Tin Titanate: the hunt for a new ferroelectric perovskite

TL;DR

This paper critically reviews existing literature on tin titanate, concluding that there is no conclusive experimental evidence for homogeneous bulk or thin-film SnTiO3, and that observed ferroelectric signals are artefacts or inhomogeneous phases.

Contribution

It provides a comprehensive critique of prior claims of ferroelectric tin titanate, highlighting artefacts and inhomogeneities that have led to false positives.

Findings

No conclusive evidence of homogeneous SnTiO3 in bulk or thin films.

Observed dielectric and ferroelectric signals are artefacts or due to inhomogeneous phases.

Recent work shows inhomogeneous SnTiO3, not suitable for ferroelectric devices.

Abstract

We review all the published literature and show that there is no experimental evidence for homogeneous tin titanate SnTiO3 in bulk or thin-film form. Instead a combination of unrelated artefacts are easily misinterpreted. The X-ray Bragg data are contaminated by double scattering from the Si substrate, giving a strong line at the 2-theta angle exactly where perovskite SnTiO3 should appear. The strong dielectric divergence near 560K is irreversible and arises from oxygen site detrapping, accompanied by Warburg/Randles interfacial anomalies. The small (4 uC/cm2) apparent ferroelectric hysteresis remains in samples shown in pure (Sn,Ti)O2 rutile/cassiterite, in which ferroelectricity is forbidden. Only very recent German work reveals real bulk SnTiO3, but this is completely inhomogeneous, consisting of an elaborate array of stacking faults, not suitable for ferroelectric devices. Unpublished TEM data reveal an inhomogeneous SnO layered structured thin films, related to shell-core structures. The harsh conclusion is that there is a combination of unrelated artefacts masquerading as ferroelectricity in powders and ALD films; and only a trace of a second phase in Cambridge PLD data suggests any perovskite content at all. The fact that X-ray, dielectric, and hysteresis data all lead to the wrong conclusion is instructive and reminds us of earlier work on copper calcium titanate (a well-known boundary-layer capacitor).