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Submitted on 1 Jan 1972
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THE ELECTRICAL PROPERTIES OF NON-LINEAR FERROELECTRIC CERAMICS WITH THE
PEROVSKITE STRUCTURE
Dr. Verbitskaya, L. Alexandrova, L. Sokolova
To cite this version:
Dr. Verbitskaya, L. Alexandrova, L. Sokolova. THE ELECTRICAL PROPERTIES OF NON-
LINEAR FERROELECTRIC CERAMICS WITH THE PEROVSKITE STRUCTURE. Journal de
Physique Colloques, 1972, 33 (C2), pp.C2-273-C2-275. �10.1051/jphyscol:1972296�. �jpa-00215032�
JOURNAL DE PHYSIQUE Colloque C2, supplkment au no 4, Tome 33, Avril 1972, page C2-273
THE ELECTRICAL PROPERTIES
OF NON-LINEAR FERROELECTRIC CERAMICS WITH THE PEROVSKITE STRUCTURE
Dr. T. N. VERBITSKAYA, senior research worker, dipl. eng. L. M. ALEXANDROVA, dipl. eng. L. S. SOKOLOVA,
V. I. Ulyanov (Lenin) Electrical Engineering Institute, Leningrad
Rkum6. - Les parametres electriques des matkriaux ferroklectriques prksentant des proprietks fortement non linkaires, utilists pour la fabrication des capacites non linkaires tels que les (( vari- conds )) ont kt6 Btudiks. La possibilitk de realiser des variconds en couches minces pour les faibles tensions est envisagke. Enfin on trouvera des exemples d'application possible des variconds.
Abstract.
-
The electrical parameters of ferroelectric materials with pronounced non-linear properties used for the manufacture of capacitive non-linear components such as variconds have been investigated. Feasibility of Nm variconds designed for low control voltages has been shown.Examples of possible applications of variconds are given.
To prepare non-linear ferroelectric ceramics with a pronounced field-strength dependence of polari- zation, we use solid solutions on the basis of barium titanate or lead titanate. The works of Smolenski, Verbitskaya and others [I]-[4] show that these compo- sitions enable to obtain materials with various elec- trical properties, differing in the Curie temperature, the initial and maximum (E,,,) values of dielectric constant, the non-linearity coefficient, the magnitude of polarization and coercive field, etc. [I], [3]. The table and figure 1 show the characteristics of BaTiO, and some ferroelectric materials used for the mana- facture of non-linear components such as variconds.
The variconds are realized in the form of both bulk and film samples for various capacitance values ranging from several picofarads to some 10 000 pico- farads and for working voltages from several volts to kilovolts [3], [4]. Special attention has been lately paid to the development of film variconds for low control voltage [5].
We have stated that with decreasing thicknesses of ferroelectrics the tickness dependence of coercive field manifest itself in ceramics earlier than in single crys- tals. Thus, for films made of materials VK-2 and VK-4 and having thicknesses up to 20 to 30 pm and for films made of material VK-6 and having thicknesses of up to 7 to 10 pm, the coercive field remains the same as with bulk samples. Films of ceramic VK-4 show high temperature stability and non-linearity, the magnitude of spontaneous polarization
PC
is about 0.8PC
of that for barium citanate single crystals, the coercive voltage Vc is equal to 10 to 15 V, the non-linearity coefficient K being equal to 15 or less.In the working operating conditions'the variconds are subjected to a strong electric field, and polarization processes associated with the change in domain struc-
FIG. 1. - Electric field dependence of the dielectric constant for barium titanate and some kinds of non-linear ferroelectric
ceramics : 1. BaTi03 ; 2. VK-1 ; 3. VK-2 ; 4. VK-5.
ture occur in them. That is why the non-linearity of ferroelectrics much depends on the peculiarities of the domain arrangement.
Data concerning the properties and domain struc- ture, the magnitude of coercive field and the polari- zation are known to be rather diverse even for BaTiO, single crystals [6]-[8]. The domain structure is still
Article published online by EDP Sciences and available at http://dx.doi.org/10.1051/jphyscol:1972296
C2-274 T. N. VERBITSKAYA, L. M. ALEXANDROVA AND L. S. SOKOLOVA
more complicated through the presence of crystallites. functions of non-linear controlled components in By controlling the composition and choosing an diverce devices. They are used as capacitive shunts appropriate method for mannfacturing ferroelectric for inductors for pulse formation and control, for ceramics, one can alter the structure of crystallites, the brightness control of electroluminophors, for measu- shape and dimensions of domain regions, the perio-
dicity of domain patterns, and thus affect the non- linear characteristics of ceramics.
Ceramics show pronounced non-linear properties only in the case where a uniform monolithic well- organized crystalline structure with minor defects is formed in the materials, and the regions of uniform polarizations involve large sections of a crystallite or even several crystallites, a regular domain structure being distinguished (Fig. 2a-e). In the case of films, the dimensions of crystallites in the direction of the film plane must be sufficiently large, reaching or even exceeding the film thickness.
In ceramics, the domains are distributed in space with equal statistical probability. Therefore, it may be supposed that a surface layer oriented in a certain manner involving a large group of the crystallites of the sample is formed less readily in single crystals than in ceramics. In ceramics, transpolarization occurs owing to simultaneous displacement of domain boun- daries in many crystallites. They appear to be connec- ted in parallel in the process of orientation. This accounts, to some extent, for a weak thickness depen- dence of the characteristics of ferroelectric ceramics as compared to single crystals.
A great variety of the electrical characteristics of ferroelectric ceramics has enabled various types of variconds to be developed. Variconds perform the
THE ELECTRICAL PROPERTIES OF NON-LINEAR FERROELECTRIC CERAMICS C2-275
FIG. 2. - Micrographs of the ferroelectric ceramics ; X 500 : a, b : barium titanate, ground ; c, d : VK-4 ceramic, unground
sample ; e : V K - 4 ceramic, ground.
rement of weak d. c. signals, for simulations of various non-linear processes, for voltage stabilization, etc. [4].
Expediency of the application of variconds in the high and super-high frequency range for adjusting the characteristics of oscillatory circuits, for creating phase shifters, attenuators, parametric amplifiers and other FIG. 2d UHF devices [9], [lo] has been shown.
Material designation
Curie temperature
OC
-
120 75+
10& i n i t at 2 to
5 V/mm and about 20 OC
-
1 700-2 000 2 300-2 500non-linearity
factor K , Note
weak non-linearity simple manufacturing
technique high value of K , high value of K ,
stable characteristics of and K in tEe region 20 to 80 OC
very high value of
K,
high stability of para-meters and square hys- terisis loops
low dielectric losses (*) Materials designed for high frequencies.
(**) Non-linearity factors K refer to d-c voltage.
References I~]~~FAOLENSKI (G. A.), ISUPOV (V. A.), J. Techn. Phys.
USSR, 1954, 24, 1375. JONA (F.), SHIRANE (G.), Ferroelectric Crystals,
(( Mir n, Moscow, 1965.
SMOLENSKI (G. A.), BOKOV (V. .A.) et al., Segnetoelec- trics and antisegnetoelectrics, (( Nauka n, Lenin- 121 VERBITSKAYA (T. N.), Dissertation. Leningrad, 1952.
131 VERBITSKAYA (T. N.), Variconds, Moscow-Leningrad, Gosenergoisdat, 1958.
141 BULYBENKO (V. Yu.), VERBITSKAYA (T. N.) et al.,
c( Variconds in pulse electronic circuits. ))
(( Sovetskoye Radio )).
151 VERBITSKAYA (T. N.), ALEKSANDROVA (L. M.) et al.
(( Izvestiya AN SSR. Ser. Fiz. )), 1967, 1853, 11.
grad, 1971.
FONSEK (J.). Proceedings of the European Meeting on Ferroelectricity. Stuttgart, 1970, p. 147.
VENDIK (0. G.), VERBITSKAYA (T. N.) et al., Izvestiya, Leningrad, Electrotech. Inst., 1966, 56, 141.
VENDIK (0. G.), DAKHNOVICH (A. A.) et al., Radio- tekhnika i Elektronika, 1969, 14, 1955.
