ENDOR AND PULSED ESR STUDY OF PROTON GLASS BEHAVIOR IN THE MIXED-CRYSTAL (BETAINE PHOSPHATE)(0.15)(BETAINE PHOSPHITE)(0.85)

The proton ENDOR spectra of BP0.15BPI0.85 taken between 90 and 290 K a llow a direct determination of the local polarization distribution W(p ) of the protons in the hydrogen bonds linking the phosphate and phosp hite groups to chains. The temperature dependence of the Edwards-Ander son glass order parameter can be described by a random-field dominated proton glass behavior in BP0.15BPI0.85 with a glass temperature of T- G=30 K and a random-field induced freezing temperature of T-f=(95+/-5) K. The experimental results do not permit one to discriminate between three-dimensional (3D) or quasi-one-dimensional interactions of the h ydrogen bonds. The experimentally determined polarization distribution function W(p) can be described to a certain extent within the 3D rand om-bond random-field model if a long-range order of the protons is int roduced by a non-zero mean (J) over tilde 0/k(B)=160 K of the random-b ond interaction. Additionally, the local field variance <(Delta)over t ilde> has to be taken as a temperature-dependent parameter with a mini mal value at the resulting phase transition at 144 K. However, even at lowest temperatures the maxima of the order parameter distribution fu nction W(p) appear at values of the local proton polarization distinct ly smaller than one. This is not describable within the above models. We conclude that proton tunneling is of importance in betaine phosphit e-phosphate proton glasses.