The structure and optical activity of the paraelectric phase of dicalcium strontium propionate

Abstract

At room temperature, dicalcium strontium propionate (DSP) is tetragonal with space group P41212(D44) or P43212(D48), with a=12.484 AA, c=17.231 AA, Z=4. Two of the propionate groups lie along a two-fold axis with their alpha and beta carbons statistically disordered in two sites on either side. The third propionate, which is in a general position, has 2-site disordered beta carbons, whereas the fourth propionate appear to be ordered. No sign of complete rotation of any groups is observed. The structure is compared with that of the Ba compound and the relationship between the two chiral forms is discussed. It is shown that the most important interactions are those of the Sr-O-Ca framework. DSP crystals with space group P43212 are found to be dextrorotatory. A structural explanation is given for the observed ferroelastic and ferrogyrotropic orientation states.