Frustration of Exchange-Striction Ferroelectric Ordering and Growth of Electric Polarization of Phase Separation Domains in R0.8Ce0.2Mn2O5 (R = Er, Tb) Solid Solutions

The effect of rare-earth ions (R = Er3+, Tb3+, and Ce3.75+) on the dielectric properties and the electric polarization induced by local polar phase separation domains in solid solutions of R0.8Ce0.2Mn2O5 (R = Er, Tb) multiferroics has been studied. These parameters are found to qualitatively differ from those of initial RMn2O5 (R = Er, Tb) crystals studied before. It is shown that the properties of the polar phase separation domains that form in a subsystem of Mn3+ and Mn4+ ions due to a finite probability of tunneling electrons between these ions with different valences are substantially dependent on the values of crystal fields in which these domains exist. A combined influence of Er3+, Tb3+, and Ce3.75+ ions is found to substantially change the crystal field in R0.8Ce0.2Mn2O5 (R = Er, Tb) as compared to RMn2O5 (R = Er, Tb).