Ferroelectric KH2PO4 Research Articles

Deuteration removes quantum dipolar defects from KDP crystals

Dielectric properties of the hydrogen-bonded ferroelectric crystal KH2PO4 (KDP) differ significantly from those of KD2PO4 (DKDP). It is well established that deuteration affects the interplay of hydrogen-bond switches and heavy ion displacements that underlie the emergence of macroscopic polarization, but a detailed microscopic model is missing. We show that all-atom path integral molecular dynamics simulations can predict the isotope effects, revealing the microscopic mechanism that differentiates KDP and DKDP. Proton tunneling generates phosphate configurations that do not contribute to the polarization. At low temperatures, these quantum dipolar defects are substantial in KDP but negligible in DKDP. These intrinsic defects explain why KDP has lower spontaneous polarization and transition entropy than DKDP. The prominent role of quantum fluctuations in KDP is related to the unusual strength of the hydrogen bonds and should be equally important in other crystals of the KDP family, which exhibit similar isotope effects.

Self-trapped holes (small polarons) in ferroelectric KH2PO4 crystals

Density functional theory is used to establish the ground-state structure of the self-trapped hole (STH) in KH2PO4 crystals. The STHs in this nonlinear optical material are free small polarons, a fundamental intrinsic point defect. They are produced with ionizing radiation in the low-temperature orthorhombic structure of KH2PO4 and are only stable (i.e. long-lived) below approximately 70 K. A large 129-atom cluster, K19H40P14O56, is constructed to model the STH. The ωB97XD functional with the 6−31+G* basis set is used and geometry optimization is performed. Our results show that two of the oxygen ions in a PO4 unit relax toward each other and equally share the hole. These two oxygen ions do not initially have close hydrogen neighbors. This equal sharing of the hole is related to the presence of isolated, slightly distorted, PO4 units and is significantly different from the small-polaron behavior often observed in other oxide crystals where the hole is localized on only one oxygen ion. The computational results provide a detailed description of the lattice relaxation occurring during formation of the STH. Characteristic spectral features of this defect are a larger hyperfine interaction with one 31P nucleus and equal, but smaller, hyperfine interactions with two 1H nuclei. The computed values for these isotropic and anisotropic hyperfine coupling constants are in excellent agreement with results obtained from electron paramagnetic resonance experiments.

FERROELECTRIC NANOCOMPOSITES WITH GOVERNED INTERFACE ON BASE OF MAGNETIC POROUS GLASSES

Two-phase (nonporous) magnetic alkali borosilicate glasses have been produced by induction melting. Their macroscopic properties and crystal structure have been studied and it is shown that in the silica skeleton there are the agglomerates of Fe3O4. These agglomerates are formed by monodomain nanoparticles of magnetite and demonstrate the superparamagnetic properties. After special thermal treatment (liquation process) and chemical etching the nanoporous matrices with random dendrite pore structure and magnetic properties have been produced. The channels (porous space) were filled by ferroelectric materials KH2PO4 (KDP), KH2PO4+(NH4)H2PO4 (KDP-ADP or KADP), and NaNO2 and the effect of applied magnetic fields on phase transitions in these nanocomposite have been studied. It has also been established that a restricted geometry changed essentially the phase diagram of KADP.

Damping and Resonance Correlations in OH···O Bonded Ferroelectrics

The prototypic ferroelectric KH2PO4 (KDP) and most other OH···O bonded ferroelectric crystals transform to paraelectric phase above the critical temperature (Tc), which decreases at high pressure. The negative ∂Tc/∂p in KDP and in antiferroelectric squaric acid (C4H2O4, H2SQ) is generally connected to the compressed O···O distance. The ferroelectric croconic acid (C5H2O5) does not transform to the paraelectric phase until it decomposes at 450 K, and our high-pressure X-ray diffraction structural and Raman spectroscopy studies have not detected the paraelectric phase up to 5.3 GPa, either. This striking behavior of croconic acid can be explained by somewhat longer OH···O bonds as well as by the damping correlations of H-sites with atomic displacements in the structure, preventing the H-dynamics in hydrogen bonds. This structure–property relation combines the features of supramolecular aggregation and ferroelectric ordering in OH···O and NH···N bonded chemical compounds and reveals new structural factors si...

Features of the behavior of longitudinal static and dynamic dielectric, piezoelectric, and elastic characteristics of KH2PO4 and NH4H2PO4 crystals

Along with their electromechanical coupling coefficients, the longitudinal dielectric, piezoelectric and elastic characteristics in ferroelectric KH2PO4 and antiferroelectric NH4H2PO4 crystals are calculated using a modified proton ordering model that considers piezoelectric coupling and the four-particle cluster approximation. The possibility of detecting piezoactivity in solid solutions of K1 − x(NH4)xH2PO4 is substantiated.

A shell model for the H-bonded ferroelectric KH2PO4

A shell model for KH2PO4 (KDP), the prototype compound of the family of H-bonded ferroelectric materials, has been constructed by adjusting the interaction parameters to first-principles calculations. Structural properties, energy barriers, phonons, and the relative stability between the ferroelectric (FE) phase and a relevant antiferroelectric metastable structure associated to domain walls, compare very favorably to available first-principles and experimental data. Molecular dynamics simulations show that the model behaves satisfactorily within the FE phase. This model will be used to study the elusive structure of the paraelectric (PE) phase and the nature of the FE–PE phase transition.

Three‐dimensional H‐bonding and ferroelectric transition in KDP. Quantum‐chemical study

AbstractOn basis of the nonempirical methods (SCF, B3LYP, MP2‐MP4) and several cluster models, the ferroelectric KH2PO4 (KDP) and its deuteroanalogue are studied. The tunneling integrals Ω and the parameters of the effective coupling of protons/deuterons U,V (the Ising parameters) are calculated for these materials with the 3d network of H/D‐bonds. Using the obtained U,V and Ω values in the frames of molecular field approximation, it is found that the structural phase (ferroelectric) transition occurs for both crystals within the lowering of temperature. Such low‐temperature behavior differs the 3d KDP‐family materials from 0d systems, where the low‐temperature phase transition takes place only upon deuteration. It is demonstrated that this difference is associated with an abrupt Ising parameters growth for KDP if compared with the nondeuterated 0d materials. © 2009 Wiley Periodicals, Inc. Int J Quantum Chem, 2010

Experimental observation of a torus-doubling transition to chaos near the ferroelectric phase transition of a KH2PO4 crystal.

A ferroelectric KH2PO4 crystal is implemented in a simple series connection of an RLC circuit and the transition to chaos near the phase-transition temperature is investigated. The torus-doubling scenario to chaos, the theory of which was expounded by Kaneko for high-dimensional dynamical systems, has been found in the crystal. These experimental results suggest that observation of the nonlinear dynamical behavior in condensed matter can give much information about the correlation between the generation of nonlinearity and the order-parameter dynamics of the crystal near the phase-transition temperature.

Current-controlled electrical switching caused by the combined properties of ferroelectric KH2PO4 and π-conjugated polymer, poly-p-phenylene vinylene

For examination of control of conductivity of a single molecule, the dc current-voltage relation has been investigated in a system based on a ferroelectric material, potassium dihydrogen phosphate KH2PO4, and a π-conjugated polymer, poly-p-phenylene vinylene, and its system is demonstrated to cause current-controlled electrical switching that is similar to that of a chalcogenide glass alloy. The switching phenomenon occurs even in repeated runs, although the voltage drop near the critical current value in the first run is unstable compared to that in the following runs. Furthermore, little change in the temperature of the specimen is observed over the entire range in the high- and low-resistivity states. This indicates the negative possibility of a heating effect on the switching phenomenon.

Compact High-Pressure Light Scattering Cell with Low Stray Light

We have designed and constructed a compact high pressure light scattering cell which can hold a cube sample as large as 10×10×10 mm3. The cell dimension is about 10×8×10 cm3, and the body material is beryllium-copper alloy. The large sample ensures a low stray light level and the new design for the light collection window permits a large light collection angle (18°). The simple sealing method enables even inexperienced personnel to use this optical cell. We have tested the cell up to a pressure of 0.8 GPa by recording the low-lying Raman spectra of a ferroelectric crystal KH2PO4.

Pressure-induced transition of the hydrogen bond in the ferroelectric compounds KH2P04 and KD2P04

THE prototypical ferroelectric compound KH2PO4 contains hydro-gen bonds that exhibit interesting properties. The proton lies in one of two equivalent positions between oxygen atoms of two PO4tetrahedra. Below the ferroelectric transition temperature Tc there exists ordering of the protons in one of these two minima. A large increase in Tc is observed when the proton is substituted by a deuteron. Here we report results which show that in both KH2PO4and its deuterated form KD2PO4 at room temperature (that is, above Tc), the hydrogen-bond length decreases initially with increasing pressure, but then an abrupt and pronounced elongation occurs at a critical pressure Pc, corresponding to 2.7 and 4.2 GPa for KH2PO4 and KD2PO4 respectively. At Pc, the bond lengths are nearly equal to those predicted if the proton (deuteron) were to be located in a single minimum at the midpoint of the two oxygens. The P–O bond lengths in the PO4 tetrahedra also begin to decrease above Pc. These observations suggest that there may be a fairly complex interrelation of the various bond lengths involved in the ferroelectric transition, and reveal a hitherto unsus-pected property of the hydrogen bond.

Thermodynamic approach to quasielastic light scattering from crystals

Abstract Nonequilibrium thermodynamics (NETD) is utilized in theanalysis of the spectrum of light scattered quasielastically by crystals. This thermodynamic approach involves: (i) determination fo the equations satisfied by the crystal's thermodynamic variables, taking irreversible processes into account; (ii) solution of such equations for the chosen scattering vector and the relevant crystalline symmetry, and (iii) determination of the spectrum by means of the Onsager hypothesis relating the soluitons obtained and the correlation functions of the same variables. Several applications of the methodoloy are discussed. The ferroelectric KH2PO4 is considered both as a typical crystal exhibiting the standard spectrum consisting of a Rayleigh line and two Brillouin lines and also as a piezoelectric crystal, in which case an additional line a polarization relaxation line–is present in the spectrum. Another relaxation process is also considered: that associated with hopping diffusion in the superionic conductor RbAg4I5. The critical region is also discussed, in the context of the Ornstein-Zernike approximation. The applications illustrate the power and basic simplicity of the NETD approach: in many situations of interest, the parameters that come into play possess transplrent physical meaning and the spectra can be completely determined by trivial algebraic manipulations. This is to be contrasted with the standard phenomenological coupled-mode approch to quasielastic light scattering, invovling more complex manipulations and parameters whose physical meaning is often unclear and which are usually only very indirectly related to quantities measured using other experimental techniques.

Dynamic central-peak-linewidth renormalization and the piezothermoelastic response in ferroelectric KH2PO4

Dynamic central-peak-linewidth renormalization and the piezothermoelastic response in ferroelectric K<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">H</mml:mi></mml:mrow><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>P<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">O</mml:mi></mml:mrow><mml:mrow><mml:mn>4</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>

Dynamic central peak in ferroelectric KH2PO4

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On the origin of the spontaneous polarization and the isotope effects in ferroelectric KH2 PO4 crystals

physica status solidi (b)Volume 45, Issue 1 p. K25-K27 Short Note On the origin of the spontaneous polarization and the isotope effects in ferroelectric KH2 PO4 crystals I. B. Bersuker, I. B. Bersuker Institute of Chemistry, Moldavian Academy of Sciences, KishinevSearch for more papers by this authorB. G. Vekhter, B. G. Vekhter Institute of Chemistry, Moldavian Academy of Sciences, KishinevSearch for more papers by this authorA. A. Muzalevskii, A. A. Muzalevskii Institute of Chemistry, Moldavian Academy of Sciences, KishinevSearch for more papers by this author I. B. Bersuker, I. B. Bersuker Institute of Chemistry, Moldavian Academy of Sciences, KishinevSearch for more papers by this authorB. G. Vekhter, B. G. Vekhter Institute of Chemistry, Moldavian Academy of Sciences, KishinevSearch for more papers by this authorA. A. Muzalevskii, A. A. Muzalevskii Institute of Chemistry, Moldavian Academy of Sciences, KishinevSearch for more papers by this author First published: 1 May 1971 https://doi.org/10.1002/pssb.2220450147Citations: 7AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume45, Issue11 May 1971Pages K25-K27 RelatedInformation

X-ray study on thermal expansion of ferroelectric KH2PO4

The lattice parameters of KH2PO4 at various temperatures between 23.4 and —169.3 °C have been measured by using an accurate X-ray method recently developed by the authors. Specifical emphasis was laid on their temperature dependence near the ferroelectric Curie point. Small but distinct thermal hysteresis was found to occur at the onset of the para-electric-ferroelectric phase transformation. The results of temperature variation of the lattice parameters are in fairly good agreement with those of other authors except in the vicinity of the Curie point. It is noticeable that a pure shear x in a plane perpendicular to the ferroelectric axis, which directly reflects the spontaneous polarization, begins to decrease more rapidly than Ps as temperature approaches the Curie point.

Experimental Evidence for the Long-Range Interaction of Domains in Ferroelectric KH2PO4

Detailed optical observations of domain configurations, together with simultaneous electrical measurements, have been made on ferroelectric KH2PO4. These experiments demonstrate the important variation of the dielectric constant with the lateral domain-wall surface, and also provide evidence of the long-range interaction between domain tips, as well as between domain tips and defects.