Influence of Ta5+ content on the crystallographic structure and electrical properties of [001]PC-oriented (Li,Na,K)(Nb,Ta)O3 single crystals

Abstract

A series of centimeter-sized lead-free piezoelectric Li+- and Ta5+-modified (Na,K)NbO3 single crystals with an ABO3 perovskite structure was successfully grown by the top-seeded solution growth method. Effective segregation of the elements was considered in order to further develop the growth of Li+- and Ta5+-modified (Na,K)NbO3 single crystals. The crystallographic structure and electrical behaviour along the [001]PC orientation were studied. X-ray diffraction, Raman spectroscopy and dielectric studies reveal that the increase in Ta5+ content reduces the orthorhombic-tetragonal phase transition. Bipolar and unipolar strain curves were investigated at 2 kV mm-1. The highest bipolar and unipolar strains associated with a large-signal piezoelectric constant of 368 pm V-1 were achieved for Li0.02Na0.626K0.354Nb0.808Ta0.192O3. The asymmetric bipolar strain curves were observed and related to the existence of internal bias fields induced by (V′A-VO) defect dipoles, which were created during the crystal growth process.