Electrical properties of In2O3

Conductivity data for In₂O₃ both from literature and from new measurements are critically compared. They are correlated with atmospheric conditions and temperature. The conductivity data and structural considerations lead to the conclusion that non-stoichiometric In₂O₃ is an n-type semiconductor. Interstitial indium ions are probably the predominant defects.     

The thermoelectric power in In2O3

The n-type semiconductivity of In₂O₃ is confirmed by the sign of the Seebeck coefficient. From a comparison of Hall and Seebeck data a value of 0.14 m_o is deduced for the density-of-states effective mass. The incorporation of divalent cations results in a higher absolute value of the Seebeck coefficient, which is reflected in the lower charge carrier concentration, in accordance qualitatively with the defect model for In₂O₃.     

Electrochemistry of solid-phase reactions: Phase formation in the In2O3-WO3 system. Processes at the WO3|In2O3 and WO3|In6WO12 interfaces

Reactions of interactions at the WO₃|In₂O₃ and WO₃|In₆WO₁₂ heterophase reaction interfaces, whose main product is In₂(WO₄)₃, are studied by electrochemical methods for the first time ever. Due to a far greater n type conductance inherent in the initial substances, the reactions are a model object for the development of methodology of the electrochemical approach. Both reactions are discovered to proceed at the expense of the transport of components of WO₃ and no evidence is discovered for the contribution of In³⁺ into diffusion and migration. Consisted data are obtained between the polarity of a spontaneously generated reaction difference of potentials and the direction of the field that accelerates the reaction: the current that is passed through electrochemical cells accelerates the reactions exclusively at the (−)-potential of a brick of WO₃. A difference is discovered between the charge and mass transport paths—spontaneous and field-induced mass transport of WO₃ or its components occurs via heterophase interfaces and adjacent areas and does not touch upon the In₂(WO₄)₃ grains. Shown is the antibatic character of the behavior exhibited by dependences of identical properties of cells (potential drop across a cell) following a change in the dc polarity. A possible role of a reactionless electrosurface transport of WO₃ in the mechanism of reaction and evolution of electrochemical properties of model electrochemical cells is demonstrated. The obtained data may or may not testify in favor of a hypothesis that presumes a prevailing role of the {WO₄}²⁻ mobility in the In₂(WO₄)₃ structure. Original Russian Text ? A.Ya. Neiman, T.E. Kulikova, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 6, pp. 714–726. Based on the report delivered at the 8th International Meeting on Fundamental Problems of Solid-State Ionics, Chernogolovka (Russia), 2006.     

The high temperature behavior of In2O3

The electrical conductivity of In₂O₃ has been measured up to 1400°C in air. The temperature dependence of the conductivity at high temperatures yields an activation energy of 1.5 ± 0.1 eV. This activation energy is interpreted in terms of a nonstoichiometric decomposition of the compound. This interpretation is sustained by thermogravimetric analysis in combination with a gas mass analyser. Hall experiments on quenched samples are not in contradiction with this interpretation.     

Structural changes resulting from doping Ti2O3 with Sc2O3 or Al2O3

The crystal structures of (Ti_1?xSc_x)₂O₃, x = 0.0038, 0.0109, and 0.0413, and of (Ti_0.99Al_0.01)₂O₃, have been determined from X-ray diffraction data collected from single crystals using an automated diffractometer, and have been refined to weighted residuals of 25–34. Cell constants have also been determined for x = 0.0005, 0.0019, and 0.0232. The compounds are rhombohedral, space group $\text{R}\text{3}\text{c}$, and are isomorphous with α-Al₂O₃. The hexagonal cell dimensions range from a = 5.1573(2)Å, c = 13.613(1)Å for (Ti_0.9995Sc_0.0005)₂O₃ to a = 5.1659(4)Å, c = 13.644(1)Å for (Ti_0.9587Sc_0.0413)₂O₃, and a = 5.1526(2)Å, c = 13.609(1)Å for (Ti_0.99Al_0.01)₂O₃. Sc and Al substitution cause similar increases in the short near-neighbor metal-metal distance across the shared octahedral face; for Sc doping the increase is from 2.578(1) Å in pure Ti₂O₃ to 2.597(1) Å in (Ti_0.9587Sc_0.0413)₂O₃. By contrast, changes in the metal-metal distance across the shared octahedral edge appear to be governed by ionic size effects. The distance increases from 2.994(1) Å in Ti₂O₃ to 3.000(1) Å in (Ti_0.9587Sc_0.0413)₂O₃ and decreases to 2.991(1) Å in (Ti_0.99Al_0.01)₂O₃.     

Sol-gel preparation of In2O3-Al2O3 supports with controlled textural and structural properties

Alumina supports with a very narrow pore size distribution were obtained with indium-doped alumina prepared by the sol-gel method. The formation of aluminum in pentahedral coordination was identified by ²⁷Al NMR-MAS-spectroscopy. A good correlation was obtained with the Al^V NMR-MAS intensity signal and the activity in isopropanol dehydration. The insertion of In³⁺ substituting some Al³⁺ in the alumina network was suggested.     

Sm2O3Ga2O3 and Gd2O3Ga2O3 phase diagrams

Four definite compounds exist in the Sm₂O₃Ga₂O₃ binary phase diagram, namely: Sm₃GaO₆, Sm₄Ga₂O₉, SmGaO₃, and Sm₃Ga₅O₁₂. The $\text{3}\text{1}$ compound is orthorhombic (space group Pnna - Z.4) with the cell parameters: a = 11.40₀Å, b = 5.51₅Å, c = 9.07Å and belongs to the oxysel family. Sm₃GaO₆ and SmGaO₃ melt incongruently at 1715 and 1565°C; Sm₄Ga₂O₉ and Sm₃Ga₅O₁₂ have a congruent melting point at 1710 and 1655°C. With regard to the Gd₂O₃Ga₂O₃ system three definite compounds have been identified: Gd₃GaO₆, Gd₄Ga₂O₉, and Gd₃Ga₅O₁₂. Only the garnet melts congruently at 1740°C with the following composition: Gd_3.12Ga_4.88O₁₂. Gd₃GaO₆, and Gd₄Ga₂O₉ melt incongruently at 1760 and 1700°C. GdGaO₃ is only obtained by melt overheating which may yield an equilibrium or a metastable phase diagram.     

可分散的In_2O_3/Ta_2O_5复合光催化剂的制备及其光催化制氢性能

通过控制乙醇钽的水解速率,在丙酮水溶液中制备了可分散的Ta2O5微球,并以此为载体构建了In2O3/Ta2O5异质结复合光催化剂,利用扫描电子显微镜、X射线能量色散光谱、粉末X射线衍射光谱、透射电子显微镜和紫外-可见漫反射光谱等手段对样品形貌、结构和光吸收性质进行了表征.结果表明,In2O3纳米粒子分布在Ta2O5微球表面,且两相间存在明显的界面,同时In2O3的复合拓宽了Ta2O5的光吸收范围,有利于光生电子与空穴的分离,使复合光催化剂在模拟太阳光照射下表现出更高的光解水制氢活性.     

In2O3八面体的碳还原法制备及其发光性能研究

In₂O₃ octahedrons were synthesized by carbothermal reduction using In₂O₃ nanoparticles as the source material. The as-synthesized products were characterized by X-ray powder diffraction (XRD), energy dispersive X-ray(EDX), scanning electron microscopy(SEM), transmission electron microscopy(TEM), high-resolution transmission electron microscopy (HRTEM), selected-area electron diffraction analysis(SAED) and Room-temperature photoluminescence(PL) spectroscopy. The results show that the products are single-crystalline In₂O₃ octahedrons, the length of the octahedrons is in the range of 400～3 000 nm; the PL patterns display two peaks located at 447nm and 555 nm upon excitation at 380 nm, and the other two peaks located at 444 nm and 550 nm upon excitation at 325 nm; the excitation pattern shows two peaks located at 274 nm and 371 nm, respectively. The growth mechanism of the In₂O₃ octahedrons is discussed, and the high supersaturation ratio is considered as the key factor.     

Garnet-perovskite transformations in the Sm2O3Ga2O3 and Gd2O3Ga2O3 systems

The effect of heating garnet melts to various temperatures has been investigated. The previously reported decomposition of the garnet phase due to loss of Ga₂O₃ was corroborated. However, it was also observed that when gallium oxide loss is prevented and the maximum temperature of the melt exceeds a critical value, phase separation of garnet to perovskite and β-gallium oxide occurs:

$\text{RE}{}_3\text{Ga}{}_5\text{O}{}_{12}\text{?3RE}\text{GaO}{}_3\text{+}\text{Ga}{}_2\text{O}{}_3$

.The reverse reaction will occur by reheating the two-phase mixture to the garnet melting point.     

High-pressure silicate pyrochlores,Sc2Si2O7 and In2Si2O7

The silicate compounds Sc₂Si₂O₇ and In₂Si₂O₇ have been converted from thortveitite type to pyrochlore type at 1000°C, 120 kbar, with resulting cell constants of 9.287(3) and 9.413(3) Å, respectively. Invariant reflection intensities in the X-ray powder diffraction patterns allowed precise absorption corrections to be made, and refinement of thermal parameters and of the single structural parameter x gave values of 0.4313(21) and 0.4272(15), respectively. The corresponding six-coordinate SiO distances were 1.761(7) and 1.800(5) Å, and the average eight-coordinate distances for ScO₈ and InO₈ were 2.267 and 2.275 Å. Values of structure-refined bond lengths for compounds containing six-coordinate silicon are surveyed, and overall weighted average octahedral distances of 1.782(14) Å for SiO and 2.520(18) Å for OO are derived. Pyrochlore phases were not produced from rare-earth disilicate or monosilicate phases subjected to the same reaction conditions as the Sc and In compounds.     

Study on the reactivity of In2O3 in mixtures with ammonium-zeolites

In ground mixtures of In₂O₃ and NH₄Y, incorporation of In⁺ cations into the zeolitic phase occurs upon thermal treatment by partial reductive solid-state ion exchange associated with oxidation of ammonium ions or released ammonia to N₂ and NH₂OH. Cationic InO⁺ species, created in zeolites by reductive solid-state ion exchange of In₂O₃/NH₄-zeolite mixtures in hydrogen atmosphere and subsequent oxidation of the In⁺ lattice cations by oxygen, do not undergo autoreduction up to 970 K. Reductive solid-state ion exchange easily proceeds in carbon monoxide atmosphere at temperatures between 620 and 770 K. The significance of these observations for the use of indium-containing zeolites as catalysts is discussed.     

Mg掺杂In2O3-x催化剂光热催化CO2加氢

为提高光热催化CO₂加氢In₂O₃催化剂的催化活性,采用均相水热法制备Mg (OH)₂-In (OH)₃前驱体,通过高温煅烧和H₂-还原处理得到了富含氧空位的Mg掺杂In₂O_3-x(Mg-In₂O_3-x)催化剂。在300℃、常压、可见光照射条件下,CO₂加氢转化为CO的CO₂转化率可达31.20%,CO产生速率为14.22 mmol·g_cat^-1·h^-1,CO选择性为100%。相比于单一In₂O_3-x催化剂,Mg-In₂O_3-x催化剂光热催化CO₂转化率及CO产生速率明显提高,这归因于Mg成功掺杂到In₂O₃晶格中,促进In₂O₃表面氧空位的形成,进而对可见光响应效率大幅提高,并有效减缓光生电子-空穴的复合。     

Structural modulation in K2V3O8

To elucidate the phase transition at 115 K in the fresnoite-type compound K₂V₃O₈, we undertook temperature-dependent neutron powder diffraction and single-crystal X-ray diffraction (XRD). For structure refinements in the nominal space group P4bm, the most dramatic change is evidenced by the a cell edge, which initially expands on cooling, then abruptly begins to contract at 115 K. The c cell edge contracts monotonically. The atomic displacement parameters (ADPs) also deviate from their expected temperature dependence at 115 K, where the oxygen atoms in the vanadium oxide plane exhibit an increase in apparent positional disorder. Similar changes in lattice parameters and ADPs are observed from the single-crystal XRD refinements. Below 115 K, weak superlattice reflections are clearly evident in XRD patterns recorded by a CCD detector, and these extra reflections can be indexed with the wave vector ±1/3〈110〉*+1/2c*. Possible space groups for the modulated structure are P4₂bc and P4nc.     

Tunneled Intergrowth Structures in the Ga2O3–In2O3–SnO2 System

The structures of several Ga₂O₃–In₂O₃–SnO₂ phases were investigated using high-resolution electron microscopy, X-ray diffraction, and Rietveld analysis of time-of-flight neutron diffraction data. The phases, expressed as Ga_4−4xIn_4xSn_n−4O_2n−2 (n=6 and 7–17, odd), are intergrowths between the β-gallia structure of (Ga,In)₂O₃ and the rutile structure of SnO₂. Samples prepared with n≥9 crystallize in C2/m and are isostructural with intergrowths in the Ga₂O₃–TiO₂ system. Samples prepared with n=6 and n=7 are members of an alternative intergrowth series that crystallizes in P2/m. Both intergrowth series are similar in that their members possess 1-D tunnels along the b axis. The difference between the two series is described in terms of different crystallographic shear plane operations (CSP) on the parent rutile structure.     

Mg掺杂In2O3-x催化剂光热催化CO2加氢

为提高光热催化CO₂加氢催化剂In₂O₃的催化活性,采用均相水热法制备Mg(OH)₂-In(OH)₃前驱体,通过高温煅烧和H₂-还原处理得到了富含氧空位的Mg掺杂In₂O_3-x(Mg-In₂O_3-x)催化剂。在300℃、常压、可见光照射条件下,CO₂加氢转化为CO的CO₂转化率可达31.20%,CO产生速率为14.22 mmol·gcat^-1·h^-1,CO选择性为100%。相比于单一In₂O_3-x催化剂,Mg-In₂O_3-x催化剂光热催化CO₂转化率及CO产生速率明显提高,这归因于Mg成功掺杂到In₂O₃形晶格中,促进In₂O₃表面氧空位的形成,进而对可见光响应效率大幅提高,并有效减缓光生电子-空穴的复合。     

Phase formation, crystal chemistry, and properties in the system Bi2O3-Fe2O3-Nb2O5

Subsolidus phase relations have been determined for the Bi₂O₃-Fe₂O₃-Nb₂O₅ system in air (900-1075 °C). Three new ternary phases were observed—Bi₃Fe_0.5Nb_1.5O₉ with an Aurivillius-type structure, and two phases with approximate stoichiometries Bi₁₇Fe₂Nb₃₁O₁₀₆ and Bi₁₇Fe₃Nb₃₀O₁₀₅ that appear to be structurally related to Bi₈Nb₁₈O₅₇. The fourth ternary phase found in this system is pyrochlore (A₂B₂O₆O′), which forms an extensive solid solution region at Bi-deficient stoichiometries (relative to Bi₂FeNbO₇) suggesting that ≈4-15% of the A-sites are occupied by Fe³⁺. X-ray powder diffraction data confirmed that all Bi-Fe-Nb-O pyrochlores form with positional displacements, as found for analogous pyrochlores with Zn, Mn, or Co instead of Fe. A structural refinement of the pyrochlore 0.4400:0.2700:0.2900 Bi₂O₃:Fe₂O₃:Nb₂O₅ using neutron powder diffraction data is reported with the A cations displaced (0.43 Å) to 96g sites and O′ displaced (0.29 Å) to 32e sites (Bi_1.721Fe_0.190(Fe_0.866Nb_1.134)O₇, Fd3¯m (#227), ). This displacive model is somewhat different from that reported for Bi_1.5Zn_0.92Nb_1.5O_6.92, which exhibits twice the concentration of small B-type cations on the A-sites as the Fe system. Bi-Fe-Nb-O pyrochlores exhibited overall paramagnetic behavior with large negative Curie-Weiss temperature intercepts, slight superparamagnetic effects, and depressed observed moments compared to high-spin, spin-only values. The single-phase pyrochlore with composition Bi_1.657Fe_1.092Nb_1.150O₇ exhibited low-temperature dielectric relaxation similar to that observed for Bi_1.5Zn_0.92Nb_1.5O_6.92; at 1 MHz and 200 K the relative permittivity was 125, and above 350 K conductive effects were observed.     

Structural aspects of the metal-insulator transitions in V0.985Al0.015O2

The crystal structure of V_0.985Al_0.015O₂ has been refined from single-crystal X-ray data at four temperatures. At 373°K it has the tetragonal rutile structure. At 323°K, which is below the first metal-insulator transition, it has the monoclinic M₂ structure, where half of the vanadium atoms are paired with alternating short (2.540 Å) and long (3.261 Å) V-V separations. The other half of the vanadium atoms form equally spaced (2.935 Å) zigzag V chains. At 298°K, which is below the second electric and magnetic transition, V_0.985Al_0.015O₂ has the triclinic T structure where both vanadium chains contain V-V bonds, V(1)-V(1) = 2.547 Å and V(2)-V(2) = 2.819 Å. At 173°K the pairing of the V(1) chain remains constant: V(1)-V(1) = 2.545 Å, whereas that of the V(2) chain decreases: V(2)-V(2) = 2.747 Å. From the variation of the lattice parameters as a function of temperature it seems that these two short V-V distances will not become equal at lower temperatures. The effective charges as calculated from the bond strengths at 298 and 173°K show that a cation disproportionation has taken place between these two temperatures. About 20% of the V⁴⁺ cations of the V(1) chains have become V³⁺ and correspondingly 20% of the V⁴⁺ cations of the V(2) chains have become V⁵⁺. This disproportionation process would explain the difference between the two short V-V distances. Also it would explain why the T → M₁ transition does not take at lower temperatures.     

New transparent conductors with the M7O12 ordered oxygen-deficient fluorite structure: from In4Sn3O12 to In5.5Sb1.5O12

A new transparent conductor, containing pentavalent antimony, In_4+xSn_3−2xSb_xO₁₂, has been synthesized for 0?x?1.5. The latter exhibits an ordered oxygen-deficient fluorite structure with an ordered distribution of Sb⁵⁺ and In³⁺/Sn⁴⁺ species in the octahedral and seven-fold coordinated sites, respectively. More importantly, it is shown that the electronic conductivity of this transparent conducting oxide (TCO) at room temperature, is one order of magnitude larger for x=1 (In₅SnSbO₁₂) than for x=0 (In₄Sn₃O₁₂) and it turns to a semi-metallic behavior in contrast to In₄Sn₃O₁₂ which is a semi-conductor. The potential of this new material, as TCO, is also shown by its reflectance spectra, similar to In₄Sn₃O₁₂, involving only a small increase of the optical bandgap, by 0.15 eV.     

Assembly of Pt nanoparticles on electrospun In2O3 nanofibers for H2S detection

In this paper, we presented a simple and effective solution route to deposit Pt nanoparticles on electrospun In₂O₃ nanofibers for H₂S gas detection. The morphology and chemical structure of the as-prepared samples were analyzed by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectra (XPS). The results showed that large quantities of In₂O₃ nanofibers with diameters about from 60 to 100 nm were obtained and the surface of them was decorated with Pt nanoparticles (5–10 nm in size). The In₂O₃ nanofibers decorated by Pt nanoparticles exhibited excellent gas sensing properties to H₂S, such as high sensitivity, good selectivity and fast response at relatively low temperature.