Fatigue-free unipolar strain behavior in CaZrO3 and MnO2 co-modified (K,Na)NbO3-based lead-free piezoceramics

Abstract

The unipolar fatigue behavior of CaZrO3 and MnO2 co-modified (K,Na,Li)(Nb,Ta)O3 lead-free piezoceramics was investigated systematically. The well-known charge agglomeration model is shown to explain the overall changes observed during unipolar fatigue, such as the development of bias field as well as the anisotropy in bipolar strain hysteresis and field-dependent dielectric permittivity. In addition, it is found that the unipolar strain exhibits only small degradation within 3% at the field amplitude of 2 kV/mm up to 107 cycles. This exceptionally good fatigue resistance is identified due to the presence of additional process, assigned as a “softening” effect that competes against the usual fatigue effect.

Piezoelectric properties of (K0.5Na0.5)NbO3-BaTiO3lead-free ceramics prepared by spark plasma sintering

“…It is believed that the phenomenon originates from the internal bias field, which is caused by the accumulation of space charges. [33][34][35][36] The effective electric field at position r can be expressed as:…”

Enhanced bipolar fatigue resistance in CaZrO3-modified (K,Na)NbO3 lead-free piezoceramics

“…It has been extensively studied in PZT [10][11][12] and (Bi 0.5 Na 0.5 )TiO 3 (BNT)-based [13][14][15] ceramics, whereas less fatigue data are available for the KNN system. 16,17 To elucidate the fatigue behavior of piezoceramics, several mechanisms were proposed in the literature, which included domain wall pinning by point defects, 18,19 field screening resulting from the formation of a dead layer underneath the electrodes, 20 or microstructure damage in the material adjacent to the electrodes as a result of large mechanical stresses during the domain switching. 21 As fatigue-free behavior for piezoceramics is highly desirable, two possible strategies have been adopted so far to improve the fatigue resistance in two separate systems.…”

Temperature dependence of unipolar fatigue behavior of lead-free alkali niobate ceramics

“…26) The main charge carriers in PZT structures are oxygen vacancies 27) and thus unipolar fatigue effects can be attributed to their accumulation. 14) This accumulation leads to an increase of an internal bias field as well as a decrease of the switchable polarization.…”

“…This accumulation of charges forms the local bias field E bias , which has the same orientation as the applied field during fatigue. 14) In order to explain the larger bias field in LNKN6-b, we took a closer look at the dopants. From the ion radii of the different elements, we can estimate if they attach to A or B site of the perovskite structure.…”