Ferroelectric BaTiO3 (BT) constitutes a base system for many practical applications ranging from classical capacitors to tunable dielectrics. A dielectric response in BT is determined by off-centering of Ti. Usually, a set of properties required for applications is achieved by chemical substitutions which modify the ferroelectric transition temperature, dielectric response, etc. Sr and Ca are the most common constituents in practical BT-based systems. As expected from ion-size arguments, Sr substitution into BT reduces the temperature of the ferroelectric phase transition. In contrast, Ca substitution does not affect the temperature of this transition at all. The proposed experiments will use neutron total scattering to determine local atomic displacements and their correlations that are responsible for the different effects of Sr and Ca on the ferroelectric transition in BT.