Conduction and Transport Numbers in Metacomposites MeWO<Subscript>4</Subscript> ⋅ WO<Subscript>3</Subscript> (Me = Ca,Sr, Ba)

The conduction and transport numbers of charge carriers for composites in the systems MeWO₄-WO₃ (Me = Ca, Sr, Ba) are studied as a function of the temperature and the activity of oxygen in a gas phase. The transport numbers are determined by an emf method and are estimated from dependences of conductance on the activity of oxygen in a gas phase. The deficiencies of the given procedure as applied to investigation of properties of composite phases are analyzed. The materials under study are classified with a class of metacomposites. The concentration intervals of the ionic, mixed, and electronic conductions are determined. The conduction of composites of compositions (100 − x)MeWO₄ ⋅ xWO₃ is predominantly ionic at x ≤ 10 (Me = Ca), x ≤ 60 (Me = Sr), and x ≤ 45 (Me = Ba). The obtained data are explained in the framework of a model that represents a composite as a distributed matrix system where a film of surface phase MeW-s with a high mobility of oxygen ions plays the role of a connected matrix. It is presumed that the surface phase MeW-s possesses double-sided surface activity (α _MeW-s ≤ ) and a higher mobility with respect to MeWO₄ and WO₃. The discovered anomalies of dependences (T) and partial dependences , σ_el(T) are explained by a change in the stoichiometry, morphology, and the degree of connectedness of surface phase MeW-s caused by with a change in the temperature and composition of composites.__________Translated from Elektrokhimiya, Vol. 41, No. 6, 2005, pp. 680–693.Original Russian Text Copyright © 2005 by Neiman, Pestereva, Sharafutdinov, Kostikov.Published on the basis of a report delivered at the VII Meeting on Fundamental Problems in Solid-State Ionics (Chernogolovka-2004).     

Carbon nanofibers/polypyrrole nano metacomposites

Carbon nanofibers (CNFs)/polypyrrole (PPy) nano metacomposites are prepared by in situ polymerization in this article. The negative permittivity and negative permeability of CNFs/PPy nano metacomposites are achieved simultaneously. CNFs/PPy composites form different morphologies with the increase in CNFs content. Complex conductive networks formed by overlapped CNFs are present in CNFs/PPy composites with 30 and 50 wt % CNFs. The negative permittivity of the CNFs/PPy composites is attributed to the plasma oscillation of delocalized electrons, and the negative permeability results from a large number of conductive loops. The appearance of negative permeability is accompanied by the decrease in resistivity, which reflects that a large number of conductive loops are derived from complex conductive networks. Double negative property appears in the frequency range 845–1000 MHz in CNFs/PPy composites with 30 wt % CNFs content and 825–1000 MHz in CNFs/PPy composites with 50 wt % CNFs content. CNFs/PPy composites present double negative property in a wider frequency range compared with MWCNTs/PPy nanocomposites. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 1724–1729