Dielectric and Mossbauer Studies of Pb(Fe_1/2Ta_1/2)O₃Multiferroic Ceramics Sintered from Mechanoactivated Powders

Abstract

The effect of high-energy mechanical activation on dielectric and magnetic properties of PbFe 1/2 Ta 1/2 O 3 (PFT) multiferroic was studied. M€ ossbauer studies have shown that the Neel temperature T N of the antiferromagnetic phase transition in PFT powders can be changed substantially by mechanical activation and subsequent annealing. The increase of T N by more than 70 K, as compared to PFT single crystal, was achieved in the mechanically activated PFT powder annealed at 700 C. Dielectric studies have shown that in contrast to ceramics obtained by usual sintering, PFT ceramics fabricated by sintering of the mechanoactivated powder does not show the relaxorlike behavior.

Elastic and anelastic relaxation behaviour of perovskite multiferroics II: PbZr0.53Ti0.47O3 (PZT)–PbFe0.5Ta0.5O3 (PFT)

“…As shown in Table 1, values for the fit parameters from the literature are scattered. Gusev et al [42] also reported that one of their samples had a difference of not more than 0.5 K for T m measured in the range 10 3 –10 6  Hz, which is very close to being independent of frequency. The absence of a unique Vogel–Fulcher parameterisation is presumed to reflect differences between samples arising from different methods of synthesis, such as grain size and B-site cation order.…”

“…Relaxor character for PFT is revealed by a broad maximum in the dielectric constant at a temperature, T m , in the vicinity of 250 K which varies with frequency in both pure and Li-doped samples [18, 19, 28, 31–42]. This dispersion is described using the Vogel–Fulcher representation of freezing behaviour where ν is the measurement frequency for a given value of T m , ν o is an attempt frequency, E a is an activation energy, k B is the Boltzmann constant and T VF is the zero frequency freezing temperature.…”

“…In particular, increasing B-site order correlates with an increase in T m values and a reduction in their frequency dependence [34]. The data of Gusev et al [42] also show a correlation between increasing T m and decreasing width of peaks in the dielectric permittivity. Presumably, in the limit of complete order, PFT crystals would have a more typically classical ferroelectric transition at ~270 K. Dielectric loss (tan δ ) measurements show scatter between samples, but a typical form has increases in loss coinciding with the onset of freezing, frequency-dependent maxima and a tail of decreasing loss extending to lower temperatures (e.g.…”

“…There is a broad excess in the heat capacity between ~230 and ~330 K [42, 44, 45] that, by analogy with PMN [46], is expected for diffuse, relaxor behaviour. There is a small excess heat capacity associated with the transition at ~205 K, but it appears that this is not driven by a change in ferroelectric polarisation.…”

Low-temperature neutron diffraction and magnetic studies on the magnetoelectric multiferroic Pb(Fe0.534Nb0.4W0.066)O3

“…Understanding the fundamental coupling mechanism between electric and magnetic order parameters has been the hottest topic of research in the present scenario [2,3] (PFT) are the promising candidates and exhibit extraordinary dielectric constant with diffuse kind of ferroelectric phase transition [4,5].…”