Static and dynamic structure of ZnWO4 nanoparticles

Abstract

Static and dynamic structure of ZnWO 4 nanoparticles, synthesized by co-precipitation technique, has been studied by temperature dependent x-ray absorption spectroscopy at the Zn K-edge and W L 3 -edge. The complementary experimental techniques, such as x-ray powder diffraction, Raman and photoluminescence spectroscopies, have been used to understand the variation of vibrational, optical, and structural properties of nanoparticles, compared to microcrystalline ZnWO 4 . Our results indicate that the structure of nanoparticles experiences strong relaxation leading to the significant distortions of the WO 6 and ZnO 6 octahedra, being responsible for the changes in optical and vibrational properties.

The chemistry of ZnWO4 nanoparticle formation

“…it is stated that the phase is indeed ZnWO 4 , but that the crystallite size is too small to produce distinct Bragg peaks. An alternative explanation is that the precipitates investigated by Kalinko et al 63 were actually amorphous nanoparticles akin to the ones found in our study, and not ZnWO 4 nanocrystallites. Tourné-sandwich ions produce an average Zn coordination number between 5.3 and 5.7 (depending on the assumed Zn/W disorder on the sites usually occupied by W), and Kalinko et al reported an average Zn coordination number in this range.…”

Local structure relaxation in nanosized tungstates

“…The obtained information on the structure relaxation in nanosized tungstates is relevant for understanding and tuning of their functional properties [15,38,39].…”

“…3. The experimental data for NiWO 4 and ZnWO 4 were reported elsewhere [15,16]. The photoelectron wavenumber is defined as To extract structural information, the first shell EXAFS contributions χ(k)k 2 were best-fitted using a model-independent approach [17,18] allowing the reconstruction of the true radial distribution function (RDF) G(R)…”

“…(1) is that the true RDF G(R) can have an arbitrary (even strongly distorted) shape [17,18]. This point is very important in the case of tungstates, especially nanocrystalline, where strong static distortion of the metal-oxygen octahedra is present [15], particularly in the case of WO 6 and CuO 6 octahedra experiencing strong Jahn-Teller distortion [19]. The significant distortion of octahedra makes the use of conventional EXAFS data analysis approach [13], i.e., an approximation of the RDF G(R) by a set of Gaussian functions, inaccurate since such model is not able to account for an asymmetry of peaks in the RDF and is also not unique due to strong overlap between some peaks.…”

Effect of partial preferential orientation and distortions in octahedral clusters on the photoluminescence properties of FeWO4 nanocrystals

“…7,8 The second tungstate oxides exhibit a wolframite-type monoclinic structure where both M and W atoms are bonded to six oxygen atoms, which results in the formation of octahedral [MO 6 ]/[WO 6 ] clusters. 9,10 These differences in the coordination/structure cause defects in the crystal lattice and the appearance of photocatalytic, 11,12 photoluminescence (PL), [13][14][15][16] humidity sensor [17][18][19] and magnetic properties 20,21 as well as electronic properties for the tungstates.…”