Millimeter-wavelength spectroscopy of the ferroelectric phase transition in tris-sarcosine calcium chloride [(CH3NHCH2COOH)3CaCl2]

Abstract

Soft modes associated with the second-order ferroelectric phase transition in tris-sarcosine calcium chloride (TSCC) have been measured by use of a backward-wave oscillator in the region 2-30 ${\mathrm{cm}}^{-1\mathrm{}}$. A resonant mode is found in both ferroelectric and paraelectric phases. In the paraelectric $D_{2h}^{16} \mathrm{}\left(\mathrm{Pnma}\right)\mathrm{}$ phase the mode decreases from 11.2 ${\mathrm{cm}}^{-1\mathrm{}}$ at 167 K to 3.2 ${\mathrm{cm}}^{-1\mathrm{}}$ at 130 K and yields a Curie constant of 25±2 K, in reasonable agreement with low-frequency dielectric measurements. In the ferroelectric phase the mode is underdamped at most temperatures and could be measured down to 2.3 ${\mathrm{cm}}^{-1\mathrm{}}$, at which energy it is still a resonant although overdamped excitation. These new data show that TSCC is a proper, displacive ferroelectric, with a single phase transition, contrary to earlier suggestions.