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Thermal Expansion and Phase Transformation Observation
in Cs2BX4 (B=Hg, Cd; X=Br, Cl) Crystals
2. Cs2HgBr4 and Cs2CdBr4 crystals
Krupych O., Girnyk I., Trach I., Martunyuk-Lototska I., Vlokh R.,
Vlokh O.
Institute of Physical Optics, 23 Dragomanov Str., 79005
Lviv, Ukraine
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Photoelastic and acoustooptic (AO) parameters of Cs2HgBr4 and Cs2CdBr4
crystals are determined on the basis of studies for thermal expansion and
optical indicatrix rotation at the ferroelastic (Fel) phase transition
(PT) and the direct piezooptic measurements. It is shown that Cs2HgBr4
and Cs2CdBr4 crystals are good AO materials. Their photoelastic coefficients
achieve respectively the values of p44=0.12 and p44=0.2, while the AO figures
of merit are M2=126.5?10-15s3/kg for Cs2HgBr4 and M2=366.9?10-15s3/kg for
Cs2CdBr4 crystals. From the obtained results it follows that, in both Cs2HgBr4
and Cs2CdBr4, the PT to the Fel phase 2/m is a first-order improper one,
whereas the PT into the triclinic phase is of a second order. The orientations
of domain walls in the Fel phase and the phase boundary between the incommensurate
and Fel phases are determined.
PACS: 78.20.Hp, 77.84.-s
Key words: optical indicatrix, incommensurate structure, domain
structure, thermal expansion.
doi 10.3116/16091833/5/1/8/2004 |
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