High temperature piezoelectric response of polycrystalline Li-doped (K,Na)NbO3 ceramics under compressive stress

Abstract

The influence of uniaxial compressive stress on small-signal relative permittivity and direct piezoelectric coefficient of polycrystalline Li-modified (K0.5Na0.5)NbO3 (0, 2, and 4 mol. % Li) was characterized as a function of temperature from 25 to 450 °C. These data reveal corresponding anomalies in both the dielectric and piezoelectric properties near the well-known structural phase transitions in (KxNa1 − x)NbO3. In particular, increasing stress was found to shift the orthorhombic–tetragonal (TO−T) and tetragonal–cubic (TC) phase boundaries to higher temperatures, thereby stabilizing the lower symmetry phases. Experimental results also show that stress up to a critical value flattens the piezoelectric response below TO−T, above which a monotonic decrease is observed. In contrast, permittivity is increased below TO−T with increasing stress. These results are used to construct a stress–temperature phase diagram of Li-modified (K0.5Na0.5)NbO3.

Electromechanical properties of paper‐derived potassium sodium niobate piezoelectric ceramics

“…The observed high d 33 around the O‐T phase boundary is due to the influence of permittivity and polarization 34,35 . The temperature‐dependent response up to the T O‐T is consistent with those of previous reports of KNN‐based compositions 36,37 . However, interpretation of the temperature‐dependent d 33 response above 225°C is not conclusive due to the apparent contribution from the increased mobility of defects.…”

“…34,35 The temperature-dependent response up to the T O-T is consistent with those of previous reports of KNN-based compositions. 36,37 However, interpretation of the temperature-dependent 𝑑 33 response above 225 • C is not conclusive due to the apparent contribution from the increased mobility of defects. The paperderived KNN also shows a similar room-temperature 𝑑 33 value of approximately 100 pC/N, however, the dispersion of the 𝑑 33 value with measurement frequencies is higher even below the T O-T .…”

Electromechanical Properties of Robocasted Barium Titanate Ceramics

“…Similar temperature‐dependent d 33 results were also observed by Anton et al, [ 59 ] although the indirect piezoelectric coefficient was presented. It should be noted that for other material systems, such as PZT [ 59,60 ] or KNN, [ 58 ] the depolarization temperature was found to be on the order of 6–10 °C lower than the Curie temperature, which might depend on the order of the transition as well as the thermal stability of ferroelectric domains in different materials. BT is well known to have the first‐order ferroelectric–paraelectric transition.…”

“…[ 43 ] Other material classes with T O − T , such as K 0.5 Na 0.5 NbO 3 (KNN), show an analogous maximum at ferroelectric–ferroelectric phase transition temperatures. [ 58 ] At temperatures between 75 and 100 °C, the piezoelectric charge coefficient remained constant at 110, 130, and 135 pC N −1 , for the reference, BT50, and BT52 samples, respectively.…”

In situ combined stress‐ and temperature‐dependent Raman spectroscopy of Li‐doped (Na,K)NbO3

“…22 Although there are limited data on the mechanical properties of NKN, investigations of the macroscopic stress-strain behavior have revealed a closed mechanical hysteresis and the corresponding loss of remanence for Li-doped NKN in the vicinity of the T PPT , strongly indicating a stress-induced structural phase transition. 22 This is supported by work on the temperature and stress-dependent piezoelectric and dielectric response of Li-doped NKN that showed an increase in both the T c and T PPT with increasing uniaxial compressive stress, 23 as well as in situ stress-dependent synchrotron X-ray diffraction that revealed a stress-modulated monoclinicto-tetragonal phase transformation in 6 mol.% Li-modified NKN (LNKN6a) at room temperature. 24 Although, stressand temperature-dependent macroscopic measurements have indicated the variation in phase transition temperature in NKN-based materials, the influence of simultaneously applied mechanical field and temperature on the structural phase transition is not well-known.…”