Microwave tunability in tin substituted barium titanate

The relationship between low and high frequency tunabilities in tin substituted barium titanate (BaTi1-xSnxO3, Sn-BTOx, x = 0.12, 0.14 and 0.16) ceramics is investigated. Although X-ray powder diffraction reveals an average non-polar cubic structure, Raman spectroscopy and piezoresponse force microscopy, along with ferroelectric and strain measurements under applied voltage reveal the presence of polar nanoclusters, while larger ferroelectric domains are seen in Sn-BTO12. Although the highest low frequency tunability was obtained for SnBTO12 (79.2 %), at microwave frequencies comparable tunabilities were achieved for Sn-BTO12 (39.2 %) and Sn-BTO14 (38.2 %). The difference in relative tunabilities between low and high frequencies is attributed to the difference in activities between larger ferroelectric domains and polar nanoclusters at these frequencies, with the former relatively inactive at high frequencies. This study demonstrates that low frequency tunability is not always a good indicator of the high frequency performance due to the lack of a domain contribution.