High-Performance [00l]-Textured BiAlO₃-Doped K_0.5Bi_0.5TiO₃ Ceramics

[00 l ] grain-oriented 0.95K 0.5 Bi 0.5 TiO 3 –0.05BiAlO 3 (named K5BA-T) ceramics were prepared via the reactive template grain growth (RTGG) and tape casting technique. High-aspect-ratio K5BA powder was prepared using a plate-shape 4-layer aurivillius oxide (K 0.5 Bi 4.5 Ti 4 O 15 ) powder as the template. The effects of grain morphology modification and texturing on the structural, dielectric, and piezoelectric properties of K5BA-T were systematically investigated. The average plate size of ∼6.5 μm with a thickness of ∼400 nm was observed in the K5BA sample. X-ray diffraction (XRD) and bulk texture measurements confirmed the texturing of K5BA-T in the [00 l ] crystallographic direction with a calculated Lotgering factor of ∼80%. Two anomalies in the temperature-dependent dielectric plot of the poled K5BA-T sample signified additional poling-induced phase transition. A lower value of room-temperature (RT) dielectric constant (ε r ) of ∼ 200 (at 1 MHz) and a higher piezoelectric charge coefficient ( d 33 ) of ∼145 pCN –1 were obtained in the poled K5BA-T ceramic compared to that of the 0.95K 0.5 Bi 0.5 TiO 3 –0.05BiAlO 3 ceramic with randomly oriented grains (named K5BA-R). Consequently, the piezoelectric voltage coefficient ( g 33 ) estimated for the textured ceramic showed a 650% increment ( g 33 ∼ 80 × 10 –3 V mN –1 ) over the K5BA-R sample ( g 33 ∼ 12.5 × 10 –3 V mN –1 ). The transduction coefficient ( d 33 · g 33 ) of K5BA-T ceramic was calculated to be ∼11 600 × 10 –15 m 2 N –1, which is nearly 9 times higher compared to its random counterpart. Further, a piezodevice fabricated using poled ceramic for energy harvesting showed an output voltage of ∼7 V with a current response of ∼2 μA under normal finger-tapping motion.