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RESEARCH PRODUCT

Hopping Conductivity in Hydrogen-Bonded Antiferroelectric Compounds

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Antiferroelectric betaine phosphate (BP: (CH3)3NCH2COO · H3PO4) and ferroelectric betaine phosphite (BPI: (CH3)3NCH2COO · H3PO3) are molecular crystals of the amino acid betaine and the phosphoric or phosphorous acids, respectively. In both compounds the inorganic components are linked by hydrogen bonds to one-dimensional chains. The two isostructural compounds form solid solutions BPxBPI1-x at any concentration. Here we report measurements of the dielectric permittivity for concentrations 0.85 ≤ × ≤ 1 at frequencies 10−2 ≤ v ≤ 109 Hz and temperatures 2 K ≤ T ≤ 300 K. The dielectric response in BP:BPI (x = 0.95) is dominated by contributions from pure hopping conductivity which we ascribe to the motion of the protons along the one-dimensional chains. The onset of electric order supresses the a.c. conductivity. It will also be seen that BP:BPI (x = 0.95) shows dc conductivity in addition to the observed ac conductivity. These results are contrasted to BP and BP:BPI (x = 0.85) which reveal pure relaxational behavior.