Physico-Chemical nanomaterials science 

Photocatalytic performance of mixed lithium niobates-tantalates prepared by mechanochemical methods
Sydorchuk V.1, Sugak D.2, Hurskyi S.3, Samsonenko M.1, Khalameida S.1, Vasylechko L.2 
1Institute for Sorption and Problems of Endoecology, NAS of Ukraine, 14 Naumov St, Kyiv-03164, Ukraine. 
E-mail: mashuna.08@gmail.com
2 Lviv Polytechnic National University, 12 Bandera St., 79013 Lviv, Ukraine
3 Institute for Energy Research and Physical Technologies, Clausthal University of Technology, 19B Am Stollen, Goslar, Germany

Lithium niobate LN and tantalate LT are among the most frequently used materials of functional electronics. Recently LiNb1−xTaxO3 (LN-LT) solid solutions have been studied, since they offer the prospects for combining the advantages of both pure materials. The nanoparticles of LN-LT can be more attractive for some practical applications. As the wide-gap semiconductors, LN and LT powders are also prospective photocatalysts under UV irradiation. High energy milling belongs to effective method for preparation of oxide materials in nano-sized state. It promotes activation of reagents and their interaction with perovskite phase formation.
Thus, dry milling of Li2CO3-Nb2O5-Ta2O5 mixtures with different ratio of oxides at 600 rpm for 15 h results in formation of intermediates consisting predominantly of X-ray amorphous and low-crystalline niobates-tantalates [1]. After next calcinations at 700ºC, intermediates are converted into perovskites with a solid solution structure and a particle size of 20-80 nm. 
Since both obtained intermediate and pure perovskite powders absorb visible light and have band gap within 3.00-3.25 eV, they were tested as photocatalysts under visible irradiation in process of dyes degradation in aqueous media. Calcined high-crystalline niobates-tantalates show moderate photocatalytic activity. At the same time, as-milled intermediates and especially those after hydrothermal treatment exhibited high performance, apparently due to the higher specific surface area. Praseodymium-doped sample has the highest activity which is obviously associated with smallest value of the band gap.
 
1.	Vasylechko L. et al. Investigations of LiNb1−xTaxO3 Nanopowders Obtained with Mechanochemical Method // Crystals -2021.-11.-P. 755.