Phases in the lithia-alumina-silica phase diagram (LAS) are of great importance owing to the technologically property of ultra-low thermal expansion (ULTE) that they frequently exhibit. Applications of these compounds range from oven-to-table cookware and cooker hobs to telescope mirror blanks and supersonic aircraft glazing. The most studied compounds have either the composition of spodumene or petalite and are formed by taking these materials to high temperatures at which point they undergo irreversible structural changes that gives rise to ULTE behaviour. Recently, an HRPD study has shown the compound petalite itself exhibits ULTE behaviour, ie not requiring high temperature sintering.We are proposing to understand the internal mechanism that permits ULTE behaviour in petalite by using single crystal neutron diffraction.