Search

The effect of magnetoactive cations on the stability and properties of Aurivillius phases (1) Bi5Ti2(TiFe)1−x(NiNb)xO15, (2) Bi4Ti3−2.5x(Nb1/2Fe1/2)x(Nb2/3Ni1/3)1.5xO12, (3) Bi3Ti1−2.5xNb1+1.5x(Fe1/2Ni1/2)xO9, (4) Bim+1Fem−3Ti(3−x)(Ni1/3Nb2/3)xO3m+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 d33 and piezoelectric voltage coefficient g33 reach 7 pC/N and 3.5 mV m/N, respectively; the saturation magnetization Ms and remanent magnetization Mr increase with increasing x, while the coercivity remains almost unchanged. Thermal studies indicate phase transitions in Bi5Ti2(TiFe)1−x(NiNb)xO15, and Bim+1Fem−3Ti(3−x)(Ni1/3Nb2/3)xO3m+3 at ~ 300–400, 750 and 840 °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 °C that is supposed to be a ferromagnetic Curie point. [ABSTRACT FROM AUTHOR]

This paper was the first to present the results of studying the influence of structural defects on the physical properties of pre-synthesized ytterbium iron garnet (YbIG). The concentration and type of structural defects were controlled by mechanically activating the powders using Bridgman anvils. Using scanning electron microscopy and X-ray diffraction (XRD), it was revealed that the particle morphology, the unit cell parameters, mean size of the coherent scattering regions (D ) and microstrains ( Δ d / d ) vary in a wide range. Using optical spectroscopy, XRD and FTIR to study the dynamic properties of the crystal lattice, showing that the bandgap and force constants of dodecahedral-coordinated ytterbium (Yb–O)d and octahedral-coordinated iron (Fe–O)o change non-monotonically with decreasing crystallite size. By analyzing the dependence of the magnetic hysteresis loop M (H) on the crystallite size D , it was concluded that there was a critical crystallite size ( D crit = 75 nm) of YbIG, at which the coercive force H c has a maximum value. For the first time, changes in g-factor and the half-width Δ H of the electron paramagnetic resonance (EPR) spectra of nanoscale crystallites were found to be correlated with the parameters of the magnetic hysteresis loop M (H) . [ABSTRACT FROM AUTHOR]