Potassium Dihydrogen Arsenate Research Articles

Theoretical investigation, of Cochran’s mode frequency, and electrical permittivity of KH2AsO4 (KDA) crystal by using Zuberav’s statistical Green function technique

Potassium dihydrogen arsenate KH2AsO4 crystal is investigated theoretically. It is an order disorder type of ferroelectrics. Another type is displacive like SrTiO3, LiNbO3, etc. The earlier model Hamiltonian (PLCM) is modified by adding some extra terms into it. Applying two time thermal dependent statistical Green function technique employing modified model, formulae for, Cochran’s mode frequency, electrical permittivity, Curie temperature, tangent delta, shift and width, are derived for the potassium dihydrogen arsenate crystal. Model values are fitted for KH2AsO4 crystal to obtain variation with temperature. Results are compared with experimental variations shown by Kaminow et al. [4] for the alkali phosphate potassium dihydrogen arsenate KH2AsO4 crystal.

Temperature dependence of dielectric properties in Potassium dihydrogen arsenate crystal

Potassium Dihydrogen Arsenate (KH2AsO4, KDA) is an inorganic arsenate ferroelectric crystal which is a KDP-family member and undergoes a ferroelectric phase transition at 96 K. A simple pseudospin lattice coupled mode model (PLCM) with some higher order terms like direct spin–spin interaction, third and fourth-order phonon anharmonic interaction terms and external electric field term, with two-time temperature dependent Green’s function technique has been employed for the evaluation of expression of response function. We can obtain and calculate soft mode frequency (Ω^), Dielectric constant (ε), and loss tangent (tanδ) expressions from response function for KDA crystal. We have shown temperature dependence of soft mode frequency (Ω^), Dielectric constant (ε), and loss tangent (tanδ) in Figs. 1-3. We have compared our findings, which seemed to be in fair alignment with experimental evidence.

No evidence for Evans’ holes in the A, B, C vibrational structure of potassium dihydrogen arsenate

We have used inelastic neutron scattering (INS) spectroscopy to study the "A, B, C" region of the hydrogen bond in potassium dihydrogen arsenate. The broad spectral feature observed in infrared spectroscopy is shown to be associated with a ridge of constant intensity in the INS, which follows the recoil line for a unit-mass particle. The onset energy of the ridge is unclear but, we believe, is associated with the optical "C" feature at 1610 cm(-1), and which we assign to nu(O-H). The "B" and "A" optical bands were both demonstrated to be two-quantum events and are, thus, not associated with the fundamental nu(O-H). They are readily assigned to the harmonic overtone delta(OH)(0-2) and the combination gamma(OH)(0-1)+delta(OH)(0-1), which both sit astride the ridge and there is no evidence for Evans' holes. The other overtone, gamma(OH)(0-2), has been assigned to a very weak feature, observed for the first time at 1900 cm(-1). A simple model was used to describe the intensity distributions.

Determination of hyperfine interactions from the magnetic field dependence of nuclear modulation frequencies: An electron spin echo envelope modulation study of protons in γ-irrradiated potassium dihydrogen arsenate

A study is presented of the field dependence of proton ESEEM (electron spin echo envelope modulation) of the AsO4−4 center in γ-irradiated single crystals of KDA (potassium dihydrogen arsenate). Modulation patterns and corresponding spectra were registered over the range of external field strengths spanned by the nominally allowed EPR transitions (∼3.5 kG) with the field orientation selected along the crystallographic c axis. By tracking the external field dependence of the ESEEM frequencies of the protons attached and hydrogen-bonded to the AsO4−4 center, the absolute value of both the secular and nonsecular portions of their hyperfine interactions, as well as the sign of the secular component, are determined. The results are compared with those obtained by ENDOR (electron-nuclear double resonance) spectroscopy. The implications of this work for the determination of the magnitudes and signs of the elements, principal values, and direction cosines of the principal axes of hyperfine interaction matrices in orientationally disordered solids are discussed in detail. The large hyperfine coupling to the 75As nucleus has important ramifications upon the ESEEM spectroscopy and its analysis. In general, such couplings increase the breadth of the EPR spectrum and thereby facilitate the survey of ESEEM field dependences; they can also seriously complicate the analysis of the ESEEM results by precipitating significant deviations between the magnitude of the expectation value of the electron spin angular momentum and its nominal value, MS: ESEEM frequency expressions in which these two quantities are implicitly equated are not generally applicable. This issue is commented on in detail. Expressions are derived and discussed that elucidate the effect of a large hyperfine coupling on the magnitude of the expectation value of the electron spin, its deviations from MS, and the consequent shifts in ESEEM frequencies. Experimental situations in which these deviations and shifts are negligible are delineated. These effects are illustrated with the results of our 1H ESEEM study of the AsO4−4 center in KDA.

Ammonium dihydrogen phosphate and potassium dihydrogen arsenate impurity effects on the dielectric behavior of potassium dihydrogen phosphate crystals

The dielectric constants of two types of mixed potassium dihydrogen phosphate crystals, one with ammonium dihydrogen phosphate (ADP) impurities and the other with potassium dihydrogen arsenate (KDA) impurities, have been measured at various impurity concentrations. The change of transition temperature and the dielectric behavior of the mixed crystals obtained from the dielectric-constant measurements are related to the role of impurities in the phase transition of the crystals. The transition temperatures of both mixed crystals decrease linearly as the impurity concentration increases, but the rate of decrease is strongly dependent on the type of impurity. The change of transition temperature in the mixed crystals is more sensitive to the concentration of ADP impurities than of KDA impurities. Domain-wall mobility in the region below the transition temperature remains high for crystals with ADP impurities, but becomes low for crystals with KDA impurities. A modified proton-lattice coupled model introduced here has proved to be a good theoretical model for explaining our experimental results and the roles of impurities in the crystals.

Dielectric measurements in potassium dihydrogen arsenate

Dielectric measurements in potassium dihydrogen arsenate

Mise en evidence par rpe de transformations radicalaires a la transition de phase para-ferroelectrique du cristal de KH 2AsO 4 irradie

Reversible transformations of free radicals have been observed by EPR at the para-ferroelectric phase transition in X or gamma irradiated crystals of potassium dihydrogen arsenate. In particular, the existence of a transformation of a radical of type AsO 2- 3 into a radical of type AsO 4- 4 suggests that these two radical families result from a common cause during irradiation, namely the capture of an electron on the original AsO 3- 4 tetrahedron.

Protonic conduction in potassium dihydrogen arsenate

Protonic conduction in potassium dihydrogen arsenate

Linear Electro-optic Effects in Tetragonal Arsenates

THE crystals of potassium dihydrogen arsenate (KDA, KH2AsO4) and its isomorphs, belonging to the point group symmetry &42bar;m, crystallize in the tetragonal system in the paraelectric phase at room temperature. This group, together with the &43bar; m symmetry group of the cubic system, are the only crystals which possess linear electro-optic effect free of background birefringence. The crystals of the first group, however, possess relatively large electro-optic constants. These crystals have been grown in an effort to find better electro-optic modulators. Measurements of the half-wave retardation voltage Vλ/2 performed on these single crystals are presented here.

Stark effect of 75As NQR and asymmetric 1H- 75As level crossing in paraelectric potassium dihydrogen arsenate

The nuclear quadrupole coupling constant of 75As in paraelectric KH 2AsO 4 (KDA) increases when an electric field is applied along the c-axis. The very large shift | ∂( e 2Qq 2h ) ∂E | of 75As is 9.1 kHz kV cm −1 at T = 106°K = T c + 10°. At room temperature, when the proton NMR frequency exceeds the α' frequency of 75As by Δν, the proton relaxation rate T 1 −1 is greater than when Δν has the opposite sign.

Some Physical Properties of Single Crystals of Normal and Deuterated Potassium Dihydrogen Arsenate. I. Piezoelectric and Elastic Properties

The elastic and piezoelectric constants of single crystals of potassium dihydrogen arsenate, grown in H2O, and of potassium dideuterium arsenate, grown in D2O, have been measured in the temperature range of 20°–80°C. The shear elastic constants S44 and S66 increase, while the extensional elastic constants S11 and S33 decrease on deuteration. The piezoelectric constants d14 and d36 increase on deuteration. Since the temperature coefficients of frequency of useful cuts are in excess of −100 ppm/°C, these crystals are not useful for electromechanical application.

Some Physical Properties of Single Crystals of Normal and Deuterated Potassium Dihydrogen Arsenate. II. Electro-optic and Dielectric Properties

The electro-optic and dielectric constants of single crystals of potassium dihydrogen arsenate, grown in H2O, and potassium dideuterium arsenate, grown in D2O, have been measured. On deuteration, the relative dielectric constant K33 is increased from 24 to 31 and K11 is increased from 60 to 70, measured at 25°C. The half-wave retardation voltage Vλ/2, measured at 500 nm is decreased from 5.9 to 3.3 kV, and the electro-optic constant γ63 in increased from 11.0×10−10 cm/V to 19.5 cm/V on deuteration. The loss tangent tanδ33 measured at 1 kHz and at 25°C is about 0.30 for KDA and 0.18 for D-KDA. The specific resistivity ρ33 for KDA is 7.2×108Ω·cm, and that for D-KDA is 5.1×108Ω·cm, measured at 25°C. The input power requirement using these crystals in an electro-optic modulator is compared to that of KDP.

Electron spin resonance of an X-ray irradiated single crystal of potassium dihydrogen arsenate, KH2AsO4

The electron spin resonance of an x-ray irradiated single crystal of potassium dihydrogen arsenate has been examined and a radical which is thought to be AsO4 4- identified. Analysis of the spectra for various orientations of the crystal with respect to the external magnetic field leads to an axially symmetric hyperfine interaction tensor which is in agreement with what would be expected for the AsO4 4- radical. Semi-empirical LCAO molecular orbital calculations for the AsO4 4- radical with symmetry D 2d trapped in the tetragonal KH2AsO4 crystals leads to the conclusion that the odd electron enters a molecular orbital with A 1 symmetry. The isotropic part of the hyperfine interaction tensor is calculated from this theory to be 2098 Mc/s which must be compared with the experimental value of 3038·6 Mc/s, The anisotropic part of the hyperfine interaction calculated from the theory, however, is much too low when compared with the value estimated from the experimental data. It is possible that part of this dif...

X-ray determination of the thermal expansion of potassium dihydrogen arsenate

X-ray determination of the thermal expansion of potassium dihydrogen arsenate

Laue Photographs of Sub-crystalline Regions in 'Hybrid' Crystals of Potassium Dihydrogen Phosphate

ATTENTION has recently been directed1 to the break-up of single crystals of Rochelle salt and of potassium dihydrogen phosphate (KH2PO4) into crystal 'hybrids' when these substances are cooled below their transition points. A similar phenomenon has now also been established by means of Bragg photographs in the case of potassium dihydrogen arsenate (KH2AsO4).

A Determination of Parameters in Potassium Dihydrogen Arsenate and Silver Arsenate

A Determination of Parameters in Potassium Dihydrogen Arsenate and Silver Arsenate

Anomaly of the Specific Heat of Potassium Dihydrogen Phosphate at the Upper Curie Point

THE dielectric properties of Rochelle salt, potassium dihydrogen phosphate and potassium dihydrogen arsenate, depend on the electric field in the same way that the properties of ferromagnetic substances depend on the magnetic field. The spontaneous polarization is large between the two Curie points and depends on temperature. Approaching the higher (normal) Curie point from lower temperatures, the spontaneous polarization vanishes. As a consequence the specific heat shows an anomaly, corresponding to the magneto-caloric effect in ferromagnetics.