20‑carbon can also maintain dynamic stability under a high pressure of 100 GPa. It is an anisotropic superhard material with a Vickers hardness of 46.62 GPa. Notably, the cage structure gives it a low density, which has a really small value among superhard carbon allotropes. In addition, it is worth noting that oI20‑carbon has an indirect ultrawide band structure with a bandgap of 4.55 eV (HSE06), which is higher than that of most previously reported superhard carbon allotropes. All these outstanding properties show that it is a potential material for high-temperature, high-frequency electronic devices and the aerospace industry.

The crystal structures and magnetic properties of TiFeSi coexisting in hexagonal and orthorhombic symmetries

The intertwisted helix framework of the chiral FeSi-type structure with the space group P213 (S.G. P213) inspired us to investigate other non-centrosymmetric compounds, particularly 111-type phases with different FeSi frameworks. Various FeSi-containing 111-type phases have been summarized according to their valence electron counts and space group. In this work we have focused on the non-centrosymmetric TiFeSi phase. The crystal structure analysis of the hexagonal Fe2P-type and the reported orthorhombic TiFeSi-type (α-TiFeSi) indicate a superlattice relationship exists between the two structures, which drove us to perform the total energy calculations of the hexagonal and orthorhombic models of TiFeSi. Following the theoretical predictions, a hexagonal TiFeSi phase (β-TiFeSi) is proposed and successfully synthesized at high temperature using arc melting. The crystal structure of the high-temperature hexagonal phase was determined by powder and single crystal X-ray diffraction. After the annealing of the arc-melted samples, TiFeSi crystallizes into an orthorhombic structure with the space group Ima2. The systematic magnetic characterizations indicate ferromagnetic properties are present in the non-centrosymmetric orthorhombic α-TiFeSi phase with possible helical magnetic ordering at low temperatures. Moreover, to compare with the centrosymmetric cases, the electronic and magnetic properties of the antiferromagnetic TiNiSi-type MFeSi (M = Zr and Hf) compounds were also examined using both density functional theory and experimental magnetic measurements.

A \u03b2 Ti\u201320Nb\u201310Ta\u20135Zr Alloy with the Surface Structured on the Micro- and Nanoscale

This alloy is shown to be homogeneous (Ti 65%, Nb 20%, Ta 10%, Zr 5%). A change in the elemental composition is observed only in the layer close to the surface with a thickness of about 100 nm. The alloy surface is depleted in titanium (∼20%) and enriched in tantalum (∼20%). There is also a large amount of oxides on the surface (∼50%). The alloy is single-phase with a β-Ti-type crystal lattice (cubic system, space group Im3m). The alloy has yield strength of about 550 MPa and a tensile strength of about 700 MPa. The Young’s modulus is about 50 GPa. The relative elongation of the alloy is about 1.4%. On a microscale, folds and longitudinal comb-like structures up to 0.5 μm in height are found on the surface of wires and plates made of the Ti–20Nb–10Ta–5Zr alloy. When analyzing nanotopology, it is found that, even between comb-like structures or at their tops, there are irregularities up to 100–150 nm in height.

Synthesis and Physico-chemical Characterization of Solid Solution (1-x)CCTO−xPbTiO3

The composite materials of (1-x)CaCu3Ti4O12, xPbTiO3((1-x)CCTO−xPT) were prepared by a modified solid-state method in several steps. The Rietveld refinement indicates the formation of the pure cubic and tetragonal phases for calcium copper titanate (CCTO) and lead-titanate (PT) pure ceramics, respectively. While for CCTO-PT composites, the coexistence of the two cubic and tetragonal phases was detected with the space group Im-3 and P4mm, respectively. The Raman spectra confirmed these phase formations. The SEM images indicated a change in grains shape from quadratic to semi-spherical with increases of PT contents and a reduce in average grains size with increase of PT content. The dielectric measurements as function of temperature showed two anomalies which exhibit a relaxation-like phenomenon and a clear diffuseness behaviour for all the samples. In addition, the conductivity of these materials decreases and the resistance of grain boundaries was found to increase with the increase of PT addition.