Field-induced strain behavior for potassium sodium bismuth titanate ceramics

Data are reported for the dielectric, piezoelectric, electrostrictive, and ferroelectric properties of potassium-substituted sodium bismuth titanate, [(K
_x
Na
_1-x
)
_0.5
Bi
_0.5
]TiO
₃
. For the morphotropic phase boundary composition x = 0.2, relaxor-type behavior was observed at room temperature with piezoelectric (effective d
₃₃₃
= 325 ldr10
^-12
m/V) and ferroelectric properties (P
_R
= 25 muC/cm
²
, E
_c
= 30 kV/cm). A transition to a relatively frequency-independent, diffuse phase transformation region occurred with increasing temperature, with no remanent strain or coercive field. Above the transition temperature, the field-induced strain was consistent with contributions from elec-trostriction and field-induced piezoelectricity (M
₃₃₃₃
= 1.9 ldr 10
^-16
m
²
/V
²
and d
₃₃₃
= 81ldr10
^-12
m/V at 100degC). Information is given for the temperature dependence of properties, e.g., 0.14% strain induced at 50 kV/cm at 200degC. Higher potassium content x = 0.6 stabilized the ferroelectric piezoelectric region to temperatures above 200degC, with a relatively stable (d
₃₃₃
= 150-145 ldr 10
^-12
m/V between 25degC and 200degC. Pb-free KNBT ceramics appear competitive with PZT, especially for higher temperature electromechanical applications.