Optical Investigations of Phase Transitions in (NH4)2SbF5 Crystal |
| B. Andriyevskya, Z. Czaplab and V. Stadnyka aLviv State I. Franko University, Kyryla and Mefodiya 8, 290005 Lviv, Ukraine bInstitute of Experimental Physics, University of Wrocław, Pl. M. Borna 9, 50-204 Wrocław, Poland |
| Received: March 29, 1994; revised version: September 6, 1994 |
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| Results of optical thickness and refractive indices measurements for (NH4)2SbF5 crystal in the temperature range 100-310 K are presented. The measurements were done with interference method using He-Ne laser (λ = 632.8 nm). At Tc1 = 292 K and TC2 = 168 K two continuous phase transitions with critical indices β1 = 0.38 and β2 ≤ 0.57 were observed. Additional anomaly of temperature changes of interference order with maximum at Tc3 ≈ 132 K were found. This anomaly resembles a diffused transition. Temperature-averaged values of derivatives of refractive indices dng /dT = -3.3 × 10-5 K and dnm/dT = -2.9 × 10-5 K-1 evidenced a decrease in optical anisotropy (birefringence) along the b-axis on heating run. |
| DOI: 10.12693/APhysPolA.87.611 PACS numbers: 64.70.Kb, 78.20.Fm |