Crystal growth and structure of a high temperature polymorph of SrTiO with tetrahedral Ti-coordination, and transition to the Ruddlesden-Popper tetragonal phase

• Published in: CrystEngComm 2022-05, Vol.24 (2), p.3731-374
• Main Authors: Pulmannová, Dorota, Besnard, Céline, Bezdi ka, Petr, Hadjimichael, Marios, Teyssier, Jéremie, Giannini, Enrico
• Format: Article
• ISSN: 1466-8033
• DOI: 10.1039/d2ce00366j

Single crystals of transition metal oxides forming the Ruddlesden-Popper series are necessary for complete studies of their often exciting physical properties. In the strontium titanate family, crystal growth of all compounds apart from SrTiO 3 has been elusive so far. We have successfully grown crystals of the high-temperature polymorph of Sr 2 TiO 4 , by using a floating-zone melt growth followed by a rapid cooling procedure. We report the crystal structure of the new modification, which is isostructural to the orthorhombic Sr 2 VO 4 and Sr 2 CrO 4 . This structure hosts an uncommon layered sub-lattice of TiO 4 tetrahedra and transforms into the tetragonal low-temperature polymorph via a complex reconstructive transition. The transformation mechanism between the two phases was studied and explains the reasons for the unsuccessful growth of tetragonal Sr 2 TiO 4 . The orthorhombic Sr 2 TiO 4 is an insulator, with a band gap of 3.9 eV. It has a large ( 40) dielectric constant, but despite its polar structure does not show any signatures of a ferroelectric order. We have grown single crystals of a new polymorph of Sr 2 TiO 4 . It contains titanium in an unusual tetrahedral coordination and transforms to the Ruddlesden-Popper structure with an interesting orientational relationship.