In 1823, a kind of sodium and tungsten oxide Na_xWO₃ was synthesized, its color is gold that similar to bronze, and it has electrical conductivity, therefore it’s known as tungsten bronze. Subsequently, there have been new compound oxide bronze being discovered and studied. Most of the transition metal element may be formed into bronze, except tungsten bronze, molybdenum bronze, bronze vanadium, niobium, tantalum, bronze and bronze are common as well.

 

Due to historical reasons, sometimes the oxides of tungsten bronze are also referred as bronze in the literature, bronze oxide can be represented as the formula A_xMO_n. In A_xMO_n Formula, A is positively charged atoms, M is a transition metal, n can be either an integer or a non-integer. A_xMO_n has following characteristics in structure. (1) the M in MOn is usually octahedral, and it’s often covalently linked between M-O. The octahedra further connected to form a skeleton structure with polyhedral open pores; (2) A_xMO_n partial skeleton structure is similar with MO_n; (3) A is constantly electropositivity atom, filling cavities in the skeleton; (4) With the filling of A, transition metal M appears allotropy divalent ions, that becomes mixed valence ion, thereby forming a nonstoichiometric compound.

 

Tungsten bronze Aa_xWO₃ (0 <x <1) belongs to such nonstoichiometric compounds, it can be widely used in optical, electrical and chemical fields because of its rich physical properties, such as the electrically induced discoloration device, photochromic mechanism and humidity sensors, etc. There are many synthesis ways of it. High temperature solid state reaction method and molten salt electrolysis method is the common method of synthesizing tungsten bronze, and there are also chemical synthesis machinery, high pressure sintering, thermal degradation, microwave synthesis, aqueous reduction method for the synthesis of this materials, and it has recently been reported that tungsten bronze can also be obtained by gas permeation method.