We request 1 day of beam-time on POLARIS to collect Neutron Diffraction (ND) data on the Sillenite Bi12SiO20 (gamma-Bi2O3) that we have recently discovered to exhibit a dielectric relaxation at 500 - 600 K, well below the gamma to beta polymorphic transition at ~ 930 K. Variable temperature Raman Spectroscopy shows changes in the Bi-O framework vibrations and the relaxor-type dielectric behaviour is attributed to non-correlated local dipole moments associated with the BiO5E (E= 6s2 lone pair) units in the framework. The purpose of the beam time is to acquire ND data over a range of temperatures (300 - 1150 K) to establish accurate crystallographic information related to the Bi-O framework to elucidate the structure-property relationships in this 'ideal' Sillenite. This will facilitate further studies on other Sillenite family members that are being targeted for dielectric applications.