H. Metz

Esr–investigations on γ–irradiated ferroelectric betaine compounds

Abstract Part of this work was supported by the BMFT. Valuable support by J. Huttermann and J. Albers, Universitat des Saarlandes, are gratefully acknowledged.

Effects of lattice defects on the phase transitions of betaine calcium chloride dihydrate

Abstract We have studied the effects of Br and Mn impurities and γ-irradiation defects on the phase transition sequence of BCCD using dielectric and Raman spectroscopic measurements at hydrostatic pressures p < 420 MPa and temperatures 20 K < T < 250 K. The (T, p)-phase diagrams of 5%Mn doped BCCD and three γ-irradiated BCCD crystals have been determined and compared to those of 2%, 7% and 28%Br doped BCCD. We have localized the incommensurate phases and obtained the modulations δ of the commensurate phases of the doped crystals and an irradiated one by Raman spectroscopy. The effects of the different types of defects on the phase transition sequence of BCCD are discussed. A freezing process in the dipole system appears to be present at least in some of the studied substances.

Electron nuclear double resonance of 13C nuclei with natural abundance in trissarcosine calcium chloride doped with Mn2+ ions

Abstract 13 C ENDOR measurements were performed at 4.2 K on single crystals of trissarcosine calcium chloride doped with Mn 2+ ions. Hyperfine coupling tensors were measured for six 13 C nuclei of the carboxyl groups. An attempt is made to interpret the data in terms of electron-transfer and dipole—dipole contributions.

EPR lineshape of Mn in BCCD single crystals in the incommensurate phase

Abstract For the interpretation of the EPR lineshape of incommensurate phases there exist many theoretical models. We suppose a simple physical model to interpret the lineshape of the Mn 2+ EPR spectrum of the first incommensurate phase of betaine calcium chloride dihydrate (BCCD) and discuss it in comparison with other models. Furthermore, we investigate the critical behavior of BCCD at the normal to incommensurate phase transition on the basis of our model. The influence of the Mn 2+ impurities on the phase sequence of BCCD is investigated by dielectric measurements.

EPR and ENDOR investigations on irradiated and manganese doped betaine calciumchloride dihydrate

Abstract EPR investigations on Mn2+ doped betaine calciumchloride dihydrate show that Mn2+ incorporated at Ca2+ sites is a good indicator for the modulated phases of BCCD. At low temperatures the existence of a nonmodulated phase with low symmetry was confirmed. ENDOR measurements show that a radical arises at gamma irradiation of BCCD with nearly sp2 hybridization and two states.

Structure and dynamics of radicals created by gamma-irradiation in betaine phosphate single crystals : an ENDOR study

Abstract Structure and dynamics of radicals created by γ irradiation in betaine phosphate are investigated by EPR and ENDOR. The analysis of the ENDOR spectra shows that the nine hydrogen atoms of the three methyl groups in the nitrogen radical N(CH3)3 are magnetically equivalent. At room temperature the N(CH3)3 radical undergoes a fast reorientation. This reorientation can not be described by a free rotation. The rhombic deformation of the 1H and 14N hfs tensor indicates a jump like 120° reorientation around a pseudo threefold axis.

EPR probes in incommensurate BCCD

In BCCD the EPR probes Mn 2+ , VO 2+ , and as an irradiation centre the radical N(CH 3 ) 3 monitor the incommensurate modulation. Interesting results on the influence of defects on the order parameter were obtained using Mn 2+ taking into account the influence of second-order effects on the EPR line shifts.