Anomalous Temperature Dependence of Piezo-Optic Birefrigence in Li₂Ge₇O₁₅ Crystals

Abstract

Peaks are observed in the temperature dependences of the photoelastic coefficients C _zx and C _zy at temperatures ∼ 279 K. These are attributed to the occurrence of paraelectric to ferroelectric phase transition and the spontaneous polarization along c-axis of the crystals Li ₂ Ge ₇ O ₁₅ . A thermal hysteresis is observed in a cooling and a heating cycle besides a valley around 289 K. The results are interpreted in terms of the soft mode and relaxational mode related to the phase transition. The phase transition temperature appears to shift linearly downwards with the increase in the uniaxial stress along the crystallographic c-axis.

Keywords:

• Lithium heptagermanate
• Weak ferroelectric
• photoelastic coefficients
• phase transition
• piezo-optic hysteresis

Acknowledgment

One of the authors (A. K. BAIN) is thankful to the Indian Government for providing him financial assistance under the ICCR scheme.