Dielectric and Pyroelectric Properties of Ammonium Hydrogen-DL-Malate Monohydrate, NH4(C4H5OS) H2O

The dielectric and pyroelectric properties of ammonium hydrogen-DL-malate monohydrate NH® (OOCCHOHCH2COOH) • H 2 0 were studied as a function of temperature and crystallographic direction. The components of the dielectric tensor at room temperature are within the limits 5.9 S e ^ 8.6. The pyroelectric coefficient \p\ increases from « 18 (iC m~ K at T = 100 K to 32 (iC m" K at room temperature. The angular variation of p in the ac-plane of the crystal with symmetry Cc is ~ 10°. Using an INDO procedure which includes crystal field effects in a self-consistent way (SCEF) the charge distribution in the solid was calculated. With the therefrom resulting dipole moment and together with the dielectric measurements the pyroelectric coefficient j p \ and the change of \p \ with temperature was calculated. Experiment and theoretical result agree satisfactory.