Magnetic behaviour of perovskite compositions derived from BiFeO3

The phase content and sequence, the crystal structure, and the magnetic properties of perovskite solid solutions of the (1−y)BiFeO3–yBiZn0.5Ti0.5O3 series (0.05 ≤ y ≤ 0.90) synthesized under high pressure have been studied. Two perovskite phases, namely the rhombohedral R3c and the tetragonal P4mm, which correspond to the structural types of the end members, BiFeO3 and BiZn0.5Ti0.5O3, respectively, were revealed in the as-synthesized samples. The rhombohedral and the tetragonal phases were found to coexist in the compositional range of 0.30 ≤ y ≤ 0.90. Magnetic properties of the BiFe1−y [Zn0.5Ti0.5]yO3 ceramics with y < 0.30 were measured as a function of temperature. The obtained compositional variations of the normalized unit-cell volume and the Néel temperature of the BiFe1−y [Zn0.5Ti0.5]yO3 perovskites in the range of their rhombohedral phase were compared with the respective dependences for the BiFe1−yB 3+yO3 perovskites (where B 3+ = Ga, Co, Mn, Cr, and Sc). The role of the high-pressure synthesis in the formation of the antiferromagnetic states different from the modulated cycloidal one characteristic of the parent BiFeO3 is discussed.publishe

Complex antipolar root 2 x 4 x 2 root 2 structure with Pnma symmetry in BiFeO3 and BiFe1/2Sc1/2O3: First-principles calculations

First principles calculations are done for a root 2 x 4 x 2 root 2 Pnma structure, which has been recently discussed in several attempts to describe experiments in complex magnetoelectric perovskites and which experimentally was shown to compete with several ferroelectric phases. This makes these materials extremely attracting as switchers, starters, field-stimulated capacitors, high-voltage converters, transmitters, etc. The relative energies of the root 2 x 4 x 2 root 2 Pnma structure have been calculated from first principles and analyzed as a function of pressure in BiFeO3. The stability of two polymorphs of the root 2 x 4 x 2 root 2 Pnma structure has been studied for solid solution BiFe1/2Sc1/2O3. The main distortions and relative energies of these two polymorphs in BiFe1/2Sc1/2O3, in terms of Pm (3) over barm parent symmetry, have been calculated from first principles as well

The orthorhombic-tetragonal morphotropic phase boundary in high-pressure synthesized BiMg0.5Ti0.5O3–BiZn0.5Ti0.5O3 perovskite solid solutions

(1–x)BiMg0.5Ti0.5O3− xBiZn0.5Ti0.5O3 [(1− x)BMT–xBZT] ceramics of perovskite solid solutions, in which BMT and BZT are lead-free structural analogs of PbZrO3 and PbTiO3, respectively, have been synthesized under high pressure. It was found that the as-prepared compositions with a relative BZT content of <75 mol% are orthorhombic (space group Pnnm), while those with a BZT content above this value are tetragonal (P4mm). In the solution with x = 0.75, both phases coexist forming a morphotropic phase boundary (MPB). The compositional dependence of the normalized unit cell volume exhibits a ~5% jump at x = 0.75. At the same time, the microstructure of the obtained (1–x)BMT− xBZT ceramics shows no particular variation with the chemical composition over MPB. Piezoresponse force microscopy measurements indicate the ferroelectric state of the studied materials and allowed one to estimate their intrinsic piezoelectric coefficients.publishe