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Item Comment on “dielectric study of the ferroelectric transition of KH2PO4”(1976-08) Western, Arthur B.; Schmidt, V. HugoWe reanalyze a.c. dielectric data taken by Eberhard and Horn for KH2PO4 near Tc, and obtain a much lower value of the critical bias field, near 300 V/cm in accord with results found by other workers.Item Soft modes and proton tunneling in PbHPO4, squaric acid and KH2PO4, type ferroelectrics(1984-01) Blinc, Robert; Schmidt, V. HugoIt is pointed out that the huge observed differences in the soft mode frequencies of KH2PO4, PbHPO4, CsH2PO4 and squaric acid do not necessarily reflect a large difference in the proton 0—H———O tunneling frequencies but rather result from a difference in the short range correlations renormalizing the single proton O——H—O tunneling frequency.Item Slater-senko model for CsH2PO4(1984-04) Schmidt, V. HugoThis model for CsH2PO4 considers all six Slater H2PO4 configurations and employs the Senko long-range interaction to obtain a ferroelectric transition above 0 K. Model predictions are compared with experimental results for susceptibility, spontaneous polarization, and correlation length.Item EPR study of the symmetry breaking effect in ferroelectric cesium dihydrogen phosphate doped with Cr5+ ions(1984-11) Waplak, S.; Schmidt, V. HugoThe (PO4)3− units in a CsH2PO4 (CDP) crystal were replaced in a small fraction of sites by (CrO4)3− groups and the EPR of the Cr5+ center was investigated. Splitting of the EPR line appears at T∗c=245 K, 91 K higher that the ferroelectric transition temperature Tc=154 K. The electronic wave function of Cr5+ (3d1) is identified as dx2−y2. The dx2−y2 function couples with the near protons and the reorientation of this unit in the two possible configurations occurs in the paraelectric phase and breaks the symmetry far above Tc. The observed correlation time 10−9 sec and associated activation energy ΔU=0.215 eV are discussed.Item Deuteration and pressure effects on landau free energy expansion coefficents in RbDXH2-xPO4(1981-10) Schnackenberg, P. T.; Pipman, J.; Schmidt, V. Hugo; Tuthill, G. F.Results are presented for undeuterated, 30% deuterated and 97% deuterated monocrystals of rubidium dihydrogen phosphate (RDP) for which the polarization was measured at various applied fields and accurately controlled temperatures within a degree above the ferroelectric transition temperature. The ferroelectric transition was found to be of second order at all deuterations. Some of these results were presented earlier.1–3Item Tricritical Point in KH_{2} PO_{4}.(1976-11) Schmidt, V. Hugo; Western, Arthur B.; Baker, A. G.