Zeolites and Negative Thermal ExpansionRachel Pallant, Josie Paton,

Alen Akhabaev, Ross Davies

Zeolites Microporous Minerals

› Microporous – Contains pores with diameters <2nm

› Mineral – Naturally occurring substance that is a stable solid rtp

206 structures identified Base SinO2n, other molecules can be

included

Negative Thermal Expansion

•Caused by decrease in bond angles•With no/little energy bond angle is 180°•Energy provided by heat overcomes electrostatic forces of electron groups mutually repelling•Molecule bends, Si-Si distance now smaller although bonds are longer

Zeolites chosen Control – MEP Positive thermal expansion – DON Negative thermal expansion – EDI, YUG Detail - STI

MEP (1104 atoms) Already proven to have negative

thermal expansion

DON (1152 atoms) Was modelled to have positive thermal

expansion

EDI (1872 atoms) Was modelled to have negative

thermal expansion

YUG (2160 atoms) Was modelled to have negative

thermal expansion

STI (2592 atoms) Showed an unusual shift

STI Detail (1728 atoms) Using smaller temperature steps still

just showed a sudden shift Only two of the side lengths changed,

not all three

STI Structure Animation Structure of STI at 90K

Thank You!