Syntheses, structures and characterizations of novel arsenotungstates : NLO, conductivity, band-gap and thermal expansion properties

Abstract

Three groups of tungsten compounds: tungsten oxides, tungsten bronzes and tungstates (VI) are reviewed. Based on the first alkali metal arsenotungstate, we synthesized two novel compounds by replacing alkali metals. Of them, the sodium arsenotungstate is isotypic to the potassium compound, but the lithium compound has a completely new framework. The structures were discussed in detail along with diffraction, Raman and infrared spectra, thermal analysis and properties like nonlinear optical. We discussed the temperature-dependent properties of these three products, especially thermal expansion behavior. From the diffraction data, the metric parameters can be extracted and modeled using Grüneisen first-order approximation for the zero-pressure equation of state. Using Raman spectra data and the autocorrelation method, we can get consistent results. We also measured electrochemical impedance spectroscopy to know conductivity properties. The phase diagram of the system K2O-As2O5-WO3 was intensively studied by selecting the special points with different molar ratios of raw materials and analyzing products via powder X-ray diffraction patterns.