PHASE FORMATION AND PROPERTIES OF BISMUTH FERROTITANATES SUBSTITUTED BY HEAVY LANTHANIDE IONS (Tb, Er, Ho, Yb); [ФАЗООБРАЗОВАНИЕ И СВОЙСТВА ФЕРРОТИТАНАТОВ ВИСМУТА ПРИ ЗАМЕЩЕНИИ ИОНАМИ ТЯЖЕЛЫХ ЛАНТАНОИДОВ (Tb, Er, Ho, Yb)]

The purpose of this study was to investigate the effect of cation substitutions on the formation of Aurivillius phases at various annealing temperatures using solid-state synthesis. The phase formation of lanthanide bismuth ferrotitanates with the Aurivillius phase structure Ln2Bi3FeTi3O15, where Ln = Tb, Ho, Er, Yb, has been studied. The obtained samples were characterized by X-ray diffraction, infrared spectroscopy, differential thermal and thermogravimetric analysis, and their elemental composition was studied. The predominant formation of a phase with a pyrochlore structure was revealed in the entire series studied in the chosen synthesis conditions. The exception was the sample containing ytterbium(III) cations, in which phases of the pyrochlore type and layered perovskite with the Aurivillius structure coexist. The main pyrochlore-type phase in all samples crystallizes in the cubic syngony. It is shown that in the Ln2Bi3FeTi3O15 samples, where Ln = Tb, Ho, Er, the crystal lattice parameters decrease due to a decrease in the cationic radius of the Ln(III) ions. However, in the last sample of the studied series Yb2Bi3FeTi3O15, this pattern is violated because of Yb(III) ions distribution between the perovskite and pyrochlore phases. It has been established that the thermal effects observed in the samples Ln2Bi3FeTi3O15, where Ln = Tb, Ho, Er, can be attributed to an order-disorder phase transition in the pyrochlore structure. When studying the temperature behavior of a two-phase sample of Yb2Bi3FeTi3O15, two reversible phase transitions were revealed: a low-intensity thermal effect characterizes changes in the pyrochlore-type structure, and a more intense thermal effect can be attributed to a ferroelectric phase transition in the structure of a layered perovskite of the Aurivillius family. © (2025), (Ivanovo State University of Chemistry and Technology). All rights reserved.