Structural and functional characterisation of KNNS–BNKZ lead-free piezoceramics

Abstract

Promising piezoelectric properties have been reported recently for lead-free 0.96(K0.48Na0.52Nb0.95Sb0.05)-0.04Bi0.5(Na0.82K0.18)0.5ZrO3 (KNNS-BNKZ) ceramics. The presence of coexisting ferroelectric rhombohedral and tetragonal phases is thought to play a key role in their functional properties, but a thorough understanding is currently lacking. In this experiment, (1-x)KNNS-(x)BNKZ ceramics with x = 0 to 0.05 were prepared by the mixed-oxide method. High resolution synchrotron x-ray powder diffraction (SXPD) measurements reveal that the addition of BNKZ into KNNS ceramics leads to an increase of the rhombohedral-orthorhombic phase transition temperature (TR-O) and a reduction of the orthorhombic-tetragonal phase transition temperature (TO-T) leading to orthorhombic-tetragonal and rhombohedral-tetragonal phase coexistence at room temperature for compositions with x = 0.02 and 0.04, respectively. By combining the results of the SXPD measurements with microstructural examination using SEM, evidence is also found for the occurrence of chemical heterogeneity, which could provide an additional means to control the functional properties. The structural observations are correlated with changes in the dielectric properties, obtained as permittivity-temperature plots, and variations in the polarisation and coercive field values, obtained from measurements of the ferroelectric hysteresis loops.

Thermally-induced phase transformations in KNNS-BNKZ lead-free piezoceramics

“…Thermal evolution of (a),(b) lattice parameters and (c),(d) phase fractions of rhombohedral (R), orthorhombic (O) and tetragonal (T) phases for 0BNKZ and 1BNKZ compositions showing the widening of the phase transition range. Note that the uncertainties in lattice parameters and phase fractions are typically less than 0.002% and 1%, respectively.Although the identification of phase formation at room temperature described in previous work indicated the occurrence of O-T coexisting phases in the 1BNKZ composition[31], the contour plots of the thermally-induced SXPD profiles(Figure 4) in the present results revealed contradictory results. The coexistence of R-O was observed clearly in the temperature range of -73C to -43C, whereas the O-T mixed phase occurred for temperatures between 87C and 117C, as seen in the figure.…”

“…For tan, the highest loss values near room temperature were found for the 0BNKZ composition because of its low relative density (<90%) as described previously. [31] A comparison of the contour maps of the {200} p XRD peak profiles, dielectric permittivity and loss tangent in the temperature range from 50C to 200C for 0BNKZ and 4BNKZ is presented in Figure 10(a) and (b) respectively, in order to study the relationship between the O-T structural phase transformation and dielectric properties. It was found that the abrupt change of dielectric permittivity for 0BNKZ starts at 100C and reached a peak at 125C, while the crystal structure fully transforms to tetragonal beyond 125C.…”

“…[30] However, the precise nature of phase coexistence in KNNS-BNKZ ceramics and the influence of the polymorphic phase transformations on their temperature-dependent functional properties have yet to be clarified. [30,31] Therefore, the influence of BNKZ content on the thermal evolution of structure and functional properties of (1x)KNNS-(x)BNKZ ceramics were investigated in the present study.…”

Some Optical, Electrical Properties of Lead Free KNN-CZN Ceramics

“…In recent years, many various lead-free ceramic systems with perovskite structure have been success-fully studied [1] [2] [3] [4] [5], among which (Na,K)NbO 3 (KNN) based ceramics have attracted a lot of attention due to their strong ferroelectricity, high Curie temperature (about 420˚C). With compositional modification by combining KNN with other perovskite compounds to form KNN-based new solid solutions, such as KNNL [6] [7], KNNLS [8], KNNLST [9], KNNS-BNKZ [10], KNNS-BKZZ [11], the piezoelectric properties of ceramics are further enhanced (d 33 > 400 pC/N) [12] [13] [14], thereby it has become one of the most promising candidates for replacing Pb-based ceramics in the piezoelectric field. However, most of these studies focused on electrical properties, while the optical properties of the material are rarely mentioned.…”

Structure and formation mechanisms of (K0.46Na0.46La0.08)(Nb0.94Sb0.06)O3 particles under hydrothermal conditions

“…Recently, the alkaline niobate-based lead free piezoelectrics have attracted considerable attention to replace lead-containing ceramics. Among them, potassium sodium niobate [(K,Na)NbO 3 , abbreviated as KNN] is considered as one of the best promising candidates to replace PZT [4][5][6]. Nevertheless, the piezoelectric activity of KNNbased ceramics is still inferior to that of most PZT materials because the alkaline elements of KNN are highly volatile at high temperature required for the synthesis of KNN [7].…”