Structural and electrical properties of BKT rich Bi0.5K 0.5TiO3-K0.5Na0.5NbO3 system

Abstract

A new lead free (1-x) Bi0.5K0.5TiO3-(x) K0.5Na0.5NbO3 (BKT-KNN) system (0.0 x 0.15) with density of 94-97 is reported. Tetragonal structure of BKT-KNN is apparent for 0 x 0.06 with 1.02 (ca) 1.012. Compositions with x 0.15 show orthorhombic structure (like KNN) and x 0.08 x 0.10 are pseudocubic. Addition of KNN by a small amount (up to 4 mole ) is shown to improve piezoelectric properties, keeping the ferroelectric and dielectric values comparable to those of BKT. Optimized properties with d33 129 pCN, kp 29, P max 35 μCcm2, Pr 24 μCcm2, m 4600, Tm 370 °C and Td 260 °C are observed for x 0.03 sample. In the tetragonal range, a correlation between lattice distortion (ca), piezoelectric coefficient (d33) and depolarization temperature Td is established. Decrease in ca seems to result in easy poling by field and easy depoling by temperature, leading to an increase in d33 but a decrease in Td. A phase diagram for 1-xBKT-xKNN (0 x 0.10) is proposed. It is shown that addition of more than 6 mole of KNN leads to the lowering of Td (where the structure becomes tetragonal to pseudocubic) considerably, resulting into a shift in tetragonal- pseudocubic phase boundary towards lower temperature. © 2013 Copyright 2013 Author(s). This article is distributed under a Creative Commons Attribution 3.0 Unported License.