FERROELECTRIC AND PIEZOELECTRIC PROPERTIES OF KNbO3 CERAMICS CONTAINING SMALL AMOUNTS OF LaFeO3

• Published in: Jpn.J.Appl.Phys ,Part 1. Vol. 42, no. 9B, pp. 6102-6105. 2003 Vol. 42; no. 9B; pp. 6102 - 6105
• Main Authors: Kakimoto, K, Masuda, I, Ohsato, H
• Format: Journal Article
• Language: English
• Published: 2003
• ISSN: 0021-4922
• DOI: 10.1143/JJAP.42.6102

Dense KNbO3 ceramics have been synthesized by pressure-less sintering under optimized heat-treatment conditions using a small amount of La2O3 and Fe2O3 additives. KNbO3 forms (K1-xLax)(Nb1-xFex)O3 solid solutions and changes in the crystal system, depending on the additive content, from orthorhombic to tetragonal at x of 0.020, and from tetragonal to cubic at x of 0.200 or higher. When only 0.002 mol of La2O3 and Fe2O3 (x=0.002) was added into KNbO3, the highest value (98.8%) of the theoretical density was obtained. This specimen showed orthorhombic symmetry with a high Curie temperature of 420 C, and demonstrated a well-saturated ferroelectric hysteresis loop with large remanent polarization (Pr) of 18 mu C /cm2, which is comparable to the value reported for pure KNbO3 ceramics fabricated by hot pressing. Furthermore, the x=0.002 specimen showed a planar electromechanical coupling ratio (kp) of 0.17 and piezoelectric d33 constant of 98 pC/N, regardless of the unsaturated poling state. 12 refs.