Dielectric properties of (Pb,La)Zr0.55Ti0.45O3 ceramics have been investigated as functions of temperature and frequency. The dielectric constant as a function of temperature can be represented over a considerable temperature interval by a quadratic law of the type: ε−1=ε−1max + C(T−TC')2. The permittivity versus temperature curves are strongly broadened around TC' (where ϵ is at a maximum) and the dielectric behaviour is at least partly of a relaxational nature. Interpretation of the dielectric behaviour (broadening, frequency dependence, quadratic law) seems possible by assuming a distribution of local Curie temperatures; the standard deviation of which can be correlated with the La concentration.
Wolters, M., & Burggraaf, A. J. (1975). Relaxational polarization and diffuse phase transitions of LA-substituted Pb (Zr,Ti)O3-ceramics. Materials research bulletin, 10(5), 417-423. https://doi.org/10.1016/0025-5408(75)90013-6