Effects of Sn²⁺ Ion Size on Sn Doped SrTiO₃

Abstract

We discuss the doping effect of Sn2+ on ATiO3 perovskites by comparing with those of Pb and Ba. The solution energy of Sn into A sites of ATiO3 perovskites shows minimum when the lattice size is almost the same as that of SrTiO3 (STO), as determined by first-principles calculations. In dielectric measurements of these STO-based ceramics, the Sn2+-doped STO ceramics showed a higher peak temperature than the Pb2+- or Ba2+-doped STO ceramics at the same doping amount. In addition, the maximum polarization obtained in the Sn2+-doped STO ceramics was larger than that obtained in the Pb2+- or Ba2+-doped ceramics in terms of the relationship between the polarization and electric field curve measurement at room temperature. The piezoresponse was also observed in the Sn2+-doped STO ceramics at room temperature by piezoresponse force microscopy. We propose that these effects originate from the bond length between Sn2+ and O2- which is smaller than that between Pb2+ and O2-. The Sn2+ ion prefers the off-center position at the Sr2+ site because of the retention of the stable bond length between Sn2+ and O2-. These leads to the formation of polar regions and which can assist in the generation of a larger polarization.

Average and local structure of the Pb-free ferroelectric perovskites(Sr,Sn)TiO3and(Ba,Ca,Sn)Laurita1, Page2, Suzuki3 et al. 2015Phys. Rev. BSelf Cite303220View full textAdd to dashboardCite

“…Previous work by Suzuki et al reported substitution of Sn 2+ on both the A and B sites of SrTiO 3 . 8,9 Refinements that modeled this two-site substitution were attempted, but the additional refined occupancies were unstable and the refined model inconclusive. In addition to Sn-substitution on A-site occupancies were determined using the diffraction data collected on the NOMAD diffractometer (wider Q-range of data) and applied to these refinements.…”

“…8,9 However, off-centering of an ion in a mixed (alloy) site cannot be refined against Bragg-scattering data, and indeed, this was found to be true insofar as any attempt to do this yielded unstable refinements. Sn 2+ off-centering is supported from a perspective of bond valence sums (BVS), with an Sn 2+ BVS of 1.16 in the 1a Wyckoff site of P m3m.…”

“…8,9,[15][16][17][18] Time-of-flight (TOF) neutron scattering data were collected on powdered samples on the Nanoscale Ordered Materials Diffractometer (NOMAD) at the Spallation Neutron Source (SNS) located at Oak Ridge National Laboratory (ORNL) with a collection time between 2 h to 4 h per sample. 23 Samples were loaded in a fused silica capillary, and an empty capillary was collected and subtracted as background.…”

“…7 However, substitution of Sn 2+ into the Sr 2+ site of SrTiO 3 induces a relaxor-like ferroelectric transition. 8,9 Raman spectroscopic observations of polar transverse optic modes at room temperature suggest the ferroelectric behavior arises due to the formation of percolative polar nanoregions formed in the material.…”

“…These compounds have been previously characterized from the viewpoint of their dielectric properties, Raman spectroscopy, average x-ray structure, and electron microscopy. 8,9,[15][16][17][18] Some of the key findings that emerge include that despite the small substitution levels, the Sn 2+ lone pairs drive the local ordering behavior. The local structure of both compounds more closely follow the behavior of PbTiO 3 than that of the parent compounds SrTiO 3 and BaTiO 3 , respectively.…”