Classic theory of crystal growth states that all crystals grow by adding new building units (i.e., atoms, ions, molecules or their complexes) to their surfaces from solution, melt, vapor or another solid phase [1]. However, there is another theory of the alternative mechanism of the crystal growth – micro-block mechanism – that suggests that the crystal growth occurs by the intergrowth of the independently grown smaller crystals that made a contact in the course of their size increase. The latter approach, initially developed by P. Goubert as early as in the 19-th century, was actively pursued and developed by E. S. Fedorov, A. Traube, M. P. Shaskolskaya, A. V. Schubnikov, N. N. Sheftal, D. Balarev, N. P. Yushkin [2], A. M. Askhabov, I. V. Melikhov and other. The propriety of the micro-block mechanism has been confirmed by scanning (SEM) and transmission (TEM) electron microscopy as well as other experimental nano-methods [3-5]. In our presentation, we would like to report our novel results related to the formation of nanopowders in the course of their co-precipitation from aqueous solutions. Our data confirm the aforementioned micro-block mechanism of crystal growth for the obtained fluoride nanopowders (TEM measurements were carried out at the Center of mutual use of equipment at Prokhorov General Physics Institute). Specifically, we would like to emphasize the following features of the observed processes: 1. The formed primary particles are not X-ray amorphous, they are nanocrystals. 2. Nanoparticles can mutually orient each other in colloid solutions as well as in solid-state phases. 3. Usually, the first step of crystal formation is not the particle merge to an existing large single crystal; instead, it includes primary merging of already formed nanoparticles. 4. Crystallization has a step-wise hierarchical nature with the periods of rapid nanoparticle growth changing to the relaxation periods; the latter periods include processes of imperfection decrease and stress elimination. 5. The above transformations occur at the temperatures much lower than the melting temperature (i. e., the so-called Tammann temperature T < 0.6*Tmelt). 6. In aqueous media, the aforementioned processes are typical for the crystal growth of the substances with low solubility. We consider that the driving force of the observed non-classical micro-block crystallization is the thermodynamic tendency to minimize the system free energy in the course of crystal growth. Describing the dynamics of the nanoparticle formation, one may name this force as “orientation ordering force” for convenience purpose.

References [1] L.N. Rashkovich, J.J. De Yoreo, C.A. Orme, and A.A.Chernov. Crystallography Reports, 51(6), (2006), pp. 1063-1074. [2] N.P. Yushkin. Theory of micro-block crystal growth in natural heterogeneous solutions. Syktyvkar, 1971 (in Russian). [3] P.P. Fedorov, A.A. Luginina, S.V. Kuznetsov, and V.V. Osiko. J. Fluorine Chemistry. Vol.132. (2011) pp.1012-1039. [4] P. P. Fedorov, M. N. Mayakova, S. V. Kuznetsov, V. V. Voronov, V. V. Osiko, R. P. Ermakov, I. V. Gontar’, A. A. Timofeev, and L. D. Iskhakova. Nanotechnologies in Russia. Vol.6. (2011) pp. 203–210. [5] P.P. Fedorov, V.K. Ivanov. Doklady Physics. Vol.56. (2011) pp. 205-207.

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