Abstract
The effect of magnetoactive cations on the stability and properties of Aurivillius phases (1) Bi5Ti2(TiFe)(1-x)(NiNb)(x)O-15, (2) Bi4Ti3-2.5x(Nb1/2Fe1/2)(x)(Nb2/3Ni1/3)(1.5x)O-12, (3) Bi3Ti1-2.5xNb1+1.5x(Fe1/2Ni1/2)(x)O-9, (4) Bim+1Fem-3Ti(3-x)(Ni1/3Nb2/3)(x)O3m+3 has been investigated. The range of existence of solid solutions was found to be limited to the values of x = 0-0.10 (1), 0-0.3 (2), and 0-0.2 (3). Although the solid solutions exist in the whole concentration range studied (x = 0-0.07) in the series (4), the stability is limited to the value of m = 6-7. The unit cell volumes increase with increasing x, which is expected due to the ionic radii of the dopant cations that are larger than those of the substituted cations. The coexistence of piezoelectric and magnetic properties was observed in the samples of solid solutions (1) and (4): the values of the piezoelectric coefficient d(33) and piezoelectric voltage coefficient g(33) reach 7 pC/N and 3.5 mV m/N, respectively; the saturation magnetization M-s and remanent magnetization M-r increase with increasing x, while the coercivity remains almost unchanged. Thermal studies indicate phase transitions in Bi5Ti2(TiFe)(1-x)(NiNb)(x)O-15, and Bim+1Fem-3Ti(3-x)(Ni1/3Nb2/3)(x)O3m+3 at 300-400, 750 and 840 degrees C. Additionally, these samples demonstrate a magnetodielectric effect of up to 50% when applying a DC magnetic field of 1 T in the temperature range of 340-350 degrees C that is supposed to be a ferromagnetic Curie point.