Phase Transformation and Tunable Piezoelectric Properties of Lead‐Free (Na_0.52K_0.48−xLi_x)(Nb_1−x−ySb_yTa_x)O₃ System

Abstract

Lead-free (Na 0.52 K 0.48Àx )(Nb 1ÀxÀy Sb y )O 3 -xLiTaO 3 (NKNS-LT) piezoelectric ceramics have been fabricated by ordinary sintering. A special attention was paid to the composition design through which the dielectric and piezoelectric properties of the (Li, Ta, Sb) modified NKN systems were significantly promoted. A property spectrum was generated with a particular discussion on the relationship between the Sb content, the LT content, the polymorphic phase transition, and the electrical properties and their temperature stability. Excellent and tunable electrical properties of d 33 5 242-400 pC/N, k p 5 36%-54%, e 33 T ¼ 750À 2500, and T c 5 2301-4301C demonstrate a tremendous potential of the compositions studied for device applications.

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“…The results of conventional mixed oxide reactions for these compositions reveal that Li + and Sb 5+ diffuse into the parent lattices to form a solid solution with a perovskite structure 31 , but this seems to reduce its orthorhombicity because of the coexistence of orthorhombic and tetragonal phases 14 . Also, the T c decreased gradually with increasing Sb content.…”

“…However, several researchers have examined solid solution formation of related compositional series to the one presented here, involving different NKN-LT binary compositions and extending along the join to LiSbO 3 (Table 1) 14, 26-31 ; e.g., (1−x)[(K 0.5 Na 0.5 )(Nb 0.925 Ta 0.075 )O 3 ]-x LiSbO 3 with x between 0 and 0.1, and also (Na 0.52 K 0.48 − x Li x )(Nb 1 − x − y Sb y Ta x )O 3 (0 < x < 0.07, 0 < y < 0.16) 14,31 . The results of conventional mixed oxide reactions for these compositions reveal that Li + and Sb 5+ diffuse into the parent lattices to form a solid solution with a perovskite structure 31 , but this seems to reduce its orthorhombicity because of the coexistence of orthorhombic and tetragonal phases 14 .…”

“…Among them, the mixed alkali niobate-tantalates solid solution system [Na 0.5 K 0.5 NbO 3 ] 1 − x -[LiTaO 3 ] x (NKN-LT) has been reported to exhibit a polymorphic phase boundary (PPB) between orthorhombic and tetragonal phasefields near room temperature at 0.05 < x < 0.06 11 . Unlike that of the PZT system, this crystal structure transition from orthorhombic to tetragonal symmetry with doping is not due to the MPB in the NKN-LT system but compositionally shifting polymorphic phase transitions downward to near or at room temperature [12][13][14] . The PPB is quite similar to the frequently used MPB to enable phase coexistence but the crystal structure of the compositions near a PPB seems more sensitive to temperature.…”

(K,Na)NbO3-based Lead-free Piezoelectric Materials: An Encounter with Scanning Probe Microscopy

“…For a compositionally optimized Li-doped composition, its piezoelectric coefficient d 33 can be increased up to 324 pC/N even from a considerably high value (190 pC/N) by means of re-poling treatment after room temperature aging; such a high d 33 value is only reachable in literature for KNN ceramics with complicated modifications using Ta and Sb dopants [46,98,99]. Table 2 shows the piezoelectric coefficient d 33 as well as tetragonal-orthorhombic phase transition temperature (T O-T ) of Li-doped KNN ceramics with respect to Li content, after both the first and second poling, respectively.…”

Strain Mechanisms in Lead-Free Ferroelectrics for Actuators

“…These exceptional properties were achieved through a complex texturing process. In subsequent investigations it was demonstrated that KNN-based materials depict promising small [280][281][282][283] and large 136 signal properties with conventional solid state synthesis. However, this family of materials presents major synthesis difficulties that need to be overcome for entering a reliable large scale production.…”