Bismuth ferrite, BiFeO3, is a much-studied ceramic showing both dielectric and magnetic ordering at relatively high temperatures. In order to improve its properties there has been much interest in doping BiFeO3, but rarely has there been structural characterisation of these materials. We have shown that it is possible to replace bismuth ions by strontium together with oxygen vacancies. Increasing composition of strontium lowers the transition temperatures so that the high-symmetry cubic phase becomes stable at room temperature, but with remaining antiferromagnet and ferromagnetic order. We will use high-resolution powder diffraction to study the ferroelectric phase transitions as a function of temperature in samples of different Sr-content.