CONDUCTIVITY RELAXATION IN STRUCTURE Pt-LIQUID V2O5-Pt

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CONDUCTIVITY RELAXATION IN STRUCTURE Pt-LIQUID V2O5-Pt

A. Aleksiejünas, R. Bareikiené, V. Bondarenko, S. Gečiauskas

To cite this version:

A. Aleksiejünas, R. Bareikiené, V. Bondarenko, S. Gečiauskas. CONDUCTIVITY RELAXATION IN

STRUCTURE Pt-LIQUID V2O5-Pt. Journal de Physique Colloques, 1981, 42 (C4), pp.C5-1059-C5-

1062. �10.1051/jphyscol:19814232�. �jpa-00220863�

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JOURNAL DE PHYSIQUE

CoZZoque C4, suppZdment a u nOIO, Tome 42, o c t o b r e 1982 page C4-1059

C O N D U C T I V I T Y

RELAXATION I N

STRUCTURE P t - L I Q U I D V205-Pt

A. Aleksiejcnas, R. ~areikien;, V. Bondarenko and S. ~esiauskas

Semiconductor P h y s i c s I n s t i t u t e , Academy o f S c i e n c e s , L i t h u a n i a n SSR, K. ~ o z e ~ o s 52, 232600, V i l n i u s , USSR

Abstract.

-

T h e voltage c u r r e n t (V-I) c h a r a c t e r i s t i c s a n d conductivity relaxation in liquid V 2 0 5 have been investigated. T h e experimental r e s u l t s in given interpretation show that the asymmetry of V-I c h a r a c t e r i s t i c s a n d conductivity relaxation in liquid V 2 0 5 a r e c a u s e d by the re-distribution of the concentration of the oxygen i o n s in the electric field.

T h e data on the electrical properties of liquid vanadium pentoxide a r e not sufficient.. F o r example, the physical c a u s e of V-1 c h a r a c t e r i s t i c s of the structure metal electrode-liquid V 0

2 5 interpreted a s being due to p-n junction [l] i s to be doubted, b e c a u s e there exist a n inadequacy of temperature v a l u e s in the

d e s c r i b e d experiments. In o d e r to explain this question a n d c a u s e s which a r e responsible for the conductivity relaxation of liquid V 2 0 5 when the direct current s o u r c e i s connected to the structure

121 ,

the investigation of the electrophysical properties of V 2 0 5 a t different temperatures w a s undertaken.,

T h e measurements were carried out using the platinum cell which a t the same time s e r v e d a s one of the electrodes. Tempe- rature w a s registered by ~ t - ~ t / ~ h thermocouple, the platinum wire of whick w a s u s e d a s the other electrode., V-I characteris-

t i c s were investigated by d.c. a n d pulse techniques. All. measurements were fulfilled in the air.

T h e typical V-1 c h a r a c t e r i s t i c s of the structure measured in static regime a r e shown in Fig. l., Curve 1 i s obtained when the temperature difference between the e l e c t r o d e s w a s (1058-1019) K, c u r v e 2

-

(959-933) K. F u r t h e r on, we will be c o n c e r n e d with the direct part (low r e s i s t a n c e state) of V-I c h a r a c t e r i s t i c s

(line OA, Fig. l), which w a s obtained when the negative electrode of the d.c.+ s o u r c e w a s connected to the hotter electrode of the structure a n d the r e v e r s e p s r t (high r e s i s t a n c e state) corresponding to the positive polarity of the mentioned electrode (line G B ,

Fig. 1).

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:19814232

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JOURNAL DE PHYSIQUE

Fig.L T h e statical V-I c h a r a c t e - Fig.2. R e s i s t a n c e d e p e n d e n c i e s ristic of liquid V205.. T h e tem- on time. Curve 1

-

formation of perature difference between low r e s i s t a n c e state; c u r v e 2

-

e l e c t r o d e s for c u r v e s 1

-

(1058- formation of high r e s i s t a n c e -1019) K a n d 2

-

(959-933) K ; s t a t e ; c u r v e 3

-

own transition

from low to high r e s i s t a n c e state.

R, ^Q

T K

It w a s found that V-I characteristic w a s l i n e a r a n d

40 symmetrical when measured by

pulse technique. In t h i s c a s e

36 the r e s i s t a n c e of the structure

to the pulse current c o r r e s p o n -

iooo

ded to the d.c. r e s i s t a n c e of the 20

r e v e r s e part of the static V-I 950 c h a r a c t e r i s t i c s when the tempe-

do rature difference a n d d i s t a n c e

between the e l e c t r o d e s were the 0 0.5 LD F 5 &,mm same.. T h e r e s i s t a n c e of the

structure changed depending on Fig.8, T h e r e s i s t a n c e distribu- _._S _- the polarity of the connected tion in liquid V 2 0 5 in the high d.=. voltage. Typical r e s i s t a n c e

a n d low r e s i s t a n c e s t a t e s

( c u r v e s 1 a n d 2 respectivly). d e p e n d e n c i e s on time a r e shown T h e temperature distribution i n Fig. 2. Curve 1 illustrates (curve 3).

the c a s e when the d.c., voltage of 2 U (corresponding to the direct part of the V-I c h a r a c t e r i s t i c s ) i s connected to the structure in high r e s i s t a n c e state, W h e n the polarity of the d.c.. voltage i s abruptly changed, the r e s i s t a n c e of

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the structure r i s e s t b the initial high resistance value (Fig* 2, curve 2).,Curve 3 in Fig. 3 illustrates the transition of the structure to the high resistance state when the voltage of 2 V, which formed the low resistance state w a s lowered abruptly to zero*

In Fig. 2 c u r v e s 1 and 2 correspond to the lower scale of time, curve 3

-

the upper one.

The nonlinearity and asymmetry of V-I characteristics and conductivity relaxation were found only in the c a s e when the temperatures of the electrodes were not equal and V-I characteristics were measured by d x . + technique. The temperature distribution and the resistance distribution in liquid V 0 were measured.. The

2 5

results a r e shown in Fig. 3 where c u r v e s 1 and 2 represent the resistance distribution along the axis joining the central electrode with the platinum cell in the c a s e of the high and low resistance states of liquid respectively. Curve 3 shows the t e m p e r ~ t u r e distribution,

The asymmetry coefficient of the V-I characteristics w a s determined a s

K

=

Id / 1, .

^{H e r e}

Id

i s currsnt in the direct and

I p

in the reverse parts of the V-I characteristic, when

me

applied voltages a r e equal. Then for curve l in Fig. 1 we find K l r 7 a n d for curve 2

-

^KZ"--¹⁵^(U⁼²^V). One c a n s e e that the asymmetry of the V-I characteristics

was found both in the c a s e when the temperature difference between the electrodes includes the temperature of the thermo-

-e.m.f. sign change (T 'V 1023 I< [3] ) and in the c a s e when

C

this difference does not include it, but the value of coefficient K i s greater in the latter case. This permits u s to claim that the explanation of the V-I characteristics asymmetry by the origins of the p-n junction in liquid V205 [l] i s not satisfactory.

It i s known that the conductivity of liquid V205 i s a f f e c t e i by electron jumps between V S+ and

v4+

ions and it i s in proportion to the

v 4 +

ion concentration

143 .

^From ^[43 results, it is possible to show that the

v4+

concentration in liquid V 0 i s in

n 2- 2 5

proportion to CO1-

,

where CO*- i s

0

ion concentration and

n > 0 .

In .the c a s e of temperature difference, concentrations

of '+V and

02-

ions in different regions of liquid a r e different.

If the negative potential i s applied to the hotter region of liquid, the flow of

0

2- Ions to the lower temperature region occurs. This makes the resistance of the latter region to d e c r e a s e and the

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JOURNAL DE PHYSIQUE

structure p a s s e s into a low r e s i s t a n c e state a s w a s found in the experiment. If the positive potential i s applied to the hotter region of liquid, the negative s p a c e c h a r g e which i s n e a r e r to the hotter electrode p r e v e n t s the

0'-

ion flow a n d the structure remains in a high r e s i s t a n c e state., T h e a b w e -mentioned w a s confirmed by the r e s u l t s whichare shown in Fig., 3 whence it follolvs that the transition into a low r e s i s t a n c e state i s c a u s e d

by a d e c r e a s e in the resistivity of the colder region of liquid and, b e s i d e s , this p r o c e s s i s not a s s o c i a t e d with the heating d u e to electr-ic current. B e s i d e s , the r e s i s t a n c e relaxation time with the voltage applied i s l e s s than the one when the equilibrium in liquid i s restored by the ion thermal movement.

O n e c a n conclude that the asymmetry of static V-1 c h a r a c - teristics a n d the r e s i s t a n c e relaxation of liq~lid V O 5 are c a u s e d

2

by the re-deslribution of the concentration of the oxygen i o n s in the electric field.

References

1 Zoljan

l's.,

Fizika Technika Poluprovodnikov

(SW.), 6

(1972) 2056.

2 ~ l e k s i e j u n a s A.A., ~ a r e i k i e n ; R.V., Bondarenko V.M*

~ s i a u s k a s S.J+ Siktorov N.K+ Lietuvos fizikos rinkinys ( ~ d v . 4 , (1981) in pP'ess+

3 Zofjan ^T&.t, Regel A.R., Solid State P h y s i c s (sov..),

6

(1964) 1520.

4 P a s t u c h o v E.A., Jesin O.A., Vatolln N.A., Neorganitcheskije materialy

(SW.), 4

(1968) 1 9 6 0 , ~