Deuteration and pressure effects on landau free energy expansion coefficents in RbDXH2-xPO4 (original) (raw)
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Journal of Physics C: Solid State Physics, 1982
The Raman spectra of the isomorphous compounds (CH&NMnCls, (CDs)dNMnC13 and (CH3)4NCdC13 in the regions of the lattice vibrations and of the internal modes of the tetramethylammonium skeleton are reinvestigated at temperatures ranging from 300 to 25 K. On the basis of the hypothesis that group-to-subgroup relations exist between the high-and low-temperature phases of these compounds, a group theoretical analysis of possiblephase transitions has been made. Thecompatibility between the observed spectra and those predicted by group theory leads to the conclusion that for the cadmium compound the phase sequence could be 118K 104K P&/m (2 = 2)-P2Jm (2 = 2)-P24m (2 = 8). For the manganese compounds, when these results are compared with previous NMR and neutron diffraction data one obtains 126K P&/m (2 = 2)-P2Jb (2 = 8). A Landau-type treatment of these phase transitions as they are expected to occur in TMMC andTMCC supports these conclusions and in addition suggests the possibility of the existence of incommensurate phases in these systems.
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The anomalously large dielectric aging in ferroelectric partially deuterated potassium dihydrogen phosphate (DKDP) is found to have multiple distinct mechanisms. Two components cause decreases in dielectric response over a limited range of fields around the aging field. Substantial aging occurs on time scales of ~1000s after a field change, as expected for a hydrogen/deuterium diffusion mechanism. A slower component can give almost complete loss of domain-wall dielectric response at the aging field after weeks of aging. There is also a particularly unusual aging in which the dielectric response increases with time after rapid cooling.
Ab initiostudy of the one-dimensional H-bonded ferroelectricCsH2PO4
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We studied the microscopic mechanism of the paraelectric-ferroelectric (PE-FE) phase transition of CsH 2 PO 4 (CDP) by means of first-principles electronic structure calculations. The calculated structural parameters in the PE and FE phases as well as the total spontaneous polarization P s obtained with the Berry phase formalism for CDP are in good agreement with experiments. The main contribution to P s originates from a large yx component of the calculated Born effective-charge tensor for the disordered protons. Moreover, this component is ≈2.7 times larger than the zx component of the proton effective-charge tensor relevant to the polarization in the H-bonded FE KH 2 PO 4 (KDP). This is the main feature that compensates the different number of protons per formula unit involved in the phase transitions for CDP and KDP to give close values for their measured P s. Correlations among protons and heavy atoms along chains in the b direction lead to larger instabilities for the global and local FE distortions in CDP and its deuterated counterpart DCDP. We conclude that the tunneling particle is a dressed proton (deuteron) in agreement with experiments and with recent ab initio results for KDP.
Impact of 3D curvature on the polarization orientation in non-Ising domain walls
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Ferroelectric domain boundaries are quasi-two-dimensional functional interfaces with high prospects for nanoelectronic applications. Despite their reduced dimensionality, they can exhibit complex non-Ising polarization configurations and unexpected physical properties. Here, the impact of the three-dimensional (3D) curvature on the polarization profile of nominally uncharged 180° domain walls in LiNbO 3 is studied using second-harmonic generation microscopy and 3D polarimetry analysis. Correlations between the domain wall curvature and the variation of its internal polarization unfold in the form of modulations of the Néel-like character, which we attribute to the flexoelectric effect. While the Néel-like character originates mainly from the tilting of the domain wall, the internal polarization adjusts its orientation due to the synergetic upshot of dipolar and monopolar bound charges and their variation with the 3D curvature. Our results show that curved interfaces in solid crystals may offer a rich playground for tailoring nanoscale polar states.
Journal of Applied Physics, 2010
The ferroelectric phase transition of three single crystals of ͑TGSe͒ 1−x ͑DTGSe͒ x has been described by using specific heat, latent heat, and dielectric permittivity measurements. Pure, half-deuterated, and highly-deuterated TGSe single crystals were analyzed. Transition temperature and latent heat increase with increasing deuteration. Irrespective of the degree of deuteration, a 2-4-6 Landau model is suitable to describe the phase transition. The fourth-rank prefactor in Landau potential is found to be very sensitive to deuteration while the second-rank and the sixth-rank prefactors smoothly change with composition. The pyroelectric figure of merit for these materials has also been derived from the theoretical model.