Strontium titanate: From symmetry changes to functionality

Abstract

Pure strontium titanate exhibits a cubic perovskite-type structure at room temperature, but many approaches to break this high degree of symmetry are accessible. The present review summarizes some possible methods by discussing the effects of stoichiometry variation, ion implantation, temperature treatment and external electric fields. Since oxygen vacancies are the most prominent and most mobile defect species in strontium titanate, they play a crucial role also for structural changes due to external influences. Possible functionalities range from tuning of permittivity, band gap and conductivity to field-induced structure changes, which lead to applications as solid-state battery or switchable pyroelectric.

Sample chamber for synchrotron based in-situ X-ray diffraction experiments under electric fields and temperatures between 100 K and 1250 K

“…This ferroelectricity can be stabilized by a variety of external factors such as compressive strain, which allows the investigation of the ferroelectric phase at much higher temperatures. Here, our chamber was used to conduct a resonant XRD experiment at different low temperatures between 96 K and 300 K at nine oblique Bragg reflections to study an expected structural relationship (Nentwich et al, 2021) to a recently discovered piezo-and pyroelectric phase, the so-called migration-induced fieldstabilized polar (MFP) phase (Khanbabaee et al, 2016;Hanzig et al, 2013Hanzig et al, , 2015Stö cker et al, 2017) with the resonantly suppressed diffraction (RSD) approach (Richter et al, 2018). This new method allows sub-picometre precision by analyzing a purposely induced intensity minimum of an research papers energy-dependent Bragg reflection.…”

“…The presented sample environmental chamber was recently used for the combined variation of temperature and electric field during the study of structural symmetry reduction in the MFP phase of SrTiO 3 (Hanzig et al, 2013(Hanzig et al, , 2015Khanbabaee et al, 2016;Stö cker et al, 2017). The application of approximately 1 MV m À1 causes a structural transition of cubic SrTiO 3 with space group Pm 3 3m ð221Þ (Hanzig et al, 2013) to a P4mm tetragonal structure with elongated c direction accompanied by a polar distortion of the TiO 6 octahedra in the field direction (Richter et al, 2018).…”

“…The application of approximately 1 MV m À1 causes a structural transition of cubic SrTiO 3 with space group Pm 3 3m ð221Þ (Hanzig et al, 2013) to a P4mm tetragonal structure with elongated c direction accompanied by a polar distortion of the TiO 6 octahedra in the field direction (Richter et al, 2018). This involves the change of mechanical properties at the cathode side due to oxygen vacancy accumulation (Stö cker et al, 2010) as well as the appearance of new physical properties in the MFP layer at the anode side such that the SrTiO 3 crystal becomes partially piezo- (Khanbabaee et al, 2016) and pyroelectric (Hanzig et al, 2015). Up to now, the research of the MFP phase is limited to 284 K to 323 K (Hanzig et al, 2016).…”

Characterization study of flax/strontium titanate/polypropylene composite for low‐k dielectric applications

“…Also, Stocker et al's. 27 study on symmetry changes of strontium titanate suggested that structural phase transition occurs where this cubic structure of strontium titanate became tetragonal structure when temperature of 105 K or above was supplied (from hot press compression molding). The phase change phenomenon increases the chances of large spontaneous polarization which distinctively could have increased the dielectric permittivity of the composite.…”

Oxygen Exchange Kinetics of SrTiO3 Single Crystals: A Non‐Destructive, Quantitative Method

“…Strontium titanate (SrTiO 3 ) is, due to its ability to incorporate and transport oxygen, a promising candidate for such systems . Furthermore, the unique defect chemistry of SrTiO 3 is known to be responsible for peculiar new properties like pyroelectricity and acting as an all‐solid battery . Despite those technological applications, however, SrTiO 3 is one of the most important mixed‐conducting electroceramics, which has often been used as a model system in surface physics and defect chemistry in general .…”