We will use the high resolution of HRPD and the excellent long d-spacing data available on OSIRIS to investigate the phase transitions in Sr1-xNaxFe2As2 which are associated with the competition between antiferromagnetism and superconductivity in the range 0.3 < x < 0.35. In particular we will investigate the evolution of the magnetic scattering and the detailed structural evolution of the competing tetragonal and orthorhombic phases which coexist in two regions of temperature. The detailed behaviour of these compounds appears to be unique amongst the iron-based superconductors and may shed further light on these intriguing materials.