SrTiO₃ (strontium titanate): structure, properties and uses

SrTiO₃ is the textbook perovskite. Each titanium sits at the centre of an octahedron of six oxygen atoms, the TiO₆ octahedra share all their corners, and each strontium fills a cavity between eight octahedra with twelve oxygen neighbours (Bartel et al. 2019).

At room temperature the structure is the ideal cubic one, with a cell edge of 3.905 Å and one formula unit per cell (Leroy et al. 2025). In that cell Ti–O is half the edge, 1.953 Å, and Sr–O is a/√2, 2.761 Å (calculated from a); the calculated density is about 5.12 g cm⁻³.

On cooling to about 105 K, SrTiO₃ undergoes an antiferrodistortive (AFD) transition from cubic to tetragonal. It is driven by a rotation of the TiO₆ octahedra about one axis, in opposite senses in neighbouring octahedra, which doubles the primitive unit cell. In Glazer notation the cubic phase is a⁰a⁰a⁰ and the tetragonal phase a⁰a⁰c⁻ (Leroy et al. 2025).

The transition is a rotation of the octahedra, not a polar shift, and does not by itself make bulk SrTiO₃ ferroelectric (Leroy et al. 2025).

SrTiO₃ is an incipient ferroelectric. As it cools, its polar TO1 phonon (about 2.6 THz at room temperature) softens and the dielectric constant rises steeply, signalling that a ferroelectric phase is close (Leroy et al. 2025). Yet the transition never happens: quantum fluctuations suppress the ferroelectric order, so SrTiO₃ stays paraelectric down to the lowest temperatures (Leroy et al. 2025). A material that stays paraelectric for this reason is called a quantum paraelectric.

Because it is so close to the edge, small perturbations tip it over. Epitaxial strain from a suitable substrate raises the ferroelectric transition by hundreds of degrees and makes SrTiO₃ films ferroelectric at room temperature, with a permittivity of nearly 7,000 at 10 GHz (Haeni et al. 2004). Doping a very low concentration of carriers into SrTiO₃ makes it a dilute superconductor (Leroy et al. 2025).

Kawasaki et al. showed in 1994 that treating the (100) surface with a pH-controlled NH₄F–HF solution leaves an atomically smooth, TiO₂-terminated surface with steps one unit cell high, on which SrTiO₃ grows layer by layer. The terminating layer can be switched to SrO by homoepitaxy, giving a well-defined starting surface for atomically controlled growth of perovskite films such as YBa₂Cu₃O₇₋δ (Kawasaki et al. 1994).

LaAlO₃ and SrTiO₃ are both insulators. Ohtomo and Hwang grew LaAlO₃ on SrTiO₃ while controlling the terminating layer at the interface atom by atom. In the simple ionic picture the interface carries an extra half electron or half hole per two-dimensional unit cell, depending on its stacking. The hole-doped interface stays insulating, but the electron-doped interface conducts, with carrier mobilities above 10,000 cm² V⁻¹ s⁻¹ and magnetoresistance oscillations at low temperature that point to quantum transport (Ohtomo & Hwang 2004).

Particulate photocatalysts that split water into H₂ and O₂ in a 2:1 ratio usually reach quantum efficiencies below 10%. Takata et al. used aluminium-doped SrTiO₃ and photodeposited the hydrogen-evolution cocatalyst Rh/Cr₂O₃ and the oxygen-evolution cocatalyst CoOOH on different crystal facets, so that electrons and holes are carried to separate faces. The result was overall water splitting with an external quantum efficiency of up to 96% at 350–360 nm, equivalent to an internal quantum efficiency of almost unity (Takata et al. 2020).

• Substrate for oxide films. Atomically flat TiO₂-terminated surfaces for epitaxial growth (Kawasaki et al. 1994).
• Oxide interfaces. The LaAlO₃/SrTiO₃ electron gas (Ohtomo & Hwang 2004); SrTiO₃ is one of the most studied materials in oxide thin films and heterostructures (Leroy et al. 2025).
• Tunable dielectrics. Strained SrTiO₃ films with a large, field-dependent permittivity at microwave frequencies (Haeni et al. 2004).
• Photocatalysis. SrTiO₃:Al for overall water splitting (Takata et al. 2020).
• Fundamental physics. Quantum paraelectricity, soft modes and dilute superconductivity (Leroy et al. 2025).

For a paper, slide or poster, draw the cubic cell with a TiO₆ octahedron at the centre and Sr at the corners, or eight corner-sharing octahedra around one Sr; use the cell edge of 3.905 Å for scale. To show the low-temperature phase, rotate neighbouring octahedra in opposite senses about the c axis (a⁰a⁰c⁻). For an interface figure, stack LaAlO₃ layers on TiO₂-terminated SrTiO₃. In LabCanvas you can draw the perovskite cell in the figure editor, show the TiO₆ polyhedra, repeat the cell and export a high-resolution image.