Other Ionic Structures.

Perovskite:“ABO3”

B-siteBO6 octahedra A-site

12 Oxygen neighbors

For perfect cube: A-O/B-O = √2 “Goldschmidt tolerance factor”

• Flexible & tolerant: smaller A (A-O/B-O < √2): tilting

Very large number of examples

• Perovskite: most widely studied oxide structure

• Wide range of chemistries possible- thousands of examples known

- high Tc cuprate superconductors- Colossal Magneto-Resistance (La,SrMnO3)- fast ion conduction (Li+, O2-), batteries, fuel cells- mixed electronic/ionic conduction, fuel cells- oxidation/reduction catalysts- ferroelectric / piezoelectric ceramics (BaTiO3, Pb(ZrTi)O3)- important mineral structure in lower mantle (MgSiO3)- frequency filters for wireless communications : Ba(Zn1/3Ta2/3)O3

Unique properties of perovskites:

Dipoles in BaTiO3

- ferroelectric- piezoelectric

Pole sample to align dipoles

• Many applications: non-volatile memories; sensors, actuators, ultra-sonic imaging

Write using nano-tips

• Memories/nano-lithography

High Temperature Superconductors:CuO based

Zero electrical resistance to ~ 135K

La3+Mn3+O3

Replace by Sr2+ each substituted Sr oxidizes Mn3+ to Mn4+

“mixed valent” Mn show unique electronic/magnetic properties

ZSM-5: silicate based microporous solids; Catalysts;

Molecular sieves; chemical separation