Ferrielectricity in a metal-organic ferroelectric tris-sarcosine calcium chloride

We report a paradigm of ferrielectricity in a single-phase crystal, tris-sarcosine calcium chloride [TSCC; (CH3NHCH2COOH)3CaCl2]. Ferrielectricity is well known in smectic liquid crystals but almost unknown in true crystalline solids. C. F. Pulvari [Ferrielectricity, Phys. Rev. 120, 1670 (1960)] reported it in 1960 in mixtures of ferroelectrics and antiferroelectrics (AFEs), but only at high fields. Tris-sarcosine calcium chloride exhibits a second-order displacive phase transition near Tc=130K that can be lowered to a quantum critical point at 0 K via Br or I substitution and phases previously predicted to be AFE at high pressure and low temperatures. Unusually, the size of the primitive unit cell does not increase in the so-called AFE phase. We measure hysteresis loops and polarization below T=64K and provide clear Raman evidence for this paraelectric-ferrielectric transition.