Publications by Colleges and Departments (MSU - Bozeman)
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Item EPR investigation of Cu2+ tetramers in ferroelectric CsH2PO4(1985-07) Waplak, S.; Schmidt, V. Hugo; Drumheller, John E.EPR study of CsH2PO4 (CDP) single crystals with 0.005 mol % of Cu2+ at room temperature reveals isolated Cu2+ (S=(1/2)) complexes with four ligand coordination and spin Hamiltonian parameters gpara=2.2575, g⊥=2.1866, Apara=30 G, and A⊥=27 G. At temperatures below 250 K the spectra were observed to have fine structure and are described as arising from a Cu2+ tetramer with effective spin S=2 and spin Hamiltonian parameters D=0.181 cm−1, E=-0.081 cm−1, a=0.001 cm−1, b=0, and c=-0.021 cm−1. Also reported are transitions within the S=1 multiplet of the tetramer, and a microscopic model of superexchange interaction has been used to evaluate the parameters Dx=0.543 cm−1 and Ex=-0.159 cm−1. A tetramer model as well as a temperature dependence of the ratio of tetramer–to–single-ion intensity is presented.Item EPR determination of three-dimensional correlations below the ferroelectric phase transition in pseudo-one-dimensional CsH2PO4:Cu2+(1986-11) Waplak, S.; Schmidt, V. Hugo; Drumheller, John E.The polarization fluctuations of ferroelectric CsH2PO4 above Tc are generally classified as a quasi-one-dimensional phenomenon. The temperature dependence of the EPR line splitting of the S=1 state of the Cu2+ tetramer, however, exhibits a critical exponent below Tc of β=0.5 indicating that the correlations associated with the order parameter are three dimensional below Tc.Item Dielectric Properties of Lithium Hydrazinium Sulfate.(1971-12) Schmidt, V. Hugo; Drumheller, John E.; Howell, Francis L.The dc conductivity and ac dielectric susceptibility of normal and deuterated lithium hydrazinium sulfate have been measured over a wide temperature range at frequencies up to 9.33 GHz. Over a very large temperature and frequency range the real and imaginary parts of the susceptibility are very large (up to ε′≃ε''≃106) and vary with frequency somewhat as f−12. This unusual behavior is shown to result form the nearly one-dimensional protonic conductivity and its extreme sensitivity to barriers caused by local structural defects. Etching studies indicate that the crystal is not ferroelectric, implying that the apparent hysteresis loops result from saturation of the ac conduction.