Thermal analysis of the Ce<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Tb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> pigments

Compounds based on CeO₂ were synthesized as high-temperature environment-friendly inorganic pigments with interesting hues. The pigments have been synthesized by using the solid state reaction in the temperature range from 1,300 to 1,600 °C. The host lattice of these pigments is CeO₂ that is doped by terbium ions. The incorporation of doped ions provides interesting orange colours after application into ceramic glaze. The goal was to develop conditions for the synthesis of these compounds and to determine the influence of calcination temperature on their colouring effects. The simultaneous TG-DTA measurements were used for determination of the temperature region of the pigment formation and thermal stability of pigments. The pigments were also evaluated from the standpoint of their structure and particle sizes.     

Hydrothermal synthesis of Zn<Subscript>2</Subscript>Sn<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Ti<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>4</Subscript> as anode material for lithium-ion batteries

A novel electrode material, Zn₂Sn_{1 − x} Ti _x O₄ (x = 0 and 0.1), which is superior in its electrochemical characteristics to the reverse spinel Zn₂SnO₄, is synthesized by hydrothermal method. The admixture of TiO₂ levels out the volume expanding caused by the Li-Sn and Li-Zn alloy formation thus improving the material’s cyclability.     

Preparation of mesoporous Ce<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> mixed oxides and their catalytic properties in methane combustion

Mesoporous Ce_{1 ? x} Fe _x O₂ mixed oxide catalysts of different molar ratios (x = 0.1–0.5) were prepared by the citric acid sol-gel method and the microwave technique. The activities of Ce_{1 ? x} Fe _x O₂ mixed oxides on methane combustion were investigated, and the structure and reductive properties were characterized by XRD, BET, DRS, and TPR. The data showed that Ce_{1 ? x} Fe _x O₂ mixed oxides prepared were mesoporous material. When x ≤ 0.2, the transition metal Fe incorporated into the lattice of CeO₂ to form cubic Ce_{1 ? x} Fe _x O₂ solid solutions, and mixed phases of cubic Ce_{1 ? x} Fe _x O₂ solid solutions and α-Fe₂O₃ existed when x > 0.2. Ce_{1 ? x} Fe _x O₂ solid solutions show higher activity for methane combustion than pure CeO₂, especially for Ce_0.9Fe_0.1O₂.     

High-temperature ion transport in La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>FeO<Subscript>3−δ</Subscript>

The conductivity of the entire solid solution La_1–xSr_xFeO_3–, where x=0.2, 0.4, 0.5, 0.7 and 0.9, in the oxygen partial pressure range 10^–19 to 0.5 atm and temperatures between 750 and 950 °C is reported. The analysis of the isothermal pressure dependences of the conductivity reveal that the lanthanum-strontium ferrites can be characterized as mixed ion-electron conductors in the low-oxygen pressure/high-oxygen deficiency limit. The partial contribution to conductivity from oxygen ions increases with strontium content and attains a maximal value at x=0.5. Further increase in doping results in the development of oxygen vacancy ordering phenomena and deterioration of the conducting properties.Presented at the OSSEP Workshop Ionic and Mixed Conductors: Methods and Processes, Aveiro, Portugal, 10–12 April 2003     

Electronic peltier effect in Li<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>(2 − <Emphasis Type="Italic">x</Emphasis>) − δ</Subscript>S

Temperature dependences of the Peltier coefficient are studied in the temperature range of 300–700 K under variation of the composition of the Li _x Cu_{(2 − x) − δ}S samples. The obtained values of the Peltier coefficient of the Li_0.05Cu_{1.95 − δ}S samples with a different copper content are within the range of 0.1–0.4 J/A, which is somewhat higher than the similar parameters of bismuth telluride, the basic material of semiconductor coolers.     

Catalytic properties of Ce<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>1–<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> prepared using a template in the oxidation of CO

The catalytic activity in CO oxidation of Ce _x Zr_1–x O₂ double oxides prepared using pine sawdust and cetyltrimethylammonium bromide (CTAB) as templates is compared. It is found by means of SEM and the low-temperature adsorption of N₂ that biomorphic oxides reproduce the macropore structure of the template. It is shown via XRD and Raman spectroscopy that all samples contained mixed ceria-zirconia oxide. The double oxides form a cubic phase with a lattice of the fluorite type at a ratio of Ce: Zr = 4, regardless of the nature of the template; when Ce: Zr = 1, the biomorphic mixed oxide forms a tetragonal phase. According to Raman spectroscopy and XRD it was shown that the distortion of the oxygen sublattice is higher in biomorphic samples. Energy dispersive analysis shows that Ca impurities were present in the biomorphic samples, introducing additional distortions in the lattice of double oxide and leading to the formation of anionic vacancies. It is found that when Ce: Zr = 4, the conversion of CO on biomorphic oxide in the range of 100–350°C is higher than that observed for Ce _x Zr_1–x O₂ (CTAB); reducing the Ce: Zr ratio in the biomorphic sample to 1 results in a marked decrease in CO conversion at 100–200°C. It is concluded that these differences are due to changes in the mobility of the lattice oxygen.     

Electrotransport Properties of Ceramics Based on Bi<Subscript>4</Subscript>V<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Fe<Subscript>x</Subscript>O<Subscript>11 − <Emphasis Type="Italic">x</Emphasis></Subscript>

Conditions for the formation of single-phase compounds in the synthesis of solid solutions Bi₄V_{2 − x} Fe_xO_{11 − x} are studied. The sequence of phase transitions is determined. Parameters of unit cells of solid solutions are determined. The net conductance as a function of temperature and composition is studied.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 607–609.Original Russian Text Copyright © 2005 by Emel’yanova, Buyanova, Zhukovskii.     

Density-Functional Theory of Vibrations in Ni<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>V<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript> Clusters

We have performed the calculation of the vibrational frequencies, Fermi energy and binding energy for several clusters of Ni and vanadium atoms by using the first principles. The calculations are performed by using the density-functional theory in the local-density approximation with spin polarized orbitals. The calculation of vibrational frequencies shows that some of the clusters have positive vibrational frequencies which describe the oscillations of the stable clusters. The negative vibrational frequencies indicate that these clusters are instable with respect to these vibrations when no energy of this frequency is supplied. We find that for vanadium concentration less than 11.1% the clusters of Ni and V atoms are not stable. Hence ferromagnetism in Ni is predicted below 11.1% vanadium. We find the vibrational frequencies of several clusters for which the vanadium concentration is more than 11.1%. We are able to find a phase transition by use of quantum mechanics alone without the use of classical mechanical variables or thermodynamic variables such as temperature.     

Ionic conduction of Li<Subscript>8 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Mg<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>ZrO<Subscript>6</Subscript> solid solutions

A boundary of existence of solid solutions in the Li_8−2x Mg _x ZrO₆ system is found to be 7 mol % MgO. The transport properties of Li_{8 − 2x} Mg _x ZrO₆ solid solutions (the electronic component of total conductivity, the temperature and concentration dependences of conductivity and activation energy) are studied. It is supposed that, for Li₈ZrO₆ phase and solid solution based on it, an abrupt change of conductivity in the temperature range from 663 to 713 K is caused by the transition of electrolyte into the superionic state.     

Potassium–conducting K<Subscript>1 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Pb<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>GaO<Subscript>2</Subscript> solid electrolytes

Solid electrolytes with potassium-cation conductivity in the K_{1 − 2x} Pb _x GaO₂ system were synthesized and studied. It was found that solid solutions based on potassium monogallate are formed in a wide range of compositions. They contain vacancies in the potassium sublattice that provide for high conductivity of electrolytes. The relationship is considered between electric characteristics of solid electrolytes and the composition and structure of solid solutions. The results are compared to the earlier obtained data for similar solid electrolytes based on potassium monoaluminate and monoferrite.     

Potassium-conducting solid electrolytes in K<Subscript>1 − 2<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>GaO<Subscript>2</Subscript> system

New solid electrolytes with a high conductivity by K⁺ ions in the K_{1 − 2x} Sr _x GaO₂ system are synthesized and studied. It is found that the introduction of Sr²⁺ ions into potassium monogallate leads to the formation of solid solutions with KGaO₂ structure in a wide range of additive concentration. These solid solutions exhibit a high conductivity; the conductivity increases monotonically with increasing concentration of strontium within the single-phase range. The electrical characteristics are related to the electrolyte structure. The results are compared with the earlier data for the gallate solid electrolytes with the additives of four-charged cations and the systems based on potassium monoferrite and monoaluminate.     

Synthesis of (Ni<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Co<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>)<Subscript>2</Subscript>P (0 ≤ <Emphasis Type="Italic">x</Emphasis> ≤ 0.65) substitution solid solution

The phosphides (Ni_{1 ? x} Co _x )₂P (0 ≤ x ≤ 0.65) crystallizing in the hexagonal system, space group P \(\bar 6\)2m, were synthesized in two steps starting from the continuous solid solution (Ni_{1 ? x} Co _x )₃(PO₄)₂ · 8H₂O. The initial phosphates were first completely dehydrated at 800°C and then reduced with hydrogen at 900–1000°C for 1–2 h.     

Synthesis and electrochemical evaluation of La<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>MnO<Subscript>3</Subscript> catalysts for zinc-air batteries

La_1-x Sr _x MnO₃ (x?=?0.1～0.4) catalysts for primary and rechargeable zinc-air batteries have been successfully synthesized by the citrate method and their electrochemical properties measured. The materials can catalyze both ORR and OER, and the one with ideal composition of La_0.8Sr_0.2MnO₃ catalyst exhibits the highest catalytic activity and durability in alkaline medium. The resulting primary zinc-air cell shows a peak power density of 146 mW cm^?2 at 235 mA cm^?2. The secondary cell exhibits a charge-discharge voltage gap of 1.0 V at 10 mA cm^?2, which is highly stable over many charge-discharge cycles.     

Oxygen Nonstoichiometry and Transport Properties of Mixed-Conducting Ce<Subscript>0.6–<Emphasis Type="Italic">x</Emphasis></Subscript>La<Subscript>0.4</Subscript>Pr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2–δ</Subscript>

The oxygen nonstoichiometry and electrical conductivity of fluorite-type solid solutions Ce_0.6?xLa_0.4Pr _x O_2–δ (x = 0.1–0.2) were studied in the oxygen partial pressure range 10^–19–0.35 atm at 1023–1223 K. It was confirmed that the Pr^4+/3+ and Ce^4+/3+ redox pairs, which determine the concentration of p- and n-type electron charge carriers, play the dominant roles under oxidizing and reducing conditions, respectively. The conductivity vs. charge carrier concentration dependencies in these conditions are almost linear. Increasing praseodymium content leads to a substantially higher hole conductivity and an expanded range of the oxygen nonstoichiometry variations at high oxygen partial pressures. Under reducing conditions when praseodymium cations become trivalent opposite trends are observed on doping.     

Electrochemical characterization of praseodymium centers in Pr<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>Zr<Subscript>1−<Emphasis Type="Italic">x</Emphasis></Subscript>O<Subscript>2</Subscript> zirconias using electrocatalysis and photoelectrocatalysis

The voltammetry of nanoparticles and scanning electrochemical microscopy are applied to characterize praseodymium centers in tetragonal and monoclinic zirconias, doped with praseodymium ions (Pr _x Zr_1−x O₂), prepared via sol–gel routes. Doped zirconia nanoparticles were synthesized by a sol–gel liquid-phase route and characterized by different techniques, including X-ray diffraction powder pattern, ultraviolet–visible diffuse reflectance spectroscopy, infrared spectroscopy, and transmission electron microscopy (TEM). Gels annealed at around 400 °C yielded tetragonal Pr _x Zr_1−x O₂ phases. The monoclinic forms of Pr-doped ZrO₂ were obtained by annealing at temperatures higher than 1,100 °C. TEM micrographs proved that the size of the nanoparticles produced was dependent on their crystalline form, around 15 and 60 nm for tetragonal and monoclinic, respectively. The electrochemical study confirmed that a relatively high content of praseodymium cation was in the chemical state (IV), i.e., as Pr⁴⁺, in both zirconia host lattices. The catalytic and photocatalytic effects of Pr⁴⁺ centers located in the monoclinic zirconia lattice on nitrite reduction and oxygen evolution reaction were studied.     

Storage performance of LiFe<Subscript>1 − <Emphasis Type="Italic">x</Emphasis></Subscript>Mn<Subscript><Emphasis Type="Italic">x</Emphasis></Subscript>PO<Subscript>4</Subscript> nanoplates (<Emphasis Type="Italic">x </Emphasis>= 0, 0.5, and 1)

Although LiFePO₄ (LFP) is considered to be a potential cathode material for the lithium-ion batteries, its rate performance is significantly restricted by sluggish kinetics of electrons and lithium ions. Several attempts have been made so far to improve the performance of LiFePO₄ by reducing the grain size, doping with aliovalent atoms, and coating conductive materials such as carbon or RuO₂. We report here synthesis of LFP nanoplates by solvothermal method, tailoring the thickness as well as carbon coverage at surfaces to explore their influence on the storage performance. Due to the fact that Li⁺ ion diffuses along the b-axis, solvothermal method was aimed to control the thickness of nanoplates across the b-axis. We synthesized several nanoplates with various plate thicknesses along b-axis; among those, nanoplates of LFP with ～30-nm-thick b-axis having thin (2–5 nm) and uniform layer of carbon coating exhibits high storage capacity as well as high rate performances. Thus, a favorable morphology for LiFePO₄ has been achieved via solvothermal method for fast insertion/extraction of Li⁺ as compared to spherical nanoparticles of carbon-coated LFP. Galvanostatic cycling shows a capacity of 164?±?5 mAh g^?1 at 0.1 C rate, 100?±?5 mAh g^?1 at 10 C rate, and 46?±?5 mAh g^?1 at 30 C rate, with excellent capacity retention of up to 50 cycles. Further attempts have been made to synthesize LiMnPO₄ (LMP) as well as Li(Fe_1???x Mn _x )PO₄/C (x?=?0.5) nanoplates using solvothermal method. Although LiMnPO₄ does not exhibit high storage behavior comparable with that of LiFePO₄, the mixed systems have shown an impressive storage performance.     

Heat capacity of GdBaSr(Cu<Subscript>3−x</Subscript><Emphasis Type="Italic">M</Emphasis><Subscript>x</Subscript>)O<Subscript>7−δ</Subscript> superconductor (<Emphasis Type="Italic">M</Emphasis>=Zn and Ni)

In this study, GdBaSr(Cu_3−x M _x)O_7−δ bulk samples (M=Zn and Ni; 0≤x≤0.1) were prepared via solid-state reaction. Specific heat measurement (measured with thermal relaxation technique using PPMS) shows an obvious specific heat jump around the T _c for GdBaSrCu₃O_7−δ sample as observed in most of the high temperature superconductors. It shifts towards lower temperature with increasing of both Zn and Ni doping contents, whose tendency is similar to the decreasing of T _c. Debye temperature, Θ_D (derived from specific heat measurements) calculated at around 10 K is found to be directly proportional to the T _c.     

The synthesis and transport properties of the cuprates La<Subscript>2 − <Emphasis Type="Italic">x</Emphasis></Subscript>Sr<Subscript>1 + <Emphasis Type="Italic">x</Emphasis></Subscript>Cu<Subscript>2</Subscript>O<Subscript>6 + δ</Subscript>

The cuprates La_{2 ? x} Sr_{1 + x} Cu₂O_{6 + δ}(x = 0, 0.1, 0.2) are synthesized by solid-state method. Their dc conductivity was studied over the 373 to 1173 K temperature range and 10 to 2.1 × 10⁴ Pa oxygen partial pressure range by using four-probe technique. It is shown that the cuprate conductivity in air is maximal at ～673 K; it is 60 S/cm for La₂SrCu₂O_6.09; 68 S/cm, for La_1.9Sr_1.1Cu₂O_6.18; and 81 S/cm, for La_1.8Sr_1.2Cu₂O_6.10. The thermal expansion coefficient of La₂SrCu₂O_6.09 is determined by thermomechanical method and high-temperature X-ray diffraction method; its value (16 ppm K^?1) shows that the material is compatible with the ceria-based solid electrolytes during the thermal cycling.