Archives

• 1. Estimation of Refractive Index of Some Binary Organic Liquid Mixtures By-  Mohd. Kalim Ahmad1 and Isht Vibhu2  
  ( Posted On : 20-11-2015 )
• 2. The Contribution of the Flux Cancellation Mechanism in Coronal Mass Ejections By-  Aradhna Sharma1* and S.R. Verma2  
  ( Posted On : 20-11-2015 )
• 3. Study of North-South Distribution of Soft X-Ray Solar Flares in Association with Coronal Mass Ejections during the Period 2005 to 2010 By-  Lalan Prasad, Beena Bhatt  
  ( Posted On : 20-11-2015 )

Dielectric studies are performed on twist grain boundary phases in the frequency range 100 Hz to 1 MHz at different temperatures and bias. The sample investigated shows TGBC*-TGBA*--N*- BP- I phase sequence. The dielectric measurements are performed near the transition TGBA*-TGBC*. Without DC bias, the dielectric absorption spectra indicates one relaxation process for the TGBC* phase and two relaxation processes for the TGBA* phase. The TGBC* relaxation process could be attributed to the Goldstone mode. The dielectric behavior of the TGBC* phase is completely different with and without bias. The Goldstone mode is strongly attenuated at high DC bias near the transition TGBA*-TGBC*. This is well explained by two distinct orientations of the helical axis-perpendicular to the sample without bias and parallel under bias. The relaxation frequency is found to increase with temperature and decrease with the increase in bias. At sufficiently high bias the relaxation frequency for the Goldstone mode is found to remain constant with temperature well in the TGBC* phase. The dielectric spectra for the TGBA* phase in the absence of the direct bias voltage exhibits two relaxation processes. These are assigned as the soft mode and the molecular relaxation process in the grain boundaries (PGB). The effect of direct bias voltage on the dielectric response of the TGBA* phase is different from the SmA phase in that the relaxation frequency of the soft mode decreases instead of increasing with increase in bias voltage.

- Manisha Chaudhry1*, Anjuli Khandelwal2, S. S. Bawa3 *