Magnesium bismuthate

Description

This compound is semiconducting and is employed in small batteries used in portable electronic devices. Magnesium bismuthate is prepared by the reaction of sodium bismuthate with a soluble Mg salt.
MgBi₂O₆ can be classified as a transparent conducting oxide (TCO) that possess an unusual combination of properties; high transparency across most of the visible spectrum, coupled with high-electrical conductivity. TCO’s have a wide variety of applications, including use in flat panel displays, solar cells, energy-efficient windows, gas sensors, antistatic coatings, and heating elements.

Physical properties

MgBi₂O₆ reveals temperature- independent conductivity (0.01 S/cm²), a negative Seebeck coefficient (20.025 mV/K), and an optical band gap that falls at the low-energy end of visible region (1.8 eV). This combination of attributes, indicating that this compound is a degenerate n-type semiconductor, a trait that has not previously been reported in a Bi⁵⁺ oxide.
It consists of a ring structure of octahedral BiO₆^2- octagonal units with interspersed Mg²⁺ cations. Characterization of polycrystalline samples of the trirutile oxide Bi⁵⁺ revealed temperature-independent conductivity (0.4 and 0.01 S/cm), a negative Seebeck coefficient ( 0.035 and 0.025 mV/K), and an optical band gap that falls at the low-energy end of visible region (1.7 and 1.8 eV). This combination of attributes indicates that this compound is a degenerate n-type semiconductor, a property that has not previously been observed in a Bi⁵⁺oxide.

Preparation

The preparation of magnesium bismuthate, MgBi₂O₆, was accomplished in a sealed PTFE-lined pressure vessel. The pressure vessel and contents were heated to and held at 135°C for 2.5 days. The pressure vessel was cooled to room temperature before opening. After separation of the solid by filtration and drying at 60°C for 24 h, a dark brown powder was obtained.