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Optical and Dilatometric Manifestations of Phase Transitions in K_{2}SeO_{4} Crystal

100%

Andriyevsky B., Myshchyshyn O.

Acta Physica Polonica A

1997

vol. 92

issue 3

557-562

Temperature dependencies of the characteristic optical paths difference D(Τ) of K2SeO4 crystal in the range of 80-295 K were measured using the Jamen type interferometer. Significant anomalies of D(Τ) dependencies in the vicinity of incommensurate-paraelectric phase transition (T_{i} = 130 K) are observed. On the basis of D(Τ) temperature dependencies measured experimentally and linear expansion l(Τ) known, the temperature derivative of the refractive indices dn/dT are found to be negative in the ranges above and below the temperature T_{i}=130 K.

Optical and Dilatometric Properties of (CH_{3})_{2}NH_{2}Al(SO_{4})_{2}·6H_{2}O Crystals in Paraelectric and Ferroelectric Phases

81%

Podsiadła D., Czapla Z., Andriyevsky B., Myshchyshyn O.

Acta Physica Polonica A

1999

vol. 96

issue 3-4

409-416

Experimental investigation of the thermal linear expansion l(T) and temperature dependencies of the interference optical path difference D(T) were carried out for (CH_{3})_{2} NH_{2}Al(SO_{4})_{2}·6H_{2}O crystal, in the range of 120-310 K for three crystal physical directions. Decrease in electrostriction coefficients g of crystal was observed on approaching the phase transition point T_{c} ≈ 150 K in ferroelectric phase. Relative temperature changes of the lengthening δl/l and refractive index δn/(n-1) are of the same order of magnitude. Peculiarities of temperature dependence of dilatometric and optical parameters of (CH_{3})_{2}NH_{2}Al(SO_{4})_{2}·6H_{2}O testify for qualitative reconstruction of chemical bonds in the crystal when temperature changes in the same phase.

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2 Acta Physica Polonica A

1 1999

1 1997

2 Andriyevsky B.

2 Myshchyshyn O.

1 Czapla Z.

1 Podsiadła D.

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Optical and Dilatometric Manifestations of Phase Transitions in K_{2}SeO_{4} Crystal

Optical and Dilatometric Properties of (CH_{3})_{2}NH_{2}Al(SO_{4})_{2}·6H_{2}O Crystals in Paraelectric and Ferroelectric Phases