Search

Iron-enriched ferroelectrics are of particular interest as piezoactive components of piezoelectric-ferrite ME ceramics. This is due to the phase composition similarity and the reduction of expected interfacial doping effects during high-temperature calcination. This idea seems attractive, but laborious due to the significantly limited number of possible piezoelectric–ferrite combinations. Therefore, there is practically no data on such systems in the literature. ME composite ceramics based on the highly efficient Fe-containing Pb(Fe 0.5 Nb 0.5) 0.935 Ti 0.065 O 3 (PFNPT) ferroelectric has been studied. (100-х) wt.% Pb(Fe 0.5 Nb 0.5) 0.935 Ti 0.065 O 3 (PFNPT) + х wt.% Ni 0.9 Co 0.1 Cu 0.1 Fe 1.9 O 4-d (NCCF) composite systems has been obtained by the solid-state method at 1050 °C, with no foreign phases. The specimens densities amounted to ∼80% of the theoretical. It has been shown that the ME conversion efficiency and other composites properties are significantly influenced by the PFNPT precursor pre-treatment method. The maximum value of the ME coefficient ΔΕ/ΔΗ = 75 mV/(cm Oe) has been observed for specimens with x = 50–60 made from PFNPT powder with the addition of Li 2 CO 3. An increase in the ME composites sintering temperature to 1150 °C leads to the formation of Pb 2 Nb 2 O 7 foreign phase with a pyrochlore structure along the grain boundaries. The ME coefficient ΔΕ/ΔΗ does not exceed 15 mV/(cm⋅Oe). There is an threefold decrease in the composites piezoelectric parameters (piezoelectric coefficients d ij , g ij), as well as in their magnetic properties (magnetizations M S , M R) due to piezophase degradation, which is presumably associated with a change in the cations distribution over A and B sublattices of the spinel structure. [ABSTRACT FROM AUTHOR]

The preferences of the end members of the lanthanide series (Er3+, Tm3+, Yb3+ and Lu3+) for Bi and Fe sites in BiFeO 3 were investigated in this paper using X-ray powder diffraction. It was shown that: (1) the crystal structure of the BiFeO 3 -derived solid solutions remains rhombohedral in the Ln3+ concentration range from 0.01 to 0.1; (2) for the Er3+-, Tm3+- and Yb3+-doped materials, the unit cell parameters of solid solutions (Bi 1-x Ln x FeO 3 or BiFe 1-x Ln x O 3 , x = 0–0.1) decrease with increasing x regardless of the selected stoichiometry; (3) for the materials with the same x , the unit cell parameters increase across the Er3+ - Tm3+ - Yb3+ series despite the decrease in ionic radius that occurs across the lanthanide series; and (4) for the Lu3+-doped materials, the unit cell parameters show only a minor increase. These results suggest that with the decreasing ionic radius of the lanthanides, simultaneous doping on the A and B sites corresponding to the formula Bi 1-x+z Ln х-z Fe 1-z Ln z O 3 (Tm3+, Yb3+) gradually replaces dominant A-site doping (Er3+) and eventually finishes with B-site doping (Lu3+). Variations in the magnetic properties of the doped samples indirectly confirm systematic changes in the preferences of the end members of the lanthanide series for Fe sites in BiFeO 3 : the values of M s and M r decrease drastically with the decreasing size of the Ln3+ cation to the extent that the hysteresis loops for the Lu3+-containing samples have a narrow and lenticular shape, which may be due to the dilution of the Fe-sublattice by Lu3+ cations. The samples show a piezoelectric coefficient d 33 of 15 pC/N on average and up to 30 pC/N in individual specimens. Despite belonging to a class of multiferroics, Ln3+-containing solid solutions of BiFeO 3 show no magnetoelectric or magnetodielectric response due to the weak coupling between piezoelectric and magnetic subsystems. [ABSTRACT FROM AUTHOR]