ИСТИНА

Growth of NaGd(MoO4)2 Crystals from Non-Stoichiometric Melts Evgeny V. Zharikov,1 Kirill A. Subbotin,1,2 Anatolii I. Titov,1,2 Valerii V. Voronov,1 Valerii G. Senin,3 Valentina B. Dudnikova,4,1 and Denis A. Lis1 1Prokhorov General Physics Institute RAS, Vavilova str. 38, Moscow 119991, Russia, 2Mendeleev University of Chemical Technology of Russia, Moscow, Russia, 3Vernadsky Inst. of Geochemistry and Analytical Chemistry RAS, Moscow, Russia, 4Lomonosov Moscow State University, Moscow, Russia е-mail: evzh@mail.ru Scheelite-like disordered NaGd(MoO4)2 (NGM) single crystal is a promising laser host. It provides the broad and strong luminescence bands of Ln3+ dopants, appropriate for femtosecond laser pulses generation in mode-locked regime as well as for tunable lasing. Laser application of NGM is constraining by its rather poor mechanical durability and fragility. Meanwhile, according to our previous studies, mechanical properties of scheelite-like crystals strongly depend on the actual crystal composition, which can vary in rather broad range, depending on composition of the melt, from which the sample was grown. This study was aimed to reveal dependences of the actual NGM crystal compositions, as well as of their micro-hardness and crack-resistance on the melt composition. The series of NGM single crystals were grown by Czochralski technique from the melts with the composition NaxGdy(MoO4)2 (x = 0,4 ÷ 1,2; y = 0,933 ÷ 1,2). The values of x and y were chosen in such a manner that the content of oxygen would be strictly 4x2 for each melt. The sum (x+y) ≠ 2 for non-stoichiometric melts, thus, the defectiveness was initially introduced into the (Na + Gd) site. The crystal compositions were measured by microprobe analysis. We found the congruent melting point for this system as follows: Na2O:Gd2O3:MoO3 = 14,4:17,4:68,2 (mol. %). The sample grown from this melt showed the difference between crystal and melt compositions just slightly exceeding the measurement error. The unit cell parameters and hydrostatic densities of NGM series were measured, and actual molar weights of crystals were calculated. It allowed revealing the crystal compositions taking into account the cationic vacancies. Pronounced contents of vacancies in (Na + Gd) sites have been found even for the crystals grown from stoichiometric melt, whereas vacancy-free samples crystallize only from the melts with pronounced (Na + Gd) excess (x + y > 2,4). Micro-hardness of the crystals slowly increases with increment of Gd3+ content, whereas the changes in crack resistance do not exceed the measurement errors for the studied crystals. Acknowledgments: This study was partially supported by Russian Scientific Fund (18-12-00517)