Ambient pressure synthesis of corundum-type IN2O3

This communication reports the formation of the high-pressure modification of indium (III) oxide (so-called corundum-type or hexagonal In2O3) under ambient pressure. Corundum-type In2O3 was obtained by precipitation from the solution of indium nitrate in methanol by adding concentrated ammonia solution and subsequent calcination of the obtained precipitate at 250-500 degrees C. The role of the impurities and the additives in the stabilization of corundum-type In2O3 is discussed.     

常压水热法合成玉米棒状In_2O_3及其性能研究

以In(NO_3)_3·4.5H_2O和(NH_2)_2CO为原料,采用常压水热法于95℃反应22 h制得氧化铟(In_2O_3)前驱物氢氧化铟,于600℃煅烧2 h合成了In_2O_3粉体,其结构、形貌及性能经紫外-可见(UV-Vis)光谱、X-射线衍射(XRD)、拉曼光谱和扫描电镜(SEM)表征。以甲基橙为目标降解物,研究了In_2O_3粉体的光催化活性。结果表明:In_2O_3粉体为体心立方晶系方铁锰矿结构和亚稳相刚玉六方结构的混合体,In_2O_3的UV-Vis谱图中出现了明显的蓝移。当In(NO_3)_3·4.5H_2O和(NH_2)_2CO物质的量比为1∶7时,In_2O_3粉体中出现了玉米棒状结构,棒状体长度约为500 nm,直径约150 nm;该棒状结构的In_2O_3对甲基橙有较好的光催化活性,在紫外光照射6.5 h后甲基橙的降解率为69.7%。     

Bixbyite-type V2O3--a metastable polymorph of vanadium sesquioxide

A metastable polymorph of vanadium sesquioxide was prepared by the reaction of vanadium trifluoride with a water-saturated gaseous mixture of 10 vol % hydrogen in argon. The new polymorph crystallizes in the bixbyite-type structure. At temperatures around 823 K a transformation to the well-known corundum-type phase is observed. Quantum-chemical calculations show that the bixbyite-type structure is about 9 kJ/mol less stable than the known corundum-based one. This result, in combination with the absence of imaginary modes in the phonon density of states, supports the classification of the bixbyite-type phase as a metastable V(2)O(3) polymorph. At ~50 K a paramagnetic to canted antiferromagnetic transition is detected.     

Preparation and thermal decomposition of indium hydroxide

Summary Indium hydroxides were prepared by the mixing of aqueous indium nitrate solution with sodium or ammonium hydroxide solutions under various conditions. The thermal decomposition of the resulting materials was examined by thermogravimetry, differential thermal analysis, X-ray diffraction study and infrared spectroscopy. It has been found that sodium hydroxide solution is more suitable than the addition of ammonium hydroxide solution to prepare indium hydroxide in well crystallization; the thermal decomposition of indium hydroxide, in which the composition is In(OH)₃·xH₂O where x￡2, proceeds according to the following process: In(OH)₃·xH₂O?cubic In(OH)₃?cubic In₂O₃     

High-pressure synthesis and local structure of corundum-type In(2-2x)Zn(x)Sn(x)O(3) (x ≤ 0.7)

The corundum-type In(2-2x)Zn(x)Sn(x)O(3) solid solution (cor-ZITO, x ≤ 0.7) was synthesized at 1000 °C under a high pressure of 70 kbar. cor-ZITO is a high-pressure polymorph of the transparent conducting oxide bixbyite-In(2-2x)Zn(x)Sn(x)O(3) (x ≤ 0.4). Analysis of the extended X-ray absorption fine structure suggests that significant face-sharing of Zn and Sn octahedra occurs, as expected for the corundum structure type. In contrast to the ideal corundum structure, however, Zn and Sn are displaced and form oxygen bonds with lengths that are similar to those observed in high-pressure ZnSnO(3). Powder X-ray diffraction patterns of cor-ZITO showed the expected unit cell contraction with increased cosubstitution, but no evidence for ilmenite-type ordering of the substituted Zn and Sn. A qualitative second harmonic generation measurement, for the solid solution x = 0.6 and using 1064 nm radiation, showed that Zn and Sn adopt a polar LiNbO(3)-type arrangement.     

铟颗粒上具有不同直径氧化铟纳米锥的原位合成与光致发光特性

以Au作催化剂, 通过金属铟与氧气在850～1000 ℃的氧化反应, 在单质铟表面原位大面积生长出了In2O3纳米锥. 通过反应温度的改变实现了纳米锥的可控合成. 采用激光拉曼光谱、X射线衍射、扫描电镜和透射电镜对产物进行了表征分析. 结果表明, 纳米锥为立方相单晶结构的In2O3, 其直径和高度分别在0.1～0.6 μm和0.2～2.9 μm范围内可调控. 提出了In2O3纳米锥可能的生长机理. 在室温下研究了它们的发光性质, 发现了发光峰位于416和439 nm强的蓝光发光, 这一蓝光发光起源于氧化铟纳米锥中氧空位中的电子与铟-氧空位中心中的空穴之间的复合.     

Phase behavior of a thermotropic cubic mesogen 4'-n-hexadecyloxy-3'-nitro- biphenyl-4-carboxylic acid under pressure

The phase behavior of an optically isotropic cubic mesogen 4'-n-hexadecyloxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC-16) was investigated under hydrostatic pressures up to 200 MPa using a high-pressure DTA, a polarizing optical microscope equipped with a high-pressure hot-stage and a wide-angle X-ray diffractometer equipped with a high-pressure vessel. In the T vs. P phase diagram constructed in the heating mode, a triple point exists at 54±1 MPa and 205±1°C for the SmC, cubic, and SmA phases. A new mesophase, denoted here as X, appears in place of the cubic phase under pressures above about 60 MPa, while the X phase appears on cooling in the whole pressure region studied. Thus the X phase is a monotropic (metastable) phase between the SmA and Cub phases in the low pressure region, while being an enantiotropic phase between the SmA and SmC phases in the high pressure range. The X phase exhibits broken-fan or sand-like textures under pressure and a spot-like diffraction pattern, indicating the birefringent feature and no layered structure. It is suggested that the X phase is tetragonal or hexagonal columnar phase. This revised version was published online in July 2006 with corrections to the Cover Date.     

Synchronizing Substrate Activation Rates in Multicomponent Reactions with Metal–Organic Framework Catalysts

A study on the influence of the cation coordination number, number of Lewis acid centers, concurrent existence of Lewis base sites, and structure topology on the catalytic activity of six new indium MOFs, has been carried out for multicomponent reactions (MCRs). The new indium polymeric frameworks, namely [In₈(OH)₆(popha)₆(H₂O)₄]?3 H₂O ( InPF‐16 ), [In(popha)(2,2′‐bipy)]?3 H₂O ( InPF‐17 ), [In₃(OH)₃(popha)₂(4,4′‐bipy)]?4 H₂O ( InPF‐18 ), [In₂(popha)₂(4,4′‐bipy)₂]?3 H₂O ( InPF‐19 ), [In(OH)(Hpopha)]?0.5 (1,7‐phen) ( InPF‐20 ), and [In(popha)(1,10‐phen)]?4 H₂O ( InPF‐21 ) (InPF=indium polymeric framework, H₃popha=5‐(4‐carboxy‐2‐nitrophenoxy)isophthalic acid, phen=phenanthroline, bipy=bipyridine), have been hydrothermally obtained by using both conventional heating (CH) and microwave (MW) procedures. These indium frameworks show efficient Lewis acid behavior for the solvent‐free cyanosilylation of carbonyl compounds, the one pot Passerini 3‐component (P‐3CR) and the Ugi 4‐component (U‐4CR) reactions. In addition, InPF‐17 was found to be a highly reactive, recyclable, and environmentally benign catalyst, which allows the efficient synthesis of α‐aminoacyl amides. The relationship between the Lewis base/acid active site and the catalytic performance is explained by the 2D seven‐coordinated indium framework of the catalyst InPF‐17 . This study is an attempt to highlight the main structural and synthetic factors that have to be taken into account when planning a new, effective MOF‐based heterogeneous catalyst for multicomponent reactions.     

Tetragonal allotrope of group 14 elements

Group 14 elements (C, Si, and Ge) exist as various stable and metastable allotropes, some of which have been widely applied in industry. The discovery of new allotropes of these elements has long attracted considerable attention; however, the search is far from complete. Here we computationally discovered a tetragonal allotrope (12 atoms/cell, named T12) commonly found in C, Si, and Ge through a particle swarm structural search. The T12 structure employs sp(3) bonding and contains extended helical six-membered rings interconnected by pairs of five- and seven-membered rings. This arrangement results in favorable thermodynamic conditions compared with most other experimentally or theoretically known sp(3) species of group 14 elements. The T12 polymorph naturally accounts for the experimental d spacings and Raman spectra of synthesized metastable Ge and Si-XIII phases with long-puzzling unknown structures, respectively. We rationalized an alternative experimental route for the synthesis of the T12 phase via decompression from the high-pressure Si- or Ge-II phase.     

立方形貌ITO粉体的水热法制备及光电性能

以金属In和SnCl_4·5H_2O为原料,采用水热法在120~140℃得到In(OH)_3前驱体,该前驱体在550℃下煅烧得到立方体形貌的氧化铟锡粉体.研究了水热反应温度和反应时间对粉体形貌和晶型的影响.通过热分析仪(TG-DSC)、X射线衍射仪(XRD)、拉曼光谱仪(Raman)、透射电子显微镜(TEM)、四探针电阻仪、X射线光电子能谱仪(XPS)、紫外-可见-近红外分光光度计以及荧光光谱仪对粉体进行了表征,并对水热反应条件为140℃及12 h下制备的c-ITO的光电性能进行了分析.结果表明,随着水热反应温度的升高,ITO粉体形貌由立方体向不规则形貌转变,粉体晶型出现少量的六方相.在水热反应条件为140℃,12 h,铟离子与尿素的摩尔比为1∶5时,得到平均粒径为230 nm的立方体ITO粉体,其电阻率为1.247Ω·cm,光学能带间隙为3.685 e V,与c-In2O3相比其能带间隙更高,室温下260 nm激发波长下粉体出现光致发光,发射峰位于蓝光区域.     

High-pressure synthesis and structural behavior of sodium orthonitrate Na3NO4

Sodium orthonitrate (Na₃NO₄) is an unusual phase containing the first example of isolated tetrahedrally bonded NO₄³⁻ groups. This compound was obtained originally by heating together mixtures of Na₂O and NaNO₃ for periods extending up to >14 days in evacuated chambers. Considering the negative volume change between reactants and products, it was inferred that a high-pressure synthesis route might favor the formation of the Na₃NO₄ compound. We found that the recovered sample is likely to be a high-pressure polymorph, containing NO₄³⁻ groups as evidenced by Raman spectroscopy. The high-pressure behavior of Na₃NO₄ was studied using Raman spectroscopy and synchrotron X-ray diffraction in a diamond anvil cell above 60 GPa. We found no evidence for major structural transformations, even following laser heating experiments carried out at high pressure, although broadening of the Raman peaks could indicate the onset of disordering at higher pressure.     

A First‐Principles Study on the Electronic,Vibrational, and Thermodynamic Properties of Jadeite and its Tentative Low‐Density Polymorph

The high‐pressure clinopyroxene mineral jadeite (chemical composition NaAlSi₂O₆) was studied by density‐functional theory with respect to its electronic, vibrational, and thermodynamic properties, correctly reproducing the available experimental data. At a larger‐than‐normal volume, however, a low‐density alumosilicate phase with tetrahedral instead of octahedral Al–O coordination was identified. This low‐density phase was investigated theoretically, too, and the results were compared to jadeite and experimentally observed properties of what has been dubbed jadeite glass. It turned out that the theoretically obtained properties of this hypothetical polymorph, such as the bulk modulus, the molar volume and the vibrational frequencies, agree well with the corresponding properties of the glass phase. Hence, from an inverse structure‐property relationship we propose to model jadeite glass with the aforementioned low‐density alumosilicate phase and tetrahedral Al–O motifs, as suggested from first principles and corroborated from experiment. The possibilities as well as the limitations of electronic, phonon and thermodynamic properties calculations applied to such a polymorph are also discussed.     

Microwave synthesis of hybrid inorganic-organic porous materials: phase-selective and rapid crystallization

Microwave synthesis of two porous nickel glutarates was compared with conventional hydrothermal synthesis. The cubic nickel glutarate, [Ni20(C5H6O4)20(H2O)8] x 40 H2O (1), was synthesized by conventional electrical heating in several hours or days, depending on synthesis temperature. Crystallization was greatly accelerated by microwave irradiation, in which more stable, tetragonal nickel glutarate, [Ni22(C5H6O4)20(OH)4(H2O)10] x 38 H2O (2), was formed within a few minutes, suggesting the efficiency of the microwave technique in the synthesis of porous hybrid materials. The cubic phase 1 is formed preferentially at low pH, low temperature, and especially under conventional electrical heating. In contrast, the tetragonal phase 2 is obtained favorably at high pH, high temperature, and especially with microwave irradiation. This work demonstrates that the microwave method provides not only the very fast synthesis of a hybrid material, but also the possibility to discover a new porous hybrid material not yet identified by conventional hydrothermal synthesis. The hydrothermal formation of metal-organic hybrid materials in a matter of minutes is an important step towards developing commercially viable routes for producing this valuable class of materials.     

Use of the ternary phase diagram of a mixed cationic/glucopyranoside surfactant system to predict mesostructured silica synthesis

Mixed surfactant systems have the potential to impart controlled combinations of functionality and pore structure to mesoporous metal oxides. Here, we combine a functional glucopyranoside surfactant with a cationic surfactant that readily forms liquid crystalline mesophases. The phase diagram for the ternary system CTAB/H(2)O/n-octyl-beta-D-glucopyranoside (C(8)G(1)) at 50 degrees C is measured using polarized optical microscopy. At this temperature, the binary C(8)G(1)/H(2)O system forms disordered micellar solutions up to 72 wt% C(8)G(1), and there is no hexagonal phase. With the addition of CTAB, we identify a large area of hexagonal phase, as well as cubic, lamellar and solid surfactant phases. The ternary phase diagram is used to predict the synthesis of thick mesoporous silica films via a direct liquid crystal templating technique. By changing the relative concentration of mixed surfactants as well as inorganic precursor species, surfactant/silica mesostructured thick films can be synthesized with variable glucopyranoside content, and with 2D hexagonal, cubic and lamellar structures. The domains over which different mesophases are prepared correspond well with those of the ternary phase diagram if the hydrophilic inorganic species is assumed to act as an equivalent volume of water.     

Analysis and stability of polymorphs in tablets: The case of Risperidone

Identification of the crystal phase of an active pharmaceutical ingredient (API) in a pharmaceutical tablet is of outmost importance since different polymorphs exhibit different physicochemical properties. Furthermore, some of the crystal phases are protected by patents. Identification of Risperidone polymorph A in film coated commercial tablets was attempted using IR spectroscopy, Raman spectroscopy and X-ray powder diffraction (XRPD). The stability of this polymorph through time and during the manufacturing process was also examined. The inability of IR and Raman techniques to identify the presence of polymorph A in the tablets, despite their lower detection limits for Risperidone, left the XRPD as the only technique that could be used for identifying the presence of Risperidone A against the other crystal phases in the presence of the excipients. Polymorph A was proved to be stable during the manufacturing process and after a storage period of 2 years.     

Pressure-induced first-order phase transition in (NH4)2V3O8 fresnoite: a double coordination change for V4+ and V5+

The high-pressure behaviour of (NH(4))(2)V(3)O(8) with the fresnoite structure (P4bm, Z = 2) has been studied at room temperature with single-crystal X-ray diffraction in diamond anvil cells using laboratory and synchrotron facilities. At ambient conditions, the crystal structure is composed of layers of corner-sharing V(5+)O(4) tetrahedra and V(4+)O(5) square pyramids separated by layers of the NH(4)(+) cations. At about 3 GPa, there occurs a reversible first-order phase transition to a three-dimensional structure (P4/mbm, Z = 2) built of corner-sharing V(5+)O(5) trigonal bipyramids and V(4+)O(6) octahedra. The NH(4)(+) cations fill up the interstitial sites in the tunnels formed by the vanadate framework. Up to the phase transition, the a lattice parameter of the low-pressure polymorph does not change while the contraction perpendicular to the stacking of the V(3)O(8) slabs accounts entirely for the bulk compressibility. Above the phase transition, the a lattice parameter slightly expands. The structural features of the high-pressure phase of (NH(4))(2)V(3)O(8) are compared to those of other vanadium oxides.     

Phase behaviour of the discotic mesogen 5,10,15,20-tetrakis (4-n-dodecylphenyl)porphyrin under pressure

The phase behaviour of the discotic mesogen 5,10,15,20-tetrakis(4-n -dodecylphenyl)porphyrin (C12TPP) was investigated under hydrostatic pressures up to 300MPa by high pressure DTA and wide angle X-ray diffraction methods. The typical enantiotropic phase transitions of C12TPP, low- to high-temperature crystal (Cr2-Cr1), Cr1-discotic lamellar phase (DL), and DL-isotropic liquid (I) are observed at pressures up to 10MPa. Application of hydrostatic pressure to the sample generates a pressure-induced crystal polymorph (Cr3) between the Cr2 and Cr1 phases, and the phase transitions Cr2-Cr3-Cr1-DL-I occur reversibly in the pressure region between 10 and 180MPa. On heating at higher pressures above 180MPa, the fourth crystal polymorph (Cr4) is formed between the Cr2 and Cr3 phases at lower temperatures, and at the same time the fifth crystal polymorph (Cr5) appears abruptly between the Cr1 and DL phases at high temperatures. The Cr2-Cr4-Cr3-C1-(Cr5)-DL-I transition processes were observed at 180 200MPa. Further increasing the pressure above 270MPa induces entirely different thermal behaviour: only two peaks for the pressure-induced transition between the sixth and fifth polymorphs (Cr6-Cr5) and the Cr5-I transitions are detected at low and high temperatures on heating, while both the DTA and WAXD experiments on cooling show the formation of the DL phase as a monotropic phase between the I and Cr5 phases, indicating the I DL Cr5 Cr6 process. The thermal behaviour was ambiguous and complex in the pressure region between 200 and 260MPa because the peaks for the intermediate crystal transitions were too small to detect with confidence. The two different sequences of the Cr2-Cr4-Cr3-Cr1-DL-I and Cr6-Cr5-(DL)-I processes seems to occur competitively. The T vs. P phase diagram of a sample cooled at 300MPa was studied to determine the triple point of the DL phase and to investigate the phase stability of the pressure-induced crystal polymorphs. The Cr6-Cr5-I transition process was observed on heating at 200 and 300MPa, while the Cr6-Cr5-DL-I process was detected at lower pressures below 100MPa. Since the Cr5-DL transition temperature changes linearly with a slope dT/dP 40 degrees C/100 MPa, while the DL-I transition temperature changes slightly (dT/dP 5.5 degrees C/100MPa), the DL phase forms a triangle in the T vs. P diagram. The triple point of the DL phase was found to be 240.8MPa and 168.8 C. The Cr6 polymorph reorganized to the stable Cr2 form under atmospheric pressure on annealing at room temperature overnight.     

From the two-component system CBrCl3+CBr4 to the high-pressure properties of CBr4

The experimental phase diagram of the CBrCl3+CBr4 system has been determined by means of X-ray powder diffraction and thermal analysis techniques from 200 K to the liquid state. Before melting, the two components have the same orientationally disordered (OD) face-centered cubic phase, and solid-liquid equilibrium is explained by simple isomorphism. The application of multiple crossed isopolymorphism formalism to the low-temperature solid-solid equilibria has enabled the inference of an OD rhombohedral metastable (at normal pressure) phase for CBr4. Experimental determination of the pressure-volume-temperature and construction of the pressure-temperature phase diagrams for CBr4 reveal the existence of a high-pressure phase, the rhombohedral symmetry of which is inferred by means of the thermodynamic assessment of the experimental phase diagram and demonstrated by means of high-pressure neutron diffraction measurements. The procedure used in this work confirms the connection between the appearance of metastable phases at normal pressure and their existence at high-pressure.     

Phase behaviour of the discotic mesogen 5,10,15,20-tetrakis (4-n-dodecylphenyl)porphyrin under pressure

The phase behaviour of the discotic mesogen 5,10,15,20-tetrakis(4-n -dodecylphenyl)porphyrin (C12TPP) was investigated under hydrostatic pressures up to 300MPa by high pressure DTA and wide angle X-ray diffraction methods. The typical enantiotropic phase transitions of C12TPP, low- to high-temperature crystal (Cr2-Cr1), Cr1-discotic lamellar phase (DL), and DL-isotropic liquid (I) are observed at pressures up to 10MPa. Application of hydrostatic pressure to the sample generates a pressure-induced crystal polymorph (Cr3) between the Cr2 and Cr1 phases, and the phase transitions Cr2-Cr3-Cr1-DL-I occur reversibly in the pressure region between 10 and 180MPa. On heating at higher pressures above 180MPa, the fourth crystal polymorph (Cr4) is formed between the Cr2 and Cr3 phases at lower temperatures, and at the same time the fifth crystal polymorph (Cr5) appears abruptly between the Cr1 and DL phases at high temperatures. The Cr2-Cr4-Cr3-C1-(Cr5)-DL-I transition processes were observed at 180 200MPa. Further increasing the pressure above 270MPa induces entirely different thermal behaviour: only two peaks for the pressure-induced transition between the sixth and fifth polymorphs (Cr6-Cr5) and the Cr5-I transitions are detected at low and high temperatures on heating, while both the DTA and WAXD experiments on cooling show the formation of the DL phase as a monotropic phase between the I and Cr5 phases, indicating the I DL Cr5 Cr6 process. The thermal behaviour was ambiguous and complex in the pressure region between 200 and 260MPa because the peaks for the intermediate crystal transitions were too small to detect with confidence. The two different sequences of the Cr2-Cr4-Cr3-Cr1-DL-I and Cr6-Cr5-(DL)-I processes seems to occur competitively. The T vs. P phase diagram of a sample cooled at 300MPa was studied to determine the triple point of the DL phase and to investigate the phase stability of the pressure-induced crystal polymorphs. The Cr6-Cr5-I transition process was observed on heating at 200 and 300MPa, while the Cr6-Cr5-DL-I process was detected at lower pressures below 100MPa. Since the Cr5-DL transition temperature changes linearly with a slope dT/dP 40 degrees C/100 MPa, while the DL-I transition temperature changes slightly (dT/dP 5.5 degrees C/100MPa), the DL phase forms a triangle in the T vs. P diagram. The triple point of the DL phase was found to be 240.8MPa and 168.8 C. The Cr6 polymorph reorganized to the stable Cr2 form under atmospheric pressure on annealing at room temperature overnight.     

A new polymorph of FeAlO3 at high pressure

Synchrotron X-ray diffraction measurements confirmed that a new polymorph of FeAlO3 could be synthesized at about 1800 K and 72 GPa. This phase can be indexed on an orthorhombic cell and transforms into the trigonal form on release of pressure. The c/a ratio of about 2.71 of the trigonal phase suggests corundum structure of FeAlO3 rather than LiNbO3 or ilmenite structure. This conclusion also suggests that the high-pressure orthorhombic phase could be the Rh2O3(II) structure rather than the GdFeO3-type perovskite structure.