Scholarly Work - Physics
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Item Simple coulometer for studying protonic conduction in crystals(1965-12) Schmidt, V. HugoNOTES ON EXPERIMENTAL TECHNIQUE AND APPARATUS A simple glass coulometer with mercury electrodes was designed to measure the amount of gas evolved upon passing current through single crystals, to determine the extent to which electrical conduction in these crystals is due to protons or other gas-forming ions. It is useful if at least one coulomb can be passed through the crystal in a reasonable time interval. With single crystals of KH2PO4 and Li(N2H5)SO4 in this coulometer, the ratio of hydrogen evolution rate to crystal current indicates entirely protonic conduction.Item Dynamical Effects of Deuteron Intrabond Jumping in KD2PO4(American Physical Society, 1967-12) Schmidt, V. HugoDeuteron jumps along hydrogen bonds in KD2PO4 associated with effective motion of Slater-Takagi DPO4 and D3PO4 groups are related to the deuteron magnetic-resonance spectrum and relaxation both above and below the ferroelectric transition temperature Tc, and to the dielectric relaxation and the domain-wall mobility. Below Tc the deuterons assume ordered bond positions, but occasionally jump to the opposite positions. The correlation time for the electric-field-gradient fluctuations seen by a deuteron undergoing such motion is found to be short above Tc and even shorter below Tc. The rms amplitude of the fluctuations drops rapidly below Tc. These results are used to explain the temperature dependence of the splitting and lack of line broadening in the deuteron spectrum below Tc, and the rapid decrease of the spin-lattice transition probabilities below Tc. Relaxation data above Tc, which yielded the energies and fractional populations of DPO4 and D3PO4 groups, are reanalyzed using the recently reported field-gradient tensors at the two bond positions. The dielectric relaxation is calculated, and good agreement with the high dielectric loss measured at microwave frequencies is found. The jump time for a DPO4 or D3PO4 group is found to be near hkT, implying little correlation between successive jumps, in contrast to KH2PO4. This jump time is used in a calculation of domain-wall mobility in KD2PO4.Item Deuteron Intrabond Motion and Ferroelectricity in KD2PO4(American Physical Society, 1964-01) Silsbee, Henry; Uehling, Edwin A.; Schmidt, V. HugoThe Slater theory of the ferroelectric phase transition in KH2PO4 type crystals as modified by Takagi and extended by Senko is examined again in the light of recent measurements of parameters made on KD2PO4. Making full use of the measurements, and assigning an appropriate numerical value to one adjustable parameter which is not independently measured, the theory gives a nearly correct description of the shape of the spontaneous polarization curve. Also the value obtained for the Curie constant is probably satisfactory in view of limitations of the model and uncertainty of the high-temperature experimental data. The theory fails, however, in at least one important respect; the transition entropy is overestimated. This and other discrepancies are discussed briefly.