Solid solutions (SS) of 3- and 4-component systems based on lead titanate-zirconate were prepared by the method of solid-phase reactions and uniaxial hot pressing. The dependences of the relative permittivity of polarized samples on the electronegativity (EN) of their constituent cations have been studied. The ferro-hardness of the SS (the stability of the domain structure to external influences) is shown to be directly dependent on the EN of elements B in the corresponding oxidation states, i.e., the degree of covalence of the B–O bond. The deviation from this dependence in SS with Ni and Cd is explained by their individual features, which result in changes in the degree of bond covalence in both cationic sublattices. The conducted crystal-chemical analysis made it possible to choose promising SS when creating ferroelectric materials, including textured piezoelectric ceramic materials for piezoelectric transducers for various purposes: Piezotransformers, piezoelectric motors, ultrasonic emitters, filter devices, ultrasonic flaw detectors, accelerometers, etc.Solid solutions (SS) of 3- and 4-component systems based on lead titanate-zirconate were prepared by the method of solid-phase reactions and uniaxial hot pressing. The dependences of the relative permittivity of polarized samples on the electronegativity (EN) of their constituent cations have been studied. The ferro-hardness of the SS (the stability of the domain structure to external influences) is shown to be directly dependent on the EN of elements B in the corresponding oxidation states, i.e., the degree of covalence of the B–O bond. The deviation from this dependence in SS with Ni and Cd is explained by their individual features, which result in changes in the degree of bond covalence in both cationic sublattices. The conducted crystal-chemical analysis made it possible to choose promising SS when creating ferroelectric materials, including textured piezoelectric ceramic materials for piezoelectric transducers for various purposes: Piezotransformers, piezoelectric motors, ultrasonic emitters, filter devices, ultrasonic flaw detectors, accelerometers, etc.