Effects of Substitutions of Titanium(IV) Ions by Iron(III) and Niobium(V) Ions on Phase Formation in Lanthanide-Containi
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Effects of Substitutions of Titanium(IV) Ions by Iron(III) and Niobium(V) Ions on Phase Formation in Lanthanide-Containing Systems Comprising Layered Bismuth Titanate Ferrite A. V. Mitrofanovaa, *, E. A. Fortal’novaa, M. G. Safronenkoa, E. D. Politovab, A. V. Mosunovc, and N. U. Venskovskiia aRussian
University of Peoples Friendship, Moscow, 117198 Russia Semenov Federal Research Center for Chemical Physics, Moscow, 119991 Russia c Moscow State University, Moscow, 119991 Russia *e-mail: [email protected]
b
Received April 17, 2020; revised June 16, 2020; accepted June 27, 2020
Abstract—Phase formation in the series of Bi3Nd2Fe1 + yTi3 – 2yNbyO15 and Bi3Tb2Fe1 + yTi3 – 2yNbyO15 (y = 0.0–0.6 and Δy = 0.2) samples is studied. When Bi3Nd2Fe1 + yTi3 – 2yNbyO15 solid solutions (ss) are doped with niobium(V) ions, the formation of Bi3Nd2FeTi3O15 layered perovskite, a member of the Aurivillius phase family of general formula Am – 1Bi2BmO3m + 3 (m = 4), is not dominant in samples where y ≥ 0.2. Bi4Ti3O12 (m = 3) and NdFeO3 phases are formed in the course of phase interaction under the chosen conditions. With higher niobium(V) amounts, a Bi2Ti2O7-base pyrochlore ss phase is formed in the Bi3Tb2Fe1 + yTi3 – 2yNbyO15 multicomponent system. Dielectric spectroscopy shows that the phases in samples of both series where y > 0.0 undergo structural alterations associated with magnetic and electric ordering. Keywords: phase formation, Aurivillius phase, layered perovskite, pyrochlore structure, phase transitions DOI: 10.1134/S0036023620110133
INTRODUCTION Aurivillius phases having the general formula Am – 1Bi2BmO3m + 3 are structurally built of alternating charged layers (Bi2O2)2+ and perovskite-like blocks built of m (Am – 1BmO3m + 1)2– layers [1]. Positions A can be occupied by Na+, K+, Ca2+, Sr2+, Ba2+, Pb2+, Bi3+, and Ln3+ ions; positions B inside oxygen octahedra can be occupied by Ti4+, Cr3+, Ga3+, Mn4+, Fe3+, Co3+, Ni3+, Nb5+, Ta5+, and W6+ ions [2]. Bi5FeTi3O15, an Aurivillius phase with m = 4, has repeatedly attracted the attention of scientists and has been studied comprehensively [3–10]. At the Curie temperature TС = 740°C, Bi5FeTi3O15 experiences transition from the ferroelectric phase (orthorhombic space group A21am) to the paraelectric phase (tetragonal space group I4/mmm) [9, 11]. The properties of Bi5FeTi3O15 can be modified by modifying its composition. Ion substitutions in the bismuth(III) and titanium(IV) positions in the Bi5FeTi3O15 structure enable one to multiply expand the Aurivillius phase family [1, 12–22]; substitutions appreciably affect the electrophysical characteristics and thermal stability of ceramics [21]. These properties are important for layered perovskite-like structures to be used in
advanced electronic industry. In addition, the Curie temperature can vary widely, decreasing or increasing depending on the nature and amount of the substituent ion (Table 1). Therefore, the study of such substitutions in the structure of Aurivillius phases is import
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