Effect of Impurity Cations on the Growth and Habits of SnO2 Crystals in the SnO2-Cu2O Flux System

The effects of a small amount of cations with valence states ranging from mono- to hexavalent on the growth and habits of SnO₂ crystals growing in the SnO₂-Cu₂O flux system were systematically investigated. Trivalent cations having ionic radii closer to that of Sn⁴⁺ had a conspicuous effect upon the size and habits of SnO₂. Pentavalent cations with ionic radii similar to those of Sn⁴⁺ had some effect, whereas cations of other valence states showed no effect at all.     

Microstructural Development in SnO2-Doped ZnO–Bi2O3 Ceramics

The effects of adding small quantities of SnO₂ to the basic ZnO–Bi₂O₃ varistor composition were studied in terms of phase reactions, microstructural development, and the formation of inversion boundaries. Scanning and transmission electron microscopy studies showed that the inversion boundaries, triggered by the addition of SnO₂, cause anisotropic grain growth in the early stages of sintering. ZnO grains that include inversion boundaries grow exaggeratedly, at the expense of normal grains, until they dominate the microstructure. Higher additions of SnO₂ lead to an increase in number of grains with inversion boundaries and to a more fine-grained microstructure. The increasing amount of secondary phases is also related to a higher level of SnO₂ addition; however, the influence of these phases on ZnO grain growth is subordinate to the role of inversion boundaries.     

Solid Solubility of GeO2 in SnO2

Subsolidus equilibrium relations were reexamined in the SnO₂-rich portion of the system GeO₂-SnO₂ (60 to 98 mol% SnO₂). A limited solid solution based on SnO₂ was confirmed; 4mol% GeO₂ dissolved in SnO₂ at 1250 C, and glass was formed on quenching over the compositional range above 4mol% GeO₂. Phase relutions in the system are discussed with reference to the polymorphism of GeO₂ and its glass-forming ability, and a possible phase diagram is given .     

Sol–Gel Processing and Characterization of Pure and Metal-Doped SnO2 Thin Films

A chloride-based inorganic sol–gel route was used for preparing pure and metal (osmium, nickel, palladium, platinum)-doped SnO₂ sol. SnCl₄ was first reacted with propanol, then the resulting compound was hydrolyzed and subsequently mixed with solutions of the metal dopants. The obtained sols were used for depositing thin films by spin coating or for preparing powders by solvent evaporation at 110°C. FTIR spectroscopy and thermal analysis of the powders revealed that chlorine still bound to tin stabilized the sol against gelation by hindering the condensation reactions. Film characterizations showed that platinum and palladium, unlike nickel and osmium, were likely to form nanoparticles in the SnO₂ lattice. This result was discussed with regard to the different ways that platinum and palladium, on one hand, and nickel and osmium, on the other, modified the growth of SnO₂ grains and the film roughness and morphology. Dopants that formed nanoparticles (platinum, palladium) resulted in the roughest film, while dopants that did not form particles (nickel, osmium) resulted in SnO₂ grain size very close to that of pure SnO₂.     

Knoop Microhardness Anisotropy of Single-Crystal Cassiterite (SnO2)

The Knoop microhardness anisotropy of single-crystal cassiterite (SnO₂) was measured on the (100), (110), (001), and (111). That anisotropy is depicted as the microhardness profiles for those planes. The results are addressed first in terms of the elastic anisotropy of SnO₂ and then on the basis of the effective resolved shear stress (ERSS), the latter an approach initially advanced by Brookes and co-workers. The load dependence of the Knoop microhardness is also evaluated in terms of the classical Meyer's law for which it is demonstrated that the Meyer's law coefficient and Meyer's law exponent are related.     

Atomistic Simulation of the Surface Energy of Spinel MgAl2O4

Atomistic simulations with atomic potentials including anion polarizibility have been performed for the low-index surfaces of spinel MgAl₂O₄ with various terminations. The calculations show that for the most stable surface the surface energy is 2.27 J/m² for the {100}, about 2.85 J/m² for the {110}, and 3.07 J/m² for the {111} orientation. The ratio between the experimental values to the calculated relaxed surface energies is about 1.5. Strong surface relaxation was found for the {110} and {111} orientation but only moderate surface relaxation for the {100} surface.     

Computer Simulation of Dissociative Adsorption of Water on the Surfaces of Spinel MgAl2O4

Atomistic simulation techniques have been used to model the dissociative adsorption of water onto the low-index {100}, {110}, and {111} surfaces of spinel MgAl₂O₄. The Born model of solids and the shell model for oxygen polarization have been used. The resulting structures and chemical bonding on the clean and hydrated surfaces are described. The calculations show that the dissociative adsorption of water on the low-index surfaces is generally energetically favorable. For the {110} and {111} orientations, the surfaces cleaved between oxygen layers show high absorption and stability. The calculations also show that, for the {111} orientation, the surfaces may absorb chemically water molecules up to ∼90% coverage and have the highest stability. It is suggested that, during fracture, only partial hydration occurs, leading to cleavage preferentially along the {100} orientation.     

Habit Modification of Corundum Crystals Grown from Molten PbF2-Bi2O3

Single crystals of corundum and ruby were grown from PbF₂-Bi₂O₃ melts. Their habits and the use of La₂O₃ as a growth modifier are described. Lanthanum ions were incorporated into the growing crystals to promote the growth of equidimensional crystals. The habit modifications are interpreted as resulting from impurity adsorption on the steps on the {1011} faces and direct adsorption on the {0112} faces. The crystals grown from these melts are of good optical quality and contain few dislocations.     

Structural Studies of Ordering in the (Pb1-xBax)(Mg1/3Nb2/3)O3 Crystalline Solution Series

The ordered structures of the (Pb_{1- x} Ba _x )(Mg_1/3Nb_2/3)O₃crystalline solution series were investigated by selected area electron diffraction (SAED) and high-resolution electron microscopy (HREM). At low Ba contents (e.g., x < 0.40), the ordered structure was found to be isostructural with Pb(Mg_1/3Nb_2/3)O₃, with a doubled unit cell characterized by 1/3{111} superlattice reflections. At higher Ba contents (e.g., x > 0.60), the ordered structure was characterized by 1/3{111} superlattice reflections. For intermediate Ba contents (e.g., x - 0.60), diffuse scattering along the {111} between diffuse 1/2{111} and 1/3{111} reflections was observed. The ordering is attributed to the distribution of the B-site cations between multiple sublattices. Strong fluctuations in the B-site cation ratio between ordered and disordered regions are believed not to exist; however, the possibility of weak fluctuations is consistent with the observed lattice images.     

Effect of Neutron Irradiation on Knoop Microhardness Anisotropy in MgO·3Al2O3 Single Crystals

MgO·3Al₂O₃ single crystals were irradiated with neutron fluences of 8.3 × 10²² n/m² at 100°C and 2.4 × 10²⁴ n/m² at 470°C ( E > 1.0 MeV) in the Japan Materials Testing Reactor. The Knoop microhardness of several orientations on the (100) plane of both the irradiated and unirradiated crystals were measured with different indentation loads. The change in hardness profile of the crystals was almost the same after the two irradiation conditions. The hardness increased by 4–15% because of the irradiations depending on the crystallographic orientation, the larger change being observed at orientations between the (001) and (011) directions. While both the {111}     and {110}     slip systems are simultaneously active in the unirradiated MgO·3Al₂O₃, the {111}     system may be the dominant slip system in the neutron-irradiated crystals. It is concluded that the restriction of the {110}     slip system is caused by irradiation-induced interstitial ions.     

(Pr, Co, Nb)-Doped SnO2 Varistor Ceramics

The effect on microstructure and electrical properties of (Co, Nb)-doped SnO₂ varistors upon the addition of Pr₂O₃ was investigated by scanning electron microscopy and by determining I – V , ɛ– f , and R – f relations. The threshold electric field of the SnO₂-based varistors increased significantly from 850 to 2280 V/mm, and the relative dielectric constants of the SnO₂-based varistors decreased greatly from 784 to 280 as Pr₂O₃ concentration was increased up to 0.3 mol%. The significant decrease of the SnO₂ grain size, from 4.50 to 1.76 μm with increasing Pr₂O₃ concentration over the range of 0–0.3 mol%, is the origin for the increase in the threshold voltage and decrease of the dielectric constants. The grain size reduction is attributed to the segregation of Pr₂O₃ at grain boundaries hindering the SnO₂ grains from conglomerating into large particles. Varistors were found to have a superhigh threshold voltage and a comparatively large nonlinear coefficient α. For 0.15 mol% Pr₂O₃-doped sample, threshold electric field and nonlinear coefficient α were measured to be 1540 V/mm and 61, and for 0.3 mol% Pr₂O₃-doped sample, V and α were 2150 V/mm and 42, respectively. Superhigh threshold voltage and large nonlinear coefficient α qualify the Pr-doped SnO₂ varistor as an excellent candidate for a high voltage protection system.     

Compositional Dependence of Microwave Dielectric Properties in (1 −x)(Na1/2Nd1/2)TiO3−xNd(Mg1/2Ti1/2)O3 Ceramics

The compositional dependence of microwave dielectric properties has been investigated in the (1 − x )(Na_1/2Nd_1/2)TiO₃− x Nd(Mg_1/2Ti_1/2)O₃ (NNT-NMT) system. The addition of NMT results in significant improvement in the quality factor and the temperature coefficient of frequency, but gradually decreases the dielectric constant from ∼100 for pure NNT to ∼25 for pure NMT. The single perovskite phase is observed with various { hkl } superlattice reflections over the entire compositional range. The increasing tendency of peak splitting with increasing x at some perovskite reflections strongly suggests that the crystal structure of the system changes to lower symmetry structures. This is confirmed using infrared reflectivity spectra. The superlattice reflections related to structural deviation become more predominant as the composition reaches pure NMT. Particularly, {111} superlattice reflections are believed to be associated with the 1:1 cation ordering and responsible for the observed abrupt increase in quality factor at x > 0.7.     

Hot Isostatic Pressing of Reactive SnO2 Powder

Tin(IV) oxide (SnO₂) crystallizes at room temperature by adding hydrazine monohydrate ((NH₂)₂· H₂O) to a hydrochloric acid solution of tin, followed by washing and drying. Well-densified SnO₂ ceramics (99.8% of theoretical) with an average grain size of 0.9 μm have been fabricated by hot isostatic pressing for 2 h at 900°C and 196 MPa. Their Vickers hardness and bending strength are 14.4 GPa and 200 MPa, respectively. They exhibit an electrical conductivity of 2 × 10⁻³−9 × 10⁻³ S·cm⁻¹ at room temperature.     

A Comparative Study of Thermal Conductivity in ZnO- and SnO2-Based Varistor Systems

We performed a comparative study of electrical and thermal properties of ZnO- and SnO₂-based varistor. The electrical properties of commercial ZnO-based varistor are equivalent to that found in SnO₂-based varistor system. In spite of this, the SnO₂ showed a thermal conductivity higher than commercial samples of ZnO-based varistor, which allied with its simpler microstructure and lower dopant concentration is a remarkable result that point out to the use of this system to compete commercially with ZnO-based varistor devices.     

A Rapidly Responding Sensor for Methanol Based on Electrospun In2O3–SnO2 Nanofibers

In this paper, we presented a simple and effective electrospinning technique for the preparation of In₂O₃–SnO₂ composite nanofibers. The morphology and chemical structure of the as-prepared samples were analyzed by scanning electron microscopy, transmission electron microscopy, and X-ray diffraction. The results showed that large quantities of In₂O₃–SnO₂ composite nanofibers with diameters from 60 to 100 nm were obtained. The In₂O₃–SnO₂ composite nanofibers exhibited excellent gas sensing properties to methanol, such as fast response/recovery properties, high sensitivity, and good selectivity.     

Low-Temperature Preparation and Magnetic Properties of V-Doped SnO2 Nanoparticles

A solid solution of vanadium (V)-doped tin oxide (SnO₂) particles of average diameter 2 nm and V content of 19 at.% was prepared at normal pressure and low temperature (100°C) by mixing wet SnO₂ gel SnO₂· x H₂O with a boiling solution of vanadium oxide (V₂O₅). Experimental characterizations using X-ray, electron diffraction, and transmission electron microscope show evidence of a pure single phase. The nanoparticles exhibit a mixed magnetic behavior, namely paramagnetic and ferromagnetic. Their thermal stability is also investigated. At higher temperature, 850°C, some amount of Fe precipitates from the solid solution.     

Electrical Conductivity of Heat-Treated SnO2 Films

Variations in electrical conduction which were caused by heat treatment of SnO₂ films vapor-deposited on glass were studied. In the range 20° to 230°C, the relative importance of semiconduction processes attributed to 3 types of donors (probably O vacancies, interstitial Sn ions, and Cl ions) was determined as a function of heat treatment. A decrease in conductivity at constant temperature above 230°C was ascribed to grain growth of the SnO₂ crystals deposited initially.     

Knoop Microhardness Anisotropy of Single-Crystal Stoichiometric MgAl2O4 Spinel

Microhardness anisotropy profiles for the (100) and (111) planes of single-crystal stoichiometric MgAl₂O., spinel were determined at room temperaturé. The (100) microhardness profile has ahardness maximum in tiie [001] and a minimum in the [O11], which supports the previous suggestion that the primary slip system is the {111}〈11¯0〉. The microhardness of the (111) plane is independent of indenter orientation, also consistent, with a {111}〈11¯0〉 primary slip system. It is concluded that these microhardness profiles are in accord with other experimental observations that the {111}〈11¯0〉 is the primary slip system in stoichiometric MgAl₂O₄ spinel.     

Growth Sequence of Gadolinium-Iron Garnet Crystals in Molten PbO-B2O3, Solutions

Gadolinium-iron garnet crystals grown from low-volatility molten PbO-B₂O₃ solutions exhibit macroscopic dendritic growth patterns indicative of their growth sequence and mechanism. There exists a growth anisotropy preferring the [001] direction from which (100) and (010) axial-plane dendrites radiate. The equilibrium {211} and {110} faces grow from intermediate branch dendrites which are attached to the (100) and (010) dendrites.     

Preparation of Necklace-Structured TiO2/SnO2 Hybrid Nanofibers and Their Photocatalytic Activity

TiO₂/SnO₂ nanonecklace-structured hybrid nanofibers have been prepared via an electrospinning method. These hybrid nanofibers are characterized with SnO₂-rich beads and pure TiO₂ chains. It is found that TiO₂ in the beads shows a rutile structure, and the one in the chains is entirely composed of anatase phase. This novel microstructure enhanced the photocatalytic activity, as well as its ideal recyclable character. We believe that this fire-new type of nanofiber may potentially serve as a new generation photocatalyst in environmental remediation.