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switching Processes in fields frequency of 50 Hz

The classical procedure of observation of loops of the dielectric hysteresis, featured in Sawyer-Tower operation, allows to gain oscillograms of loops at endurance of samples in electric fields of various amplitudes of industrial frequency (fig.

4.1). The observational equipment existing till now was oriented on examination of loops of the dielectric hysteresis in fields of industrial frequency (50 Hz) as in this case it is convenient to use amplification of mains voltage to necessary value in experiment. In our installation the raising transformer was applied to this purpose with the dissolved windings.

In the spent cycle of examinations on frequency of an electric field of 50 Hz, peak value of a submitted voltage changed in the range from 560 In to 2100 Century

Fig. 4.1 Plan of observation of loops of the dielectric hysteresis, offered by Sawyer-Tower [Sawyerl930].

Processes of formation of a loop of the dielectric hysteresis, occurring in the sample of piezoelectric ceramics of compositions ЦТС-19 by area S = 4.9 sm2 have been viewed.

For samples of ceramics ЦТС-19, also, as well as for monocrystals CBN32, at endurance of the sample in time in the field of constant amplitude there is a change of the shape of a loop to a simultaneous self-warming up of the sample (fig. 4.2 - 4.7). The view of a hysteresis curve and temperature of a self-warming up (table 4.1) depended on quantity of an electric field submitted on the sample. In fields more low 500 In/mm private loops of the dielectric hysteresis were not observed even, i.e. the linear relation of polarisation from a field took place. At delivery on the sample of an electric field the amplitude to 2000 In/mm on all interval of time of endurance observed only private loops of the dielectric hysteresis (fig. 4.2 - 4.6,). The saturated loop managed to be gained only in the field 2100 In/mm (fig. 4.7,) at which the sample was warmed up to the peak temperature. In loop big fields were not explored, as the further magnification of a field gradient could lead to an electrical breakdown on perimetre of the sample (the voltage of a disruption for dry air makes 2 kv/mm). It is necessary to score, that during the initial moment of time (at insert of a field 2100 In/mm) the private loop was still observed only, but in the course of a self-warming up was gradually transformed to the full. For the private loops observed during the initial moment of time, the electric intensity magnification led to magnification of the area of a loop (fig. 4.9).

At the moment of insert of an electric field by amplitude from 560 - FROM In/mm a voltage on the sample exceeded submitted with the transformer (table 4.1). Earlier similar effect of magnification of a voltage was observed on crystals pure SBN and featured in operations [Малышкина2004, Malyshkina2005]. The field gradient magnification led smaller, in comparison with submitted, to value of a voltage at the moment of field insert.

Fig. 4.2 Loop of the dielectric hysteresis (); dependences of switched polarisation (), temperatures of a self-warming up and the voltage relation on the sample to submitted from the transformer () from time of endurance of sample ЦТС-19 in sinusoidal floor Em = 560 Century/mm f = 50 Hz.

S = 4.9 sm2. Gauge on an axis OH: 280 In/has put, OY: 20 In/has put

Fig. 4.3 Loop of the dielectric hysteresis (); dependences of switched polarisation (), temperatures of a self-warming up and the voltage relation on the sample to submitted from the transformer () from time of endurance of sample ЦТС-19 in sinusoidal floor Em = 710 Century/mm f = 50 Hz. S = 4.9 sm2. Gauge on an axis OH: 280 In/has put, OY: 20 In/has put

Fig. 4.4 Loop of the dielectric hysteresis (); dependences of switched polarisation (), temperatures of a self-warming up and the voltage relation on the sample to submitted from the transformer () from time of endurance of sample ЦТС-19 in sinusoidal floor Em = 850 Century/mm f = 50 Hz. S = 4.9 sm2. Gauge on an axis OH: 280 In/has put, OY: 20 In/has put

Fig. 4.5 Loop of the dielectric hysteresis (); dependences of switched polarisation (), temperatures of a self-warming up and the voltage relation on the sample to submitted from the transformer () from time of endurance of sample ЦТС-19 in sinusoidal floor Em=ИЗО Century/mm / = 50 Hz. S = 4.9 sm2. Gauge on an axis OH: 280 In/has put, OY: 20 In/has put

Fig. 4.6 Loop of the dielectric hysteresis (); dependences of switched polarisation (), temperatures of a self-warming up and the voltage relation on the sample to submitted from the transformer () from time of endurance of sample ЦТС-19 in sinusoidal floor Em = 1700 Century/mm f = 50 Hz. S = 4.9 sm2. Gauge on an axis OH: 280 In/has put, OY: 20 In/has put

Fig. 4.7 Loop of the dielectric hysteresis (); dependences of switched polarisation (), temperatures of a self-warming up and the voltage relation on the sample to submitted from the transformer () from time of endurance of sample ЦТС-19 in sinusoidal floor Em = 2100 Century/mm f = 50 Hz. S = 4.9 sm2. Gauge on an axis OH: 280 In/has put, OY: 20 In/has put

Table 4.1 the Peak temperature of a self-warming up and a voltage

On the sample for different electric fields

Submitted field The peak temperature of a self-warming up Voltage on the sample
At the moment of field insert At a temperature exit on saturation
Em, In/mm T0C J - max? IN IN
560 64 870 720
710 85 975 745
850 95 1080 770
990 107 FROM 770
FROM 115 1170 765
1270 122 1210 760
1410 132 1215 750
1530 133 1285 690
1700 134 1290 680
2100 135 1345 640

Attracts attention that fact, that at endurance in the field from 560 to 710 In/mm, at the moment of an exit of temperature of a self-warming up on saturation, a voltage on the sample impinged, but still remaining above submitted from the transformer (fig. 4.2, 4.3,). At delivery on the sample of a voltage to 1200 In a voltage fixed on an oscillograph, surpasses submitted (fig. 4.8). At excess of this value the voltage on the sample appears less submitted (fig. 4.9, fig. 4.10). Voltage reduction by the sample concerning submitted (fig. 4.4 - 4.7,) can be related to the conductivity beginning at the raised temperatures of the sample.

Fig. 4.8 Change of a voltage on the sample concerning submitted value during the initial moment of insert of a field (a curve 1) and after an exit of temperature of a self-warming up on saturation (a curve 2) for sample ЦТС-19, S = 4.9 sm2

In an electric field 2100 In/mm during the initial moment of time, as well as for all smaller values of amplitudes of intensity, the private loop of the dielectric hysteresis was observed. Thus at the moment of an exit of temperature of a self-warming up on saturation (136 0C) the loop evolved in the full. Time formovki has made loops of 2 minutes. The voltage on the sample has made 1345 In, and the coercive field has fallen on 430 In/mm (from initial in 820 In/mm) and for the generated loop has made 390 Century/mm the Further endurance did not lead to loop transformation. Value of a voltage for the generated loop has made 30 % from the submitted.

The power failure was accompanied by decrease in value of switched polarisation (fig. 4.13,). Thus, first minutes of endurance of the sample in fields to FROM In/mm, inappreciable growth of switched polarisation (fig. 4.2 - 4.4,) took place.

Fig. of 4.9 Loops of the dielectric hysteresis, fields of different amplitude observed at the moment of delivery for sample ЦТС-19, S = 4.9 sm2. Gauge on an axis OH: 280 In/has put, OY: 20 Century/affairs f = 50 Hz. Numerals score a voltage submitted on the sample

Fig. of 4.10 Loops of the dielectric hysteresis, observed after the termination formovki in the field of different amplitude for sample ЦТС-19, S = 4.9 sm2. Gauge on an axis OH: 280 In/has put, OY: 20 Century/affairs / = 50 Hz. Numerals score a voltage submitted on the sample

At endurance of the sample in a variation field the self-warming up temperature leaves on saturation (fig. 4.11). It is possible to see, that depending on quantity of a put field, the sample was warmed up to different temperature (fig. 4). Time during which the temperature of the sample leaves on saturation, decreases at magnification of amplitude of a submitted field (in drawing it is scored by a dotted line). In variation fields at which private loops did not reveal, also as well as in constant fields to 2100 In/mm, the self-warming up of samples missed.

Fig. 4.11 Dependence of temperature of a self-warming up on endurance time

At various values of a submitted voltage of frequency of 50 Hz for sample ЦТС-19, S = 4.9 sm2

The peak values of temperature to which the sample is warmed up, depending on a voltage submitted from the generator are presented on fig. 4.12. The self-warming up temperature starts to leave on saturation in the field of 1410 Century/mm the Further magnification of the amplitude, a field put to the sample, does not lead to essential growth of the peak temperature.

Fig. 4.12 Dependence of the peak temperature of a self-warming up on a submitted voltage for sample ЦТС-19, S = 4.9 sm2

Switched polarisation monotonously increases with growth of quantity of a switching field on all explored interval of amplitudes (to 2100 In/mm) (fig. 4.13,), that can testify to constant insert in process of a polarisation reversal of new fields of the sample. Thus switched polarisation Prevв each floor depends on time only first 1-2 minutes of endurance in the field (fig. 4.13,).

Fig. 4.13 Dependence of the peak value of switched polarisation (Prev) from amplitude of a field submitted on the sample () and time dependence Prevдля of different amplitudes of voltages () for sample ЦТС-19, S = 4.9 sm2

According to the blanket theory of processes of switching the coercive field is the performance of a material and does not depend on geometrical parametres of explored samples. At the same time examination of samples of the different sizes in switching electric fields on identical frequency has shown, that disclosing of loops of the dielectric hysteresis at identical value of a field took place for the sample bolshego the size (4.9 sm2) whereas for the sample with the smaller area (0.25 sm2) loops were not observed. Distinction in the peak temperatures of a self-warming up was thus observed. So for the sample the area of 4.9 sm2 (fig. 4.14, a curve 1) the peak temperature of a self-warming up has made 95 0C, and for the sample the area of 0.25 sm2 - 34.5 0C (fig. 4.14, a curve 2). From here follows, that formovka loops it is spotted not by so much quantity of an electric field put to the sample, how many temperature to which the sample is warmed up.

Fig. 4.14 Dependence of temperature of a self-warming up for samples: ЦТС-19, S = 4.9 sm2, ЦТС-19, S = 0.25 sm2 at endurance in the field amplitude 850 In/mm on frequency of 50 Hz.

4.2

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A source: Yeliseyev Anton Jurevich. PROCESSES of SWITCHING And the DIELECTRIC HYSTERESIS of CERAMICS TSIRKONATA-TITANATA of LEAD And MONOCRYSTALS NIOBATA of BARIUM of CALCIUM. The dissertation on competition of a scientific degree of the candidate of physical and mathematical sciences. Tver - 2016. 2016

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