Reversible Electrical Field-Induced Formation of Ruddlesden-Popper Phases in Strontium Titanate at Room Temperature
- PDF / 210,687 Bytes
- 6 Pages / 612 x 792 pts (letter) Page_size
- 52 Downloads / 157 Views
0928-GG14-21
Reversible Electrical Field-Induced Formation of Ruddlesden-Popper Phases in Strontium Titanate at Room Temperature Dirk C. Meyer, Alexandr A. Levin, Tilmann Leisegang, Emanuel Gutmann, Marianne Reibold, Peter Paufler, and Wolfgang Pompe Technische Universität Dresden, Dresden, 01069, Germany
ABSTRACT On base of the structural characteristics of near-surface regions of a SrTiO3 (001) (STO (001)) single-crystal plate revealed by means of wide-angle X-ray scattering (WAXS), X-ray fluorescence spectroscopy and high-resolution transmission electron microscopy, structural changes in the STO (001) single-crystal plate under the influence of an external electric field at room temperature can be described as the tunable and reversible formation of RuddlesdenPopper-phases of the quasi-binary system SrO-TiO2. The WAXS behavior implies the use of the reversible phase-transition for adaptive X-ray optics, data storage and signal conversion. INTRODUCTION SrTiO3 (STO) single-crystalline wafers are widely used as substrates for deposition of thin films with different physical properties. The bulk STO remains cubic still at room temperature (RT) (space group Pm¯3m, a = 3.905 Å [1]). Besides the stoichiometric STO, a formation of crystalline SrO and Srn+1TinO3n+1 (n = 1, 2) Ruddlesden-Popper phases (RP) at temperatures between ~1300 °C and ~1800 °C were found at equilibrium conditions in the SrOrich regions (≥ 50 mol. % of SrO) according to the quasi-binary SrO-TiO2 equilibrium phase diagram [2]. Additionally, the n = 3 member was obtained by sintering of powder [3]. According to a simulation of strains induced by incorporation of SrO planes in a perovskite STO matrix, the limit of stable RP phases is found around n = 3 [4]. However, RP phases with higher n = 4…11 have been detected in thin films [5]. The coherent intergrowth of RP lamellae and STO is widely observed [5]. The structures of RP phases (n = 1-3) were first characterized in [3, 6] (tetragonal, space group I4/mmm, a ≈ 3.9 Å for all series members, c ≈ 12.6 Å, 20.4 Å and 28.1 Å for n = 1, 2 and 3, respectively) using powder X-ray diffraction data The formation of RP (n = 1, 2, 3) phases in near-surface regions of a single-crystalline STO plate was observed after annealing in oxygen atmosphere at a temperature of about 800 °C [7]. The chemical potential of oxygen atoms yielding the growth of SrO-rich layers in nearsurface regions was considered as driving force. The investigation of concentration profiles of oxidized STO single crystal plates by ion mass spectroscopy revealed chemical inhomogeneities of the near surface regions resulting in the formation of SrO-rich RP phases at the surface and of TiO-rich phases in deeper layers due to diffusion of SrO complexes in direction to the surface during the annealing [8]. Like thermal treatment, electric fields have a strong influence on the state of the surface of single-crystalline plates of STO. At temperatures of 100 °C - 325 °C, a characteristic electrocoloration of reduced material near the cathode and oxidi
Data Loading...
