DIELECTRIC MEASUREMENTS ON PILE IRRADIATED BaTiO3, SINGLE CRYSTALS

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Submitted on 1 Jan 1972

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DIELECTRIC MEASUREMENTS ON PILE IRRADIATED BaTiO3, SINGLE CRYSTALS

A. Quittet, M. Lambert

To cite this version:

A. Quittet, M. Lambert. DIELECTRIC MEASUREMENTS ON PILE IRRADIATED Ba- TiO3, SINGLE CRYSTALS. Journal de Physique Colloques, 1972, 33 (C2), pp.C2-142-C2-142.

�10.1051/jphyscol:1972248�. �jpa-00214984�

A. M. QUITTET AND M. LAMBERT

DIELECTRIC MEASUREMENTS ON PILE IRRADIATED BaTiO, SINGLE CRYSTALS

Abstract. - When irradiated with rapid neutrons, the tetragonal structure of Baryum Titanate becomes cubic and ferroelectricity disappears [I], ^[2]. We performed systematic measurements in order to check the ferroelectric properties : dielectric constant and spontaneous polarization, along with structural properties by using the anomalous X ray scattering for samples irradiated with doses between 1 x ¹⁰¹⁸ n/cm2 and ¹⁰²⁰ n/cm2.

For normal samples, X ray scattering patterns [3]

& / 1 0 ~ ~ Dielectric conitant

show some local order in the paraelectric phase, that is chain correlations along linear rows. The para-

ferroelectric transition can be interpreted as an order- ^{Ba Ti O3} disorder one in which the elementary dipole is the Integrated doses

whole chain of correlated lattice cells. Such a model ^25- (neutrons /cm2)

provides an explanation of the high value of the Curie Weiss constant. In fact, the Curie Weiss constant as

computed from Landau's theory is : 20

- a 2 ~b ^nicm2

3 1d8 n/cmZ 1 I

1 p,2 o &.lo" ^{nlcm2 I I}

c

2 N k l o g 2 15 -

I I

I I

k being the Boltzman constant, P, the saturated spontaneous polarization in the ferroelectric phase, N the number of chains per unit volume. As the chains become longer, Ndecreases and C increases. The above equation is well verified for correlation of 10 or 12 cells in one chain which is in good agreement with the width of the X ray scattering.

There are three types of measured dielectric proper- -

.-.-=

ties depending on the ranges of irradiation (see Fig.). 0 30 50 70 90 110 130 T("&

For low doses (' 10L8 n1Cm2) a neat peak is Dielectric constant versus temperature or BaTi03 single crystals observed. In the paraelectric phase, the dielectric irradiated with rapid neutrons.

constant follows a Curie Weiss law. The transition temperature (with thermal hysteresis) shifts down somewhat, conversely the Curie temperature shifts up, so that the maximum value of the dielectric constant increases. The spontaneous polarization and Curie Constant increase slightly but the correlation length seems to remain unchanged.

For intermediate doses (between 2 and 8 x 1018 n per cm2), thc dielectric maximum is smoothed and widly broadened so that the value of the dielectric constant remains high in a large temperature range and no longer follows a Curie Weiss law. In addition the spontaneous polarization cannot be determined

from the observed distorted hysteresis loop. On the other hand, the correlation length definitly decreases.

For large doses ( 2 10'' n/cm2) the dielectric cons- tant value becomes low (- 100) and does not change with temperature. All ferroelectric characters and chain correlation h a ~ e disappeared.

Those results show that ferroelectricity is strongly related to local order, i. e. to chain correlations in the crystal structure. Nevertheless a more accurate quanti- tative study seems difficult and in any case would be restricted to low doses of irradiation.

References

[I] WITTELS (M. C.), SHERRILL (F. A.), JOUY. Appl. Phys., 1957,28, 5, 606.

[2] WEIK (H.), SCHNEIDER (J.), Phys. Letters, 1966, 19, 8, 619.

[3] LAMBERT (M.), COMES (R.), Sol. St. Comm., 1969,7, 305.

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972248