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PROPERTIES OF FERROELECTRIC Cd2(NH4),(SO4)3
M. Glogarová, J. Fousek, B. B_ezina
To cite this version:
M. Glogarová, J. Fousek, B. B_ezina. PROPERTIES OF FERROELECTRIC Cd2(NH4),(SO4)3.
Journal de Physique Colloques, 1972, 33 (C2), pp.C2-75-C2-76. �10.1051/jphyscol:1972221�. �jpa- 00214957�
JOURNAL DE PHYSIQUE Colloque C2, supplkment au no 4, Tome 33, Avril 1972, page C2-75
PROPERTIES OF FERROELECTRIC Cd,(NH,),(SO4),
M. GLOGAROVA, J. FOUSEK, and B. B ~ E Z I N A Institute of Physics, Czech. Acad. Sci., Prague
RBsum6. - Un comportement non anormal des proprietes dielectriques et Blastiques dans la phase pardlectrique et I'absence de non-linearit6 dielectrique au-dessus de Tt, indiquent que le CAS est un pseudo-ferroBlectrique.
On Bclaircit la structure en domaines qui depend des contraintes et qui est differente pour les echantillons isoles et pour les Cchantillons en court-circuit.
On determine les proprietks optiques des domaines isolBs et les orientations des parois de domaines.
Abstract. - Non-anomalous behaviour of the dielectric and elastic properties in the paraelectric phase and the absence of dielectric nonlinearity above Ttr indicate that CAS is an improper ferro- electric. The domain structure which is different for insulated and for shortcircuited samples and depends on the stress was deciphered. Optical properties of individual domains and domain wall orientations were determined.
Dicadmium diamonium sulphate (CAS) is known proves the transition to be of the 1st order. The to be ferroelectric [I]. In view of its unusual permitti- transition temperature is not influenced by applied vity behaviour [2] - a sudden increase of E at electric field : aT,,/aE 5 2 x lo-$ deg cm/V. Above
T,,, no dielectric nonlinearity has been observed.
T,, = 92 OK By self-resonance method, we have measured the but no anomaly above it - we have undertaken its elastic moduli at constant E. The results, given in complex study. figure 2, show all sij's to be nearly constant in the PE
8k8 I
90 92 94 96
TPK)
-
phase, including the component sf4, which determines<>
I. Crystal growth. - Single crystals of CAS have
been prepared from water solutions. Since the tempe- 439 rature dependence of its solubility coefficient is nega- 4.8 tive, we use the method of isothermal evaporation of
saturated solutions with pH = 1 to 2, at 80 OC. The 4g7- crystals grown on seeds reach 1 to 2 cm3 in volume.
? ; ,
Their octahedral habit reflects the symmetry of the 3 cubic point group 23 in the paraelectric phase. 6 1,7
11. Behaviour in the paraelectric (PE) phase. - - -. 1.6 Figure 1 shows the weak-field permittivity of a free
-$
1,s16
the difference between the free and clamped values of
FIG. 1. - Temperature dependence of 8 at lkc/s.
permittivity - E" = d?4/s$4. The clamped permit-
2 7'
-
E
- s,, --
- s:~= s: --
- +
iivity was found previously [3] to be temperature inde- : On si constant Ttr. Its sudden pendent. Thus the piezoelectric constant dl, has no increase at T,, varying at different cooling runs and anomaly in the PE phase either.
for different samples results from the occurrence of a
domain structure and is not connected with any para- 111. Optical and domain properties in the ferroelec- electric dielectric anomaly. Temperature hysteresis tric (FE) phase. - The spontaneous polarization P,
-
- ~ X P x
6 e o a u - - - -
- 0,5
100 200 300
T("K)-
FIG. 2. - Elastic moduli versus temperature.
12 -
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972221
(22-76 M. GLOGAROVA, J. FOUSEK AND B. BREZINA arises along the PE twofold axes, creating 6 domains
in the F E phase which has the monoclinic point symmetry 2. Supposing there is no direct interaction between the birefringence and the transition parame- ters, the indicatrix in the cubic coordinate system is (Bo f R13 p:)~:
+
( 8 0 $. R ~ ~ P : ) x ; f+
(Bo+
Rll P?)+
2 r 4 ~ Ps XI ~2 = 1for P, along x,. Here, Rij and rij are the components of the quadratic and linear electrooptic tensor, resp.
This equation determines the extinction positions and birefringence values in different domains. The anti- parallel cc x3-domains )), with P, perpendicular t o the (001) plate, differ in the extinction positions by an angle 2 a, where tan 2 a = 2 r4,/(RI3
-
R12) P,.Experimentally we found 2 a = 180. The principal birefringence measured in these domains An = 0.002 4 is temperature independent. The ct xi-domains )> and
t( x2-domains )) with P, lying in the plate are also optically distinguishable due to the different bire- fringence.
The domain pattern in CAS depends strongly on the electrical and mechanical boundary conditions.
In an insulated (001) plate, the typical pattern consists of stripes with (1 10) boundaries (Fig. 3a). One stripe is an c( x l or x,-domain B, the nieghbouring one consists of a dense network of antiparallel cr x3- domains D, divided by (010) or (100) domain walls.
From the viewpoint of mechanical compatibility conditions [4], these 1800 walls are the only permissible walls in CAS. The stress fields at the non-permissible (110) boundaries are obviously relieved by the dense structure of antiparallel domains.
If the (001) plate is electroded and shortcircuited (Fig. 3b), x3-domains may occupy large portions of the sample. From the x,-domains they are separated by walls with indices close to ( 750 ) ; the theory [4]
shows these wells to be stressed. Crystal cemented even in one point reveal a very restricted electrical switching. Only plates mounted stress-free in an exchange-gas chamber can be made single domain in a field of 15 kV/cm. Antiparallel switching proceeds via needle-shaped domains with permissible walls (100) or (010) (Fig. 3 4 . Even a small scratch in one of the electrodes results in the occurrence of dense anti- parallel x3-domains in this area. This proves the role of the depolarizing field in the resulting domain structure.
[I] JONA (F.), PEPINSKY (R.), Phys. Rev., 1956, 103, 1126.
[2] JONA (F.), SHIRANE (G.), Ferroelectric Crystals, Per-
gamon Press, 1962.
[3] OHSIMA (H.), NAKAMURA (E.), J. Phys. Chem. Solids, 1966, 27, 481.
[4] FOUSEK (J.), Czech. J. Phys., 1971, B 21, 955.
FIG. 3. - The domain patterns in (001) plates for a) insulated sample, b) shortcircuited sample, c) sample mounted in a
stress-free way, under field.
IV. Conclusions. - The non-anomalous PE beha- viour shows that polarization is not the parameter of the transition and CAS is an improper ferroelectric.
An inhomogeneous temperature dependent lattice mode must be responsible for ferroelectricity [5] and its freezing down at T,, should produce a superstruc- ture. The space group of the FE phase is not known so that a thermodynamic analysis, worked out by Dvofgk [6], [7] for GMO and boracites, is not yet possible for CAS. Nevertheless, the insensitivity of T,, to electric fields and the behaviour of clamped E [3]
suggest that similarly as in GMO 181, the inhomoge- neous mode produces the spontaneous deformation by direct coupling while P, arises as an indirect conse- quence through piezoelectricity.
In CAS, 6 domains can exist, but only antiparallel domains are separated by normal walls. Differing from other 3-axial ferroelectrics (perovskites, bora- cites), 900 walls must be stressed. The ct optical readi- bility )) of antiparallel x,-domains exceeds by one order of magnitude that in other ferroelectrics (Rochelle Salt, GMO, KDP). The domain structure and switch- ing is strongly influenced by mechanical and electrical boundary conditions.
[5] INDENBOM (V. L.), SOY. Phys.-Crystallogr., 1960,5, 106.
[6] DvoilA~ (V.), Phys. stat. sol. (b), 1971, 46, 763.
[7] D V O ~ A K (V.), Czech. J. Phys., 1971, B 21, 1250.
[IS] AXE (J. D.), DORNER (B.) and SHIRANE (G.), Phys. Rev.
Letters, 1971, 26, 519.
