Pb-based materials such as PbZrxTi1-xO3 (PZT) are widely used as transducers, actuators and sensors in a range of modern technologies due to their excellent piezoelectric and ferroelectric properties. However, the toxicity of Pb raises serious environmental concerns and the application of these materials is to be limited by new legislation. It is therefore necessary to develop new Pb-free analogues to PZT, with Bi3+ compounds emerging as strong candidates due to the similar stereochemistry of the 6s2 Pb2+ and Bi3+ ions which gives rise to electrical polarisation. Our recent work using high-resolution diffraction data from HRPD has shown that Pb-free ferroelectrics based on BiFe2/8Mg3/8Ti3/8O3 (BTFM) can be modified by chemical substitution to substantially improve their ferroelectric properties.