Phase relations in the Zn<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript>-Cu<Subscript>2</Subscript>V<Subscript>2</Subscript>O<Subscript>7</Subscript> system from room temperature to melting

Phase relations in the Zn₂V₂O₇-Cu₂V₂O₇ system were studied by high-temperature X-ray diffraction and differential thermal analysis. The major phase constituents of the system are solid solutions based on Zn₂V₂O₇ and Cu₂V₂O₇ polymorphs and their coexistence regions. The generation of α-Zn_{2 − 2x} Cu_2x V₂O₇ solid solution, where 0 ≤ x ≤ 0.30, leaves almost unchanged the stabilization temperature of the high-temperature zinc pyrovanadate phase. The α-Cu_{2 − 2x} Zn_2x V₂O₇ homogeneity range is 5 mol % Zn₂V₂O₇. In the range 0.050 ≤ x ≤ 0.09 from 20 to ∼ 620°C, there is the two-phase field of α-Cu₂V₂O₇ and β-Cu₂V₂O₇ base solid solutions. At still higher temperatures, β-Zn_{2 − 2x} Cu_2x V₂O₇ and α-Cu_{2 − 2x} Zn_2x V₂O₇ coexist in the mixed-phase region. β-Zn_{2 − 2x} Cu_2x V₂O₇ solid solution, where 0 ≤ x ≤ 0.30, exists above 610 ± 5°C. The extent of the β′-Cu₂V₂O₇-base solid solution is 9 to 65 mol % Zn₂V₂O₇ at 615 ± 5°C, expanding to 0 mol % Zn₂V₂O₇ with rising temperature. Original Russian Text ￠ T.I. Krasnenko, M.V. Rotermel’, S.A. Petrova, R.G. Zakharov, O.V. Sivtsova, A.N. Chvanova, 2008, published in Zhurnal Neorganicheskoi Khimii, 2008, Vol. 53, No. 10, pp. 1755–1762.     

The synthesis and selected properties of Co<Subscript>2</Subscript>InV<Subscript>3</Subscript>O<Subscript>11</Subscript>

It has been demonstrated that Co₂V₂O₇ and InVO₄ react with each other forming a new compound of the Co₂InV₃O₁₁ formula, when their molar ratio is equal to 1:1, or among CoCO₃, In₂O₃ and V₂O₅, mixed at a molar ratio of 4:1:3. This compound melts incongruently at the temperature of 960±5°C, depositing crystals of InVO₄. It crystallizes in the triclinic system and the unit cell parameters amount to: a=0.6524(6) nm, b=0.6885(5) nm, c=1.0290(4) nm, α=96.5°, β=104.1°, γ=100.9°, Z=2. The phase equilibria being established in the Co₂V₂O₇–InVO₄ system over the whole components concentration range up to the solidus line were described.     

Wetting and conductivity of BiVO<Subscript>4</Subscript>-V<Subscript>2</Subscript>O<Subscript>5</Subscript> ceramic composites

The conductivity and transport number of oxygen ions of BiVO₄-(5, 7, 10, 12) wt % V₂O₅ ceramic composites are measured using the four-probe and coulomb-volumetric methods, respectively, in the temperature range from 500 to 660°C. The phase transition of wetting of grain boundaries with eutectic melt at 640°C is discovered. It is shown that the grain boundary wetting significantly raises the ionic conductivity of composites.     

Thermal behaviour and properties of Na<Subscript>2</Subscript>O-TiO<Subscript>2</Subscript>-P<Subscript>2</Subscript>O<Subscript>5</Subscript> glasses

Differential scanning calorimetry (DSC) and thermomechanical analysis (TMA) were used to study the thermal behaviour of (50-x)Na₂O-xTiO₂-50P₂O₅ and 45Na₂O-yTiO₂-(55-y)P₂O₅ glasses. The addition of TiO₂ to the starting glasses (x=0 and y=5 mol% TiO₂) resulted in a nonlinear increase of glass transition temperature and dilatation softening temperature, whereas the thermal expansion coefficient decreased. All prepared glasses crystallize under heating within the temperature range of 300–610°C. The contribution of the surface crystallization mechanism over the internal one increases with increasing TiO₂ content. With increasing TiO₂ content the temperature of maximum nucleation rate is also gradually shifted from a value close to the glass transition temperature towards the crystallization temperature. X-ray diffraction measurements showed that the major compounds formed by glass crystallization were NaPO₃, TiP₂O₇ and NaTi₂(PO₄)₃. The chemical durability of the glasses without titanium oxide is very poor, but with the replacement of Na₂O or P₂O₅ by TiO₂, it increases sharply.     

Thermal behaviour and fragility of Sb<Subscript>2</Subscript>O<Subscript>3</Subscript>-containing zinc borophosphate glasses

Thermal behaviour of the glass series (100-x)[50ZnO-10B₂O₃-40P₂O₅]·xSb₂O₃ (x=0-42 mol%) and (100-y)[60ZnO-10B₂O₃-30P₂O₅]·ySb₂O₃ (y=0-28 mol%) was investigated by DSC and TMA. The addition of Sb₂O₃ results in a decrease of the glass transition temperature and crystallization temperature in both compositional series. All glasses crystallize on heating in the temperature range of 522–632°C. Thermal expansion coefficient of the glasses monotonously increases with increasing Sb₂O₃ content in both series and varies within the range of 6.6–11.7 ppm °C⁻¹. From changes of thermal capacity within the glass transition region it was concluded that with increasing Sb₂O₃ content the ‘fragility’ of the studied glasses increases.     

Microstructure and Conduction of Composites Bi<Subscript>2</Subscript>CuO<Subscript>4</Subscript>-Bi<Subscript>2</Subscript>O<Subscript>3</Subscript> Near the Eutectic Melting Point

Microstructure and conduction of ceramic composites Bi₂CuO₄ + xBi₂O₃ (x = 5, 10, 15, 20 wt %) near the eutectic melting point (770°C) are studied. Bismuth oxide, initially randomly distributed over the ceramics bulk, after quenching from temperatures exceeding the eutectic melting point, becomes localized at triple junctions and grain boundaries in Bi₂CuO₄, which is caused by wetting grain boundaries and forming a liquid-channel structure. The jumpwise change in the composites’ conductivity near 730 and 770°C caused by polymorphic transformation of Bi₂O₃ and the eutectic melting with simultaneous formation of a liquid-channel structure. Transport numbers of the oxygen ion are measured at 770°C by coulomb-volumetric method. The conduction by oxygen ions increases in the composites with decreasing average size of Bi₂CuO₄ crystallites.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 596–601.Original Russian Text Copyright © 2005 by Lyskov, Metlin, Belousov, Tret’yakov.     

Electrical conductivity studies in the system Li<Subscript>2</Subscript>TiO<Subscript>3</Subscript>-Li<Subscript>1.33</Subscript>Ti<Subscript>1.67</Subscript>O<Subscript>4</Subscript>

Electrical conductivity in the monoclinic Li₂TiO₃, cubic Li_1.33Ti_1.67O₄, and in their mixture has been studied by impedance spectroscopy in the temperature range 20–730 °C. Li₂TiO₃ shows low lithium ion conductivity, σ₃₀₀≈10^–6 S/cm at 300 °C, whereas Li_1.33Ti_1.67O₄ has 3×10^–8 at 20 °C and 3×10^–4 S/cm at 300 °C. Structural properties are used to discuss the observed conductivity features. The conductivity dependences on temperature in the coordinates of 1000/T versus log_e(σT) are not linear, as the conductivity mechanism changes. Extrinsic and intrinsic conductivity regions are observed. The change in the conductivity mechanism in Li₂TiO₃ at around 500–600 °C is observed and considered as an effect of the first-order phase transition, not reported before. Formation of solid solutions of Li_{2– x} Ti_{1+ x} O₃ above 900 °C significantly increases the conductivity. Irradiation by high-energy (5 MeV) electrons causes defects and the conductivity in Li₂TiO₃ increases exponentially. A dose of 144 MGy yields an increase in conductivity of about 100 times at room temperature. Electronic Publication     

Specific heat on Sr<Subscript>2</Subscript>Nb<Subscript>2</Subscript>O<Subscript>7</Subscript> and Sr<Subscript>2</Subscript>Ta<Subscript>2</Subscript>O<Subscript>7</Subscript>

Summary Specific heats on the single crystals of Sr₂Nb₂O₇, Sr₂Ta₂O₇ and (Sr_1-xBa_x)₂Nb₂O₇ were measured in a wide temperature range of 2-600 K. Heat anomalies of a λ-type were observed at the incommensurate phase transition of T_INC (=495 K) on Sr₂Nb₂O₇ and at the super-lattice phase transition of T_SL (=443 K) on Sr₂Ta₂O₇; the transition enthalpies and the transition entropies were estimated. Furthermore, a small heat anomaly was observed at the low temperature ferroelectric phase transition of T_LOW (=95 K) on Sr₂Nb₂O₇. The transition temperature T_LOW decreases with increasing Ba content x and it vanishes for samples of x>2%.     

Impact of Pb substitution on the formation of high <Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> superconducting phase in BSCCO system derived through sol-gel process

Sol-gel process was employed to synthesize the Pb-BSCCO system having general composition Bi_2−xPb_xSr₂Ca₂Cu₃O_10−δ, where x=0.2, 0.4 and 0.8. Fourier transform infrared (FTIR) spectroscopy, X-ray diffraction (XRD), dilatometry and vibrating sample magnetometer (VSM) were employed to study the materials produced at different stages. Two-stage heating firstly at 300 and then 800°C was adopted in order to avoid the burning of the materials and formation of carbonates. The carbonate formation was avoided by heating the materials firstly at 300°C for 2 h and without intermediate cooling moved to the furnace having temperature 800°C and hold for 2 h. The sintering behaviour of samples was studied by dilatometry and the results revealed that the sample having x=0.4 was stabled up to a temperature of 700°C while samples having x=0.2 and 0.8 to a temperature of 625°C. The maximum shrinkage was observed at 850°C in all the samples. On the basis of dilatometry results, the samples were sintered at 845°C for 60 h to observe the superconducting phases. The highest volume fraction of high superconducting phase (2223) was noticed in the sample containing x=0.4 having onset T _c=110 K.     

Structure and properties of H<Subscript>8</Subscript>(PW<Subscript>11</Subscript>TiO<Subscript>39</Subscript>)<Subscript>2</Subscript>O heteropoly acid

Heteropoly acid (HPA) H₈(PW₁₁TiO₃₉)₂O·xH₂O (I) is synthesized by three different ways and studied by chemical analysis, potentiometric titration, mass-spectrometry, IR, ³¹P, ¹⁸³W, and ¹⁷O NMR spectroscopy, thermogravimetry, and transmission electron microscopy. Anion I consists of two subparticles of the Keggin structure bridged by Ti-O-Ti. The dimeric anion exists in HPA aqueous solutions at [I] > 0.02 M. At pH > 0.6 it splits to a [PW₁₁TiO₄₀]⁵⁻ monomer stable up to pH ∼ 6. When heated (150–400)°C, I splits into H₃PW₁₂O₄₀ and, apparently, H₃PW₁₀Ti₂O₃₈ without phase separation. Thermolysis products are soluble and when dissolved in water turn again into I. Complete decomposition of I to oxides occurs at ∼450°C.     

Subsolidus phase relations in the Al<Subscript>2</Subscript>O<Subscript>3</Subscript>-Li<Subscript>2</Subscript>O-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript> (Nb<Subscript>2</Subscript>O<Subscript>5</Subscript>) systems

The phase composition has been studied and an equilibrium phase diagram has been designed for the Al₂O₃-Li₂O-R₂O₅ (R = Ta or Nb) systems in the subsolidus region up to 1000°C and 85 mol % Li₂O. New phases with the composition Li_1+x Al_1?x O_2?x , where x = 0–0.67, have been found.     

Phase diagram of the system NaF-SnF<Subscript>2</Subscript>

The phase diagram of the binary system NaF-SnF2 was determined by using the thermal analysis method. In addition to the crystallisation fields of pure components the formation of three other crystallisation fields was observed and these were attributed to the compounds: NaF·2SnF₂, NaF·SnF₂ and 2NaF·SnF₂. The coordinates of the four eutectic points are: e ₁: 70 mol% NaF, 30 mol% SnF₂ and 255°C e ₂: 58 mol% NaF, 42 mol% SnF₂ and 238°C e ₃: 44 mol% NaF, 56 mol% SnF₂ and 246°C e ₄: 18 mol% NaF, 82 mol% SnF₂ and 191°C The model independent on the real structure of the melt was applied for the calculation of phase diagram comprising the calculation of excess molar Gibbs energy of mixing. The probable inaccuracy in the calculated phase diagram is σ=2.0°C. XRD analysis of solidified mixtures was performed in order to confirm the formation of expected compounds.     

Phase equilibria in the system Li<Subscript>2</Subscript>O-MgO-B<Subscript>2</Subscript>O<Subscript>3</Subscript>

The subsolidus region of the Li₂O-MgO-B₂O₃ system has been studied by X-ray powder diffraction and differential thermal analysis. Isothermal sections at 500–550 and 650–700°C have been designed. The following complex borates have been found to form: at 500–550°C, Li₂MgB₂O₅ and LiMgBO₃ are formed; at 650–700°C, a new phase Li₄MgB₂O₅ is formed along with LiMgBO₃; and at 5500–600°, Li₂MgB₂O₅ is formed.     

Phase diagram of V<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript>-Ag<Subscript>2</Subscript>O system

The results concerning the synthesis, structure and thermal properties of V₂O₅-MoO₃-Ag₂O samples in the vanadium rich region of ternary system are presented in the form of quasi-binary phase diagrams in which at constant V₂O₅/MoO₃ molar ratios, equal 9:1, 7:3 and 1:1, the content of Ag₂O was variable. A new ternary phase isostructural with NaVMoO₆ has been detected in the investigated system.     

Preparation of CuCr<Subscript>2</Subscript>O<Subscript>4</Subscript> nanopowders using two different chromium sources

CuCr₂O₄ spinel powders were synthesized starting from different chromium sources, namely (i) chromium oxide (α-Cr₂O₃) and (ii) ammonium dichromate ((NH₄)₂Cr₂O₇). The copper source was a Cu(II) carboxylate-type complex. The Cu(II) carboxylate complex was obtained by the redox reaction between Cu(NO₃)₂·3H₂O and 1,3-propanediol (1,3PG) at 130 °C. In the first case (i), we have started from a mixture of α-Cr₂O₃, Cu(NO₃)₂·3H₂O and 1,3PG that upon heating formed the copper malonate complex, which decomposed around 220 °C forming an oxide mixture (CuO + α-Cr₂O₃). In the second case (ii), (NH₄)₂Cr₂O₇, Cu(NO₃)₂·3H₂O and 1,3PG were homogenously mixed. Heating this mixture at 130 °C resulted, in situ, in the Cu(II) complex. On controlled temperature increase, the violent decomposition of (NH₄)₂Cr₂O₇ took place at 180 °C along with the decomposition of the Cu(II) complex, leading to an amorphous oxide mixture of Cr₂O_3+x and CuO. By annealing the samples in the temperature range 400–1000 °C, the spinel phase (CuCr₂O₄) was obtained in both cases: (i) at 800 °C and (ii) at 600 °C as a result of the interactions between the precursors used, when the oxide system was amorphous and highly reactive. The presence of CuCr₂O₄ was highlighted by XRD and FTIR analyses.     

Phase formation in the V<Subscript>2</Subscript>O<Subscript>5</Subscript>-Ta<Subscript>2</Subscript>O<Subscript>5</Subscript>-MoO<Subscript>3</Subscript> system

Solid-phase interactions in the V₂O₅-Ta₂O₅-MoO₃ system were studied. The formation of com- pounds TaVO₅ and VTa₉O₂₅ in the V₂O₅-Ta₂O₅ binary system was verified. Tetragonal VTa₉O₂₅-base solid solutions of the general formula Ta_{5 + 4x} V_{5 − 4x} O₂₅ (x = 0.25–1) and TaVO₅-base solid solutions of the general formula Ta _x Mo_{1 − x} V_{2 − x} O_{8 − 3x} (x = 0.625–1) were found to form. Subsolidus phase equilibria in the V₂O₅-Ta₂O₅-MoO₃ were determined.     

Production of bscco bulk high <Emphasis Type="Italic">T</Emphasis><Subscript>c</Subscript> superconductors by sol-gel method and their characterization by ftir and XRD techniques

The production of bulk high T _c superconducting phase (2223) by EDTA-gel (ethylenediaminetetraacetic acid) techniques has been investigated. It is shown that close control of pH is necessary for the production of a well-complexed precursor which allows subsequent decomposition in two stages at 300 and 800°C. The problem of carbonate formation was investigated experimentally and solved. Precursors are characterised by Fourier transform infrared (FTIR) spectroscopy and X-ray diffraction (XRD) and the sintering behaviour was monitored by dilatometry. At least three different phases Bi₂Sr₂Ca_x−1Cu_xO_8+y (BSCCO); where x=1, 2, 3 were identified within superconducting pellets using XRD, named as Bi₂Sr₂CuO₇ (2201), Bi₂Sr₂CaCu₂O₉ (2212) and Bi₂Sr₂Ca₃O₁₀ (2223). The superconducting properties of the sintered samples were studied by vibrating sample magnetometer (VSM). Transition to a superconducting state around 80 K appeared in samples (sintered at 845°C) containing the Bi₂Sr₂Ca₁Cu₂O_y (2212) phase. Liquid phase sintering of the samples aided the formation of Bi₂Sr₂Ca₂Cu₃O_x (2223) phase at high temperature (860°C), which showed a superconducting transition temperature of 108 K.     

Synthesis and colour properties of pigments based on terbium-dopped Mg<Subscript>2</Subscript>SnO<Subscript>4</Subscript>

The main aim of this work was to synthesize the magnesium orthostannate doped by terbium cations and tested whether these materials can be used for colouring of the different materials, e.g. organic binder and ceramic glazes. Initial composition of pigments was counted according the general formula 2MgO(1 − x)SnO₂–xTbO₂, where values of x varied from 0.1 to 0.5 in 0.1 steps. The simultaneous TG/DTA measurements of mixture containing tin oxide, magnesium carbonate hydroxide and terbium oxide showed that the formation of a new compound started at temperature 1,029 °C, but single-phase system was not prepared. Granulometric compositions of samples that were prepared by calcining at temperatures 1,300–1,400 °C are characterized by values of median (d ₅₀) in range 4–8 μm. The calcining temperature 1,500 °C caused the increase of the particle sizes at around 12 μm. The composition of sample 2MgO–1.5SnO₂–0.5TbO₂ and heating temperature 1,500 °C are the most suitable conditions for preparation of colourfully interesting pigment that can be recommended also for colouring of ceramic glazes. Especially, for colouring of decorative lead containing glaze G 07091 containing 5 wt% of PbO and 8 wt% of Al₂O₃.     

Ionic conduction of a high-temperature modification of Lu<Subscript>2</Subscript>Ti<Subscript>2</Subscript>O<Subscript>7</Subscript>

A nanoceramic product of the composition Lu₂Ti₂O₇ is synthesized by a coprecipitation method with a subsequent sublimation drying and an annealing at 650–1650°C. The conduction of Lu₂Ti₂O₇ synthesized at 1650°C is ionic (10^–3 S cm^–1 at 800°C). Thus, a new material with a high ionic conduction has been discovered. The ordering in Lu₂Ti₂O₇ is studied by methods of RFA, RSA, IK spectroscopy, electron microscopy, and impedance spectroscopy. The existence of a low-temperature phase transition fluorite-pyrochlore at 800°C and a high-temperature conversion order-disorder at 1650°C are established.Translated from Elektrokhimiya, Vol. 41, No. 3, 2005, pp. 298–303.Original Russian Text Copyright © 2005 by Shlyakhtina, Ukshe, Shcherbakova.     

XAFS investigation of [Pd(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>][AuCl<Subscript>4</Subscript>]<Subscript>2</Subscript> and its thermolysis products

Thermolysis of double complex salt [Pd(NH₃)₄][AuCl₄]₂ has been studied in helium atmosphere from ambient to 350 °C. The XAFS of Pd K and Au L₃ edges and thermogravimetry measurements have been carried out to characterize the intermediates and the final product. In the temperature range 115–160 °C the complex is decomposed to form Pd(NH₃)₂Cl₂ and AuCl_4−x N _x species with x ranging from 2 to 3. Subsequent heating of the intermediate up to 300 °C leads to the total loss of NH₃. The Au–Cl and Au–Au bonds form the local environment of Au at the stage of decomposition while only four chlorine atoms are around Pd. At the temperature of 330 °C the Au and Pd nanoparticles as well as residues of palladium chloride are detected. The final product consists of separated Au and Pd nanoparticles.