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THE PECULIAR DOMAIN STRUCTURE AND ITS UNUSUAL BEHAVIOUR IN THE β-PHASE OF THE FERROELECTRIC NaH3(SeO3)2

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THE PECULIAR DOMAIN STRUCTURE AND ITS UNUSUAL BEHAVIOUR IN THE β-PHASE OF THE

FERROELECTRIC NaH3(SeO3)2

L. Shuvalov, A. Askochensky, V. Kirikov

To cite this version:

L. Shuvalov, A. Askochensky, V. Kirikov. THE PECULIAR DOMAIN STRUCTURE AND ITS

UNUSUAL BEHAVIOUR IN THE

β-PHASE OF THE FERROELECTRIC NaH3(SeO3)2. Journal

de Physique Colloques, 1972, 33 (C2), pp.C2-163-C2-164. �10.1051/jphyscol:1972256�. �jpa-00214992�

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JOURNAL DE PHYSIQUE Colloque C2, supplkment au no 4, Tome 33, Avril 1972, page C2-163

THE PECULIAR DOMAIN STRUCTURE AND ITS UNUSUAL BEHAVIOUR IN THE p-PHASE OF THE FERROELECTRIC NaH,(SeO,),

L. A. SHUVALOV, A. A. ASKOCHENSKY and V. A. KIRIKOV Institute of crystallography, Academy of Sciences of the U. S. S. R., Moscou, U. S. S. R.

Resume.

-

On Btudie les particularites du comportement de la structure au domaine dans la phase fi de NaHs(Se03)~. Nous montrons que les parois du domaine qui ne sont pas ti 180°, et qui sont parall&les au champ appliquB se chargent. Dans ce cas les processus de polarisation du cristal sont le sibge d'un &tat qui n'a jamais C t e observe a notre connaissance : le remplacement irrbversible de pressions chargees pour des parois non chargees et stables perpendiculaires a E. Les particularites des courbes P(E) correspondent au comportement specifique de la structure au domaine.

Abstract.

-

The peculiarities of the behaviour of the domain structure in p-phase NaH3(Se03)2 are studied.

It is shown that non 1800 domain walls being parallel to the applied field become charged.

In this case the further process of polarization of the crystal contains the stage, which has not been observed so far : irreversible replacing of charged walls by stableuncharged walls perpendicular to E. The peculiarities of curves P(E) correspond to the specific behaviour of the domain structure.

The triclinic P-phase of NaH,(SeO,), (STHS) is the first ferroelectric in which two ferroelectric axes were observed [I], [2]. Correspondingly the domain struc- ture of the /?-phase has some characteristic peculiarities in static and dynamic properties studied in this paper (see also

ill,

PI,

PI).

Since initial a-phase STHS is centrosymmetrical only non 1800-domains are distinguishable in /?-phase by the polarising microscope.

Non 1800-domain walls are oriented along the bissectors of the angles between the Ps-axes, i. e. parallel to the two-fold axis (y-walls), or to the mirror plane m of the a-phase (m-walls). In the virgin crystal y- and m-domains should have undistinguishable 1800-sub- structure for the compensation of the microscopical polarization (Fig. 1).

If virgin specimen had only y- (or m) domain structure than the applied electric field perpendicular to domain walls did not change visible domain structure.

In spite of that, the saturated Px(Ex)

-

or Py(Ey)

-

loops were observed. P(E)-curves obtained for the loops had usual character and practically coincided in increasing and decreasing fields.

It is obvious that in this case the undistinguishable 1800-switching of domains occurred, but non 18O0- switching was absent, because the field did not create any preference between two Ps-axes. This situation is unusual : the full 1800-switching of domains and saturated P(E)-loops correspond to the immovable visible domain structure and to the switching of only one component of Ps(Psx or Psy).

If electric field was applied along x- or y-direction t o the specimen consisted only of the m- or y-domains parallel to the non 1800-domain walls, than the visible domain structure was not changed at first. But P(E)- loops were observed and curves P(E) had tendency to a saturation (Fig. 2a, curve 1)). This means, that the partial 1800 switching took place in the sample with inevitable appearance of the charged walls [2]. During the further increasing of the field the metastable charged walls rapidly changed to the perpendicular stable domain structure (Fig. 3).

Correspondingly the slope of the P(E)-curve changed ubruptly. During the next increase and decrease of field new visible domain structure did not change and curves P(E) became smooth (Fig. 2a, curve 2).-1f the FIG. 1.

-

Scheme of the domain structure of B-phase

virgin specimen has the y- and m-domains only than NaH~(Se03)z : a, d,-virgin structure with 180°-substructure;

uncharged (b, f ) and charged (c, e) y (b, c)

-

and rn (e, f ) - the knee of the P(E)-curve was smaller (Fig- 2a, domain walls when Ez (b, c) and Ey (c, f) are applied. curve 3).

Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972256

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C2-164 L. A. SHUVALOV, A. A. ASKOCHENSKY AND V. A. KIRIKOV

s

J

0 Z 5 .

V 1 e 3 4

-

E xrcm-f

(4

FIG. 2. - P(E)-curves for the samples with different virgin domain structure and different direction of applied fields : a) P,(E,)-curves for the samples with m-domain structure (1) with y-domain structure (2) ; with the mixed structure (3) ; b) P(E)-curves at E

11

Ps (1) ; reversed curve P(E) (2) ; scheme (3) : two plots, correspond to the switching of the 180-walls with the replacing of m-domain structure by y-structure, third plot

connect with the turning of the Ps along one direction.

Manipulation with fields E, and Ex gives the possibi- lity to transform the m-domain structure into y- structure and vice versa.

If applied field was parallel to the Ps axis than the preference of the Ps-axes did not take phase and the process of polarization consisted of the different overlaped stages : the 1800-switching along one and then along the second P,-axes, then replacing of charg- ed walls by uncharged ones with the continuation of the 1800-switching and, at last, irreversible turn Ps from one axis to the other with the disappearence of the visible domain structure. In the next cycles of the field reversal the visible domain structure did not appear any more, i. e. 1800-switching along one P,-axis kept stable.

FIG. 3. -The photographies of the domain structure (2-cut, T = 170 OK, 75 x ) : a) the virgin m-domain structure ; 6) the

same specimen after application of the E,.

According to this processes the P(E) curve at first had knees (Fig. 2b, curve 1) but in the next cycles they irreversible disappeared (Fig. 2b, curve 2). The scheme (Fig. 2b, curve 3) of non overlaped stages of polariza- tion shows the same knees as experimental curve.

The analysis of the geometry of the domains shows, that in the case of the y-domain, non 1800-walls become charged only when the direction of the field lies in the plane of Ps-axes inside the angle

+

(90

-

cp)

from the y-axes (cp E 340 is the angle between the y- and P,-axes) ; and in the case of m-domain sample when the direction of the field lies inside the angle

+

9 from the x-axis.

All considered peculiarities of the behaviour of the domain structure in the p-phase in STHS will be caracteristic to any ferroelectric phase with the plane configuration of the Ps-axes.

The optical observation of specimens of Na(D,H,-,),(SeO,), crystals shows us that the nucleation

p

and y-phase at the a +

P

and a + y phase transitions took place with the movement of the phase front through the crystal.

It was found that the visible domain structure might survive for a long time (up to several hours) 10-15O below the transition temperature Toy. This agrees with the uncertainty of the dielectric [I] and dilatometric [5]

determinations of the TBy with decreasing T.

At increasing

T

the large temperature hysteresis was observed in some cases, and the visible domain struc- ture (i. e. the P-phase) appeared only near Tga in accordance with (1). It seems that such temperature behaviour of STHS crystals are caused by the peculiari- ties of the domain structure ofp-phase.

References

[I] SHUVALOV (L. A.), IVANOV (N. R.), Phys. Stat. Sol., [4] SHUVALOV (L. A.) e t GI., Report on the 2nd European

1967,22,279. meeting on ferroelectricity.

12] SHUVALoV et a'.7 J . Phys. Suppl.y [5] MIKI (H.), MANTA (Y.), J. Phys. SOC. Japan, 1970,28, 1970, 28, 75.

[3] ASKOCHENSKY (A. A.) e t al., Izv. Akad. Nauk S. S. S. R., 143.

Ser.fiz., 1971,35,1877.

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