DOI: https://doi.org/10.30970/jps.03.139
ON THE EXISTENCE OF INCOMMENSURATE PHASE IN Li2B4O7 CRYSTALS
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Journal of Physical Studies 3(2), 139–143 (1999)
DOI: https://doi.org/10.30970/jps.03.139 ON THE EXISTENCE OF INCOMMENSURATE PHASE IN Li2B4O7 CRYSTALS |
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O. S. Kushnir
The Ivan Franko State University of Lviv, Chair of Nonlinear Optics
8 Kyrylo i Mefodii Str., Lviv, UA-290005, Ukraine
Using the universal null–polarimeter for crystal optical studies and the Senarmont technique, temperature dependences of the birefringence, the optical indicatrix rotation and the optical activity in Li$_2$B$_4$O$_7$ are measured in the range of 20–200$^\circ$ C. It is shown that the latter two phenomena are absent, in compliance with the point symmetry group $4ıt mm}$ of the crystal. A quasi–staircase temperature behaviour of the birefringence, hysteresis and a thermooptical memory effect are found. The analysis testifies that the most possible reason for those peculiarities should be an incommensurately modulated phase in Li$_2$B$_4$O$_7$ but not a combined influence of pyroelectric and electrooptic effects.