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Browse Prior Art Database

New Devices Using Mixed (Ion and Electron) Conductors

IP.com Disclosure Number: IPCOM000118172D
Original Publication Date: 1996-Oct-01
Included in the Prior Art Database: 2005-Apr-01
Document File: 6 page(s) / 209K

Publishing Venue

IBM

Related People

Locquet, J-P: AUTHOR [+2]

Abstract

Disclosed is a novel use for mixed conductors. Mixed conductors are conductors which contain several mobile species which are in general of electronic (electrons or holes) or ionic nature (cation and anions). The movement of these latter species is either achieved by thermal activation, a concentration gradient (diffusion) or the application of an electric field (migration). Although this definition is not very strict, a conductor is called mixed from the moment that the ionic contribution to the conductivity equals roughly '10' sup-3. times the electronic contribution, while for large ionic conductivities it is called an ionic conductor. There is ample use of such ion conductors in the fields of sensors, energy storage (batteries), and energy production (fuel cells).

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New Devices Using Mixed (Ion and Electron) Conductors

      Disclosed is a novel use for mixed conductors.  Mixed
conductors are conductors which contain several mobile species which
are in general of electronic (electrons or holes) or ionic nature
(cation and anions).  The movement of these latter species is either
achieved by thermal activation, a concentration gradient (diffusion)
or the application of an electric field (migration).  Although this
definition is not very strict, a conductor is called mixed from the
moment that the ionic contribution to the conductivity equals roughly
'10' sup-3.  times the electronic contribution, while for large ionic
conductivities it is called an ionic conductor.  There is ample use
of such ion conductors in the fields of sensors, energy storage
(batteries), and energy production (fuel cells).  Several generic and
simple properties of bulk ion conductors are made use of, i.e., on
the one hand, the ability to locally move ionic species under an
applied electric field and on the other hand, the ability to change
the physical properties of the material by changing the local
concentration of ionic species.  This change in properties can be as
fundamental as the change of an insulator into a metal or
superconductor or a change in the carrier type (n- to p-type
semiconductor).

      The major applications of ion conductors or solid state
electrolytes are related to their ability to transport chemically
active species through their matrix under the influence of a
concentration gradient or an electric field and are, therefore, used
in batteries and  fuel cells.  For such applications, a mixed
conductor is not desired as  the electronic species could
short-circuit the electric field.  On the  other hand, mixed
conductors have applications in the field of ceramic  membranes
designed to separate oxygen from air and contact layers (cathode) for
fuel cells.

      The proposed devices rely on several properties of these
materials: i) the possibility to create locally (on a microscopic
range) regions with a large concentration of ionic species; ii) the
ability to migrate some of these ionic species from one region to the
other region under an applied electric field; iii) as these species
are migrating along, where they reside they change the physical
properties of the matrix.  The combination of these three properties
on a microscopic scale allows to taylor a series of novel devices.

      One example of such a material in which these properties can be
easily changed is the 'La' sub 2 'CuO' sub 4 compound.  For an ideal
sample (no defects and no oxygen vacancies or interstitials), this
material is an insulator.  Upon doping with oxygen (which ends up as
interstitials in the lattice) the material becomes a mixed conductor
with oxygen ions as ionic species and with holes as electronic
species.  Using the electrochemical oxidation technique, it is
possible to prepare oxygen rich domain...