Effects of chemical substitution on the structural and optical properties of α-Ag_2−2xNi_xWO₄(0 ≤ x ≤ 0.08) solid solutions

Abstract

In this work, we investigated the effects of chemical substitution on the structural, electronic, and optical properties of α-Ag2-2xNixWO4 (0 ≤ x ≤ 0.08) solid solutions prepared by a facile microwave-assisted hydrothermal method. The results showed that the increase of Ni concentration in α-Ag2WO4 microcrystals as a host matrix caused a morphological transformation and a shift of the electronic and optical properties. Based on first principles calculations and using Wulff's construction, particle shapes and their transformations in α-Ag2WO4 and α-Ag2-2xNixWO4 can be affected by controlling the ratios of surface energy values between the different facets. In addition, theoretical calculations revealed that Ni substitution in α-Ag2WO4 is more favorable in the Ag2 and Ag4 positions, in which the local coordination of Ag atoms corresponds to clusters with coordination numbers of seven and four, respectively. This behavior could be related to the degree of medium-range structural disorder in α-Ag2-2xNixWO4 crystals. The experimental results were correlated with theoretical simulations to achieve a deeper understanding of the relationship between morphology and properties. These results provide the basis for a rational design for the compositional modulation of structural and optical properties.

Computational Simulations of Morphological Transformations by Surface Structures: The Case of Rutile TiO2 phase

“…Several methodologies can be found in the literature about theoretical simulation to explain surface influences and the modification at the equilibrium stage 34,35 . Our group has used a method to evaluate the routes based on the modulation of the relationship between the surface stabilities of different faces and the areas of those parts which are exposed in the final shape 1,4,5,36 .…”

“…Experimental nanoparticles usually present morphologies found on the right side of the map showing that the surfaces (111) and (110) are more commonly stable in comparison with other surfaces. In spite of the simplicity, the explanatory power of this method has helped in the evaluation of morphological changes with the variation of the synthesis environment besides the connection between some system characteristics and the exposed surfaces 4,37 . There are several situations that the morphology map can be useful.…”

“…Recently, our research group has applied theoretical methods to study the effects of surface stability on the morphological transformation of different metals and metal oxides (Ag, TiO 2 (anatase), BaZrO 3 , and α-Ag 2 WO 4 ) 1,4,5 . By means of this method, morphologies of crystalline materials can be used as a very useful tool for the design and knowledge of synthesis of new materials.…”

Ag2–xCuxWO4 Solid Solution: Structure, Morphology, Optical Properties, and Photocatalytic Performance in the Degradation of RhB under Blue Light-Emitting Device Irradiation

“…The good intensity band at 880 cm −1 is assigned to asymmetric stretching (A 1g ) of ←O−W−O/O−W−O→ bonds from octahedral [WO 8 ] clusters also reported for other tungstates. 19 Asymmetric stretching of W−O bonds from [WO 8 ] clusters were identified at 779 (A 1g ) and 805 (A 2g ) cm −1 , as well as the symmetric stretching of WOOW groups at 666 and 749 cm −1 , were found. 4 In the interval from 306 to 510 cm −1 , bending and wagging of WOOW groups denoted by A 2g and B 2g active modes were identified.…”

“…To change the photon absorption region from UV to visible light, the investigation of structural, optical, and photocatalytic properties of silver tungstate as solid solutions (Ag 2−x M x WO 4 ), where M is the transition metal, has been recently reported. Pereira et al 19 report the study of structural, morphological, and optical properties of pure α-Ag 2 WO 4 and solid solution α-Ag 2−2x Ni x WO 4 with expressive photoluminescence emission at 454 nm. On the other hand, α-Ag 2−2x Zn x WO 4 solid solutions were efficiently obtained by Pereira et al 14 with different morphological and photoluminescence properties.…”