Electron paramagnetic resonance study of Mn²⁺ in tris-sarcosine calcium bromide

Abstract

Electron paramagnetic resonance of Mn²⁺ in a single crystal of tris-sarcosine calcium bromide (TSCBr), as a function of temperature and orientation, has been studied. These studies suggest the existence of two chemically equivalent but physically non equivalent Mn²⁺ site in a unit cell of TSCBr. Of the two space groups determined by neutron diffraction studies, Pnma and Pn2₁a, EPR studies are in conformity with the space group Pnma. The dielectric constant measurements in TSCBr do not show any anomaly in the temperature interval 300-100 K. Tris-sarcosine calcium chloride (TSCC, space group Pnma in the paraelectric phase) undergoes a ferroelectric phase transition at 127 K. Replacement of Cl by Br is expected to introduce changes in the N-H..X bond (X=Cl, Br) and hence, we believe, protons in the N-H..Cl bond may be playing an important role in the mechanism of ferroelectricity in TSCC.