Baroemf
in O2 – ZrO2 – YBa2CuO7-x (YBCO)
system
Rahimbekov
A.Zh., Azimzhan A.N.
I.Zhansugurov
University, 040008 Taldykorgan, Kazakhstan
We have studied baroemf of Pt, O2
│ZrO2│Pt, O2, YBCO cell induced by load
applied to YBCO sample in equilibrium with one of the gas electrodes. Superionik
- this is a solid superionic compound, one of the sublattices, which,
figuratively speaking, melted. Issue is devoted to the superionic state is now
a lot of theoretical and experimental studies. More work is associated with the
creation of a variety of devices that use a high ionic conductivity
superionikov [1] . In the superionic state atomic lattice does not form a
periodic potential inherent in the crystal. This leads to new problems still
unresolved. For example, electrons and holes are not ordinary kvachastitsami
and their energy states are no longer determined by conventional Brillion zone.
The lattice vibrations superionika not describe, using the representation of
phonons. New problems arise in the description of contact phenomena. On the
border with superionika electrode, in addition to the contact potential
difference, there are mechanical stresses. This fact leads to a kind of
potential barrier, whose influence on ion transport and is considered in this
paper [2]. It is known that YBCO compound is easily equilibrated
at comparatively low temperatures with gas phase by absorption of liberation of
pxygen. In this case the sample volume changes the oxygen absorption resulting
in decrease an not increase of volume. Therefore, according to the Le Chatelier
principle, the decrease of the sample volume induced by an external load should
lead to adsorption of oxygen by the sample and6 consequently, to rise of its
weight and change in chemical potential of atomic oxygen. As a result baroemf
E= / 2e appears at the cell electrodes (e is the electron charge,
- the increment of chemical potential of atomic oxygen in the
sample and gas phase environment induced by load) [3].
Let us consider
two particular cases corresponding to conditions: c>>v and v <<
v, where v is the gas volume around
the sample and
v is the change of this volume at
constant gas pressure produced by the action of the load. In the first case the
loading would lead to an increase of oxygen content in the sample but the
oxygen pressure around the sample would remain practically constant and baroemf
will be close to zero. In the second case the oxygen content in the sample
would remain practically constant (since there is not enough oxygen in the cell
for significant change of oxygen content to occur) but the oxygen pressure
around the sample would change and baroemf appear. We shall take into account
that chemical potential of the oxygen atoms in YBCO depends in the lattice
constant a, b, c, which depend in their turn on the load. We shall assume also
that polycrystalline sample consists of there equal parts, the direction of
load action coinciding with the direction of “a” axis of microcrystal in the
first part, with the direction of “b” axis in the second part, and with the
direction of “c” in the third part. Then in the first approximation we can
write
(1)
where is stress,
/
/
,
/
components of contribution of oxygen atoms into deformation
potential and da/d
,db/d
,
dc/d
- values of linear compressibility which
can be obtained from experimental dependences of the lattice constants on the
oxygen pressure and on stress, respectively [4]. The dependence
(x) calculated from (1) has singularities at the points x=0.2 and
x=0.5 connected with “phase separation” and transition to tetragonal phase,
correspondingly. Experimental studies have shown that YBCO compound absorbs
actually oxygen under the load. The baroemf values observed are in fair
agreement with the estimates from (1)
Literature
1. Chandra S. Superionic Sol., North-Holland, 1981. 885 p.
2. Phys., Superionic Conductors / ed. M. B. Salamon, Springer - Verlag,
Berlin-Heidelberg-New York, 1979. 364 p.
3. Ukshe EA, NG Bukun Solid electrolytes. Moscow: Nauka, 1977. 146 with.
4. Chebotin V., M. Perfiliev Electrochemistry of solid electrolytes. Moscow:
Khimiya, 1978. 345.