ADP Crystals Research Articles

Ion beam interaction with insulating crystals: Studies on KH2PO4and NH4H2PO4

Abstract Different damage effects are observed in KDP and ADP when irradiated with light and heavy ion beams. Color centres stable up to 240 K are observed in both compounds irradiated with beams of 22 MeV 2H+ and fluences below 1 × 1016 ions/cm2; a tentative mechanism for their generation is given. For fluences between 1 × 1016 and 2 × 1016 ions/cm2 no further damage is observed in KDP; but ADP crystals show a light color stable up to the melting point and for higher fluences they appear white and opaque: X-ray diffraction patterns show no amorphization; a broad band due to electronic excitations, besides the characteristic Raman spectra is observed. No spontaneous cleavage was ever observed. With 88 MeV 16O6+ ions, as dense valence-electronic and nuclear interactions become important, clustering of point defects and creation of extended defects take place; different damage steps appear progressively, including radiation induced spontaneous cleavage; threshold fluences are given.

Growth and characterization of sulphate mixed L-arginine phosphate and ammonium dihydrogen phosphate/potassium dihydrogen phosphate mixed crystals

Our investigations on the growth of the mixed crystals of L-arginine phosphate sulphate and ammonium dihydrogen phosphate/potassium dihydrogen phosphate (ADP/KDP) are presented. The structural, mechanical, electrical and optical properties of L-arginine phosphate (LAP) and L-arginine phosphate sulphate (LAPS) crystals are discussed. Pure and mixed crystals of KDP and ADP have been grown on KDP seeds for the entire range of compositions. The etch pits observed on the (100) plane of the as-grown crystals revealed the preferential absorption on one of the two components into the lattice.

Microhardness studies in gel-grown ADP and KDP single crystals

Microhardness studies were carried out on (100) faces of gel-grown ADP and KDP single crystals. Slip lines were observed on (100) face of ADP crystal at the corners of the impressions. Microcracks around the indentation were found on (100) face of KDP crystal from 10g load which spread out as the load increased. Vickers hardness numberH v decreased with increase in load. ΔH v at 50g load for solution-grown crystals and gel-grown crystals (present case) was determined. Work hardening indexn for both ADP and KDP crystals was less than 2 showing soft-material characteristics. Using Wooster’s empirical relation, values of C11 from hardness were calculated and found to be close to the reported ones.

Computation of surface energies in an electrostatic point charge model: II. Application to zircon (ZrSiO4)

In zircon (ZrSiO4), four different Periodic Bond Chains (PBCs) can be described, i.e. [001], 〈100〉, 〈1/2 1/2 1/2〉 and 〈1/2, 1/2, 1 1/2〉. F faces which grow slowly according to a layer mechanism, are {100} and {011}. Calculation of attachment energies, which are supposed to be directly proportional to the growth rates, is performed in electrostatic point charge models, model I: Zr4+Si4+O42-, model II: Zr4+Si2+O41.5-and model III Zr4+Si0O41-. The theoretical growth form is short prismatic following {100} and is terminated by the dipyramid {011}. The lower the oxygen charge the more elongated is the crystal parallel to the c axis. The slice d011 can be defined either bounded by zirconium (d001A) or by silicate tetrahedra (d011B. As these slice boundaries differ in height of one half slice with thickness d022, and as these half slices d022Aand do22Bare F faces, the growth of {011} may also take place by elementary growth layers of thickness d022. In that case the growth rates of {011} increase and the growth models are even more prismatic. The S form {031} could only be present on the theoretical growth form with formal charges, provided that the growth of {011} takes place with half slices d022 and the adsorption of impurities establishes additional strong bonds parallel to its slice boundaries. On the models with lower silicon and oxygen charges the form {031} is not present, but a reduction of the attachment energy of less than 0.1 percent would result into the appearance of {031} on these models as well. If O-H ⋯ O bonds could be formed by adsorption of protons, silica complexes or water molecules, additional hydrogen bonds parallel to 〈110〉 would establish the F character of {110} and {001}, which has been observed sometimes on minerals and synthetic crystals. Neutrally charged solvated silica complexes, such as Si(OH)4.2H2O, present as impurities on kink sites could reduce the growth rate of the forms {110} and {001}. NH4H2PO4 (ADP, Biphosphammite) has a crystal structure similar to that of zircon. The F forms of ADP are also {100} and {011}. The typical tapering observed on ADP crystals grown from Cr bearing aqueous solutions due to the presence of {0kl} with k>l is not common for zircon. The S form of ADP has such a relatively low attachment energy that it could also be present on the theoretical growth form.

The growth rate variation of the (100) faces of ADP crystals in the presence of manganese ions

Measurements have been made of the growth rate of the (100) faces of ADP crystals grown under a constant supersaturation of 1% from static solution containing mixtures of MnCl24H2O and KMnO4 at pH=2.5. Under these conditions, manganese is incorporated into the crystal and the growth rate shows a strong oscillatory character in the early stages of growth. These oscillations dampen as growth progresses. X-ray transmission topography of larger single crystals that are grown under similar conditions and which also incorporate manganese ions reveals the development of strain bands in the (100) growth sector. A possible mechanism of lattice strain generation by incorporation of manganese ions, and its influence on growth rate variation in the (100) growth sector is discussed.

A new method of enlarging the cross‐section of KDP using ADP crystals as seed

AbstractA new method of enlarging the cross‐section of KDP crystals using an easily enlarged ADP crystal as seed for a KDP crystal, has been investigated. The growth characteristics of the ADP seeds (Z‐plate, cap, and parallelly spliced seeds) at KDP supersaturation have been observed. Chemical etching was used to characterize the grown crystals, and chemical analysis to determine the composition of both the region of the seed and the grown crystal. The mechanism of this kind of growth is discussed. In conclusion this growing method should be qualified for enlarging the cross‐section of KDP crystals.

Morphology of growing vicinal surface; prismatic faces of ADP and KDP crystals in solutions

The processes resulting in the loss of vicinal-surface morphological stability under the action of a supersaturation gradient on the face and the presence of growth-decelerating impurities have been studied by in situ laser interferometry. It has been established that these processes are most pronounced in the supersaturation range corresponding to the maximum partial derivatives of the tangential velocity of the elementary layer motion with respect to supersaturation and impurity concentration. It has been suggested that the change of the dislocation hillock shape accompanying the formation of macrosteps is due to anisotropy of the surface energy.

Intensity-induced nonlinear effects in UV window materials

Intensity-induced nonlinear effects in optical window materials have been investigated at 308 nm. The absolute two-photon absorption coefficients for fused silica, CaF2, BaF2, Al2O3 and ADP crystals have been measured by using a single 120 ps, transform-limited pulse from the second harmonic of a distributed feedback (DFB) dye laser. The nonlinear refractive index coefficient γ has been obtained from measurements of far-field intensity distributions.

Growth of dipyramidal face of dislocation-free ADP crystals; free energy of steps

The kinetics of dislocation-free growth of the dipyramidal face of ADP crystals have been studied by laser interferometry and X-ray topography in the supersaturation range 1.5% < σ < 6.4%. The reproducible growth of dislocation-free crystals ( R > 3 × 10 -9 cm/s) started at supersaturations σ n=1.5-3% in the form of spontaneous nucleation. The two-dimensional character of nucleation is confirmed by the linear character of the 1 n( R σ 5 6 ) versus 1 σ dependence. It was also revealed that the R( σ) curve consists of two linear portions intersecting at σ=4.5%. It is assumed that at σ > 4.5% the process of nucleation is homogeneous and occurs at atomically smooth terraces, whereas at σ < 4.5% it proceeds at sites more active than regular, e.g., at impurity particles. The results obtained give the effective surface energy of the step end as α 1 ⋍ 11.8 erg/cm 2 for σ > 4.5% and α 2 ⋍ 4.2 erg/cm 2 for 1.5 < σ < 4.5%. Similar treatment yields the concentration of active centers on the surface: n x s⋍1.3 × 10 3 cm -2 .

Gel growth followed by holographic interferometry case of ADP crystals grown by T-decrease

NH 4H 2PO 4 (ADP) crystals have been grown in a tetramethoxysilane gel by temperature decrease. Nucleation and growth have been followed by interferometric holography which has allowed to determine the supersaturation so that the growth proceeds by a bidimensional mechanism without generation of dislocations.

Generation of the fifth harmonic of a neodymium laser and two-photon absorption in KDP and ADP crystals

An investigation was made of cascade generation of the fifth harmonic of radiation from a wide-aperture neodymium laser in KDP and ADP crystals. It was found that the main factor limiting the efficiency of the process was two-photon absorption of the radiation. The coefficients of two-photon absorption of the radiation at the frequency of the fourth harmonic of a neodymium laser were determined for KDP (0.5 cm/GW) and ADP (0.35 cm/GW). The efficiency of conversion of the second harmonic radiation energy of a neodymium laser to the fourth harmonic was 92%, the highest achieved so far. The efficiency of conversion to the fifth harmonic was 19%, close to the maximum attainable for KDP crystals.

Behavior of77Se Hyperfine Components of SeO43-Radicals in Highly Deuterated NH4H2PO4

The authors observed the 77 Se hyperfine (hf) components of ESR spectrum of SeO 4 3- radicals doped in 94%-deuterated NH 4 H 2 PO 4 (D 0.94 ADP) and compared the result with those for D x ADP (0≦ x ≦0.70) crystals. In tlte paraelectric phase no remarkable deuteration effect was observed. In the antiferroelectric (AFE) phase, on the other hand, a new type of angular dependence of the hf line-position was found between about 185 K and T c (236 K). The results mean that the crystal field of the AFE host crystal which distorts the SeO 4 3- into the AFE configuration depends on temperature remarkably in the AFE D 0.94 ADP.

EPR studies of MoO 43- centres in ADP crystals

Paramagnetic centre MoO 3 3- is produced by γ-irradiation of MoO 4 2- doped ADP crystals. The g values of MoO 4 3- centre suggest that its ground state is d z 2. From 142 to 260 K the EPR spectra of MoO 4 3- showed a triplet super-hyperfine structure. The triplet to quintet transition has not been detected in this case.

The Quadratic Electrooptic Effect in KDP and ADP Crystals

The Quadratic Electrooptic Effect in KDP and ADP Crystals

Electrical conductivity and dielectric loss studies of MoO 4 2- -doped KH2PO4 single crystals

KH2PO 4 (KDP) and NH4H2PO 4 (ADP) crystals are protonic conductors. Murphy [1] considered the presence of L and D defects in the H2PO4 sublattice to explain the conduction mechanism in ADP. However, Harris and Vella [2], in analogy with the Har r ing tonStavelley [3] model for NH4C1 , considered that the proton migration in ADP crystal occurs in the NH4 + sublattice (A defect) in addition to the H2PO 2 sublattice. Our earlier studies on the electrical conductivity and dielectric loss of MoO I -doped KDP crystals [4] were explained in terms of L defect mechanism. ADP being isomorphous to KDP, the above mechanism should also hold here. In the present study the electrical conductivity and dielectric loss studies of MoO ] -doped ADP crystals were undertaken to verify whether proton migration in the NH2 sublattice also contributes to the conduction in the ADP crystal, in addition to the migration in the H2PO4 sublattice. Because crystals of MoO] -doped ADP were grown by the slow evaporation of the saturated solution. K2MoO 4 was used as dopant. The presence of the impurity MOO4:in the crystal was detected by studying its optical absorption. A Cary-14 spectrophotometer was used to record the optical absorption. The crystal faces were polished and coated with silver paint to give good electrical contact between the crystal and the electrodes for the transport studies. The resistance of the sample was measured using a Keithley electrometer model 610C. The temperature of the crystal could be controlled to within 4-0.5 K. For dielectric loss measurements, a GR1615 Impedance Bridge was used. The connections between the electrode and the bridge were made through lowloss cables. The optical absorption of the doped crystals showed two bands at 230 and 210 nm. The band positions agree very well with the earlier reported spectrum of MoO42 in solution [5]. The above study confirmed the presence of MoO] in the ADP crystal. Fig. 1 shows the plot of log (aT) against l IT for undoped and MoO]-doped ADP crystals. The conductivity plot shows the following characteristics: (i) there is a knee around 94 ° in case of the pure ADP crystal in agreement with the reports by Murphy [1] and Perino and Wentreck [6]; (ii) the conductivity of

Studies in crystal growth from the melt of KDP and ADP

Abstract The description of an investigation currently in progress into the feasibility of growth from the melt of single crystals of KDP and ADP is presented. Information on the phase-equilibrium properties of KDP and ADP does not abound in the literature, and this investigation has had to be primed with thermal analytical studies of these materials which are also detailed herein. This account covers the authors' work on the subject up to and including 1985.

Microscopic investigations of morphological structures on the pyramidal faces of KDP and DKDP single crystals

AbstractStudying a number of {101} faces of KDP and DKDP single crystals in the as‐grown state we found in most cases one, rarely few, clearly stepped growth hillocks covering the whole face. The geometry of these growth hillocks was determined from photomicrographs; the step heights were measured with a profilometer. To prove our results we carried out X‐ray topographic investigations and in‐situ observations on KDP crystals. In addition we studied the as‐grown faces of ADP and LiJO3 single crystals.

Growth of ADP crystals from the melt

A rationale is presented to support the speculation, and it is confirmed by experiment, that ADP can be made to melt quasicongruently and, therefore, that single crystals of this material can be grown from its melt. As is to be expected, the growth rates achieved in growth from the melt are much greater than those which are realizable in industrial-scale solution growth of crystals of the same material.

Dielectric dispersion in d-KDA

The complex electric permittivity of KD 2AsO 4 in paraelectric phase in microwave region was studied. The dielectric relaxation can be described in terms of a monodispersive process over the temperature range close to T c . The calculated macroscopic τ and microscopic τ 0 relaxation times are equal to 74 and 2.5 ps, respectively. The activation free energy is equal to 3 kJ/mol. The problem of the replacement of P by As in the family of KDP and ADP crystals is discussed.

Determination of relative signs of electro-optic and piezoelectric coefficients by measuring optical phase shifts caused by an applied electric field

A simple method for measuring the relative signs of electro-optic (EO) and piezoelectric (PE) coefficients in crystals is investigated theoretically and experimentally. The method allows us to determine the relative sign of the unclamped EO coefficient rij and the PE coefficient djk by detecting independently optical phase shifts caused by both EO and PE effects and by a PE effect only. It is shown that the sign of r63/d36 of KDP and ADP crystals is measured by this method to be negative.