What Is Barium?

Barium is a chemical element with atomic number 56 and symbol Ba, belonging to Group 2 of the periodic table as an alkaline earth metal. It is a soft, silvery-white metal with high electrical conductivity and significant chemical reactivity: barium oxidizes rapidly in air and reacts vigorously with water. In its pure elemental form it has limited direct application, but barium's compounds and alloys are essential in electronics, energy storage, and superconductor research. The element was first isolated in 1808 by Humphry Davy through electrolytic reduction of barium oxide.

Barium sits between strontium and radium in Group 2, sharing the alkaline earth pattern of a +2 oxidation state in virtually all stable compounds. Its relatively large ionic radius and polarizability allow barium to form stable perovskite-structure compounds, a crystal geometry that underlies many of its most technologically significant derivatives including barium titanate and yttrium barium copper oxide (YBCO).

Chemical Properties and Production

Barium is produced commercially by electrolytic reduction of fused barium chloride or by aluminothermic reduction of barium oxide at elevated temperatures. Because elemental barium reacts spontaneously with oxygen, nitrogen, and moisture, it is stored and handled under mineral oil or inert gas. Industrially, barium sulfate is the most widely consumed barium compound by mass, used as a weighting agent in oil well drilling fluids and as a radiopaque contrast agent in medical gastrointestinal imaging. Barium carbonate is used as a raw material for the production of other barium compounds and as a component of specialty glass formulations that increase refractive index. Barium fluoride is valued in infrared optics for its broad transparency window, which spans from approximately 0.15 to 12 micrometers, making it suitable for thermal imaging components and spectroscopic instruments. Thermochemical reference data for barium compounds are maintained by the NIST Chemistry WebBook, which provides standard enthalpies, heat capacities, and phase transition data used in materials processing calculations.

Electronic and Optoelectronic Applications

Barium titanate (BaTiO3) is a ferroelectric ceramic with a perovskite crystal structure that transitions between ferroelectric and paraelectric phases near 120 degrees Celsius. Below this Curie temperature, spontaneous electric polarization and strong piezoelectric behavior make barium titanate a core material in multilayer ceramic capacitors (MLCCs), ultrasonic transducers, and electro-optic modulators. MLCCs incorporating barium titanate dielectrics account for a large fraction of the capacitor market and are present in virtually every electronic circuit board. Barium ferrite (BaFe12O19) is a hard magnetic material used in permanent magnets, magnetic recording media, and microwave absorbers. Research from Brookhaven National Laboratory on barium-containing oxide materials has contributed to understanding the electronic structure of these compounds at the atomic level.

High-Temperature Superconductivity

Barium plays a structural and electronic role in the most important family of high-temperature superconductors. Yttrium barium copper oxide (YBa2Cu3O7, or YBCO), discovered in 1987, was the first material found to become superconducting above 77 K, the boiling point of liquid nitrogen, with a critical temperature of approximately 93 K. In the YBCO crystal structure, two barium atoms occupy positions above and below the yttrium layer, functioning as charge reservoirs that govern the carrier density in the superconducting copper-oxygen planes. YBCO is used in superconducting coated conductors for power cables, fault current limiters, and research magnets. The related lanthanum-barium-copper-oxide system (LBCO) was the first cuprate superconductor discovered, in 1986, and continues to be studied for its anomalous charge-stripe behavior at specific barium doping levels. The ScienceDirect overview of yttrium barium copper oxides provides a summary of synthesis routes and material properties for YBCO variants.

Applications

Barium and its compounds have applications in a wide range of technical fields, including:

• Multilayer ceramic capacitors and piezoelectric transducers in consumer electronics
• High-temperature superconducting tapes for power transmission and magnetics
• Drilling fluids and contrast agents in oil exploration and medical imaging
• Infrared optics components in thermal cameras and spectroscopy instruments
• Ferrite magnets in electric motors and microwave devices