Producing H2 from the splitting of water with using oxide-type semiconductors under light irradiation is an attractive way to establish a clean energy system without relying on fossil fuels. Several types of semiconductor photocatalysts such as Bi2RENbO7 (RE=Y, rare-earth) [1], In0.8M0.2TaO4 (M=Ni,Cu,Fe) [2], M-doped InTaO4 (M=Mn,Fe,Co,Ni and Cu) [3] were synthesized by the solid state reaction method. Moreover, a group of mixed oxides with the wolframite structure (ABO4 where A=Ni(II), Co(II), etc, B=W) has been studied for its interesting catalytic properties [4]. These compounds are so-called "mechano-catalytic" materials and are used for overall water splitting. The water splitting process consists in continuously converting mechanical energy into chemical energy with help of mentioned powder as catalytic materials.

In our investigations we have obtained as a result of the solid-state reaction between MWO4 (M=Ni,Co) and RE2WO6 (RE= Nd,Sm,Eu,Gd and Er) new series of compounds with the following formulas: NiRE2W2O10, Co2RE4W3O14 and CoRE4W3O16 [5]. It seems that these nickel and cobalt tungstates with rare earth ions seem to be good catalysts in many processes. In the present work, we presented the results of IR-spectroscopy, X-ray and EPR measurements showing some structural features of the compounds. The Co2RE2W3O14 as well as CoRE4W3O16 compounds crystallize in the orthorhombic system and only the basic crystallographic parameters have been determined up to now. Wide, unstructured EPR powder spectrum of these compounds and their temperature evolution have been analyzed and interpreted. The optimization of the spin-Hamiltonian parameters and EPR data simulation was performed using the software package EPR-NMR.

I thank for financial support of my participation in E-MRS 2006 given from a Nationwide Polish Catalytic Network" Nanomaterials as Catalysts for New, Environmentally Friendly Processes" (Adam Worsztynowicz)

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1. Growth and EPR properties of NdVO₄, HoVO₄ and NdVO₄ single crystals
2. EPR and optical properties of PbMoO₄:Co single crystals
3. Temperature dependence of PL and EPR spectra of Sr_0.33Ba_0.67Nb₂O₆:Cr (0.02mol.%) single crystals
4. Magnetic and optical properties of  Li_0.28Na_1.72Ge₄O₉:Cr, Mn (0.1mol%) single crystals
5. Spectroscopic and magnetic properties of gadolinium macroacyclic and macrobicyclic complexes