Pyrochlore

Pyrochlore ) is a mineral group of the niobium end member of the pyrochlore supergroup. Pyrochlore is also a term for the crystal structure Fdm. The name is from the Greek , fire, and , green because it typically turns green on ignition in classic blowpipe analysis.

Pyrochlore ore typically contains greater than 0.05% of naturally occurring radioactive uranium and thorium.

Lueshe in North Kivu, Democratic Republic of Congo, has substantial deposits of pyrochlore.

Crystal structure

The more general crystal structure describes materials of the type A₂B₂O₆ and A₂B₂O₇ where the A and B species are generally rare-earth or transition metal species; e.g. Y₂Ti₂O₇.The pyrochlore structure is a super structure derivative of the simple fluorite structure (AO₂ = A₄O₈), where the A and B cations are ordered along the direction. The additional anion vacancy resides in the tetrahedral interstice between adjacent B-site cations. These systems are particularly susceptible to geometrical frustration and novel magnetic effects.

The pyrochlore structure shows varied physical properties spanning electronic insulators (e.g. La₂Zr₂O₇), ionic conductors (Gd_1.9Ca_0.1Ti₂O_6.9), metallic conductors (Bi₂Ru₂O_7−y), mixed ionic and electronic conductors, spin ice systems (Dy₂Ti₂O₇), spin glass systems (Y₂Mo₂O₇), haldane chain systems (Tl₂Ru₂O₇) and superconducting materials (Cd₂Re₂O₇). More disordered structures, such as the bismuth pyrochlores, have also been investigated due to interesting high-frequency dielectric properties.

The crystal structure has been investigated for use in solid electrolytes for lithium iron batteries. It is alleged to provide high conductivity while inhibiting dendrite growth.

See also

• List of minerals

References