F. M. Spiridonov

On the phase relations and the electrical conductivity in the system ZrO2Sc2O3

Abstract Phase relations in the ZrO2Sc2O3 system have been investigated by the methods of high-temperature X-ray analysis, dilatometry, differential thermal analysis, and electrical conductivity measurements in the composition range 3–40 mol % Sc2O3 and the temperature range 20–2000°C. The phase diagram has been constructed in its subsolidus regions. Existence regions have been refined for three known compounds, Sc2Zr7O17, Sc2Zr5O13, and Sc4Zr3O12, and the region corresponding to high-temperature, cubic, fluorite-type solid solutions has been established. The character of the thermal dependence of the electrical conductivity for the compositions studied agrees with the phase transformations. The maximum value of the electrical conductivity at 1200°C was observed for the composition 7.5–9 mol % Sc2O3. With increasing temperature, in the field of the high-temperature solid solutions, there occurs a broadening of this maximum and a lateral displacement to higher content of scandium oxide.

Effect of oxygen partial pressure on SnO2 whisker growth

Tin dioxide whiskers have been grown from SnO vapor in a tube furnace in a flowing mixture of argon and oxygen at a constant source temperature, and the effect of oxygen concentration in the carrier gas on the morphology, structure, and phase composition of the whiskers has been studied. The whiskers are about 100 μm in length and are well crystallized. Single-phase, single-crystal SnO2 whiskers can only be obtained in a narrow range of oxygen concentrations.

Vapor growth of SnO2 whiskers

Tin dioxide whiskers have been prepared by vapor growth in a tube furnace in flowing argon at a constant evaporation temperature, and the effect of carrier-gas flow rate during growth on their morphology, phase composition, and IR spectrum has been studied. The whiskers are more than 0.5 mm in length and are well crystallized. Reducing the flow rate of the carrier gas during whisker growth makes it possible to reduce the fraction of phases containing tin in lower oxidation states and favors preferential whisker growth along the c axis.

On the structure and dehydration of hydrous zirconia and hafnia xerogels

Hydrous zirconia and hafnia xerogels of compositions ZrO2 · 2.5H2O and HfO2 · 2.3H2O are dehydrated in two steps upon heating. First, molecular water is mostly removed from the structures to form phases of compositions ZrO2 · H2O and HfO2 · 0.5H2O. Second, polycondensation of OH groups occurs. Both processes are easier for ZrO2 · 2.5H2O. Apart from these steps, the interaction of water molecules with zirconium-oxygen bridges was found to occur during dehydration of the zirconium compound. The composition of HfO2 · 0.5H2O should actually read as Hf4O7(H2O)(OH)2.

Structure and dehydration of hydrous tin dioxide xerogel

Hydrous tin dioxide xerogel with the composition SnO2 · 1.75H2O is built of tin-oxygen-hydroxide fragments. Water molecules (no more than 1 mol) in the grain structure are kept by hydrogen bonds. Xerogel is dehydrated in the range 50–890°C in two stages. Below 123°C, molecular water is removed and the polycondensation of ≡Sn-O(H)-Sn≡ bridge groups occurs. There also takes place the transition of some water molecules from the molecular to hydroxide form as follows: ≡Sn-O-Sn≡ + H2O → 2≡Sn-O-H. All processes occur within individual grains. Above 123°C, water removal is due to the polycondensation of tin-oxygen groups. As a result, grains are coarsen. After 200°C, their structure is determined as cassiterite coated by tin oxyhydrate.

Interaction of Components in the NaOH-TiO2 · H2O-H2O System at 25°C

Solubilities in the NaOH-TiO2 · H2O-H2O system at 25°C were studied. The solubility isotherm was found to have two maxima. The formation of two compounds, Na2Ti5O11 · 10H2O and Na2Ti3O7 · 7H2O, was established.

Phase formation in the ScPO4-Na3PO4-Li3PO4 ternary system

The 950°C isothermal section of the InPO4-Na3PO4-Li3PO4 ternary system was studied and constructed; one-, two, and three-phase fields are outlined. Five solid-solution regions exist in the system: solid solutions based on the complex phosphate LiNa5(PO4)2 (olympite structure), the indium ion stabilized high-temperature Na3PO4 phase (Na3(1 − x)Inx(PO4); space group Fm

Complex Phosphates in the Li(Na)3]PO4-InPO4 Systems

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Synthesis and study of yttrium aluminum garnets doped with neodymium and ytterbium

m), the complex phosphate Na3In2(PO4)3, and the α and β phases of the compound Li3In2(PO4)3. A narrow region of melt was found in the vicinity of eutectic equilibria. All the phases detected in the system are derivatives of phases existing in the binary subsystems. Isovalent substitution of lithium for sodium in Na3In2(PO4)3 leads to a significant increase in the region of a NASICON-like solid solution.

Synthesis and crystal structure of new double indium phosphates M 3 I In(PO4)2 (MI = K and Rb)

Subsolidus sections in the systems Li3PO4-InPO4 (950°C) and Na3PO4-InPO4 (800, 900, and 1000°C) have been studied by X-ray powder diffraction. The compound Li3In(PO4)2 has been synthesized, and the nasicon-type solid solution Li3(1 − x)In2 + x(PO4)3 (0.67 ≤ x ≤ 0.80). has been found to exist. In the system Na3PO4-InPO4, the solid solution Na3(1 − x)Inx/3PO4 (0 ≤ x ≤ 0.2) and two complex phosphates exist: Na3In(PO4)2 and Na3In2(PO4)3. These complex phosphates are dimorphic, with the irreversible-transition temperature equal to 675 and 820°C, respectively. Na3In(PO4)2 degrades at 920°C. Ionic conductivity has been measured in some phases in the system.