Superionic transport in solid fluoride solutions with a fluorite structure

Results of systematic research into ionic transport in solid solutions M_{1 ? x} R_xF_{2 + x} and Na_{0.5 ? x} R_{0.5 + x} F_{2 + 2x} (M = Ca, Sr, Ba, Cd, Pb; R = rare-earth elements) with the fluorite structure are reviewed. The mechanism of anionic conduction is analyzed. The link between ionic transport and defects in the structure of these crystals is discussed. Potentialities of their application in electrochemical devices are considered.     

Superionic Character of High-Temperature Conduction in Lanthanum Fluoride

The electroconduction of crystalline lanthanum fluoride is studied in the temperature range from 1320 K to the melting point (1766 K). A markedly pronounced superionic behavior of LaF₃ is established: near mp its conductivity amounts to 42% of that corresponding to a molten state. Thermodynamics of the formation of defects and their concentrations are estimated on the basis of available data on the high-temperature enthalpy of LaF₃ within a model of noninteracting defects. The Schottky and Frenkel mechanisms of ion disordering are considered. A comparative analysis of these two mechanisms supplemented with results on the conductivity favors the Frenkel mechanism of the origin of defects in LaF₃.     

Superionic fluoride ceramics RF<Subscript>3</Subscript> and R<Subscript>0.95</Subscript>Sr<Subscript>0.05</Subscript>F<Subscript>2.95</Subscript> (R = La,Ce, Pr,Nd) prepared by hot pressing

RF₃ and R_0.95Sr_0.05F_2.95 (R = La, Ce, Pr, Nd) ceramic specimens were prepared by hot pressing at 1173 K under pressure of 3 × 10⁸ Pa for 20 min. The ionic conductivity value was determined by means of impedance spectroscopy in vacuum from 293 to 823 K. For LaF₃ at 350 K, the single crystal / ceramics conductivity ratio is about 5. The difference decreases at higher temperature and disappears about 500 K. The ionic conductivity activation energy is 0.30 ± 0.05 eV. For La_0.95Sr_0.05F_2.95, the conductivity of ceramics below 500 K is slightly lower that of single crystals. At T > 500 K, the conductivity values of ceramic and single crystal specimens practically coincide. The ionic conductivity of hot pressed ceramics is about 10^?2 S/cm at 500 K and activation energy is 0.25 ± 0.02 eV.     

Eutectic Composition Systems NaF-DyF3, NaF-HoF3, and MgF2-ScF3 as Ionic Conductors

Electrophysical properties of eutectic composites formed in the NaF-DyF₃, NaF-HoF₃, and MgF₂-ScF₃ systems are studied at 18–528°C. The conductivity of 25NaF-75DyF₃, 25NaF-75HoF₃, and 55MgF₂-45ScF₃ at 20°C (9 × 10⁻⁸, 3 × 10⁻⁷, and 2 × 10⁻⁶ S/cm) exceed that of the initial materials by 2–4 orders of magnitude.__________Translated from Elektrokhimiya, Vol. 41, No. 8, 2005, pp. 1010–1013.Original Russian Text Copyright © 2005 by Sorokin, Buchinskaya, Bystrova, Konovalova, Sobolev.     

Electroconduction of Potassium Orthophosphate Modified with Triple-Charged Cations

Solid electrolytes in the systems K_{3 – 3x} Me _x PO₄ (Me = Sc, Y, In, La, Nd, Gd, Tb) are synthesized. Their phase composition and the temperature and concentration dependences of their electroconductivity are studied. In all the systems there form solid solutions based on K₃PO₄, which have a high potassium cation conductance. The latter is due to the formation of potassium vacancies at substitutions 3K⁺ Me³⁺ and, at lower temperatures, to stabilization of a high-temperature -modification of potassium orthophosphate. The electroconductivity of synthesized solid solutions, which equals (4–7) × 10^–3 and 10^–1 S cm^–1 at 300 and 700°C, is similar to that of solid electrolytes K_{3 – x} P_{1 – x} E _x ^VIO₄ and K_{3 – 4x} E _x ^IVPO₄.     

Anionic high-temperature conduction in single crystals of nonstoichiometric phases R1 ? y M y F3 ? y (R = La-Lu, M = Ca, Sr, Ba) with the tysonite (LaF3) structure

Electrophysical properties of single crystals of nonstoichiometric phases R_{1 − y} M _y F_{3 − y} , where R = La-Lu, M = Ca, Sr, or Ba, with the tysonite (LaF₃) structure, which are present in a metastable state after being grown and cooled, are measured in the temperature interval extending from 300 to 1073 K. It is discovered that, during a sufficiently long high-temperature investigation, solid solutions R_{1 − y} Ca _y F_{3 − y} , where R = Tb, Dy, or Ho, undergo irreversible variations in the phase composition in the temperature region 723 to 823 K. This level of temperatures, which correspond to partial decomposition of phases R_{1 − y} Ca _y F_{3 − y} with the rare-earth elements of the end of the period, lies above the temperatures to which the fluoride solid electrolytes are usually heated when used in solid-state electrochemical devices. The temperature and concentration dependences of the phases’ electroconduction are explained in the framework of the vacancy mechanism of anionic transport. Original Russian Text ? N.I. Sorokin, B.P. Sobolev, 2007, published in Elektrokhimiya, 2007, Vol. 43, No. 4, pp. 420–431. The paper is dedicated to the memory of Prof. M.W. Breiter, formerly of the Vienna Technical University, Austria.     

Ion Transfer in CdF<Subscript>2</Subscript>-based Iso- and Polyvalent Solid Solutions

The ionic conductivity of solid solution Cd_0.77Sr_0.23F₂ is 1.6 × 10⁻⁴ S/cm at 500 K. The conduction mechanism changes from a vacancy mechanism to an interstitial one at 523–553 K. In solid solutions Cd_0.9R_0.1F_2.1 (R = La-Lu, Y), the activation enthalpy of conduction decreases from 0.9 to 0.8 eV with decreasing ionic radius of R³⁺, raising the 500-K conductivity from 6 ×10⁻⁶ S/cm for La³⁺to 6 × 10⁻⁵ S/cm for Lu³⁺. For crystalline Cd_0.95In_0.05F_2.05, ionic and electronic conductivities at 313 K equal 5 × 10⁻⁴ and 5 − 10⁻⁶ S/cm.__________Translated from Elektrokhimiya, Vol. 41, No. 5, 2005, pp. 627–632.Original Russian Text Copyright © 2005 by Sorokin, Buchinskaya, Sul’yanova, Sobolev.     

Potassium Aluminate Crystalline Structure and Electroconduction

The crystalline structure of low- and high-temperature modifications of KAlO₂ is studied by a neutron diffraction method combined with a full-profile Rietveld analysis. At low temperatures KAlO₂ has an orthorhombic structure (spatial group Pbca), which turns tetragonal (spatial group P4₁2₁2) at 540°C. During a phase transition along the c axis there open new conduction channels with a large cross-section of voids, which is a probable reason for the conduction jump. The presumed anisotropy of conduction in the low-temperature modification disappears during the phase transition.     

Poly(dimethylsiloxane)‐Supported Ionogels with a High Ionic Liquid Loading

The immiscibility of poly(dimethylsiloxane) (PDMS) and ionic liquids (ILs) was overcome to create PDMS‐supported IL gels (ionogels) with IL loadings of up to 80 % by mass through a simple sol–gel reaction at room temperature. By stirring a mixture of a functionalized PDMS oligomer, formic acid, and an IL (or lithium‐in‐IL solution), a resin was formed that could be cast to create a freestanding, flexible ionogel. PDMS‐supported ionogels exhibited favorable ionic conductivity (ca. 3 mS cm^?1) and excellent mechanical behavior (elastic modulus: ca. 60 kPa; fatigue life: >5000 cycles; mechanically stable at temperatures up to 200 °C). The activation energy of ionic conductivity was shown to be nearly identical for the ionogel and the neat IL, in contrast to ionogel systems wherein the scaffold material is miscible with the IL. This similarity indicates that IL/scaffold chemical interactions are key to the understanding of ionogel electrical performance, especially at elevated temperatures.     

Fabrication and Properties of Polycaprolactone Composites Containing Calcium Phosphate-Based Ceramics and Bioactive Glasses in Bone Tissue Engineering: A Review

Polycaprolactone (PCL) is a bioresorbable and biocompatible polymer that has been widely used in long-term implants and controlled drug release applications. However, when it comes to tissue engineering, PCL suffers from some shortcomings such as slow degradation rate, poor mechanical properties, and low cell adhesion. The incorporation of calcium phosphate-based ceramics and bioactive glasses into PCL has yielded a class of hybrid biomaterials with remarkably improved mechanical properties, controllable degradation rates, and enhanced bioactivity that are suitable for bone tissue engineering. This review presents a comprehensive study on recent advances in the fabrication and properties of PCL-based composite scaffolds containing calcium phosphate-based ceramics and bioglasses in terms of porosity, degradation rate, mechanical properties, in vitro and in vivo biocompatibility and bioactivity for bone regeneration applications. The fabrication routes range from traditional methods such as solvent casting and particulate leaching to novel approaches including solid free-form techniques.     

Solid Electrolytes Based on KAlO<Subscript>2</Subscript>-TiO<Subscript>2</Subscript>: The Crystalline Structure and Conduction

The structure of solid high-conductance potassium electrolytes K_{1 − x} Al_{1 − x} Ti_xO₂ (x = 0.1; 0.2) at 25 and 575°C is studied by a powder neutron diffraction analysis with the application of full-profile Rietveld analysis. Inserting titanium ions removes in potassium aluminate the phase transition at 540°C and the conductance anisotropy typical for its low-temperature form. Both structures are identical (fcc lattice, space group Fd3m). Experiment and calculation coincide best under the assumption that the potassium sublattice is disordered. The conductance increase upon inserting ions Ti⁴⁺ is due, apart from stabilization of the fcc structure, to formation of additional potassium vacancies and larger channels for the migration of potassium cations (ions Ti⁴⁺ are larger than ions Al³⁺).__________Translated from Elektrokhimiya, Vol. 41, No. 7, 2005, pp. 878–883.Original Russian Text Copyright © 2005 by Burmakin, Voronin, Akhtyamova, Berger, Shekhtman.     

Spectroscopic characterization of lithium doped borate glasses

B₂O₃-xLi₂O₃ (x=0, 0.1, 0.5) glasses have been prepared by the Sol-Gel method. The evolution of the composition and the structure of the materials upon thermal treatments are analyzed. Raman spectroscopy measurements reveal that the structure transforms from crystalline to amorphous. After a thermal treatment at 400°C, the materials exhibit a strong luminescence band which disappears upon further heating. In the case of no dopant (x=0) heating at 1150°C results in a Raman spectrum which is almost identical to the one corresponding to bulk B₂O₃ glass obtained by melting and quenching.     

聚偏氟乙烯薄膜压电性的研究

本文研究了聚偏氟乙烯的压电性。聚偏氟乙烯薄膜是用DMA溶剂浇铸而成,然后进行单轴拉伸,并采用热驻极的方法使薄膜成极。实验结果表明,压电活性依赖于拉伸比、极化电场、极化温度和极化时间。此外,还研究了聚偏氟乙烯压电薄膜的稳定性和某些使用特性。     

Electroconductivity of Oxyfluoride 3NdOF · KF

Electrophysical properties of oxyfluoride 3NdOF · KF are studied. Heterovalent substitution of K⁺ ions for Nd³⁺ ions in NdOF increases ionic conductivity by two orders of magnitude (to 10^-4 S cm^-1 at 400°C).     

Synthesis of Quantum-Size Cadmium-Zinc Sulfide Particle-Doped Glasses by the Sol-Gel Method

The optical properties of extremely small particles of semiconductor materials provide a sensitive probe of the band structure in the materials. The Sol-Gel process has been applied successfully to the preparation of small particle-size CdS-doped silica glasses such that quantum size effects are significant. Transparent and colorless gels were prepared through the hydrolysis of a complex solution of Si(OC₂H₅)₄, (CH₃)₂SO, Zn(CH₃COO)₂·2H₂O and Cd(CH₃COO)₂·2H₂O. These gels were heated at 350, 500 and 750°C. The thermal treatments of samples were established by TDA/TGA analysis. By means of shift in optical absorption spectra, quantum size effects could be inferred in glasses containing these calcogenide microcrystals.     

Defect Chemistry of Singly and Doubly Doped Ceria: Correlation between Ion Transport and Energetics

Earlier studies have shown a strong correlation between the enthalpy of formation, ΔH_f,ox, and the ionic conductivity, σ_i, near room temperature in doped ceria systems, which are promising solid electrolytes for intermediate‐temperature solid oxide fuel cells (IT‐SOFCs). The present work demonstrates that this correlation holds at the operating temperature of IT‐SOFCs, 600–700 °C. Solid solutions of Ce_1?xNd_xO_2?0.5x, Ce_1?xSm_xO_2?0.5x, and Ce_1?xSm_0.5xNd_0.5xO_2?0.5x are studied. The ΔH_f,ox at 702 °C is determined by considering the excess heat content between 25 and 702 °C combined with the value of ΔH_f,ox at 25 °C. Both σ_i and ΔH_f,ox show maxima at x=0.15 and 0.20 for the singly and doubly doped ceria, respectively, suggesting that the number of mobile oxygen vacancies in these solid solutions reaches a maximum near those compositions. An increase in temperature results in a shift of the maximum in both ΔH_f,ox and σ_i towards higher concentrations. This shift results from a gradual increase in dissociation of the defect associates.     

Er~(3 )/Yb~(3 )共掺杂AlF_3基氟化物玻璃材料的频率上转换

Er3 /Yb3 共掺杂的AlF3基氟化物玻璃材料ABCY的制备及其上转换荧光性质。样品的组分为 40AlF3 2 0BaF2 2 0CaF2 (2 0 2x 2y)YF3 xEr2 O3 yYb2 O3。在 95 0nm连续LD激发下 ,观察到该材料很强的绿色上转换发光 ,研究了该体系的上转换机理 ,认为Yb3 和Er3 之间的APTE效应是最主要的上转换途径。解释了红、绿色上转换荧光强度比值增大的现象 ,指出了可能的交叉弛豫过程。用公式y =a(x -x0 ) n 对上转换荧光强度与LD工作电流的关系进行拟合 ,得到的结果与理论值很好地一致。     

Electroconductivity of Solid Electrolytes in the Systems K3–2x M x PO4 (M = Ca, Sr, Ba)

Solid electrolytes K_{3 – 2x} M _x PO₄ (M = Ca, Sr, Ba) are synthesized and the temperature and concentration dependences of their electroconductivity are studied. Adding calcium and strontium stabilizes the high-temperature -form of K₃PO₄ at room temperature, while barium-containing solid electrolytes undergo an eutectoid decomposition below 430°C. Maximum electroconductivity is exhibited by K_{3 – 2x} Sr _x PO₄ (7.1 × 10^–3 and 1.25 × 10^–1 S cm^–1 at 300 and 700°C).