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Submitted on 1 Jan 1972
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SULFATE DE GLYCOCOLLE (T. G. S.)TIME DEPENDENCE OF MATERIAL CONSTANTS OF
TGS AFTER POLARIZATION REVERSAL
J. Albers
To cite this version:
J. Albers. SULFATE DE GLYCOCOLLE (T. G. S.)TIME DEPENDENCE OF MATERIAL CON- STANTS OF TGS AFTER POLARIZATION REVERSAL. Journal de Physique Colloques, 1972, 33 (C2), pp.C2-199-C2-200. �10.1051/jphyscol:1972267�. �jpa-00215003�
SULFA TE DE GL YCOCOLLE (T. G. S.)
TIME DEPENDENCE OF MATERIAL CONSTANTS OF TGS AFTER POLARIZATION REVERSAL
J. ALBERS
Institut fiir Experimentalphysik I1
D-66 Saarbriicken, Universitatscampus 4, Germany
R6sum6. - Le mouvement des parois des domaines augmente la constante dielectrique du TGS dans la phase ferroelectrique et produit des effets secondaires aprks un renversement de polarisa- tion. Nous avons montrk que certaines constantes de matkiaux, mesur6es par des m6thodes de rksonance pikzoklectrique, sont influencees par ces effets secondaires et d'autres non.
Abstract. - Domain wall motions raise the dielectric constant of TGS in the ferroelectric phase and produce after effects after a polarization reversal. It is shown which material constants, measu- red by piezoelectric resonance methods, are influenced by these after effects and which are not.
In the ferroelectric region many material constants of TGS depend on the domain structure and the motion of domain walls. To avoid these influences, the mate- rial constants are normally measured in the presence of a dc field. Even very high dc fields not at once lead to a monodomain crystal. Therefore, it is of interest to know which material constants depend on domain structure and domain wall motions, and how long one has to wait to get values of a monodomain crystal.
The TGS samples were splitted perpendicular to the ferroelectric axis, polished with water and provided with evaporated gold electrodes on the splitted faces.
The samples were about 30 mm long (c-direction), 1 mm thick b-direction), and 3 mm broad, so that they could be used as piezoelectric resonators. The results shown here were measured at the same probe with dimensions 29.4 mm, 3.35 mm, and 0.876 mm.
The dielectric constant could be determined by bridge methods or from the ratio of voltages across the probe and across a series resistor which also served to detect the resonance and antiresonance frequencies.
Figure 1 shows the decrease of the real part
&i2
of the relative dielectric constant E~~ of the relative dielec- tric constant E~~ and the antiresonance frequency fA.The sample was kept 3 days at 60OC and cooled down to room temperature. After waiting a fur- ther day, the voltage Uo was applied and
.&
and fA were measured.&i2
decreased almost propor-tionally to the logarithm of time, in accordance with measurements made by Rewaj [I] under similar conditions. After one weak stable values of ei2 and f, are reached, which of course depend on the voltage Uo.
Even when a voltage U, = 300 V (3.4 kV/cm) lay at the crystal for half a year, the same values for ~ ; 2 and f, were measured at U, = 100 V. That means that these stable values correspond to the monodomain state. For all other measurements this stable state was the starting point instead of the badly reproducible domain structure which occurs after cooling the crystal from above the Curie point.
The time dependence of the dielectric constant after a first (part I) and a second (part 11) polarization reversal is shown in figure 2. After the second polari- zation reversal the stable state ( E / Z = 28.5) is reached again in a time which is almost equal to the period of opposite poling. The behaviour of e i 2 shows some analogies to that of the after effect of the dielectric displacement after a polarization reversal [2].
0.1 1.0 10; 0.1 1.0 t[minl--10
FIG. 2. - After effect of &;2 after a first and a second polariza- tion reversal, according to the voltage program. Measuring
voltage U = 0.1 V rms.
FIG. 1. - Variation with time of the real part E;Z of the relative dielectric constant and of the antiresonance frequency f ~ .
Measuring voltage U = 0.1 V rms.
The time dependent real and imaginary parts of the dielectric constant t2, are due to domain wall motions and depend on the amplitude and the frequency of the measuring field, as already was shown by Fousek and Janougek [3] as well as by Lauginie and ~ i l e t t a [4].
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972267
C2-200 J. ALBERS For a piezoelectric resonator, oriented parallel to the c-axis, the following two systems of linear equa- tions may be chosen to describe the coupling between the electric and elastic properties :
( S : strain, T : stress, D : dielectric displacement, E : field, s : elastic compliance coefficient, E : dielectric constant, /3 : dielectric module, d and g : piezoelectric constants, suffices D and E : constant D 2 and E,, suffix T : constant T,). The following relations bet- ween various coefficients are of interest :
&Z2
is the dielectric constant at constant S3. All coeffi- cients can be obtained from measurements of the low frequency dielectric constantEL
the resonance fre- quency fR, and the antiresonance frequency fA [5].For a monodomain crystal the coefficients are inde- pendent of time. A multidomain crystal can influence the values of coefficients by domains with false sign of the dielectric displacement and by the moving of domain walls. The coefficients d2, and gZ3 result from the electrostrictive constant Q3, [6], and their signs depend on the sign of the spontaneous dielectric displacement. Therefore, the effective values of g,, and d2, should be proportional to the effective value of the dielectric displacement. In case of d2, this assumption was tested and found to be true.
Normally the measurements of d23 and g23 were made when only a negligible part of the crystal had domains with the false sign of the dielectric displace- ment. Therefore only the effects of the domain wall motion had to be considered.
Due to domain wall motions the measured dielectric displacement D is larger than that of a monodomain crystal. For D does not appear in eq. (2b), one can assume that the coefficients d23 and S& should not show an after effect which is correlated with the after effect of the dielectric constant E ~ Z . From eqs. (3) to (6)
then there follows that bT2, eZ2, g Z 3 , and s;3 must vary with time.
The clamped dielectric constant
&Z2
was measured as usual at the frequency 2 fR. The difference&T2
-&Z2
is not exactly independent of time. But this fact is due to the dispersion with frequency between 10 kHz and 2 fR of that part of
&TZ
which results from domain wall motions as was already found by Lauginie and Giletta [4].In figure 3 are shown g23 and s3D3 depending on time after a polarization reversal. During the measuring time the elastic compliance coefficient s t 3 did not change by more than the expsrirnental error of about
+
2 x%.
The relative change of sy3 is about-
two orders of magnitude larger than the possible error in s j 3 . E
1.25 1 7 3
0.1 1.0 t [min]
-
10FIG. 3. -After effect of the elastic compliance s& and the piezoelectric constant g23 after a polarization reversal.
The piezoelectric constants d2, and g23 could be determined with an accuracy of about 1 %. During the measuring time shown in figure 3, dZ3 did not change by more than this amount, whereas the change of g,, is considerable.
As could be shown it is very important to pole a TGS crystal for a sufficient long time in order to get time independent material constants by piezoelectric resonance methods. If this is taken into consideration, correct values of a monodomain crystal can be obtain- ed. For example s!3 does not show the peak at the Curie point which was found by Ikeda et al. [6].
Acknowledgment. The author wishes to thank Prof. Dr. H. E. Miiser for his constant interest and stimulating discussions.
References
[I] REWAJ (T.), Acta. Phys. Polonica, 1964, 26, 1093. [4] LAUGINIE (P.) and GILETTA (I?.), Proc. Europ. Meeting [2] ALBERS (J.), Proc. Europ. Meeting Ferroelectricity, Ferroelectricity, Saarbriicken 1969 (Wiss. Ver-
Saarbriicken 1969 (Wiss. Verlagsges., Stuttgart, lagsges., Stuttgart, 1970), p. 219.
1970), p. 207. [5] MUSER (H. E.) and BITTEL (H.), Arch. elektr. ~ b e r t r a - auna. 1955. 9. 231.
131 FOUSEK (J.) and JANOUSEK (V.), Phys. stat. sol., 1966, [6]
IKEDA (f.),
TANAKA (Y.) and TOYODA (H.), J. Appl.13,195. Phys., 1962, 1, 13.
