Lead-free piezoceramics with giant strain in the system Bi0.5Na0.5TiO3–BaTiO3–K0.5Na0.5NbO3. II. Temperature dependent properties

Abstract

Articles you may be interested inLarge strain response based on relaxor-antiferroelectric coherence in Bi0.5Na0.5TiO3-SrTiO3-(K0.5Na0. The temperature dependence of the dielectric and ferroelectric properties of lead-free piezoceramics of the composition ͑1−x − y͒Bi 0.5 Na 0.5 TiO 3 -xBaTiO 3 -yK 0.5 Na 0.5 NbO 3 ͑0.05ഛ x ഛ 0.07, 0.01ഛ y ഛ 0.03͒ was investigated. Measurements of the polarization and strain hystereses indicate a transition to predominantly antiferroelectric order when heating from room temperature to 150°C, while for 150Ͻ T Ͻ 200°C both remnant polarization and coercive field increase. Frequency-dependent susceptibility measurements show that the transition is relaxorlike. For some samples, the transition temperature T d is high enough to allow mostly ferroelectric ordering at room temperature. These samples show a drastic increase of the usable strain under an external electric field just after the transition into the antiferroelectric state at high temperatures. For the other samples, T d is so low that they display significant antiferroelectric ordering already at room temperature. In these samples, the usable strain is relatively stable over a wide temperature range. In contrast to T d , the temperature T m of the transition into the paraelectric high-temperature phase depends far less on the sample composition. These results confirm that the high strain in this lead-free system is due to a field-induced antiferroelectric-ferroelectric phase transition and that this effect can be utilized in a wide temperature range.

Effect of uniaxial stress on ferroelectric behavior of (Bi1/2Na1/2)TiO3-based lead-free piezoelectric ceramics

“…Our previous work indicated that BNT-FE displays a higher T d and is ferroelectric at room temperature, while BNT-AFE appears largely antiferroelectric at room temperature. 13,14 The two ceramics were prepared with the conventional solid state reaction method. Sintering was carried out at 1150°C for 3 h with pellets buried in the powder of the same composition in covered alumina crucibles.…”

“…However, recent observations have cast some doubts on the designation of the field-free nonferroelectric hightemperature phase as "antiferroelectric." While the lowtemperature phase and the field-induced phase are probably indeed ferroelectric, 15 and there is a transition to a hightemperature phase, 14 the volume change during the proposed transition was observed but could account only for a small amount of the observed total strain. 16 Furthermore, some of the typical features of antiferroelectrics such as antiferroelectric domains could not be evidenced so far.…”

“…We recently observed giant electric field-induced strains ͑up to 0.45%͒ in ceramics of the ͑1−x − y͒ ͑Bi 1/2 Na 1/2 ͒TiO 3 -xBaTiO 3 -y͑K 0.5 Na 0.5 ͒NbO 3 system. [12][13][14] Near the morphotropic phase boundary at around 6 mol % BaTiO 3 ͑BT͒, ͑Bi 1/2 Na 1/2 ͒TiO 3 -BaTiO 3 exhibits fieldinduced ferroelectricity and remains ferroelectric after field removal. 15 The related ceramics containing small amounts of KNN display giant strains due to the full recovery of the original dimensions for every electric cycle.…”

“…The other one belonged to the nonferroelectric phase that has been referred to as antiferroelectric so far. 13,14 …”

The effects of Ba2+ content on depolarization temperature and pyroelectric properties of lead-free 0.94Na0.5Bi0.5TiO3–0.06Ba1+xTiO3 ceramics

“…However, there are other definitions of T d such as the steep reduction of remnant polarization [7], or the phase transition temperature from ferroelectric (FE) to anti-ferroelectric (AFE) or to relaxor anti-ferroelectric or to relaxor [8,[22][23][24][25]. In this study, T d was identified from the measurement of the dielectric loss (tand) versus temperature.…”