Abstract
Elastic and anelastic properties of ceramic samples of multiferroic perovskites with nominal compositions across the binary join PbZr0.53Ti0.47O3–PbFe0.5Ta0.5O3 (PZT–PFT) have been assembled to create a binary phase diagram and to address the role of strain relaxation associated with their phase transitions. Structural relationships are similar to those observed previously for PbZr0.53Ti0.47O3–PbFe0.5Nb0.5O3 (PZT–PFN), but the magnitude of the tetragonal shear strain associated with the ferroelectric order parameter appears to be much smaller. This leads to relaxor character for the development of ferroelectric properties in the end member PbFe0.5Ta0.5O3. As for PZT–PFN, there appear to be two discrete instabilities rather than simply a reorientation of the electric dipole in the transition sequence cubic–tetragonal–monoclinic, and the second transition has characteristics typical of an improper ferroelastic. At intermediate compositions, the ferroelastic microstructure has strain heterogeneities on a mesoscopic length scale and, probably, also on a microscopic scale. This results in a wide anelastic freezing interval for strain-related defects rather than the freezing of discrete twin walls that would occur in a conventional ferroelastic material. In PFT, however, the acoustic loss behaviour more nearly resembles that due to freezing of conventional ferroelastic twin walls. Precursor softening of the shear modulus in both PFT and PFN does not fit with a Vogel–Fulcher description, but in PFT there is a temperature interval where the softening conforms to a power law suggestive of the role of fluctuations of the order parameter with dispersion along one branch of the Brillouin zone. Magnetic ordering appears to be coupled only weakly with a volume strain and not with shear strain but, as with multiferroic PZT–PFN perovskites, takes place within crystals which have significant strain heterogeneities on different length scales.
Highlights
Solid solutions involving the disordered, magnetic III-V perovskites PbFe0.5Ta0.5O3 (PFT), PbFe0.5Nb0.5O3 (PFN) and PbFe0.5W0.5O3 (PFW) with either PbTiO3 (PT) or PbZr1-xTixO3 (PZT) have been receiving close attention for their potential as single-phase multiferroic materials [1,2,3,4,5,6,7,8,9,10,11,12,13]
Elastic and anelastic properties of ceramic samples of multiferroic perovskites with nominal compositions across the binary join PbZr0.53Ti0.47O3–PbFe0.5Ta0.5O3 (PZT–PFT) have been assembled to create a binary phase diagram and to address the role of strain relaxation associated with their phase transitions
It is likely that the strength of magnetoelectric effects, as well as the dynamics of switching, will be mediated by coupling with strain and that ferroelasticity is an important part of the overall multiferroic behaviour
Summary
Solid solutions involving the disordered, magnetic III-V perovskites PbFe0.5Ta0.5O3 (PFT), PbFe0.5Nb0.5O3 (PFN) and PbFe0.5W0.5O3 (PFW) with either PbTiO3 (PT) or PbZr1-xTixO3 (PZT) have been receiving close attention for their potential as single-phase multiferroic materials [1,2,3,4,5,6,7,8,9,10,11,12,13]. Some possess multiferroic properties at room temperature, and magnetic switching of ferroelectric domains has been achieved in PZT–PFT [1, 10]. The present work follows from Schiemer et al [16] on perovskites with compositions in the PZT–PFN solid solution and has, as its primary objective, consideration of the strength and dynamics of elastic strain relaxation mechanisms in the system PZT–PFT. The properties of PFT are significantly different from those of PFN, and a key factor in the change from ferroelectric to relaxor behaviour appears to be a significant reduction in the strength of coupling with the tetragonal shear strain
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