  In this contribution, the effect of P2O5 and SiO2 addition on the phase,
microstructure, and electrical properties of KNbO3 was studied. Sample powders
with the general formula (1-x)KNbO3.xP2O5 (x = 0.03, 0.05) and (1-x)KNbO3.xSiO2
(x = 0.1) were prepared via mixed-oxide route. The thermal behavior of the
mixed-milled powder was investigated by TG/DTA which revealed an overall weight
loss of 33.4 wt % in the temperature range of 30 < T < 1200 C and
crystallization exotherm occurring at about 795 C. The present results
indicated that P2O5 acted as a sintering aid and lowered the sintering
temperature by about 30 C and promoted densification of KNbO3. Sample
compositions at various stages of processing were characterized using X-ray
diffraction. Samples sintered at T < 1020 C revealed mainly KNbO3 together with
a couple of low-intensity K3NbO4 peaks as a secondary phase. The SEM images of
(1-x)KNbO3.xSiO2 (x = 0.1) samples showed a slight increase in the average
grain size from 3.76 um to 3.86 um with an increase in sintering temperature
from 1000 C to 1020 C. Strong variations in dielectric constant and loss
tangent were observed due to P2O5 and SiO2 addition as well as frequency of the
applied AC signals.
