Fig. 6 shows XRD patterns of the annealed ceramics. The phase
structure exhibits remarkable change with prolonged annealing
time. Variations of the room temperature electrical properties as a
function of annealing time are listed in Table 2. The variation of the
electric properties can be well rationalized by considering the
compositional and structure variations undergoing during hightemperature
annealing. A secondary phase out of the perovskite
background can be clearly identified in the patterns of the long
time annealed samples. The reflection of the secondary phase
matches well tetragonal tungsten bronze (TTB) structure. The
formation of the secondary phase generally leads to the degradation
of the dielectric and piezoelectric properties due to the
diluting effect (less ferroelectric phase), as demonstrated by the reduction of the dielectric and piezoelectric performance with the
further prolonged annealing time. The XRD results of the annealed
samples illustrated the appearance of segregation in the sample for
1080 8C, and this compositional inhomogeneity induced the worse
piezoelectric property comparing with that of 1040 8C samples.