Optical, structural and microhardness properties of KDP crystals grown from urea-doped solutions I. Pritula a, * , A. Kosinova a , M. Kolybayeva a , V. Puzikov a , S. Bondarenko a , V. Tkachenko a , V. Tsurikov a , O. Fesenko b a STC ‘‘Institute for Single Crystals’’, National Academy of Sciences of Ukraine, 60 Lenin Avenue, 61001 Kharkov, Ukraine b Institute of Physics, National Academy of Sciences of Ukraine, 46 Nauky Avenue, 68028 Kyiv, Ukraine Received 2 August 2007; accepted 18 October 2007 Available online 7 November 2007 Abstract 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 0.2–2.0 M 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 (1 0 0) and (0 0 1) crystallographic planes show an increased hardness of the doped crystals (grown in the presence of urea additive) on the plane (0 0 1) in comparison with that of pure potassium dihydrophosphate crystal. # 2007 Elsevier Ltd. All rights reserved. PACS : 81.10.h; 61.72.Ss; 81.10.Aj Keywords: A. Optical materials; B. Crystal growth; C. X-ray diffraction; D. Mechanical properties; D. Optical properties 1. Introduction Unremitting interest to potassium dihydrophosphate (KDP, KH 2 PO 4 ) crystals is caused by their unique physical properties and high manufacturability. In particular, KDP crystals which possess extremely high optical and structural perfection make it possible to produce elements for doubling and tripling of laser radiation frequency, electro-optic switches and modulators with an aperture of several tens and hundreds of square centimeters to be used, e.g. in laser fusion facilities [1]. These crystals are distinguished by rather high efficiency of non-linear conversion and a wide optical transparency range which extends far (up to 176 nm) to the short-wavelength region of the spectrum [2]. www.elsevier.com/locate/matresbu Materials Research Bulletin 43 (2008) 2778–2789 * Corresponding author. Tel.: +380 57 341 01 39; fax: +380 57 340 93 43. E-mail address: pritula@isc.kharkov.ua (I. Pritula). 0025-5408/$ – see front matter # 2007 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2007.10.040