Dielectric relaxation and freezing effect in Sn₂P₂S₆

The temperature-frequency studies of dielectric susceptibility in Sn₂P₂S₆, Sn₂P₂Se₆, (PbySn₁−y)₂P2Se₆ and crystals at low temperatures are reported. The freezing relaxation dynamics has been observed in a temperature-frequency dependence of the dielectric properties in the crystals which are in a polydomain ferroelectric state as well as in the crystals (PbySn₁−y)₂P₂Se₆ with y > 0.4 which at low temperatures are in the incommensurate phase. The nature of the effect and its interrelation with dynamics of ferroelectric domain walls and incommensurate structure is discussed.В роботі приводяться температурно-частотні дослідження діелектричної проникливості при низьких температурах в кристалах в Sn₂P₂S₆, Sn₂P₂Se₆, (PbySn₁−y)₂P2Se₆. Спостерігалося заморожування релаксаційної динаміки на температурно-частотних залежностях діелектричних властивостей, як в кристалах які при низьких температурах знаходяться в сегнетоелектричному полідоменному стані, так і в кристалах (PbySn₁−y)₂P₂Se₆ with y > 0.4, які при низьких температурах знаходяться в неспівмірній фазі. Обговорюється природа ефекту у взаємозв’язку з сегнетоелектричними доменами і неспівмірною структурою

Amorphous dielectric behavior of incommensurate ferroelectric (Pb0.45Sn0.55)(2)P2Se6 at low temperatures

Contains fulltext : 27751.pdf (publisher's version ) (Open Access

A sensitive capacitance thermometer at low temperature for use in magnetic fields up to 20 T

Contains fulltext : 27952.pdf (publisher's version ) (Open Access

Thermal expansion at the incommensurate phase transition in [N(CH3)4]2ZnCl4-xBrx crystals

The temperature dependence of the thermal expansion in the vicinity of the incommensurate phase transition in [N(CH3)4]2ZnCl4-xBrx mixed crystals is found to deviate from that predicted within the Landau theory of phase transitions. It is shown that the dominant contribution to this deviation in the immediate vicinity of Ti is due to the presence of defects. The character of the deviation is found to be in qualitative agreement with the theoretically predicted behaviour in the presence of random field type defects. In some compounds (x = 0, 2.4, 2.9), the temperature dependence of the thermal expansion coefficient at T ≥ Ti + 3 K can be described by a τα-dependence with α = 0.5. These values are in reasonable agreement with α = 0.5, corresponding to the fluctuation correction to the Landau theory. In solid solutions with a rather smeared paraelectric-incommensurate phase transition (x = 0.25, 0.45), the value of this exponent is found to be between 0.8 and 0.9. This suggests that the contribution to the thermal expansion due to the defects in these crystals is, even quite far from the phase transition, comparable to the contribution due to order parameter fluctuations.

Fluctuation effects on the thermal expansion of the incommensurate crystal Sn2P2Se6

The paraelectric-incommensurate and the incommensurate-commensurate phase transitions of the proper ferroelectric crystal Sn2P2Se6 are studied by thermal expansion measurement on crystals grown by two different techniques. For vapour-transport grown crystals the observed deviation around Ti from the Landau theory can be described by a small fluctuation correction, whereas for Bridgemann-method grown crystals this deviation is most likely to be due to random local field-type defects. For both types of crystals in the low-temperature region of the incommensurate phase an additional contribution to the spontaneous deformation above the Landau part has been revealed.

Reproducibility of low temperature capacitance thermometers based on (Pb0.45Sn0.55)(2)P2Se6 single crystal

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