Dresden 2006 – wissenschaftliches Programm
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DF: Dielektrische Festkörper
DF 3: Poster Session
DF 3.17: Poster
Montag, 27. März 2006, 09:30–17:00, P1
Muon spin rotation studies of hydrogen-bonded ferroelectrics and antiferroelectrics — •Elvezio Morenzoni, Hubertus Luetkens, Andreas Suter, Dimitry Eshchenko, Alex Amato, Thomas Prokscha, and Robert Scheuermann — Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland
We present muon spin rotation and relaxation measurements in hydrogen bonded systems of the KDP family. The positive muon and muonium behave like light proton and hydrogen isotopes and can be used to study stability and defect reactions of positive and neutral hydrogen interstitials in these ferroelectric or antiferroelectric materials, where hydrogen point defects are believed to affect the optical-absorption properties. A substantial fraction of the muons implanted into the crystals appear as neutral interstitial not reacting with the host. The hyperfine structure shows a slight axial anisotropy but is otherwise similar to that of free muonium. In the positively charged state, part of the muons form a hydrogen bond with an oxygen. In the ferroelectric KH2PO4 as well as in the antiferroelectric NH4H2PO4 we observe spontaneous precession of the muon spin in the nuclear dipolar field of the proton of the O-H bond. The temperature dependence of this frequency exhibits a marked shift at the phase transition. Our results suggest that it is possible to use this and other parameters (such as the width of the local static dipolar field) as a microscopic measure of the order parameter of the phase transition. This is interesting especially for the study of proton and deuteron glasses where the order parameter characterizing the glass transition is not accompanied by a macroscopic field.