New Room-Temperature Ferroelectric

The neutral-salt complex with glycine, di-glycine manganous chloride dihydrate, (NH₂CH₂{COOH)}₂·Mn{Cl}₂·{2H}₂$O, is found to be ferroelectric from low temperatures to +55^∘{}C. Above the latter temperature the conductivity suddenly becomes excessive. At room temperature the spontaneous polarization is 1.3×{}10^-6 coulomb/cm² and the coercive field is 5.6 kv/cm. A nonreversible surface change is observable optically above 72^∘{}C, probably due to loss of H₂O. Thermal measurements indicate onset of water loss above 35^∘{}C; electrical conductivity increases sharply and irreversibly above 55^∘{}C, and care must be taken to prevent dehydration even at room temperature. No Curie temperature can be observed. X-ray measurements of this hitherto unreported salt show space group P2₁, $a=9.96$ A, $b=8.53$ A, $c=6.86$ A, β=107±0.5^∘, density0ex0ex=1.875₀ g/cc, and two formula units per cell. The ferroelectric axis is along b. The dielectric constants at room temperature are εₐ=6.6, εb=8.1, εc=7.4; and these decrease linearly and only very slightly as the temperature is lowered to 77^∘{}K. The corresponding neutral-salt complex of two glycines with MnBr₂ is not isomorphous, occurring as a tri-hydrate, and is not ferroelectric. It has not been possible to find any metal which will replace manganese and form an isomorphous crystal.