With the newfound interest, it became evident that the commonly used solid-state synthesis from oxide and carbonate precursors often results in the formation of undesired secondary phases . These induce a deviation of the targeted composition of the matrix grains, decreasing the mechanical stability and deteriorating the electromechanical performance of the samples due to their non-ferroelectric nature. Furthermore, the secondary phase formation is detrimental for effective and controlled doping, also leading to possible limitations in the application of advanced doping strategies such as those derived from Fermi level engineering . Identification of these secondary phases, understanding of their impact on properties, and knowledge on their formation mechanisms are thus of utmost importance.