Pure KDP Research Articles

Hydrostatic pressure influence on dielectric permittivity of KH2PO4 and KD2PO4 in the piezoelectric resonance region

We measured transverse and longitudinal dielectric permittivities of KDP and DKDP in the piezoelectric resonance frequency region under the hydrostatic pressure. The transverse permittivity decreases with pressure in the paraelectric phase and increases in the ferroelectric phase. The pressure dependence of the transverse permittivity of deuterated DKDP is well described by the presented theory. The longitudinal permittivity of a pure KDP exhibits several peaks in the vicinity of the transition point. Upon increasing hydrostatic pressure, the peaks get closer and may merge.

Effect of an organic dye on the ferroelectric phase transition in KH2PO4 (KDP)

This paper reports on the first measurement of the dielectric permittivity and heat capacity of a KDP crystal doped by Chicago Sky Blue organic dye within a temperature interval including the ferroelectric phase transition at T c =122 K. Similar measurements were made on a pure KDP crystal under the same conditions for the sake of comparison. The heat capacities of the pure and doped crystals were shown to differ substantially within an interval 1 K wide in the vicinity of T c , where an anomaly in the heat capacity of the doped crystal was observed to wash out without producing any change in the temperature position of its maximum. The doping reduces the permittivity in the polar phase markedly. The observed effects are associated with the influence of nonisomorphic defects on the ferroelectric phase transition in a piezoelectric crystal.

An Investigation on the Lattice Distortion in Urea and KCl Doped KDP Single Crystals by X-ray Diffraction Studies

Potassium dihydrogen phosphate (KDP) doped with different mole concentrations of urea and KCl were grown using low temperature solution growth technique. X-ray diffraction studies were carried out on the grown crystals using a Shimadzu X-ray diffractometer with CuK α radiation. X-ray study revealed that the structures of the doped crystals are slightly distorted compared to the pure KDP crystal. This may be attributed to strains on the lattice by the adsorption of urea and KCl.

High-temperature phase transition in K 1− x(NH 4) x H 2PO 4

Thermogravimetric analysis (TGA), differential scanning calorimetry (DSC) and X-ray diffraction (XRD) were used to study the high temperature phase behaviour of mixed crystal of K 1− x (NH 4) x H 2PO 4 in the KDP rich region ( x<0.02). All of the mixed crystals show phase-transition like phenomena at a characteristic temperature T p, few degrees above that for pure KDP, i.e. 180°C. Our results show that T p marks the onset of a thermal dehydration of the samples when they are heated above this temperature. The rate of the corresponding dehydration reaction is faster for samples with ADP impurities indicating that the density of reaction sites or their propagation from the surface to the interior of the crystal increase with the impurities.

Mutual solubility and metastable zone width of NH 4H 2PO 4KH 2PO 4 mixed solutions and growth of mixed crystals

Mutual solubility of ammonium dihydrogen phosphate (ADP) and potassium dihydrogen phosphate (KDP) has been determined for the full series of composition at 35°C. Stability of the mixed saturated solutions with different compositions has been assessed by measuring the metastable zone width by a nucleation method. Mixed crystals of size 15 × 15 × 75 mm 3 have been grown from ADP or KDP rich solutions on pure ADP and KDP seeds by a slow cooling method.

Pyroelectric measurements of glassy characteristics in (KDP)1−x(ADP)xsystem

Abstract Pyroelectric current measurements are applied to obtain the temperature dependence of the field-cooled polariza1, ion P FC and zero field-cooled polarization P ZFC of (KDP)1−x(ADP)x pellet samples over the whole range of x between x = 0(pure KDP) and x = 1(pure ADP). Remanent polarization P R was observed in both ferroelectric and proton glass regimes of x but not observable with s in the antiferroelectric regime. Nonergodicity, phase coexistence and diffuse phase transition characteristics seem to be well identified by the pyroelectric measurements of P FC , P ZFC and P R .

The effect of CrO42- ions on the electro-optic properties of KDP single crystals

Sufficiently large yellowish single crystals of KDP doped with various concentrations of K2CrO4 have been grown for electro-optic device applications, by the slow-evaporation Holden's rotary crystallizer technique. These crystals have been characterized for their ferroelectric and linear electro-optic properties. The doped crystals have low half-wave voltages as compared with that of pure KDP while there are no significant changes in the ferroelectric properties.

Raman studies on potassium-ammonium dihydrogen phosphate systems

We have studied pressed-pellet samples of potassium-ammonium dihydrogen phosphate [${(\mathrm{KDP})}_{1\ensuremath{-}x}{(\mathrm{ADP})}_{x}$] by Raman scattering for $x=0$, $x=0.5$, and $x=1$ at room temperature and liquid-nitrogen temperature. The liquid-nitrogen-temperature spectra of pure KDP and ADP pellets showed the characteristics of their ferroelectric and antiferroelectric phases, respectively. However, the low-temperature spectra of the ${(\mathrm{KDP})}_{0.5}$${(\mathrm{ADP})}_{0.5}$ pellets showed features that were characteristic of a structural glass formation as found previously in single-crystal samples of rubidium-ammonium dihydrogen phosphate [${(\mathrm{RDP})}_{1\ensuremath{-}x}{(\mathrm{ADP})}_{x}$], such as the persistence of the continuum soft-mode structure and local freezing of N${\mathrm{H}}_{4}^{+}$ units.

Non-Ohmic behaviour of doped KDP

Abstract A systematic study of intensity versus voltage curves for pure and doped KDP is presented. For doped samples non-ohmic behaviour has been observed at all temperatures for high enough fields. Increasing the pH of the KDP growing solution results in the same effect as doping. Some possible explanations are briefly discussed

Lattice polarization and proton ordering in KDP crystal with ADP impurities

Abstract ADP impurity effects on the dielectric constant anomaly and the softmode dependence on temperature in KDP crystals are studied: for ADP concentration of 0.13% the ferroelectric transition temperature is lowered by 2.9 K and the soft-mode of the ADP doped crystal is observed to continue to soften across the hard core repulsion temperature 132 K of the soft-mode in pure KDP crystals.

Optical absorption and thermoluminescence of X-irradiated KDP

Optical absorption and thermoluminescence spectra of nominally pure X-irradiated KDP have been obtained between 13K and room temperature. Absorption spectra and their associated thermal bleaching curves exhibit a strong dichroism. Two glow peaks are observed at 73K and 123K which correlate well with main decay steps on the bleaching curve. From these data the existence of two different centres with activation energies of approximately 0.042 eV and approximately 0.22 eV is concluded. Different possibilities for the structure of these centres are discussed.