High Curie temperature Pb(Fe_1/2Nb_1/2)O₃‐based ferroelectrics: 0.40Pb(Fe_1/2Nb_1/2)O₃–0.34PbZrO₃–0.26PbTiO₃

Abstract

High‐Tm (∼270 °C) relaxor ferroelectrics 0.40Pb(Fe1/2Nb1/2)O3–0.34PbZrO3–0.26PbTiO3 (PFN40‐PZ34‐PT26) with pure perovskite phase were synthesized using conventional ceramic processing via a B‐site oxide mixing route for applications in high‐temperature high‐power‐density electrotransducers and high‐temperature capacitors. The relaxor behavior is confirmed by studying the frequency and temperature dependence of the dielectric response and polarization relaxation. The ceramics exhibit a large room‐temperature dielectric constant of ∼1540 and the dielectric constant is nearly independent of frequency with a temperature gradient of ∂ε/∂T = 5.2/°C in the low‐temperature region 250 K < T < 400 K. A strong frequency dependency and abnormal increase of dielectric constant are observed at temperatures around and below Tm, which is considered to be correlated with the phase transition from tetragonal ferroelectric phase to cubic paraelectric phase confirmed by high‐temperature X‐ray diffraction measurements. The diffused dielectric behavior arises mainly from the compositional fluctuation and/or the substitutional disorder in the arrangement of cations in the perovskite crystallographic sites. The frequency‐dependent remanent polarization scales well with the existing models of random field states, which indicates that the relaxor behavior correlates with the creation of chemical heterogeneity caused by localized cationic ordering. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Elastic and anelastic relaxation behaviour of perovskite multiferroics I: PbZr0.53Ti0.47O3 (PZT)–PbFe0.5Nb0.5O3 (PFN)

“…4-9). This is clearly related to the ferroelectric transition and is similar to the variation in dielectric constant observed for other ceramic samples with nearby compositions in the ternary system [48,65,67,68,70]. Magnetisation data show that this moment tends to zero in the vicinity of 500 K. There is no overt evidence for a magnetic transition below room temperature, but there are additional anomalies in the data for all three samples below *50 K. The high-temperature ferromagnetism is most likely due to the impurity phases but the low temperature effects are more likely to be intrinsic to the perovskite.…”

“…The rounded maximum in capacitance and lack of frequency dependence for T m are closely similar to reported results for the dielectric properties of other PZT-PFN ceramics [48,65,67,68,70]. Minor impurity phases do not appear to affect the main conclusions which can be drawn from elastic and dielectric properties measured at a macroscopic scale, but it would be incautious to relate any of the observed ferromagnetic properties to the perovskite.…”

“…The temperatures of a peak in the dielectric constant, T m , at three compositions along the binary join [48] and at one composition close to it [70] fall along a linear trend between the transition temperatures for Pm 3m À P4mm in the two end members (Fig. 2) [52]), but there appears to be no analogous evidence for these in data reported for samples within the PZT-PFN binary being considered here [3, 48,65,68]. A further constraint on the topology of the binary system comes from the fact that it cuts the expected location of the room temperature MPB at two compositions, corresponding to *1-7 and *69-75 % PFN.…”

“…Solid bars location of ternary MPB from Fang et al [48]; solid circles location of MPB in PT-PZ from Jaffe et al [38], and in PT-PFN from Singh et al [33], Sitalo et al [32]. Blue squares tetragonal samples at room temperature [3, 46,47,64,[68][69][70]. Brown squares ternary compositions described as cubic by Amonpattaratkit et al [47] but which are most likely rhombohedral or monoclinic with small strains.…”

“…Evidence for a temperature below which polar nanoregions (PNR's) might be present is provided by acoustic emission (564-603 K [30]), thermal expansion data (*690 K [104]) and the onset of elastic softening (*550 K [28]). No information is yet available for local ordering in ternary PZT-PFN, but ceramics near the MPB have dielectric maxima related to the ferroelectric transition which are reported to be generally broad and independent of frequency [65,67,68,70].…”