Dihydrophosphate Crystals Research Articles

Origin of non-monotonic behaviour of electrical conductivity of potassium dihydrophosphate crystals depending on gamma-irradiation dose

Origin of non-monotonic behaviour of electrical conductivity of potassium dihydrophosphate crystals depending on gamma-irradiation dose

Modeling of Hydrodynamics and Mass Transfer Processes in KDP Crystal Growth

The turbulent hydrodynamics in a conventional operating crystallizer for growing kalium dihydrophosphate crystals is analyzed by physical modeling methods. The potentialities of an axisymmetric crystallizer, which has similar tools for stirring solution but is able to ensure controlled laminar hydrodynamic flows are considered. A combined mathematical model is formulated, which takes into account both the convective salt transfer in the crystallizer on the basis of solving the Navier–Stokes and diffusion equations and the kalium dihydrophosphate crystal growth on the basis of the theoretical model. A parametric calculation is performed to determine the effect of each mechanism of solution motion, including the directed solution outflow from a tube into the crystallizer and the rotation of crystal and stirrer.

Second-order nonlinear susceptibilities of the crystals of some metal tartrates

The relative (with respect to a powder potassium dihydrophosphate crystal) effective second-order nonlinear susceptibilities have been measured for gel-grown single crystals of some tartrates with the general formula MeC4H4O6 · nH2O on powder samples upon the excitation of the second harmonic of laser radiation with a wavelength of 1.064 μm. The unit-cell parameters and the symmetry space groups have been determined for the single crystals under study.

Resonant diffraction of synchrotron radiation in rubidium dihydrophosphate crystals

Purely resonant Bragg reflections 006, 5\( \bar 5 \)0, and 666 in a rubidium dihydrophosphate (RbH2PO4) crystal at the K edge of rubidium have been experimentally and theoretically investigated. These reflections remain forbidden when the resonant dipole-dipole (E1E1) contribution to the resonant atomic factor is taken into account; they may be due to the dipole-quadrupole (E1E2) transitions as well as to the anisotropy atomic factor, which is caused by thermal atomic displacements (thermally induced contribution) and/or local jumps of hydrogen atoms. A numerical simulation showed that, at room temperature (experimental conditions), the thermally induced contribution to the “forbidden” reflections is dominant.

Optical, structural and microhardness properties of KDP crystals grown from urea-doped solutions

Potassium dihydrophosphate single crystals were grown from aqueous solutions onto a point seed using temperature reduction method by doping with different molar values of urea. The characterization of the grown crystals was made by visible and Fourier transform infrared spectroscopy, Vicker's hardness studies, X-ray powder diffraction, non-linear optical and laser damage threshold measurements. By comparing these crystals with the ones grown from the pure solution, it is shown that 0.2–2.0M of the urea additive enhances the laser damage threshold and the second harmonic efficiency more than by 25 and 20%, respectively. By means of the Bond method using a multipurpose three-crystal X-ray diffractometer it is shown that the presence of urea additive increases the crystal lattice parameter c of the grown crystals, whereas the lattice parameter a is by an order less sensitive to the changing urea concentration in the solution. The Vicker's hardness studies at room temperature carried out on (100) and (001) crystallographic planes show an increased hardness of the doped crystals (grown in the presence of urea additive) on the plane (001) in comparison with that of pure potassium dihydrophosphate crystal.

Structural conditionality for the quadratic nonlinear susceptibility of Sr1−x Ba x Nb2O6 crystals

The intensity of the second harmonic generated in powdered samples of the compositions Sr0.75Ba0.25Nb2O6, Sr0.61Ba0.39Nb2O6, and Sr0.50Ba0.50Nb2O6 under irradiation by a pulsed-periodic YAG: Nd laser is measured. The effective values of the quadratic nonlinear susceptibility of these materials with respect to the reference sample of potassium dihydrophosphate crystals are estimated. The results obtained are compared with the precise parameters of the atomic structure of the single crystals with the corresponding compositions. It is established that the dominant contribution to the nonlinear optical susceptibility of the single crystals under investigation comes from the chains aligned parallel to the c axis of the crystal and composed of Nb octahedra with regularly alternating increased and decreased Nb-O interatomic distances. The occurrence of such a sequence in the crystal structure suggests an alternation of stronger and weaker chemical bonds in the chains −O=Nb−O=Nb−O=. These bonds are characterized by different charge electron densities, a phenomenon confirmed by the X-ray diffraction analysis, which indicates not only a difference in the Nb-O bond lengths but also an anharmonicity in the thermal vibrations of the niobium atoms. The revealed anharmonicity is associated with the difference between the chemical bonds of the niobium atoms with the oxygen atoms located in trans positions in the octahedra.

Fluctuations of steps at the faces of potassium dihydrophosphate crystals in a solution

The time dependence of the step-displacement fluctuations at the faces of a prism and a bipyramid of potassium dihydrophosphate (KDP) crystals is determined by in situ atomic-force microscopy in the line-by-line scanning mode. It is shown that the build-up of fluctuations follows a t1/4 law and not a t1/2 dependence as for a single diffusing particle. Measurements are made during growth and dissolution in the vicinity of the equilibrium position. It is found that the fluctuations at the prism face during dissolution are stronger than those during growth. Voronkov’s theory is used to compute the basic parameters of crystallization and to interpret the obtained results.

Anisotropy of the nonreciprocal linear birefringence in crystals

Results are presented of an experimental investigation of nonreciprocal linear birefringence (a difference between the phase velocities of counterpropagating waves having the same linear polarization) in lithium iodate and potassium dihydrophosphate crystals in a magnetic field. An original double-pass optical measuring system using two linear quarter-wave phase plates (Fresnel rhombs) is used to demonstrate a new method of studying the effect which can give a fairly high sensitivity and avoid accompanying effects.