SrTiO3 is a perovskite-type crystal consisting of SrO and TiO2 layers stacked in sequence and has a cubic crystal structure at room temperature. As a congruent-melting compound, a single crystal can be obtained from the melt, but a phase transition (cubic ⇔ tetragonal) occurs around 110 K at lower temperatures than room temperature. However, due to the characteristic of Ti oxides, which are prone to oxygen deficiency at high temperatures and in reducing atmospheres, it is essential to grow crystals under conditions that do not cause metallization. Therefore, it is difficult to control the atmosphere in growing methods using crucibles and components such as Ir (iridium) and Mo (molybdenum), which oxidize, melt and/or vaporize at high temperatures, and it is not easy to obtain good quality single crystals with good reproducibility. Although there are reports of good quality crystals being grown by the TSSG (Top Seeded Solution Growth) method using the solution method and the FZ (Floating Zone) method, which does not use crucibles, crystals grown by the Flame-Fusion (Verneuil) method are now widely used commercially due to cost and production volume.
Unit cell of SrTiO3
Although the Flame-Fusion method grows crystals under non-metalizing atmospheric conditions, as-grown SrTiO3 crystals contain many oxygen defects, are dark blue in color and are conductive. Generally, as colorless, insulating SrTiO3 crystals with low oxygen deficiency are required, heat treatment (oxidative annealing) is carried out to compensate for the oxygen. Normally, it is preferable to anneal in an oxygen atmosphere or similar in order to fully compensate for oxygen, but in the case of SrTiO3 crystals, annealing in an oxygen atmosphere causes them to brown, so a process is used whereby annealing in a hydrogen atmosphere makes them colorless.
SrTiO3 boule
