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Peculiarities of Dielectric Relaxation in DMAAS Ferroelectric Crystals

100%
Kapustianik V., Czapla Z., Czukwinski R.
Acta Physica Polonica A
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2002
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vol. 102
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issue 3
365-372
EN
This paper presents the results of investigations of the dielectric properties of NH_2(CH_3)_2Al(SO_4)_2×6H_2O crystals performed in a wide frequency range. In particular, the temperature and frequency dependences of the dielectric permittivity were measured in the region of ferroelectric phase at different rates of temperature change. The thermal dipole relaxation with a critical slowing-down at T_{c1} was observed at comparatively low frequencies of measuring field. The relaxation connected with the domain freezing takes place at still lower frequencies (below 100 kHz) and was found to be strongly dependent on the rate of the temperature change. It was shown that deuteration results in a noticeable change of the parameters characterising this process including the temperature of domain wall freezing.
2
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Investigations of High Temperature Phase Transitions in (NH_{3}c_{2}H_{5})_{2}CuCl_{4} Crystals

88%
Kapustianik V., Korchak Y., Sveleba S., Tchukvinskyi R., Girnyk I.
Acta Physica Polonica A
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1999
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vol. 95
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issue 3
351-357
EN
On the basis of dilatometric, optical, and dielectric investigations of (NH_{3}C_{2}H_{5})_{2}CuCl_{4} crystals the existence of phase transitions at T_{1}=364 and T_{2}=356 K was confirmed. Anomalous behaviour of the thermal expansion coefficient and optical birefringence around T_{3}=330 K was related to earlier unknown phase transition. Besides, it was shown that these crystals are characterised by considerable protonic conductivity, the nature of which is fairly well explained in the framework of Grotthus mechanism of proton transport.
3
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Dielectric and Dilatometric Properties of NH(CH_3)_3CuCl_3·2H_2O Low Dimensional Ferroics

76%
Korchak Y., Kapustianik V., Batiuk A., Girnyk I., Czapla Z., Dacko S.
Acta Physica Polonica A
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2004
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vol. 106
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issue 1
39-49
EN
On the basis of dilatometric and dielectric investigations of NH(CH_3)_3CuCl_3·2H_2O crystals the earlier unknown phase transition with considerable temperature hysteresis was found at T_1^c=198 K and T_1^h=223 K, respectively, in cooling and heating runs. Existence of the characteristic dielectric dispersion was revealed within the high-temperature phase. It corresponds to the single dielectric relaxator below 250 K as well as to co-existence of two relaxators above this temperature. The determined values of the activation energy and relaxation time are characteristic of the co-operative reorientation of the trimethylammonium cation (high-frequency relaxator) whereas the combined reorientation motions of the CuCl_2·2H_2O chains would be responsible for the low-frequency relaxation process. It was found that the above mentioned quasi-Debye type processes are involved into the mechanisms of the protonic conductivity.
4
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Radiation Effects in DMAAS:Cr Ferroelectric Crystal

76%
Kapustianik V., Czapla Z., Eliyachevskyy Y., Korchak Y., Kulyk B., Rudyk V.
Acta Physica Polonica A
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2003
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vol. 104
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issue 6
571-580
EN
This paper presents the results of investigations of the radiation effects in NH_2(CH_3)_2Al(SO_4)_2×6H_2O crystals doped with chromium. On the basis of absorption spectroscopy and resonance Raman scattering study it has been shown that comparatively low doses of radiation first of all causes recharging of Cr^{3+} on Cr^{4+} ions. Besides, the processes of dehydrogenation and the changes in arrangement of the hydrogen bond network were observed. These changes are followed by distortion of the complexes bonded by such a type of bonds.
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