Phase Transitions in Crystalline Divalent Metal Dicalcium Propionates. II. Proton Magnetic Resonance Investigation

Abstract

Abstract The motions of the propionate anions in strontium-, lead-, and barium-dicalcium propionates were examined with the proton magnetic resonance method at low temperatures. It was found that the methyl groups rotate about the C3-axes even at 20°K in the Sr-, and the Ba-salts. In the Sr-salt the gradual decrease of the second moment below the ferroelectric transition point was observed and this phenomenon was related to the large angle torsional oscillations of the ethyl groups about the C3′-axes as introduced in Part I: Near the ferroelectric transition point the observed second moment shows the possibility of excitation of the C3′-rotation which would make the crystal to be paraelectric above the transition point. It was expected that the C3′-torsion is to some extent excited in the Pb-salt at liquid nitrogen temperature, a slight discrete change being observed at the lower transition point. A sharp line width transition was also observed in the Ba-salt and this fact resulted in the finding of a new λ-type phase transition with the peak at about 204°K by the differential thermal analysis. A slight decrease of the second moment was observed at the upper transition point and the C3′-rotation was assumed to be fully excited above that point.