Morphotropic phase boundary in (1−x)Bi0.5Na0.5TiO3–xK0.5Na0.5NbO3 lead-free piezoceramics

Abstract

The electromechanical behavior of (1−x)Bi0.5Na0.5TiO3–xK0.5Na0.5NbO3 (BNT-KNN) lead free piezoelectric ceramics is investigated for 0⩽x⩽0.12 to gain insight into the antiferroelectric-ferroelectric (AFE-FE) phase transition on the basis of the giant strain recently observed in BNT-based systems. At x≈0.07, a morphotropic phase boundary (MPB) between a rhombohedral FE phase and a tetragonal AFE phase is found. While the piezoelectric coefficient is largest at this MPB, the total strain further increases with increasing KNN content, indicating the field-induced AFE-FE transition as the main reason for the large strain.

Morphotropic phase boundary and electrical properties in (1−x)Bi0.5Na0.5TiO3−xBi(Zn0.5Ti0.5)O3 lead-free piezoceramics

“…6. The inset indicates the compo- sition dependent unipolar strain value, which increases monotonously with increasing x, consistent with the above composition dependence of bipolar strain and with the composition dependence of bipolar/unipolar strain of other reported BNT-based lead-free piezoceramics with well saturated P-E loops, 7 but lower than that with slim P-E loops. 15 Figure 7 shows the piezoelectric coefficient ͑d 33 ͒ and planar coupling factor ͑k p ͒ as the functions of x.…”

“…9 Actually, similar results are observed and discussed in other BNTbased piezoceramics systems. 7,15 Unipolar S-E curves are also measured and displayed, the typical unipolar S-E curve of the composition with x = 0.0375 is shown in Fig. 6.…”

“…2,[6][7][8][9] Generally, by introducing other perovskite oxides such as BT and KNN into BNT to form solid solutions, especially when the solid solutions locate in the region of so-called morphotropic phase boundary ͑MPB͒ where two different phases coexist, BNTbased piezoceramics can have greatly improved electrical performance. [6][7][8] On the other hand, tetragonal Bi͑Zn 0.5 Ti 0.5 ͒O 3 ͑BZT͒ has been reported to have very high c/a ratio of 1.21 and large calculated ferroelectric polarization of 150 C / cm 2 , whereas it is not stable in its pure form and can only be stabilized at high pressure. 10 However, it is reported that BZT-containing solid solutions can be stable in atmospheric condition and still have enhanced c/a ratio, ferroelectric polarization, and increased T c .…”

“…Some perovskite-based lead-free piezoceramics, mainly based on rhombohedral Bi 0.5 Na 0.5 TiO 3 ͑BNT͒, tetragonal BaTiO 3 ͑BT͒, and orthorhombic K 0.5 Na 0.5 NbO 3 ͑KNN͒, have been proposed as promising candidates for replacing PZT. [2][3][4][5][6][7][8][9] BNT has some advantages such as large ferroelectric polarization, high Curie temperature, thus, many BNT-based lead-free piezoceramics have been developed. 2,[6][7][8][9] Generally, by introducing other perovskite oxides such as BT and KNN into BNT to form solid solutions, especially when the solid solutions locate in the region of so-called morphotropic phase boundary ͑MPB͒ where two different phases coexist, BNTbased piezoceramics can have greatly improved electrical performance.…”

“…[2][3][4][5][6][7][8][9] BNT has some advantages such as large ferroelectric polarization, high Curie temperature, thus, many BNT-based lead-free piezoceramics have been developed. 2,[6][7][8][9] Generally, by introducing other perovskite oxides such as BT and KNN into BNT to form solid solutions, especially when the solid solutions locate in the region of so-called morphotropic phase boundary ͑MPB͒ where two different phases coexist, BNTbased piezoceramics can have greatly improved electrical performance. [6][7][8] On the other hand, tetragonal Bi͑Zn 0.5 Ti 0.5 ͒O 3 ͑BZT͒ has been reported to have very high c/a ratio of 1.21 and large calculated ferroelectric polarization of 150 C / cm 2 , whereas it is not stable in its pure form and can only be stabilized at high pressure.…”