Coexistence of ergodicity and nonergodicity in LaFeO₃-modified Bi_1/2(Na_0.78K_0.22)_1/2TiO₃relaxors

Abstract

The effect of LaFeO 3 addition to Bi 1/2 (Na 0.78 K 0.22 ) 1/2 TiO 3 ceramics on the phase stability and macroscopic functional properties was investigated. Similarly to other chemical modifiers known in the literature, LaFeO 3 addition suppresses an electric-field-induced long-range ferroelectric order, giving rise to a giant unipolar strain of ∼0.3% at 2 mol% LaFeO 3 addition. Time-dependent changes in polarization and strain hysteresis loops both during successive electrical cycling and after removal of the electric field suggest that a specimen with 2 mol% LaFeO 3 consists of both ergodic and nonergodic phases, which is unique among the known relaxor materials.

Incipient piezoelectrics and electrostriction behavior in Sn-doped Bi1/2(Na0.82K0.18)1/2TiO3 lead-free ceramics

“…17 However, it is noticed that the electrical poling still has an influence on the dielectric signal even for the BNKT0.05Sn and BNKT0.08Sn, represented as a fluctuation in the spectra around 100 C. This suggests that there should still be a trace of nonergodicity in BNKT0.05Sn and BNKT0.08Sn. 29 The small-signal dielectric permittivity e 33 (E) of BNKTxSn ceramics as a function of electric field is presented in Fig. 5.…”

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…Dielectric relaxations with the features described above are generally considered as the fingerprints of relaxors (Section 2.2.2). This behavior is also common to other lead-free materials 119,[121][122][123]127,135,437 and was associated with the relaxation of PNRs; i.e., a dynamic slowing down of the PNRs thermally activated fluctuations. 437 Therefore, as the temperature decreases, either a spontaneous transformation into a long-range ferroelectric order (non-canonical relaxor) or freezing of the PNRs fluctuations (canonical relaxor) can be expected (Section 2.2.2).…”

“…When the electric field is removed, incipient piezoelectrics with a distribution of ergodicity may retain part of the induced ferroelectric state. 119 Prior to switching, the retained domains contract, similarly as in ferroelectrics (Figure 2.8 point ), leading to nonzero . Further electric field cycles retrace the response described resulting in hysteresis.…”

“…118  A distribution in the degree of ergodicity may develop locally, which could be ascribed to different coexisting symmetries of PNRs. 119  Temperature insensitive electrostrictive strain output was discovered in some materials. 120 One of the most thoroughly investigated class of lead-free relaxors are BNT-based incipient piezoelectrics.…”

“…The non-negligible indicates a varying distribution of ergodicity, as previously reported in other materials. 119,449 It should be pointed out that the described features do not characterize the electric field induced phase transition directly, but only indicate that this phase transformation is accompanied by a considerable degree of switching. Therefore, increasing electric field above − leads to saturation.…”