Na-ion Conductivity Research Articles

Intermediate Range Order in SixSe1−x Glasses

ABSTRACTSix (chalcogen)1−x glasses represent a class of amorphous, binary, semiconducting solids of increasing theoretical and technological importance. In our laboratory, attention has been directed to these systems since they can form the basis of a remarkable series of fast ion conducting glasses. These vitreous materials are being considered as solid electrolytes for advanced electrochemical cells of high specific energy. For example, when stoichiometric SiS 2 is appropriately combined with Na2S, a Na-ion conducting glass results that has a room-temperature Na-ion conductivity that is several orders of magnitude greater than that of its oxide counterpart [1].The structures and defects present in these alkali-modified, ternary glasses are not known [2]. In fact, until recently, there has been a paucity of attention directed to the “simple” binary glass systems Si/S, Si/Se, and Si/Te. Therefore, four years ago, we began a systematic study of the structure and dynamics of Si xS1 SixSe1−x, and SixTe1−x covalent glasses. Of necessity, an interdisciplinary approach was adopted.

Phase transition in nasicon (Na 3Zr 2Si 2PO 12)

A second order phase transition has been found in Na 3Zr 2Si 2PO 12 by three independent techniques 1. i. Electrochemical investigations including ac-impedance technique showed a reversible change in the activation energy for Na-ion conduction from 34.2 kJ mol −1 at temperatures below 425 K to 20 kJ mol −1 for higher temperatures. 2. ii. Specific heat measurements show a clear indication of a phase transition at 420 K with ΔH = 2.07 kJ mol −1. 3. iii. High temperature X-ray diffraction powder patterns reveal a change from the monoclinic into the rhombohedral phase at the transition point.

Physical-chemical approach to the transient change in Na ion conductivity of excitable membranes

Physical-chemical approach to the transient change in Na ion conductivity of excitable membranes

Physical-chemical approach to the transient change in Na ion conductivity of excitable membranes

A new method is proposed for analyzing the rapid transient current component (Na ions) in voltage clamp experiments on excitable membranes. The method is based on only two very general assumptions: the Na ion conductivity of an excitable membrane is determined by some general membrane parameter, the kinetic behavior of which is consistently described by the sum of only two simple exponential terms. A least square computer analysis for the data by L. Goldman and C.L. Schauf on Myxicola axons is described [(1973) J. Gen. Physiol. 61, 361-384]. The method gives (as a result) the relationship between conductivity and membrane parameter. A physically plausible, chemical model (cycle of three states) is proposed for a dissipative control of the Na ion conductivity. The rate constants for the specific model are calculated from kinetic parameters derived only from the general analysis. These rate constants reproduce the original voltage clamp data in every feature which includes peak current ratios (h infinity)-shift with test potential. By allowing for differences in the experimental conditions, we derive essentially the same rate constants for the voltage clamp data of A.L. Hodgkin and A.F. Huxley on squid giant axons.