Orthorhombic‐pseudocubic phase transition and piezoelectric properties of (Na_0.5K_0.5)(Nb_1−xSb_x)‐SrZrO₃ ceramics

Abstract

0.96(Na 0.5 K 0.5 )(Nb 1Àx Sb x )-0.04SrZrO 3 ceramics with 0.0≤x≤0.06 were well sintered at 1060°C for 6 hours without a secondary phase. Orthorhombic-tetragonal transition temperature (T O-T ) and Curie temperature (T C ) decreased with the addition of Sb 2 O 5 . The decrease in T C was considerable compared to that in T O-T , and thus the tetragonal phase zone disappeared when x exceeded 0.03. Therefore, a broad peak for orthorhombic-pseudocubic transition as opposed to that for orthorhombic-tetragonal transition appeared at 115°C-78.2°C for specimens with 0.04≤x≤0.06. An orthorhombic structure was observed for specimens with x≤0.03.However, the polymorphic phase boundary structure containing orthorhombic and pseudocubic structures was formed for the specimens 0.04≤x≤0.06. Furthermore, a specimen with x=0.055 exhibited a large piezoelectric strain constant of 325 pC/N, indicating that the coexistence of orthorhombic and pseudocubic structures could improve the piezoelectric properties of (Na 0.5 K 0.5 )NbO 3 -based leadfree piezoelectric ceramics.

Thermally stable high strain and piezoelectric characteristics of (Li, Na, K)(Nb, Sb)O3‐CaZrO3 ceramics for piezo actuators

“…The T O‐P peak was observed at approximately 35°C for the sample with x = 0.09 (Figure E). The T O‐P peak was also observed in 0.96NK(N 1‐x S x )O 3 ‐0.04SrZrO 3 ceramics . Finally, the T C peak was only observed at 60°C for the specimen with x = 0.1, as displayed in Figure F, revealing that this specimen has a pseudocubic structure.…”

“…The pseudocubic structure is not a cubic structure and is reported to be similar to the rhombohedral structure or a mixture of tetragonal and cubic structures . Moreover, this pseudocubic structure can coexist with the orthorhombic (or tetragonal) structure upon decreasing the T C , resulting in the development of the orthorhombic‐pseudocubic (or tetragonal‐pseudocubic) PPB structures at RT . In general, the P r value of a specimen with a PPB structure is large because two structures coexist in this specimen.…”

“…Therefore, it is considered that a specimen having a pseudocubic‐based PPB structure could reveal large d 33 and k p values. Recently, specimens with orthorhombic‐pseudocubic PPB and tetragonal‐pseudocubic structures were reported to display high piezoelectric properties . However, the T C of a specimen with the pseudocubic‐based PPB structure is generally low.…”

Piezoelectric properties of (Na0.5K0.5)(Nb1‐xSbx)O3‐SrTiO3 ceramics with tetragonal‐pseudocubic PPB structure

“…The Bragg reflections at 67 o were used for the structural analysis of these specimens because the presence of the pseudocubic structure can be clearly identified by these reflections. 36,40,45 High-intensity orthorhombic (004) O , (400) O , and (222) O reflections and low-intensity tetragonal (202) T and (220) T reflections were observed from the specimen with x = 0.0, indicating the presence of an orthorhombictetragonal PPB structure in this specimen, but with the orthorhombic structure as the major structure. In our analysis, the subscripts T, O, and P are the abbreviations of tetragonal, orthorhombic, and pseudocubic, respectively.…”

“…Recently, the orthorhombic-pseudocubic PPB structure was observed in CuO-added 0.96 (Na 0.5 K 0.5 )(Nb 1-x Sb x )O 3 -0.04SrZrO 3 [CNK(N 1-x S x )-SZ] ceramics and these ceramics were found to show a large d 33 value of 325 pC/N. 40 However, the pseudocubic-tetragonal PPB structure has not yet been reported. Moreover, the piezoelectric properties of specimen with a pseudocubic-tetragonal PPB structure have not been investigated.…”