Discovery and development of advanced materials requires understanding and control of the relationship between composition, structure and function. In crystalline materials, there is considerable focus on a design process that is informed by a single macroscopic structure defined by the average crystallographic unit cell determined by Bragg diffraction. This is a powerful approach, but it has become increasingly apparent that local chemical and positional deviations from this long-range average view of the structure can have decisive effects even in crystalline systems. Here we will investigate the behaviour of best in class lead based piezoelectric crystals in order to develop insight into the microscopic mechanisms behind their macroscopic properties, in order to design lead free replacement materials.