310 / 2019-02-25 08:27:55

Synthesis of Sodium Molybdenum/Tungsten Bronzes Through High-pressure Solid-state Reaction

High pressure; Reaction; Bronzes

全体主题 > High Pressure Physics and Materials Science

ABO3 type molybdenum/tungsten bronzes are a kind of typical nonstoichiometric compound, where A is alkali metal, B is molybdenum or tungsten, and the content of A varies in the range of 0-1. Interestingly, the structure, color and physical properties of AMO3 (M=Mo,W) crystals variate greatly with the content of A. For example, when the sodium content of NaxWO3 increases from zero to unity, its color changes from yellowish-green to gray, blue, deep violet, red and finally to gold, and its electrical properties undergoes an insulator-metal transition. This makes it great potential materials in the application of electronic devices, humidity and temperature sensors. Various synthetic techniques have been reported to prepare NaxWO3, however, these traditional reducing methods require very high temperature and reducing atmospheres, and it is very difficult to prepare NaxMoO3.
Here we report an effective synthetic route to well-crystallized NaxMO3 (M=Mo,W) crystals. This simple method is based on a high pressure solid-state metathesis reaction between varying phases of Na2MO4 (M=Mo,W), boron (B), and boron oxide (B2O3). The advantage of the method lies in the potential energy and cost savings over other conventional synthetic routes. NaxMO3 (M=Mo,W) can be rapidly synthesized under 4.0 GPa and 700 °C in just 10 minutes. This discovery provides a starting point for mass production and growth of large single crystals of alkali metal molybdenum/tungsten bronzes under high pressure.