Transformation from γ to α modification in glycine crystal

Abstract

In glycine crystal the transformation from γ to α modification has been investigated using differential scanning calorimetry (DSC) and low-frequency dielectric spectroscopy methods on powder and monocrystalline samples. In monocrystalline samples the transition begins at 457.5 K. The first step is connected with cracking of the sample and growing of the ac conductivity which reaches maximum at 458.5 K. Next, ac conductivity achieves a huge maximum at the transition point 462.8 K. Additional small anomaly in the complex dielectric constant was revealed at 335 K. In powder samples this transformation measured by the DSC method goes uniformly. For these samples the ac conductivity begins to grow rapidly from 455 K and grows 2.5 times in the range of 383–387 K. In powder samples the ac conductivity at the transition point is seven times greater than in the monocrystalline samples. Conductivity anomalies are accompanied by changes in the real part of the dielectric constant.

Keywords:

• γ-glycine
• DSC
• complex dielectric constant
• phase transition
• ac conductivity