In response to the current environmental regulations against the use of lead in daily electronic devices, a number of investigations have been performed worldwide in search for alternative piezoelectric ceramics that can replace the marketdominating lead-based ones, representatively Pb(Zr x Ti 1-x )O 3 (PZT)-based solid solutions. Selected systems of potential importance such as chemically modified and/or crystallographically textured (K, Na)NbO 3 and (Bi 1/2 Na 1/2 )TiO 3 -based solid solutions have been developed. Nevertheless, only few achievements have so far been introduced to the marketplace. A recent discovery has greatly extended our tool box for material design by furnishing (Bi 1/2 Na 1/2 )TiO 3 -based ceramics with a reversible phase transition between an ergodic relaxor state and a ferroelectric with the application of electric field. This paired the piezoelectric effect with a strain-generating phase transition and extended opportunities for actuator applications in a completely new manner. In this contribution, we will present the status and perspectives of this new class of actuator ceramics, aiming at covering a wide spectrum of topics, i.e., from fundamentals to practice.

Articles you may be interested inElectric-field-temperature phase diagram of the ferroelectric relaxor system (1−x)Bi1/2Na1/2TiO3−xBaTiO3 doped with manganese J. Appl. Phys. 115, 194104 (2014); 10.1063/1.4876746Long ranged structural modulation in the pre-morphotropic phase boundary cubic-like state of the lead-free piezoelectric Na1/2Bi1/2TiO3-BaTiO3 J. Appl. Phys. 114, 234102 (2013) On the phase identity and its thermal evolution of lead free (Bi 1/2 Na 1/2 )TiO 3 -6 mol% BaTiO 3 Temperature-dependent dielectric permittivity of 0.94(Bi 1/2 Na 1/2 )TiO 3 -0.06BaTiO 3 (BNT-6BT) lead-free piezoceramics was studied to disentangle the existing unclear issues over the crystallographic aspects and phase stability of the system. Application of existing phenomenological relaxor models enabled the relaxor contribution to the entire dielectric permittivity spectra to be deconvoluted. The deconvoluted data in comparison with the temperature-dependent dielectric permittivity of a classical perovskite relaxor, La-modified lead zirconate titanate, clearly suggest that BNT-6BT belongs to the same relaxor category, which was also confirmed by a comparative study on the temperature-dependent polarization hysteresis loops of both materials. Based on these results, we propose that the low-temperature dielectric anomaly does not involve any phase transition such as ferroelectric-toantiferroelectric. Supported by transmission electron microscopy and X-ray diffraction experiments at ambient temperature, we propose that the commonly observed two dielectric anomalies are attributed to thermal evolution of ferroelectric polar nanoregions of R3c and P4bm symmetry, which coexist nearly throughout the entire temperature range and reversibly transform into each other with temperature.

Articles you may be interested inElectric-field-temperature phase diagram of the ferroelectric relaxor system (1−x)Bi1/2Na1/2TiO3−xBaTiO3 doped with manganese J. Appl. Phys. 115, 194104 (2014) . Temperature-dependent permittivity e 0 (T) and thermally stimulated depolarization currents (TSDC) of poled samples were measured under identical heating conditions to clarify the depolarization mechanism. In both methods, the influence of electric bias fields on the transition temperature was investigated. Fields applied in the poling direction shift the transition to higher temperatures, with corresponding results in e 0 (T) and TSDC measurements. While the response of transition temperature to external fields displays a similar trend in all investigated compositions, the shape of TSDC is clearly connected with the composition and, hence, the crystal symmetry of the sample. Furthermore, the comparison of e 0 (T) and TSDC data reveals a systematic shift between transition temperatures obtained with the two different methods.;

Articles you may be interested inLarge strain response based on relaxor-antiferroelectric coherence in Bi0.5Na0.5TiO3-SrTiO3-(K0.5Na0.5)NbO3 solid solutions Structural stability and depolarization of manganese-doped (Bi0.5Na0.5)1− x Ba x TiO3 relaxor ferroelectrics J. Appl. Phys. 116, 154101 (2014); 10.1063/1.4898322Electromechanical strain and bipolar fatigue inThe electric-field-temperature phase diagram for the lead-free relaxor material (1 À x)(Bi 1/2 Na 1/2 ) TiO 3 À xBaTiO 3 (x ¼ 0.03, 0.06, and 0.09) doped with 0.5 mol% Mn (BNT-100xBT:Mn) was established. Transition lines between ergodic or nonergodic relaxor states and the field-induced ferroelectric state were determined at constant temperatures with electric-field-dependent measurements of the polarization as well as of the piezoelectric coefficient and permittivity. Near the depolarization temperature T d , the switching between two ferroelectric poling directions occurs in two steps via an intermediate relaxor state. This effect is closely related to the pinching of the ferroelectric hysteresis loop. V C 2014 AIP Publishing LLC. [http://dx.

We address the unsolved question on the structure of relaxor ferroelectrics at the atomic level by characterizing lead-free piezoceramic solid solutions (100 − x)(Bi 1/2 Na 1/2 )TiO 3 -xBaTiO 3 (BNT-xBT) (for x = 1, 4, 6, and 15). Based on the relative intensity between spectral components in quadrupolar perturbed 23 Na nuclear magnetic resonance, we present direct evidence of the coexistence of cubic and polar local symmetries in these relaxor ferroelectrics. In addition, we demonstrate how the cubic phase vanishes whenever a ferroelectric state is induced, either by field cooling or changing the dopant amount, supporting the relation between this cubic phase and the relaxor state. Relaxor ferroelectrics have been intensively studied in the past 30 years because of their intriguing structural and dielectric features [1][2][3]. Despite that, the nature of their ground state remains an open question [4][5][6][7][8][9][10][11][12]. Several models have been proposed to describe this puzzling class of materials [1,[5][6][7][8]13], two of which are mainly concerned with the structure of the ground state of relaxors [4].The random field (RF) model proposes a single-phase structure broken up into ferroelectric nanodomains. These nanodomains are kept small under the constraint of quenched random electric fields which originate from chemical disorder [7,14]. The other model introduced the concept of "polar nanoregions" (PNRs) [13]. When relaxors are cooled below the Burns temperature, small and randomly oriented polarized regions (PNRs) appear within the otherwise nonpolar crystal structure. Upon further cooling, PNRs grow in size and number [11], but their percolation is prevented by structural disorder and random electric fields [8,10,12]. This behavior would imply the coexistence of PNRs and a nonpolar matrix, in contrast to the single-phase structure proposed by the RF model.An induced ferroelectric state can be established in relaxors when a strong electric field is applied. This state features macroscopic polarization and breaking of the cubic average symmetry [5,11,[15][16][17]. While the RF model suggests that this transformation and the formation of macroscopic ferroelectric domains are caused only by reorientation of previously nanometric ferroelectric domains, an additional mechanism is required when PNRs are considered. In that case, a long-range ferroelectric state can only be established if the nonpolar matrix becomes polarized, being incorporated by the growing PNRs.Two questions are raised by contrasting these two models: (1) Does the microscopic structure of relaxor ferroelectrics consist only of ferroelectric nanodomains or do regions of lower local symmetry (PNRs) coexist with a nonpolar matrix of * gerd.buntkowsky@chemie.tu-darmstadt.de † roedel@ceramics.tu-darmstadt.de undistorted structure? (2) How does the microscopic structure of relaxors evolve upon electric poling?In spite of their relevance, such questions have remained unsolved largely because the structural characterization of relaxors is a c...