ON THE ISOTOPIC EFFECTS IN THE FERROELECTRIC BEHAVIOUS OF CRYSTALS WITH SHORT HYDROGEN BONDS
An attempt to correlate the isotopic effects in the ferroelectric properties of hydrogen-bonded crystals with the observed anomalies in their i.r. and n.m.r. spectra led to the conclusion that the protons in the hydrogen bonds are tunnelling in double-minimum potential fields. The ferroelectric transition is assumed to be the result of a deformation of the protonic distribution due to electrostatic interactions. It was found that a quantum mechanical extension of Mason's and Devonshire's long-range-forces model is able to explain, by the same mechanism, the results of i.r. and n.m.r. spectroscopy as well as the dependence of the Curie point on the mass of the hydrogen isotope, the sharper increase of the spontaneous polarization with falling temperature and the larger value of the spontaneous polarization at absolute zero for deuterated than for hydrogen compounds. The proposed model predicts that a ferroelectric transition occurs only if the dipole-dipole interactions, expressed as frequencies, are greater than the tunnelling frequency on the lowest vibrational level. (auth)
- Research Organization:
- J. Stefan Institute, Ljubljana, Yugoslavia
- NSA Number:
- NSA-14-021467
- OSTI ID:
- 4172932
- Journal Information:
- Phys. and Chem. Solids, Journal Name: Phys. and Chem. Solids Vol. Vol: 13
- Country of Publication:
- Country unknown/Code not available
- Language:
- English
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