Thickness- and temperature-dependent structural and electromechanical properties of (100)-oriented Sc-doped (Na0.85K0.15)0.5Bi0.5TiO3 ferroelectric films

RSC Advances Pub Date: 2017-09-13 DOI: 10.1039/C7RA07848J

Abstract

(100)-oriented Sc-doped (Na0.85K0.15)0.5Bi0.5TiO3 (NKBT-Sc) films with different thicknesses of about 100–620 nm were grown on Pt(111)/Ti/SiO2/Si substrates by a sol–gel method. A LaNiO3 (LNO) layer of about 20 nm thickness was introduced at the film–substrate interface or alternatively with NKBT-Sc layers to form a sandwich multilayer structured film. The film thickness- and temperature-dependent structural and electromechanical properties of the films were investigated. A rhombohedral–tetragonal phase transition phase occurred with the variation of NKBT-Sc film thickness, and during this process a two-phase coexistence existed in an appropriate film thickness region, inducing an increased remnant polarization (Pr) value at an intermediate thickness (～460 nm) of about 23.7 μC cm?2. The effective piezoelectric coefficient Image ID:c7ra07848j-t1.gif initially increased from about 32 pm V?1 for the thinnest film (～100 nm) to a peak value of about 73 pm V?1 (～460 nm), but then decreased as the film thickness further increased. With the insertion of the LNO layers alternatively inside the NKBT-Sc film, the sandwich multilayer structure further enhanced the degree of the (001)-orientation and was beneficial for the crystallization process, leading to better electromechanical properties than the NKBT-Sc/LNO/substrate structure composite film. A high piezoelectric coefficient Image ID:c7ra07848j-t2.gif of about 82 pm V?1, dielectric constant εr of about 523 and remnant polarization (Pr) of about 26.2 μC cm?2, which gradually increased with the decrease of the testing temperature from 20 °C to ?120 °C, together with a with a low dielectric loss (tan?δ) of about 0.055 were simultaneously obtained in the sandwich multilayer structured film with NKBT-Sc film thickness of about 460 nm.

Graphical abstract: Thickness- and temperature-dependent structural and electromechanical properties of (100)-oriented Sc-doped (Na0.85K0.15)0.5Bi0.5TiO3 ferroelectric films
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