The 0.968 [(K 0.48 Na 0.52 )]Nb 0.95+x Sb 0.05 O 3 -0.032(Bi 0.5 Na 0.5 )ZrO 3 [KNN x S-BNZ] lead-free ceramics with nonstoichiometric niobium ion were fabricated via conventional solid-state sintering technique and their piezoelectric, dielectric and ferroelectric properties were investigated. When x = 0.010, enhanced piezoelectric properties (d 33 % 421 pC/N and k p % 0.47) were obtained due to the construction of rhombohendral-tetragonal phase boundary near room temperature. The KNN x S-BNZ ceramics possesses enhanced Curie temperature (T c ) with improved piezoelectric constant. A large d 33 of~421 pC/N and a high T c~2 56°C can be simultaneously induced in the ceramics with x = 0.010. Especially, good thermal stability was observed in a broad temperature range. The results indicated that our work could benefit development of KNN-based ceramics and widen their application range.
As the most promising lead-free piezoelectric ceramics
to replace
lead zirconate titanate (PZT) ceramics, potassium sodium niobate (KNN)
ceramics have been widely studied for their application prospects
in various electronic devices. Increasing Q
m while maintaining a high piezoelectric activity is quite important
for piezoelectric ceramics applied in ultrasonic devices. A KNN-based
ceramic with high d
33 and Q
m is prepared by a conventional solid-state technique
to construct polycrystalline phase boundaries and induce defect dipoles.
The best overall performance can reach d
33 = 260 pC/N, Q
m = 210, and T
C = 293 °C. The temperature dependence of the relevant
parameters is tested, where Q
m increases
but d
33 decreases with the rise of temperature
accompanied by escaping ferroelectric boundary, which shows that the
polarization rotation plays an important role in the two parameters.
The hardening effect of KNN-based ceramics with CuO doping is further
studied by first-principles calculations, demonstrating that the Cu
doping strongly disturbs the ferroelectric order, but the formation
of defect dipoles could stabilize the ferroelectric order. It is illustrated
that defect dipoles always find their ground state at the site near
the domain walls and the oriented defect dipoles hinder the polarization
rotation severely, confirming the role of the defect dipoles in KNN-based
materials.
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