Composition-, temperature- and pressure-induced transitions between high-pressure stabilized perovskite phases of the (1-x)BiFe0.5Sc0.5O3 - xLaFe0.5Sc0.5O3 series

Crystal structures of the high-pressure synthesized perovskite phases of the (1-x)BiFe0.5Sc0.5O3-xLaFe0.5Sc0.5O3 (0 ​= ​x ​≤ ​1) system and their temperature and pressure behaviours were studied using laboratory and synchrotron X-ray diffractions as well as neutron diffraction. At room temperature, the as-prepared phases with x ​≤ ​0.05 have an antipolar structure with the Pnma symmetry and with the √2ap ​× ​4ap ​× ​2√2ap superstructure (where ap is the pseudocubic perovskite unit-cell parameter). An incommensurately modulated phase with the Imma(00γ)s00 superspace group is observed for 0.10 ​= ​x ​≤ ​0.33, while a non-polar Pnma phase (√2ap ​× ​2ap ​× ​√2ap) is stable when x ​≥ ​0.34. The antipolar Pnma phase in the as-prepared samples with composition corresponding to x ​= ​0 transforms into the polar Ima2 one via irreversible annealing-caused transformation accompanied by a formation of a high-temperature intermediate polar R3c polymorph, while the antipolar Pnma phase in samples with x ​= ​0.05 is stable until the decomposition temperature. In the solid solutions with 0.10 ​= ​x ​≤ ​0.33, increasing temperature was found to result in a reversible transformation of the Imma(00γ)s00 phase into a non-polar Pnma one. The transition temperature decreases with increasing x. A hydrostatic pressure of few GPa was also shown to induce a reversible Imma(00γ)s00 → Pnma transformation.publishe

Exchange bias effect in bulk multiferroic BiFe0.5Sc0.5O3

Below the Néel temperature, TN ∼ 220 K, at least two nano-scale antiferromagnetic (AFM) phases coexist in the polar polymorph of the BiFe0.5Sc0.5O3 perovskite; one of these phases is a weak ferromagnetic. Non-uniform structure distortions induced by high-pressure synthesis lead to competing AFM orders and a nano-scale spontaneous magnetic phase separated state of the compound. Interface exchange coupling between the AFM domains and the weak ferromagnetic domains causes unidirectional anisotropy of magnetization, resulting in the exchange bias (EB) effect. The EB field, HEB, and the coercive field strongly depend on temperature and the strength of the cooling magnetic field. HEB increases with an increase in the cooling magnetic field and reaches a maximum value of about 1 kOe at 5 K. The exchange field vanishes above TN with the disappearance of long-range magnetic ordering. The effect is promising for applications in electronics as it is large enough and as it is tunable by temperature and the magnetic field applied during cooling.publishe

Metastable perovskite Bi1-xLaxFe0.5Sc0.5O3 phases in the range of the compositional crossover

Perovskite ceramics of the Bi1- xLaxFe0.5Sc0.5O3 composition (0.30 ≤ x ≤ 0.35) that cannot be sintered in bulk form as a single phase using the conventional ceramic route were successfully prepared using the high-pressure/high-temperature technique. It has been shown that the room-temperature compositional crossover from the antipolar phase whose incommensurate modulation of displacements of Bi/La and oxygen is described by the Imma(00γ)s00 superspace group to the non-polar Pnma phase occurs in the narrow range between x = 0.33 and x = 0.34 with no phase coexistence. The features of this compositional crossover are discussed in comparison with that observed in the Bi1- xLaxFeO3 system.publishe