Diego A. Ochoa

Evaluation of domain wall motion in lead zirconate titanate ceramics by nonlinear response measurements

Nonlinear response of pure and doped Pb(Zr1−xTix)O3 ceramics, with different compositions, has been analyzed in order to evaluate the domain wall motion in these materials. The study of dielectric and converse piezoelectric response shows a clear dependence of the domain wall mobility on the ferroelectric phase. Large lattice distortion in tetragonal samples produces a low mobility of the ferroelectric-ferroelastic domain walls. The influence of the type of defects on the nonlinear response has been explored. The results show that the relative increase of the domain walls mobility in donor-doped materials is greater than the decrease in acceptor-doped materials due to the pinning produced by complex defects. Rayleigh law has been used to evaluate the irreversible contribution of the domain walls movement to the nonlinear dielectric response. The analysis reveals that in presence of oxygen vacancies, the dielectric response cannot be attributed exclusively to the contribution of the irreversible domain wal...

Extrinsic contribution and non-linear response in lead-free KNN-modified piezoceramics

Finding lead-free ceramics with good piezoelectric properties is nowadays one of the most important challenges in materials science. The (K, Na, Li)(Nb, Ta, Sb)O3 system is one of the most promising candidates as a lead-free ceramic for transducer applications and is currently the object of important research work. In this paper, (K0.44Na0.52Li0.04)(Nb0.86Ta0.10Sb0.04)O3 was prepared by a conventional ceramic processing route. For this composition, orthorhombic-to-tetragonal phase transition was observed at temperatures very close to room temperature. As a consequence, good room temperature electromechanical properties were observed, displaying good thermal stability. We show that the most important contribution to dielectric, piezoelectric and elastic response comes from extrinsic effects, as was observed in other perovskite based materials. Nonlinearities in electromechanical properties induced by high electric field or mechanical stress were studied. Non-linear dielectric response was found to be less important than for soft PZT ceramics and was analysed within the Rayleigh framework. The results reveal that the non-linear response at room temperature in this material is mainly due to the irreversible wall domain movement.

Evidence of temperature dependent domain wall dynamics in hard lead zirconate titanate piezoceramics

This work presents a study of the domain wall dynamics in Pb(Zr1−xTix)O3 (PZT)-based piezoceramics by means of the temperature dependence non-linear dielectric response and hysteresis loop measurements. In soft PZT, non-linear response gradually increases as the temperature is raised. A similar response is displayed by hard PZT at low temperatures. However, rather more complex behavior is detected at temperatures above 200 K. The anomalous response, which is very marked at room temperature, becomes even greater when the electric field is increased. The non-linear dielectric response is analyzed in the framework of the Rayleigh model. The results suggest a clear change in the domain wall dynamics in hard PZT, which is not observed in soft PZT. Observation of the hysteresis loops confirms that a strong effect of domain wall pinning emerges near room temperature. The change in domain wall dynamics appears as the main cause of the dielectric response difference between both kinds of materials at room temperature.

Optimization of Elastic Nonlinear Behavior Measurements of Ceramic Piezoelectric Resonators with Burst Excitation

A system of nonlinear measurement and nonlinear elastic characterization of resonators is presented, which increases the possibilities and characteristics of the other classic nonlinear characterization methods. This characterization has been necessary due to the use of resonators in power devices, where their behavior departs from the linear characteristics. The use of burst signals and a system of acquisition and data processing is proposed instead of impedance analyzers, thus avoiding the thermal effects associated with the high-signal measures, which are necessary for this characterization. The measures are repeated for different amplitudes and at the same frequency near the resonance by a single amplitude sweep, which is simpler and faster to carry out than the multiple frequency sweepings used in other methods. As a last resort, a variation on the proposed method, closer to the classical measures, is put forward, in which the resonance is ensured in all the measures. Special emphasis is placed on obtaining nonlinear characterization of the piezoceramic material in order to increase its optimization in the transducers in terms of both its use and its composition and structure.

Effect of Mn-acceptor dopant on dielectric and piezoelectric responses of lead lanthanum zirconate titanate piezoceramics

Dielectric and direct piezoelectric responses in non-doped and Mn-doped Pb0.91La0.09(Zr0.65,Ti0.35)O3 ceramics are experimentally studied. The permittivity and the direct piezoelectric coefficient were measured by applying an ac electric field or a mechanical stress, respectively. The results show that the dielectric response is mainly due to an extrinsic contribution at room temperature. A notable reduction in room temperature dielectric losses by Mn-doping is verified. The temperature of the minimum of the losses depends on the Mn-content, enabling the Pb0.91La0.09(Zr0.65,Ti0.35)O3 properties to be tuned from soft to hard. A significant stabilization of the dielectric and piezoelectric responses, related to domain wall motion reduction, is confirmed in Mn-doped materials, so these materials become good candidates for transducer applications. The correlation between the dielectric constant and dielectric losses is discussed in terms of the Rayleigh model. Results show that Mn-doped PLZT response does not...

Influence of extrinsic contribution on the macroscopic properties of hard and soft lead zirconate titanate ceramics

In this work, the contribution of the extrinsic effect to the macroscopic properties in soft and hard lead zirconate titanate ceramics is directly evaluated. Close to the room temperature, poled hard ceramics show an anomalous behavior, which is notably different from that of soft ceramics, not only in dielectric but also in piezoelectric and elastic responses. Hence, at room temperature their properties are thermally stable and the losses are unusually low. It is suggested that two mechanisms are present, with one mechanism inhibiting the other.

Extrinsic response enhancement at the polymorphic phase boundary in piezoelectric materials

Polymorphic phase boundaries (PPBs) in piezoelectric materials have attracted significant interest in recent years, in particular, because of the unique properties that can be found in their vicinity. However, to fully harness their potential as micro-nanoscale functional entities, it is essential to achieve reliable and precise control of their piezoelectric response, which is due to two contributions known as intrinsic and extrinsic. In this work, we have used a (K,Na)NbO3-based lead-free piezoceramic as a model system to investigate the evolution of the extrinsic contribution around a PPB. X-ray diffraction measurements are performed over a wide range of temperatures in order to determine the structures and transitions. The relevance of the extrinsic contribution at the PPB region is evaluated by means of nonlinear dielectric response measurements. Though it is widely appreciated that certain intrinsic properties of ferroelectric materials increase as PPBs are approached, our results demonstrate that t...

Extrinsic effects in twinned ferroelectric polycrystals

The structure of medium-grain piezoelectric ceramics often consists of alternate lamellae of non-180° domains. In this work, the extrinsic effects of the electric and elastic fields on such structures are studied. A description of the extrinsic behavior of a single grain is given, and it is shown that the relations between piezoelectric and dielectric or elastic constants must be independent of the wall mobility, being solely dependent on the relation between spontaneous polarization and strain. By using an appropriate coordinate system, the conditions under which the intrinsic and extrinsic effects can be added are analyzed. The linear global behavior of a grain can then be described as a function of its orientation and of two additional parameters: the lack of equilibrium between domains α and its mean thickness d. The basis is established to describe the state of a ceramic through a distribution function that accounts for domain orientation and which depends on the poling, fatigue, and ageing of the sa...

Relaxor Ferroelectric Behavior and Structural Aspects of SrNaBi2Nb3O12 Ceramics

The SrNaBi2Nb3O12 (SNBN) powder was prepared via the conventional solid-state reaction method. X-ray structural studies confirmed the phase to be a three-layered member of the Aurivillius family of oxides. The SNBN ceramics exhibited the typical characteristics of relaxor ferroelectrics, associated with broad and dispersive dielectric maxima. The variation of temperature of dielectric maxima (T-m) with frequency obeyed the Vogel-Fulcher relationship. Relaxor behavior was believed to be arising from the cationic disorder at A-site. Pinched ferroelectric hysteresis loops were observed well above T-m.

La3+-induced (micro)structural changes and origin of the relaxor-like phase transition in ferroelectric lead barium niobate electroceramics

Lead barium niobate (Pb1−xBaxNb2O6, PBN) ferroelectric materials have been and are the subject of numerous studies in literature due to their potential for wide-ranging applications in the electronic industry. In this work, La3+-doped Pb0.56Ba0.44Nb2O6 (PBN44) electroceramics were prepared and investigated in terms of X-ray diffraction, scanning electron microscopy, thermal spectra of dielectric permittivity, Curie–Weiss law, and hysteresis loop characteristics. It was noted that La3+ doping favors the formation of orthorhombic mm2 phase in PBN44, which originally shows only the tetragonal 4mm symmetry-related phase. In particular, the PBN44 material with 1 wt% La2O3 displays (micro)structural characteristics and dielectric properties similar to those from PBN compositions lying within their morphotropic phase boundary region. Our results also show that La3+ is able to promote a change of the ferroelectric to paraelectric phase transition appearance of PBN44 from pseudo-normal to really diffuse. However, conversion to a diffuse plus relaxor transition behavior reveals directly linked to incommensurate superstructures present and dielectrically-active in PBN materials toward low temperatures, with an intrinsically frequency-dispersive dielectric response. This statement is also supported by observation of hysteresis loops showing a transformation trend to pseudo-slim-like, even in the normal-like ferroelectrics, when moving into the temperature region of incommensuration manifestation.