Irradiation Effect on Photoelastic Coefficients in Ferroelectric Li₂Ge₇O₁₅ Crystals

Abstract

The Ferroelectric single crystals Li₂Ge₇O₁₅ (LGO) was irradiated by X-ray for one hour. The photoelastic coefficients of the ferroelectric crystals Li₂Ge₇O₁₅ (both un-irradiated and x-irradiated) were studied in a cooling and a heating cycle between room temperature and 273 K. The results show an interesting photoelastic behaviour. Peaks are observed in the temperature dependences of the photoelastic coefficients C_zx and C_zy at temperature ∼279 K. These are attributed to the occurrence of paraelectric to ferroelectric phase transition and the spontaneous polarization along c-axis of the Li₂Ge₇O₁₅ crystals. Some interesting results are obtained in the case of X-irradiated LGO crystal. The peak value of C_zy increases about 20% and the value of C_zx decreases about 18% at the wave length λ = 5890 Å during cooling process of the crystal. The X-irradiation may produce internal stress and electric fields inside the Li₂Ge₇O₁₅ crystals due to defects that can change the values of photoelastic coefficients.

Keywords:

• Lithium heptagermanate
• weak ferroelectric
• photoelastic coefficients
• phase transition
• X-irradiation

Acknowledgment

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