Changes in the optical properties at phase transitions in TEA2MeCl4 (Me=Zn, Mn, Hg, Cu) crystals

Biskupski, Piotr; Słaboszewska, M.; Tylczyñski, Z.

doi:10.1016/j.physb.2005.08.037

Cited by 9 publications

(4 citation statements)

References 19 publications

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“…On cooling, the distribution of interference colours did not change up to the point of the first phase transition T C 1 ¼ 223.5 K, at which the interference colours changed abruptly and the first cracks appeared. At a few tenths of a degree below T 1 C the colour of the crystal changed into brown with single blue spots and further crack development was observed [10]. The photographs of the surface of the sample cut out in the (001) plane before (Figure 1a) and after the cooling (Figure 1b) revealed macroscopic changes on the surface of the sample, reaching the height of about 0.2 mm.…”

Section: Experimental and Resultsmentioning

confidence: 95%

Structure of TEA₂ZnCl₄crystal surfaces studied by AFM

Biskupski

Tylczyñski

2008

Phase Transitions

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The surface of the TEA 2 ZnCl 4 crystal has been studied by the atomic force microscope for the fresh (as-obtained) samples and for the samples cooled below T C 2 ¼ 223.2 K at a rate of 10 min À1 . The images obtained have revealed strong cracking of the crystal surface. For the (110) surface the cracks were perpendicular to the cleavage planes, whereas the (001) surface was completely changed. The changes lead to the brightening of the crystal samples and may suggest the ferroelastic deformation in microregions. No classical ferroelastic domain structure has been observed in the low-temperature phase.

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Section: Experimental and Resultsmentioning

confidence: 95%

Structure of TEA₂ZnCl₄crystal surfaces studied by AFM

Biskupski

Tylczyñski

2008

Phase Transitions

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“…This phenomenon has not been earlier reported in literature and its nature can be related to the thermoelastic effect-we studied monocrystalline samples and not powdered ones. At this phase transition the crystal size changes significantly, which leads to its cleavage [8] starting at a temperature a little below T 1 [4].…”

Section: Non-isothermal Measurementsmentioning

confidence: 99%

“…As follows from the symmetry changes, the low temperature phase should have ferroelastic properties and the characteristic domain structure which is, unfortunately, not observed under a polarization microscope. Only for the TEA 2 CuCl 4 crystal has the presence of ferroelastic domains of the size of micrometers been suggested, by the splitting of the XRD peaks [3] and an increase in the intensity of the polarized light passing through the crystal [4].…”

Section: Introductionmentioning

confidence: 99%

“…The relatively great changes in the crystal size reaching 1% lead to sample damage. The permittivity of the crystal has been measured in the low frequency range [9,10] and birefringence changes have been determined at the phase transitions, indicating a decrease in the symmetry from optically uniaxial to biaxial [4]. However, the kinetics of the phase transitions taking place in this crystal has remained unknown, which has prompted us to investigate it by the DSC method.…”

Section: Introductionmentioning

confidence: 99%

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Kinetics of phase transitions in TEA₂ZnCl₄crystal

Tylczyñski¹,

Biskupski²,

Członkowska³

2008

J. Phys.: Condens. Matter

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The kinetics of thermal anomalies at the phase transitions in the tetraethylammonium zinc tetrachloride crystal [N(C2H5)4]2ZnCl4 has been studied by the differential scanning calorimetry method over a wide range of rate of temperature change, from 1 to 100 K min−1. The crystal is known to undergo structural phase transitions of first order at which the nucleus of the final phase characterized by a symmetry different to that of the initial phase appears and develops. The classical Johnson–Mehl–Avrami model cannot be applied to describe the two phase transitions taking place in the non-isothermal process. Making use of the isothermal process taking place below T1C, the intermediate phase has been shown to be metastable; the energy of the process is Ea = 146 ± 7 kJ mol−1, while the Avrami exponent n = 2.3 ± 0.2.

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